JPH0828963B2 - Voltage control power IC - Google Patents

Description

The present invention relates to a power IC, and more particularly to a MOS power IC suitable for switching automobile electric components.

[Conventional technology]

The switching of the electric components of the car is most easily turned on and off directly by a hand switch, but a relay may be used to make the wiring thin. Further, a power transistor is sometimes used in correspondence with microcomputer control or the like. Recently, the wire bundle tends to become thicker as the number of electrical components increases to improve the service, and in order to cope with this, an integrated wiring system using multiplex signal transmission has begun to be developed.

In that case, it is generally known that a power IC that restores a transmitted signal by a local control unit and controls a load current by a TTL level switching signal which is an output thereof is generally known.

The electrical components of the automobile are directly connected to the chassis potential (usually negative ground) so that even if a leak occurs due to water getting wet, it will not malfunction due to the current, and switching should be done on the positive side. It has become.
Therefore, as a power IC, insert it on the positive side of the load.
It must be a so-called high-side switch.

When the high-side switch is composed of MOS transistors, the gate circuit is simple if a P-type MOS is used, and if the gate potential is simply set to zero, it becomes a normal state. However, since the P-type MOS generally has a high on-resistance, the voltage drop of the switch element becomes large for a low-voltage, large-current load device such as an automobile that uses a battery as a power source, and a sufficient voltage cannot be applied to the load. However, there is a problem that the heat generated by the switch element itself is increased. Therefore, in the present technology, it is more advantageous to use an N-type MOS element having a small ON resistance. However, in that case, the gate voltage must be sufficiently higher than the source voltage (approximately equal to the battery voltage) at the time of conduction, which complicates the gate circuit.
That is, when the battery voltage is 12V, the gate voltage is 20V
Although it is preferable to provide the above, it is not a good idea to provide such a high-voltage power supply separately, so it is usual to provide a charge pump circuit for boosting from 12V to 20V or more.

An electronic switch having such a structure is shown, for example, in Japanese Published Patent Publication No. 58-500835.

However, all of them are simply electronic switches that follow the input signal as they are, and only have a built-in protection circuit against malfunctions and external noise and a diagnostic function for that operation, and a time control function for intermittent load operation. No consideration was given to the additional functions such as the duty ratio control function that makes the load voltage variable.

[Problems to be solved by the invention]

An object of the present invention is to provide the power IC itself with a time control function and a duty ratio control function necessary for controlling automobile electric components.

[Means for solving problems]

The above object is achieved by incorporating a clock generation circuit, a timer circuit, a conduction ratio setting circuit, etc. in a logic circuit portion formed in a part of a power IC chip.

[Operation] The clock generation circuit divides a high-frequency signal generated by a separately provided oscillation circuit to generate a clock signal of an appropriate frequency, and the timer circuit counts the clock signal at predetermined intervals. It controls the gate voltage. With this, the electronic switch can be repeatedly turned on and off at predetermined intervals. Further, the conduction ratio setting circuit generates a repeated conduction signal having a predetermined duty ratio from the clock signal, whereby the electronic switch can perform a chopper operation.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. N
The type MOS switch 1 is a power transistor formed on the silicon chip 2, the drain D is connected to the positive side of the battery voltage, and the source S is connected to the load side. The cathode of the free wheel diode Dd is connected to the source S, and the anode thereof is grounded. The freewheeling diode Dd is connected to the MO when an inductive load is connected.
This is to prevent a negative voltage from being applied to the source S by causing a load current to flow back when the S switch 1 is turned off.
Although this freewheel diode Dd is built in the silicon chip 2, it requires a large area because a freewheel current of the same magnitude as the load current flows, which increases the cost of the power IC. In that case, an inexpensive device such as a glass diode may be externally attached instead of being built in the silicon chip 2.

MOS switch 1 has another source electrode S ₁ ,
It is connected to the load through a resistor r. This is for current detection, and when a load current flows, for example, a current of about 1/1000 flows through the resistor r in proportion thereto, so the value of the load current is detected by measuring the voltage across the resistor r. be able to. The voltage detection circuit 10 can measure the voltage across the resistor r using an operational amplifier or the like, separately measure the resistance value of the resistor r beforehand, and obtain the current value from the known resistance value. The voltage between both ends of the resistor r is Vr, and the ratio of the current Is of the source electrode S ₁ for current detection to the load current Ic (1: 1000) GM = 10
If it is 00, the load current of the MOS switch 1 is expressed by the following equation.

The output of the current detection circuit 10 is obtained by amplifying the voltage ΔVr across the resistor r using an operational amplifier or the like, and if GM, r in the above equation (2) is known and given as a constant. ,
It can be seen that the output of the current detection circuit 10 represents a current value proportional to the load current Ic even if it is a current output, for example.

The gate G of the MOS switch 1 is connected to N by the gate circuit 3.
A sufficient gate voltage is applied to turn on the MOS switch 1 of the mold. The gate voltage is generated by the charge pump 4. The serge pump 4 boosts a pulse voltage, which is equal to or lower than the battery voltage generated by the oscillator 5, by, for example, a Cockcroft circuit or the like to obtain a DC voltage that is 2 to 3 times the battery voltage. The gate circuit 3 switches its voltage on and off in response to a command from the timer 6, and also various protection circuits 7 to
It also functions to cut off the gate voltage urgently in response to a command from 9.

The overcurrent protection circuit 7 receives the output of the current detection circuit 10 which detects the load current from the voltage generated in the resistance r for current detection, and when it exceeds a predetermined value, the gate circuit 3
Give a cutoff command to.

