JP2010225891A - Semiconductor device and electronic apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device that can stably supply a current to a load, and prevent a decrease in electric power efficiency and an increase in circuit area, and an electronic apparatus having the same. <P>SOLUTION: The semiconductor device 101 includes a semiconductor substrate B, a constant current circuit 31 formed on the semiconductor substrate B and supplying the current to the load X, and a reference voltage generating circuit 21 formed on the semiconductor substrate B and generating a reference voltage, and is equipped with a saturation detecting circuit 32 which compares a voltage level of an output stage of the constant current circuit 31 with the reference voltage and outputs a detection signal for adjusting the voltage supplied to the load X according to the comparison result, the output stage 11 of the constant current circuit 31 and an output stage 12 of the reference voltage generating circuit 21 having the same configuration. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor device and an electronic device including the same, and more particularly to a semiconductor device that supplies current to a load and an electronic device including the same.

  In electronic devices such as mobile phones and liquid crystal televisions, for example, an LED (Light-Emitting Diode) element is used as a backlight of an LCD (Liquid Crystal Display).

  As a technique for driving an LED, for example, Patent Document 1 discloses the following configuration. That is, as a technique for driving an LED, for example, Patent Document 1 discloses the following configuration. That is, the light emitting diode driving device includes a driving voltage generating unit that generates a driving voltage to be applied to the anode of the light emitting diode, a driving current control unit that performs pulse width modulation control of the driving current flowing through the light emitting diode, and the driving voltage is monitored. And a monitor voltage generation unit that generates a monitor voltage on which a variation of the drive voltage generated in the off period is superimposed with a predetermined reference voltage as a reference during the off period of the drive current, The drive voltage generator performs feedback control of the drive voltage so that the feedback voltage drawn from the cathode of the light emitting diode coincides with the reference voltage during an on period of the drive current, and an off period of the drive current The feedback control of the drive voltage is performed so that the monitor voltage matches the reference voltage.

JP 61-163738 A

  By the way, such an electronic device includes, for example, a constant current circuit that supplies current to the LED. Here, in a saturation region of the constant current circuit, that is, in a region where the output current of the constant current circuit changes according to the supply voltage, a sufficient LED is not supplied to the constant current circuit. It will stop emitting light with brightness.

  In order to prevent such saturation of the constant current circuit, a configuration in which a saturation detection circuit that detects the saturation of the constant current circuit by comparing the level of the voltage supplied to the constant current circuit with a reference voltage is conceivable.

  Here, for example, a transistor for supplying current to the LED is provided at the output stage of the constant current circuit, and the on-resistance of the transistor varies depending on manufacturing variations and ambient temperature. As a result, the supply voltage level (hereinafter also referred to as saturation threshold voltage) to the constant current circuit at the boundary where the constant current circuit shifts from the constant current region to the saturation region changes.

  For this reason, conventionally, the reference voltage used by the saturation detection circuit has to be set to a value with a margin in consideration of manufacturing variations and ambient temperature with respect to the saturation threshold voltage. In order to give a margin to the reference voltage, it is necessary to set a large voltage to be supplied to the LED, which causes a problem that power efficiency is lowered. Alternatively, in order to provide a margin for the reference voltage, it is necessary to increase the size of the transistor in the output stage of the constant current circuit to reduce its on-resistance, resulting in an increase in circuit area.

  However, Patent Document 1 does not disclose a configuration for solving such a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a semiconductor device capable of stably supplying a current to a load and preventing a reduction in power efficiency and an increase in circuit area. It is to provide an electronic device equipped with it.

  In order to solve the above problems, a semiconductor device according to an aspect of the present invention is a semiconductor device that supplies current to a load, and is a semiconductor substrate and a constant current circuit that is formed on the semiconductor substrate and supplies current to the load. And a reference voltage generation circuit for generating a reference voltage, which is formed on the semiconductor substrate, compares the voltage level of the output stage of the constant current circuit with the reference voltage, and adjusts the voltage supplied to the load based on the comparison result And a saturation detection circuit that outputs a detection signal for performing the operation, and the output stage of the constant current circuit and the output stage of the reference voltage generation circuit have the same circuit configuration.

  Preferably, the semiconductor device further includes a voltage supply circuit that supplies a voltage to the load and adjusts a voltage supplied to the load based on a detection signal received from the saturation detection circuit.

  Preferably, the constant current circuit includes a first digital / analog conversion circuit that converts control data indicating a value of a current to be supplied to the load into an analog signal, and supplies the load to the load based on the converted analog signal. The reference voltage generation circuit includes a second digital / analog conversion circuit that converts the control data into an analog signal, and adjusts the reference voltage based on the converted analog signal.

