JP2001028845A - Power supply changeover circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a power supply changeover circuit with a C-MOS process which practices a reverse current preventive function between power supplies and eliminates an excessive voltage drop. SOLUTION: When both a lithium ion battery 6 and an external power supply 8 are connected, a transistor MP1 (P-MOS) is turned off and a channel current does not flow. Since a transistor MN1 (N-MOS) is in a diode connection state at that time, a reverse current is blocked. A through-current by a parasitic bipolar transistor is not generated either. When a drive current is supplied to a node 1 from the lithium ion battery 6 only, the MP1 is turned on and the channel current is made to flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply switching circuit for disconnecting an internal power supply so that power is supplied from the external power supply to the device when the external power supply is connected to the device operated by the internal power supply.

More specifically, the present invention relates to a power supply switching device for automatically switching from an internal battery to an external power supply when an external power supply is connected to a portable device operated by a built-in battery such as a lithium ion battery. It is related to the circuit.

[0003]

2. Description of the Related Art As devices that can be operated by both an internal power supply and an external power supply, cellular phones, PHSs, and other PDAs (portable information devices) have become widespread. As an example, if a mobile phone is taken as an example, integrated circuits of built-in circuits are currently being developed, and digital LSIs (made by a CMOS process), baseband LSIs (made by a CMOS process), and power supply ICs (made by a BICMOS process). 3) configuration.

The power supply IC includes a high-precision voltage source for supplying a power supply voltage to, for example, a microcomputer, a baseband LSI, a vibrator, a memory, a synthesizer, etc. Includes charging circuit for ion battery, lithium ion battery voltage monitoring circuit, backlight driving circuit, and LED
It includes a driving power supply, a buzzer power supply, a power supply rise monitoring circuit power supply, and a logic circuit for setting an internal state. In addition, as a process for producing this power supply IC, not only can the drive voltage and the amount of current supplied from the power supply to the load side be accurately specified, but also a backflow prevention circuit using a PN diode can be incorporated. As described above, a BICMOS process has been conventionally used to enable a certain degree of integration with low power consumption.

FIG. 1 shows a general block configuration of a power supply switching circuit used in a conventionally known power supply IC. In the illustrated power supply IC block, the reference voltage generation circuit 2 and the power supply rise monitoring circuit 4 operate with both a lithium ion battery (internal power supply) 6 of about 4 V or an external power supply of about 6.5 V. Backflow between the lithium-ion battery (internal power supply) 6 and the external power supply 8 is not allowed due to the safety of the lithium-ion battery itself, and therefore diodes D1, D2, and D3 for performing the backflow prevention function are provided.
Is required.

In the conventional power supply IC using the BICMOS process, a PN diode can be used. Therefore, the diodes D1, D2, and D3 for performing the backflow prevention function can be easily formed by a known connection as shown in FIG. It is possible to configure.

[0007]

However, in the above-mentioned portable telephones, it is strongly demanded to use a two-chip structure in order to further reduce the size and cost of the telephone body. More specifically,
(A) a digital LSI and a baseband LSI are integrally formed on one chip and a power supply IC is formed on a second chip, or (B) a baseband LSI and a power supply L
There are two proposals for forming the SI integrally on one chip and forming a digital IC on the second chip.

Here, regarding the above-mentioned plan (A), the digital LSI and the baseband LSI are both CMOs.
Since it is created by the S process, it has good so-called process compatibility, but on the other hand, it is very difficult in terms of circuit configuration since digital signals and analog signals are integrated on the same chip.

On the other hand, when the baseband LSI and the power supply IC are integrated on the same chip as in the case of the above (B),
Since both ICs are analog circuits, it is easier to integrate a baseband LSI based on a CMOS process and a power supply IC based on BICMOS as compared with the above-mentioned plan (A).

However, as described above, in order to reduce the cost, it is necessary to integrate both the baseband LSI and the power supply IC using a CMOS process having a small number of masks and a small number of process steps. In other words, BIC
An important issue is how to realize a conventional power supply IC manufactured by a MOS process by a CMOS process. As an example, when applied to a mobile phone, its power supply unit independently includes a plurality of positive power supplies with a ground (common potential point) as a reference potential (0 volt). Therefore, to realize this kind of power supply,
It is necessary to create a power supply IC by a CMOS process using a P-type substrate.