The overvoltage protection circuit 8 detects a battery voltage and shuts off the gate to protect the load from an abnormal rise.

When the chip temperature detected by the temperature detection circuit 11 exceeds a predetermined value, the overheat protection circuit 9 protects the chip by cutting off the gate to prevent the load current from flowing, and the voltage detection circuit 13 is The source voltage of the switch 1 is detected by using an operational amplifier or the like. When MOS switch 1 is ON, M
Considering that the on resistance of OS switch 1 is very small,
A voltage almost equal to the drain voltage of the MOS switch 1 will be detected. When the MOS switch 1 is off, the diagnostic circuit 12 that detects the load voltage determines the load voltage by determining and reading the output voltage level of the voltage detection circuit 13 according to the on / off state of the MOS switch. You can know the status.

In this way, the diagnostic circuit 12 can detect the current and voltage flowing through the MOS switch according to the state of the MOS switch 1 without using the silicon chip. Abnormality of the entire system is judged by inputting signals from the protection circuit.

The outputs of these protection circuits 7 to 9 are given to the gate circuit 3 and also to the diagnostic circuit 12. Diagnostic circuit 12
In addition, the output of the current detection circuit 10 and the output of the voltage detection circuit 13 for detecting the output voltage applied to the load are also given to the load. There is a function to diagnose a disconnection. These diagnostic results are sent to the central microcomputer via the communication LSI to display warnings and the like.

The above is the configuration well known in the literature except for the timer 6.
The feature of the present invention is to have a timer 6, a conduction ratio control circuit 14, and an operation condition setting unit 15. The flow control circuit 14 controls the ON period of the ON / OFF signal generated by using the timer 6 at a constant frequency. In this embodiment, the pulse amplification control is performed using the timer 6, but the timer 6
Since the duty ratio control circuit 14 is configured to operate here, it is possible to generate a pulse with a higher degree of freedom as compared with normal pulse width control.

The operating condition setting unit 15 sets a repeating cycle and a pattern for the timer 6 in accordance with an external signal given to the input terminal 17, and also sets a conduction ratio for the conduction ratio control unit 14. In some cases, a command for constant current control or a command for constant voltage control is given.

That is, when a continuous operation command is given to the timer 5 and a 100% flow command is given to the flow rate control unit 14, the MOS switch 1 is continuously turned on as shown in FIG. FIG. 2B shows the case where the intermittent operation command is given to the timer 6 and the 100% flow command is given to the flow rate control unit 14.
Of course, the intermittent operation cycle and conduction width can be changed. When a continuous operation command is given to the timer 6 and a constant flow rate command is given to the flow rate control unit 14, as shown in FIG. 2 (c).
The output of the MOS switch 1 is obtained. It goes without saying that it is possible to combine the intermittent operation and the flow rate control.

Further, the operation condition setting unit 15 can give a constant voltage control command or a constant current control command to the conduction ratio control unit 14. When a constant voltage control command is given, it is compared with the output of the voltage detection circuit 13, the conduction ratio is controlled so that the difference between the two is reduced, and a so-called negative feedback control loop is formed. When a constant current control command is given, it is compared with the output of the current detection circuit 10 and feedback control is performed so that the deviation between the two is reduced.

Further, the overheat current reduction circuit 16 reduces the command to reduce the flow rate at a high temperature in accordance with the output of the temperature detection circuit 11.
As a result, the current is not cut off suddenly when the temperature becomes high, and the operation can be continued with a low current value.

According to the method of the present embodiment, if the command is given only once from the center via the communication LSI, the operation condition setting unit 15 and the timer 6 serve to independently belong to the intermittent operation. Further, when the chopper is in operation, it can be operated at a flow rate γ according to a command from the center, so it has a function of changing the speed of the load electric motor or changing the illuminance of the lamp, for example. Such a function is conventionally known as a single device, but by consolidating these functions in the driving IC of the in-vehicle signal transmission system, the load on the central microcomputer is not increased. Intermittent operation and voltage control functions can be provided.

〔The invention's effect〕

According to the present invention, voltage control can be performed by adding a timer, a duty ratio control unit, an operating condition setting unit, etc. to the logic unit of the power IC, so that the function of the automobile electrical system can be improved with a slight increase in the chip area. Can be improved. Further, since there is no external component and no plug is required to connect it, the substrate itself can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a functional configuration in an IC according to an embodiment of the present invention, and FIG. 2 is a power IC according to an embodiment of the present invention.
It is explanatory drawing which shows an output voltage waveform. 1 ... N-type MOS switch, 2 ... Silicon chip, 3 ...
… Gate circuit, 4 …… Charge pump, 5 …… Oscillator,
6 ... Timer, 14 ... Commutation rate control unit, 15 ... Operating condition setting unit.

Front page continuation (72) Inventor Tomoyuki Tanaka 4026 Kujimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Co., Ltd. (56) References JP 62-236358 (JP, A) JP, A) Electronic Technology, 22 [4] (1980) Nikkan Kogyo Shinshinsha P. 8-9

Claims (1)

[Claims] 1. A power switch composed of an N-type MOS transistor, a gate circuit including a booster circuit for controlling a gate voltage of the power switch, and a control signal given to the gate circuit are externally fetched on the same substrate. And an input terminal of, and between the gate circuit and the input terminal,
A timer circuit, an operating condition setting circuit that sets operating conditions of the timer circuit, and a conduction ratio control circuit are provided, and the conduction ratio control circuit causes the conduction of the power switch according to a command from the operating condition setting circuit. Voltage controlled power IC characterized by setting the rate.