  Preferably, the semiconductor device further includes an external terminal for supplying current to the load, and the constant current circuit includes a first conduction electrode coupled to the external terminal, a second conduction electrode, and a control electrode. A first resistor coupled to the second conduction electrode of the first transistor; a first input terminal receiving a voltage indicating a value of a current to be supplied to the load; and a first resistor of the first transistor. The saturation detection circuit is further coupled to an external terminal including a first comparator having a second input terminal coupled to the two conduction electrodes and an output terminal coupled to the control electrode of the first transistor. A second comparator having a first input terminal, a second input terminal, and an output terminal, the reference voltage generation circuit including a first conduction electrode coupled to the second input terminal of the second comparator; 2 conduction electrodes and control power Comprising a second transistor having bets, a second resistor and coupled to the second conduction electrode of the transistor.

  Preferably, the semiconductor device further includes an external terminal for supplying current to the load, and the constant current circuit includes a first conduction electrode and a control electrode coupled to each other, and a fixed voltage node to which a fixed voltage is supplied. A first transistor having a coupled second conduction electrode; a first conduction electrode coupled to an external terminal; a second conduction electrode coupled to a fixed voltage node; a control electrode of the first transistor; A second transistor having a control electrode coupled to the one conduction electrode, the reference voltage generating circuit including a first conduction electrode and a control electrode coupled to each other, and a second conduction electrode coupled to the fixed voltage node The saturation detection circuit is further coupled to a first input terminal coupled to the external terminal, and to a first conduction electrode and a control electrode of the third transistor. A comparator having a second input terminal, and an output terminal.

Preferably, the load is a light emitting element.
In order to solve the above-described problem, an electronic apparatus according to an aspect of the present invention includes a load and a semiconductor device that supplies current to the load. The semiconductor device is formed on the semiconductor substrate and the semiconductor substrate. A constant current circuit that supplies current and a reference voltage generation circuit that is formed on a semiconductor substrate and generates a reference voltage, compares the voltage level of the output stage of the constant current circuit with the reference voltage, and based on the comparison result, A saturation detection circuit that outputs a detection signal for adjusting the voltage supplied to the load, and the output stage of the constant current circuit and the output stage of the reference voltage generation circuit have the same circuit configuration.

  According to the present invention, it is possible to stably supply a current to a load, and to prevent a decrease in power efficiency and an increase in circuit area.

It is a figure which shows the structure of the electronic device which concerns on the 1st Embodiment of this invention. (A) is a figure which shows the reference voltage in the conventional semiconductor device which does not have a tracking function with respect to a saturation threshold voltage, and the design example of a transistor. (B) is a figure which shows the design example of the reference voltage and transistor in the semiconductor device which concerns on the 1st Embodiment of this invention. (A) is a figure which shows the reference voltage in the conventional semiconductor device which does not have a tracking function with respect to a saturation threshold voltage, and the design example of a transistor. (B) is a figure which shows the design example of the reference voltage and transistor in the semiconductor device which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the electronic device which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the electronic device which concerns on the 1st Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing a configuration of an electronic apparatus according to the first embodiment of the present invention.

  Referring to FIG. 1, an electronic device 201 includes a semiconductor device 101 and a load X that is, for example, an LED. The semiconductor device 101 includes a constant current circuit 31, a saturation detection circuit 32, a DC / DC converter (voltage supply circuit) 33, a semiconductor substrate B, and terminals TLx and TV. Constant current circuit 31 includes a comparator CMP1, an N-channel MOS transistor M1, and a resistor R1. The saturation detection circuit 32 includes a comparator CMP2 and a reference voltage generation circuit 21. Reference voltage generation circuit 21 includes a constant current source IS1, a bias voltage generation circuit 13, an N-channel MOS transistor M2, and a resistor R2.

  The constant current circuit 31, the saturation detection circuit 32, and the DC / DC converter 33 are included in one semiconductor chip, that is, formed on the same semiconductor substrate B.

  N-channel MOS transistor M1 and resistor R1 constitute output stage circuit 11 of constant current circuit 31. N-channel MOS transistor M2 and resistor R2 constitute output stage circuit 12 of reference voltage generation circuit 21.

  The constant current circuit 31 draws the current ILx from the load X into the constant current circuit 31 via the terminal TLx.

  The saturation detection circuit 32 detects the saturation of the constant current circuit 31, that is, the saturation of the N-channel MOS transistor M1. More specifically, the saturation detection circuit 32 includes a reference voltage generation circuit 21 that generates the reference voltage Vref, compares the voltage level VLx of the output stage circuit 11 of the constant current circuit 31 with the reference voltage Vref, and the comparison result Based on the above, the detection signal VCONT for adjusting the voltage supplied to the load X is output to the DC / DC converter 33.

  The DC / DC converter 33 adjusts the voltage supplied to the load X based on the detection signal VCONT received from the saturation detection circuit 32. More specifically, the DC / DC converter 33 supplies, for example, a voltage obtained by boosting the power supply voltage Vd to the load X via the terminal TV, and changes the boost rate based on the detection signal VCONT received from the saturation detection circuit 32.

  The load X is a light emitting element such as an LED, for example, and emits light based on the current ILx supplied from the semiconductor device 101.

  In the semiconductor device 101, the output stage circuit 11 of the constant current circuit 31 and the output stage circuit 12 of the reference voltage generation circuit 21 have the same circuit configuration.

  More specifically, in constant current circuit 31, N-channel MOS transistor M1 has a drain connected to terminal TLx, a source, and a gate. Resistor R1 has a first end connected to the source of N-channel MOS transistor M1, and a second end coupled to ground node Vs to which a fixed voltage, for example, ground voltage Vs is supplied. Comparator CMP1 has a non-inverting input terminal receiving control voltage VICT, an inverting input terminal connected to the source of N-channel MOS transistor M1, and an output terminal connected to the gate of N-channel MOS transistor M1.

  In the saturation detection circuit 32, the comparator CMP2 has an inverting input terminal connected to the terminal TLx, a non-inverting input terminal connected to the output of the constant current source IS1, and an output terminal. N-channel MOS transistor M2 has a drain connected to the non-inverting input terminal of comparator CMP2, a source, and a gate. Resistor R2 has a first end connected to the source of N-channel MOS transistor M2, and a second end coupled to ground node Vs.

  The comparator CMP1 controls the output voltage so that the source voltage of the N-channel MOS transistor M1 becomes equal to the control voltage VICT. That is, comparator CMP1 compares the voltage at the connection node between the source of N channel MOS transistor M1 and resistor R1 with control voltage VICT, and outputs a voltage to the gate of N channel MOS transistor M1 based on the comparison result. The control voltage VICT indicates the value of the current to be supplied to the load X, for example, the luminance of the LED that is the load X.

  N-channel MOS transistor M1 is turned on based on the voltage received from comparator CMP1 at the gate, and outputs current ILx. This current ILx is supplied to the load X. When the drain voltage of N channel MOS transistor M1, that is, the level of the voltage supplied from DC / DC converter 33 via load X and terminal TLx is sufficiently large, N channel MOS transistor M1 operates in a constant current region. To do. In this constant current region, when the resistance value of the resistor R1 is R1 and the on-resistance value of the N-channel MOS transistor M1 is Ron1, the voltage level VLx of the output stage circuit 11 of the constant current circuit 31, that is, the voltage level at the terminal TLx is as follows: (1).

VLx = ILx * (R1 + Ron1) (1)
On the other hand, when the drain voltage of N channel MOS transistor M1, that is, the level of the voltage supplied from DC / DC converter 33 via load X and terminal TLx is not sufficiently high, N channel MOS transistor M1 operates in the saturation region. To do. In this saturation region, output current ILx of N-channel MOS transistor M1 changes according to the level of voltage supplied from DC / DC converter 33 via load X and terminal TLx.

  Comparator CMP2 receives the voltage at the drain of N-channel MOS transistor M2 as a reference voltage Vref at the non-inverting input terminal.

  The bias voltage generation circuit 13 supplies a bias voltage to the gate of the N channel MOS transistor M2.

  The constant current source IS1 outputs a constant current Iref. When the resistance value of the resistor R2 is R2 and the on-resistance value of the N-channel MOS transistor M2 is Ron2, the reference voltage Vref is expressed by the following equation (2).

Vref = Iref × (R2 + Ron2) (2)
FIG. 2A and FIG. 3A are diagrams showing a design example of a reference voltage and a transistor in a conventional semiconductor device that does not have a tracking function with respect to a saturation threshold voltage. FIG. 2B and FIG. 3B are diagrams showing design examples of the reference voltage and the transistor in the semiconductor device according to the first embodiment of the present invention.

The on-resistance of the N-channel MOS transistor M1 in the output stage circuit 11 of the constant current circuit 31 varies depending on manufacturing variations and the ambient temperature. As a result, the saturation threshold voltage V _DM1, that is, the voltage level at the boundary where the constant current circuit 31 moves from the constant current region A2 to the saturation region A1 changes. Here, V _DM1WORST in FIGS. 2 and 3 is the maximum value of the saturation threshold voltage V _DM1 . Therefore, as shown in FIG. 2A and FIG. 3A, the reference voltage Vref used by the saturation detection circuit 32 conventionally has a margin in consideration of manufacturing variation and ambient temperature with respect to the saturation threshold voltage V _DM1 . It was necessary to set to the given value. In order to give a margin to the reference voltage Vref, it is necessary to set a large voltage to be supplied to the load X, which causes a problem that power efficiency is lowered. Alternatively, in order to provide a margin for the reference voltage Vref, it is necessary to increase the size of the N-channel MOS transistor M1 in the output stage circuit 11 of the constant current circuit 31 and reduce its on-resistance, which increases the circuit area. There was a problem of end.

  However, in the semiconductor device according to the first embodiment of the present invention, the series circuit of the N-channel MOS transistor M1 and the resistor R1 constitutes the output stage circuit 11 of the constant current circuit 31. A series circuit of the N channel MOS transistor M2 and the resistor R2 constitutes the output stage circuit 12 of the reference voltage generation circuit 21. The constant current circuit 31 and the saturation detection circuit 32 are formed on the same semiconductor substrate B. That is, the output stage circuit 11 of the constant current circuit 31 and the output stage circuit 12 of the reference voltage generation circuit 21 have the same circuit configuration and are formed on the same semiconductor substrate B.

  Then, since N channel MOS transistors M1 and M2 are formed on the same semiconductor substrate B, the ratio of the ON resistance of N channel MOS transistor M1 to the ON resistance of N channel MOS transistor M2 is a manufacturing variation of semiconductor device 101. It is substantially constant regardless of the ambient temperature. Further, since the resistors R1 and R2 are formed on the same semiconductor substrate B, the ratio of the resistors R1 and R2 is substantially constant regardless of manufacturing variations of the semiconductor device 101 and the ambient temperature.

  Therefore, from the equations (1) and (2), in the semiconductor device according to the first embodiment of the present invention, the reference voltage Vref is changed following the change in the voltage level VLx due to the manufacturing variation and the change in the ambient temperature. Can be made.

With such a configuration, the reference voltage Vref of the saturation detection circuit 32 can be changed following the manufacturing variation of the output stage circuit 11 of the constant current circuit 31 and the change in electrical characteristics due to the ambient temperature. For this reason, it is not necessary to set the reference voltage Vref used by the saturation detection circuit 32 to a value having a margin with respect to the saturation threshold voltage V _DM1 . Thus, it is not necessary to set a large voltage to be supplied to the load X, and it is not necessary to increase the size of the N-channel MOS transistor M1 in the output stage circuit 11 of the constant current circuit 31 and to reduce its on-resistance.

  Referring to FIG. 2B, in the semiconductor device according to the first embodiment of the present invention, when it is desired to improve the power efficiency, the N-channel MOS transistor M1 in the output stage circuit 11 of the constant current circuit 31 is referred to. Is set to the same size as before. On the other hand, the reference voltage Vref of the saturation detection circuit 32 is set smaller than in the conventional case. Thereby, since the output voltage of the DC / DC converter 33 supplied to the load X, that is, the step-up rate can be set small, the power efficiency can be improved.

  Referring to FIG. 3B, in the semiconductor device according to the first embodiment of the present invention, when it is desired to reduce the size of the circuit, the reference voltage Vref of the saturation detection circuit 32 is set to be the same as the conventional one. To do. On the other hand, the size of the N-channel MOS transistor M1 in the output stage circuit 11 of the constant current circuit 31 is set smaller than the conventional one. As a result, the semiconductor device can be miniaturized.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to a semiconductor device to which a current adjustment function is added as compared with the semiconductor device according to the first embodiment. The contents other than those described below are the same as those of the semiconductor device according to the first embodiment.

FIG. 4 is a diagram showing a configuration of an electronic apparatus according to the second embodiment of the present invention.
Referring to FIG. 4, electronic device 202 includes semiconductor device 102 and a load X that is, for example, an LED. The semiconductor device 102 includes a constant current circuit 41, a saturation detection circuit 42, a DC / DC converter (voltage supply circuit) 33, a semiconductor substrate B, and terminals TLx and TV.

  Constant current circuit 41 includes a comparator CMP1, an N-channel MOS transistor M1, a resistor R1, and a D / A converter 14. The saturation detection circuit 42 includes a comparator CMP2 and a reference voltage generation circuit 22. Reference voltage generation circuit 22 includes a D / A converter 15, a bias voltage generation circuit 13, an N-channel MOS transistor M2, and a resistor R2.

  The constant current circuit 41, the saturation detection circuit 42, and the DC / DC converter 33 are included in one semiconductor chip, that is, formed on the same semiconductor substrate B.

  N-channel MOS transistor M1 and resistor R1 constitute output stage circuit 11 of constant current circuit 41. N-channel MOS transistor M 2 and resistor R 2 constitute output stage circuit 12 of reference voltage generation circuit 22.

The constant current circuit 41 supplies a current ILx to the load X through the terminal TLx.
The saturation detection circuit 42 detects the saturation of the constant current circuit 41, that is, the saturation of the N-channel MOS transistor M1. More specifically, the saturation detection circuit 42 includes a reference voltage generation circuit 22 that generates a reference voltage Vref, compares the voltage level VLx of the output stage circuit 11 of the constant current circuit 41 with the reference voltage Vref, and the comparison result Based on the above, the detection signal VCONT for adjusting the voltage supplied to the load X is output to the DC / DC converter 33.

  The DC / DC converter 33 adjusts the voltage supplied to the load X based on the detection signal VCONT received from the saturation detection circuit 42. More specifically, DC / DC converter 33 supplies, for example, a voltage obtained by boosting power supply voltage Vd to load X via terminal TV, and changes the boost rate based on detection signal VCONT received from saturation detection circuit 42.

  The load X is a light emitting element such as an LED, for example, and emits light based on a current ILx supplied from the semiconductor device 102.

  In the semiconductor device 102, the output stage circuit 11 of the constant current circuit 41 and the output stage circuit 12 of the reference voltage generation circuit 22 have the same circuit configuration.

  More specifically, in the constant current circuit 41, the N-channel MOS transistor M1 has a drain connected to the terminal TLx, a source, and a gate. Resistor R1 has a first end connected to the source of N-channel MOS transistor M1, and a second end coupled to ground node Vs to which a fixed voltage, for example, ground voltage Vs is supplied. Comparator CMP1 has a non-inverting input terminal receiving control voltage VICT, an inverting input terminal connected to the source of N-channel MOS transistor M1, and an output terminal connected to the gate of N-channel MOS transistor M1.

  In the saturation detection circuit 42, the comparator CMP2 has an inverting input terminal connected to the terminal TLx, a non-inverting input terminal connected to the D / A converter 15, and an output terminal. N-channel MOS transistor M2 has a drain connected to the non-inverting input terminal of comparator CMP2, a source, and a gate. Resistor R2 has a first end connected to the source of N-channel MOS transistor M2, and a second end coupled to ground node Vs.

  The D / A converter 14 converts the control data ICONT indicating the value of the current to be supplied to the load X into an analog signal. The constant current circuit 41 adjusts the current supplied to the load X based on the analog signal converted by the D / A converter 14.

  The D / A converter 15 converts the control data ICONT into an analog signal. The saturation detection circuit 42 adjusts the reference voltage Vref based on the analog signal converted by the D / A converter 15.

  More specifically, the D / A converter 14 receives the control data ICONT that is a digital signal, changes the control data ICONT to the control voltage VICT that is an analog voltage, and outputs the control data ICONT to the comparator CMP1. Note that the control data ICONT indicates the luminance of the LED that is the load X, for example.

  Comparator CMP1 controls the output voltage so that the source voltage of N-channel MOS transistor M1 is equal to control voltage VICT received from D / A converter 14. That is, comparator CMP1 compares the voltage at the connection node between the source of N channel MOS transistor M1 and resistor R1 with control voltage VICT, and outputs a voltage to the gate of N channel MOS transistor M1 based on the comparison result.

  The D / A converter 15 receives the control data ICONT that is a digital signal, and supplies a constant current Iref to the N-channel MOS transistor M2 in accordance with the value of the control data ICONT.

  Comparator CMP2 receives the voltage at the drain of N-channel MOS transistor M2 as a reference voltage Vref at the non-inverting input terminal.

  The bias voltage generation circuit 13 supplies a bias voltage to the gate of the N channel MOS transistor M2.

In this way, by changing the value of the control data ICONT, the saturation threshold voltage V _DM1, that is, the supply voltage level to the constant current circuit 32 at the boundary where the constant current circuit 32 shifts from the constant current region to the saturation region is adjusted. Can do. That is, the current supplied to the load X in the constant current region of the constant current circuit 32 can be adjusted. Further, the reference voltage Vref can be changed following this adjustment.

  Since other configurations and operations are the same as those of the semiconductor device according to the first embodiment, detailed description thereof will not be repeated here. Therefore, in the semiconductor device according to the second embodiment of the present invention, as in the semiconductor device according to the first embodiment of the present invention, the current is stably supplied to the load, and the power efficiency is reduced. An increase in circuit area can be prevented.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Third Embodiment>
The present embodiment relates to a semiconductor device in which the method of the constant current circuit is changed as compared with the semiconductor device according to the first embodiment. The contents other than those described below are the same as those of the semiconductor device according to the first embodiment.

FIG. 5 is a diagram showing a configuration of the electronic device according to the first embodiment of the present invention.
Referring to FIG. 5, the electronic device 203 includes a semiconductor device 103 and a load X that is, for example, an LED. The semiconductor device 103 includes a constant current circuit 51, a saturation detection circuit 52, a DC / DC converter (voltage supply circuit) 33, a semiconductor substrate B, and terminals TLx and TV. Constant current circuit 51 includes N-channel MOS transistors M11 and M12 and a constant current source IS11. The saturation detection circuit 52 includes a comparator CMP12 and a reference voltage generation circuit 23. Reference voltage generation circuit 23 includes a constant current source IS12 and an N-channel MOS transistor M21.

  The constant current circuit 51, the saturation detection circuit 52, and the DC / DC converter 33 are included in one semiconductor chip, that is, formed on the same semiconductor substrate B.

  N-channel MOS transistors M11 and M12 constitute an output stage circuit of constant current circuit 51. N-channel MOS transistor M 21 forms an output stage circuit of reference voltage generation circuit 23.

The constant current circuit 51 supplies the current ILx to the load X through the terminal TLx.
The saturation detection circuit 52 detects the saturation of the constant current circuit 51, that is, the saturation of the N-channel MOS transistor M11. More specifically, the saturation detection circuit 52 includes a reference voltage generation circuit 23 that generates the reference voltage Vref. The saturation detection circuit 52 compares the voltage level VLx of the output stage circuit of the constant current circuit 51 with the reference voltage Vref, and determines the comparison result. Based on this, a detection signal VCONT for adjusting the voltage supplied to the load X is output to the DC / DC converter 33.

  DC / DC converter 33 adjusts the voltage supplied to load X based on detection signal VCONT received from saturation detection circuit 52. More specifically, DC / DC converter 33 supplies, for example, a voltage obtained by boosting power supply voltage Vd to load X via terminal TV, and changes the boost rate based on detection signal VCONT received from saturation detection circuit 52.

  The load X is a light emitting element such as an LED, for example, and emits light based on the current ILx supplied from the semiconductor device 103.

  In the semiconductor device 103, the output stage circuit of the constant current circuit 51 and the output stage circuit of the reference voltage generation circuit 23 have the same circuit configuration.

  More specifically, in constant current circuit 51, N-channel MOS transistor M12 includes a drain connected to constant current source IS11, a gate connected to the drain, and a ground node supplied with a fixed voltage, for example, ground voltage Vs. And a source coupled to Vs.

  N-channel MOS transistor M11 has a drain connected to terminal TLx, a source coupled to ground node Vs, and a gate connected to the gate and drain of N-channel MOS transistor M12.

  In saturation detection circuit 52, N channel MOS transistor M21 has a drain and a gate connected to each other, and a source coupled to ground node Vs.

  Comparator CMP12 has an inverting input terminal connected to terminal TLx, a non-inverting input terminal connected to the drain and gate of N-channel MOS transistor M21 and the output of constant current source IS12, and an output terminal.

  N channel MOS transistors M11 and M12 form a current mirror circuit. That is, N channel MOS transistors M11 and M12 output a current corresponding to the current received by N channel MOS transistor M12 from constant current source IS11 as a current ILx from N channel MOS transistor M11. This current ILx is supplied to the load X. When the drain voltage of N channel MOS transistor M11, that is, the level of the voltage supplied from DC / DC converter 33 via load X and terminal TLx is sufficiently large, N channel MOS transistor M11 operates in a constant current region. To do. In this constant current region, if the on-resistance value of the N-channel MOS transistor M11 is Ron11, the voltage level VLx of the output stage circuit of the constant current circuit 51, that is, the voltage level at the terminal TLx is expressed by the following equation (3).

VLx = ILx × Ron11 (3)
On the other hand, when the drain voltage of N channel MOS transistor M11, that is, the level of the voltage supplied from DC / DC converter 33 via load X and terminal TLx is not sufficiently high, N channel MOS transistor M11 operates in the saturation region. To do. In this saturation region, output current ILx of N channel MOS transistor M11 changes according to the level of voltage supplied from DC / DC converter 33 via load X and terminal TLx.

  Comparator CMP12 receives the voltage at the drain and gate of N channel MOS transistor M21 as reference voltage Vref at the non-inverting input terminal.

  The constant current source IS12 outputs a constant current Iref. When the on-resistance value of the N-channel MOS transistor M21 is Ron21, the reference voltage Vref is expressed by the following formula (4).

Vref = Iref × Ron21 (4)
Hereinafter, FIG. 2 and FIG. 3 used in the first embodiment of the present invention will be described by applying to the third embodiment of the present invention.

The on-resistance of the transistor M11 in the output stage circuit of the constant current circuit 51 varies depending on manufacturing variations and the ambient temperature. As a result, the saturation threshold voltage V _DM1, that is, the supply voltage level to the constant current circuit 51 at the boundary where the constant current circuit 51 shifts from the constant current region A2 to the saturation region A1 changes. Therefore, as shown in FIGS. 2A and 3A, conventionally, the reference voltage Vref used by the saturation detection circuit 52 has a margin in consideration of manufacturing variation and ambient temperature with respect to the saturation threshold voltage V _DM1 . It was necessary to set to the given value. In order to give a margin to the reference voltage Vref, it is necessary to set a large voltage to be supplied to the load X, which causes a problem that power efficiency is lowered. Alternatively, in order to provide a margin for the reference voltage Vref, it is necessary to increase the size of the N-channel MOS transistor M11 in the output stage circuit of the constant current circuit 51 to reduce its on-resistance, thereby increasing the circuit area. There was a problem.

  However, in the semiconductor device according to the third embodiment of the present invention, N-channel MOS transistors M11 and M12 constitute an output stage circuit of constant current circuit 51. N-channel MOS transistor M 21 forms an output stage circuit of reference voltage generation circuit 23. The constant current circuit 51 and the saturation detection circuit 52 are formed on the same semiconductor substrate B. That is, the output stage circuit of the constant current circuit 51 and the output stage circuit of the reference voltage generation circuit 23 have the same circuit configuration and are formed on the same semiconductor substrate B.

  Then, since N-channel MOS transistors M11 and M21 are formed on the same semiconductor substrate B, the ratio between the on-resistance of N-channel MOS transistor M11 and the on-resistance of N-channel MOS transistor M21 is a manufacturing variation of semiconductor device 103. It is substantially constant regardless of the ambient temperature.

  Therefore, from the equations (3) and (4), in the semiconductor device according to the third embodiment of the present invention, the reference voltage Vref is changed following the change in the voltage level VLx due to the manufacturing variation and the change in the ambient temperature. Can be made.

With such a configuration, it is possible to change the reference voltage Vref of the saturation detection circuit 52 following the manufacturing variation of the output stage circuit of the constant current circuit 51 and the change in the electrical characteristics due to the ambient temperature. For this reason, it is not necessary to set the reference voltage Vref used by the saturation detection circuit 52 to a value having a margin with respect to the saturation threshold voltage V _DM1 . Thus, it is not necessary to set a large voltage to be supplied to the load X, and it is not necessary to increase the size of the N-channel MOS transistor M11 in the output stage circuit of the constant current circuit 51 to reduce its on-resistance.

  Referring to FIG. 2B, in the semiconductor device according to the third embodiment of the present invention, when it is desired to improve the power efficiency, the N-channel MOS transistor M11 in the output stage circuit of the constant current circuit 51 The size is set to the same as before. On the other hand, the reference voltage Vref of the saturation detection circuit 52 is set smaller than in the conventional case. Thereby, since the output voltage of the DC / DC converter 33 supplied to the load X, that is, the step-up rate can be set small, the power efficiency can be improved.

  Referring to FIG. 3B, in the semiconductor device according to the third embodiment of the present invention, when it is desired to reduce the size of the circuit, the reference voltage Vref of the saturation detection circuit 52 is set to be the same as the conventional one. To do. On the other hand, the size of the N-channel MOS transistor M11 in the output stage circuit of the constant current circuit 51 is set smaller than the conventional one. As a result, the semiconductor device can be miniaturized.

  Since other configurations and operations are the same as those of the semiconductor device according to the first embodiment, detailed description thereof will not be repeated here. Therefore, in the semiconductor device according to the third embodiment of the present invention, similarly to the semiconductor device according to the first embodiment of the present invention, the current is stably supplied to the load, and the power efficiency is reduced. An increase in circuit area can be prevented.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  11, 12 Output stage circuit, 13 Bias voltage generation circuit, 14, 15 D / A converter, 21, 22, 23 Reference voltage generation circuit, 31 Constant current circuit, 32 Saturation detection circuit, 33 DC / DC converter (Voltage supply circuit) ), 41 constant current circuit, 42 saturation detection circuit, 51 constant current circuit, 52 saturation detection circuit, 101, 102, 103 semiconductor device, 201, 202, 203 electronic equipment, B semiconductor substrate, TLx, TV terminal, CMP1, CMP2 , CMP12 comparator, IS1, IS11, IS12 constant current source, M1, M2, M11, M12, M21 N-channel MOS transistor, R1, R2 resistance, X load.

Claims (7)

A semiconductor device for supplying current to a load,
A semiconductor substrate;
A constant current circuit formed on the semiconductor substrate and supplying a current to the load;
A reference voltage generation circuit that is formed on the semiconductor substrate and generates a reference voltage, compares the voltage level of the output stage of the constant current circuit with the reference voltage, and supplies the reference voltage to the load based on the comparison result A saturation detection circuit that outputs a detection signal for adjusting the voltage,
A semiconductor device in which an output stage of the constant current circuit and an output stage of the reference voltage generation circuit have the same circuit configuration. The semiconductor device further includes:
The semiconductor device according to claim 1, further comprising a voltage supply circuit that supplies a voltage to the load and adjusts a voltage supplied to the load based on a detection signal received from the saturation detection circuit. The constant current circuit is:
Including a first digital / analog conversion circuit for converting control data indicating a value of a current to be supplied to the load into an analog signal, and adjusting a current supplied to the load based on the converted analog signal;
The reference voltage generation circuit includes:
The semiconductor device according to claim 1, further comprising: a second digital / analog conversion circuit that converts the control data into an analog signal, and adjusting the reference voltage based on the converted analog signal. The semiconductor device further includes an external terminal for supplying a current to the load,
The constant current circuit is:
A first transistor having a first conduction electrode coupled to the external terminal, a second conduction electrode, and a control electrode;
A first resistor coupled to a second conduction electrode of the first transistor;
A first input terminal receiving a voltage indicating a value of a current to be supplied to the load, a second input terminal coupled to a second conduction electrode of the first transistor, and a control electrode of the first transistor A first comparator having a connected output terminal,
The saturation detection circuit further includes:
A second comparator having a first input terminal coupled to the external terminal, a second input terminal, and an output terminal;
The reference voltage generation circuit includes:
A second transistor having a first conduction electrode coupled to a second input terminal of the second comparator, a second conduction electrode, and a control electrode;
The semiconductor device according to claim 1, further comprising a second resistor coupled to a second conduction electrode of the transistor. The semiconductor device further includes an external terminal for supplying a current to the load,
The constant current circuit is:
A first transistor having a first conduction electrode and a control electrode coupled to each other and a second conduction electrode coupled to a fixed voltage node to which a fixed voltage is supplied;
A first conduction electrode coupled to the external terminal; a second conduction electrode coupled to the fixed voltage node; and a control electrode coupled to the control electrode and the first conduction electrode of the first transistor. Two transistors,
The reference voltage generation circuit includes:
A third transistor having a first conduction electrode and a control electrode coupled to each other and a second conduction electrode coupled to the fixed voltage node;
The saturation detection circuit further includes:
The comparator of claim 1, comprising a comparator having a first input terminal coupled to the external terminal, a second input terminal coupled to a first conduction electrode and a control electrode of the third transistor, and an output terminal. Semiconductor device.   The semiconductor device according to claim 1, wherein the load is a light emitting element. Load,
A semiconductor device for supplying a current to the load,
The semiconductor device includes:
A semiconductor substrate;
A constant current circuit formed on the semiconductor substrate and supplying a current to the load;
A reference voltage generation circuit that is formed on the semiconductor substrate and generates a reference voltage, compares the voltage level of the output stage of the constant current circuit with the reference voltage, and supplies the reference voltage to the load based on the comparison result A saturation detection circuit that outputs a detection signal for adjusting the voltage,
An electronic apparatus in which an output stage of the constant current circuit and an output stage of the reference voltage generation circuit have the same circuit configuration.

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