However, the conventionally used B
If the power supply IC as shown in FIG. 1 is to be formed by a CMOS process using a standard P-type substrate instead of the ICMOS process, the PN diodes D1, D2, and D3 formed by the BICMOS process cannot be used. Therefore, a reverse current prevention function equivalent to that of the PN diodes D1, D2, and D3 in FIG. 1 must be provided only by the MOS transistors.

FIG. 2 shows the PN diode D shown in FIG.
Instead of D1, D2 and D3, NM of diode connection form
FIG. 9 is a circuit diagram when three OSs are used. That is, the diode-connected MN1, MN2, and MN3 are
Are used in place of the PN diodes D1, D2, and D3.

In FIG. 2, when the power supply voltage is supplied to the node 1 through the diode connection MN2 and MN3 of the NMOS connected to the external power supply 8, the voltage of the external power supply 8 is high (this example). 6.5V), it is possible to secure a voltage sufficient for the reference voltage generation circuit 2 and the power supply rise monitoring circuit 4 to operate. However, when the power supply voltage is supplied from the lithium ion battery (internal power supply) 6 via the NMOS diode connection MN1, the voltage drop at the diode-connected NMOS is:
Considering that the voltage of the lithium ion battery drops to 2.7 V, the voltage of the node 1 drops to about 1.5 V at the worst. Therefore, it is necessary to secure a sufficient voltage for operating the reference voltage generation circuit 2 and the power supply rise monitoring circuit 4. Is impossible.

From the above, even if the circuit configuration shown in FIG. 2 is formed by a CMOS process, it is actually useless and some contrivance is required. That is, how to configure the backflow prevention circuit connected to the lithium ion battery (internal power supply) 6 on the CMOS process is a point of realizing the power supply IC by the CMOS process.

Accordingly, an object of the present invention is to provide
An object of the present invention is to provide a power supply switching circuit using a CMOS process, which performs a function of preventing backflow between power supplies and removes an extra voltage drop.

[0016]

In order to achieve the above-mentioned object, a power supply switching circuit according to the present invention, when an external power supply is connected to a device operated by an internal power supply, supplies power from the external power supply to the device. A power supply switching circuit for disconnecting the internal power supply so as to supply the P-type MOS transistor connected between an output terminal of the internal power supply and the device, and the P-type MOS transistor in response to connection of the external power supply Connecting means for turning off the P-type MOS transistor and an output terminal of the internal power supply,
And a diode-connected N-type MOS transistor. Here, the P-type MOS transistor and the N-type MOS transistor can be formed on a common P-type substrate. Further, the connection means may be configured to apply an output voltage of the external power supply to a gate of the P-type MOS transistor.

[0017]

FIG. 3 shows an example of a power supply switching circuit to which the present invention is applied. In this figure, a P-type M is provided between a lithium ion battery (internal power supply) 6 and a node 1.
The OS transistor MP1 and a diode-connected N-type MOS transistor MN1 are connected in parallel. Here, the bulk of MP1 (PMOS) is connected to the source of MN1 (NMOS diode-connected).

Between the external power supply 8 and the node 1, there are provided two diode-connected N-type MOS transistors MN2 and MN2.
MN3 is connected in series.

These MOS transistors are formed on a common P-type substrate PSUB, as shown in FIG.

In order to explain the operation of the circuits shown in FIGS. 3 and 4, MN of FIG.
Circuits excluding 1 (NMOS) are shown in FIGS.
However, in this auxiliary drawing, the bulk of MP1 (PMOS) is connected to the node 1.

First, in the circuit configuration of FIG. 5, as shown in FIG. 6, it is necessary to clearly recognize the existence of a parasitic element (parasitic PNP bipolar transistor) generated by a standard P-substrate CMOS process. This will be described below.

5 and 6, a voltage of 6.5 V is applied from an external power supply 8 and a voltage of 4 V is applied from a lithium ion battery 6.
When V is applied to the power supply IC, MP1 is turned off, so that backflow from the external power supply 8 to the lithium ion battery 6 is prevented.

When the external power supply 8 is removed and MP1 is turned on, current is supplied from the lithium ion battery 6 to the internal circuit (node 1).
1 and a diode-connected forward current of the parasitic PNP transistor 50 caused by forward biasing of the PN diode between the drain and bulk of MP1. This MP1 (PMOS)
Is a separate component, the problem of the parasitic element does not occur, but on the CMOS substrate, the parasitic PNP transistor 3
0 exists. The forward current of the PN diode between the drain of the MP1 (PMOS) and the bulk also becomes the base current of the parasitic PNP transistor 30, and the MP1 (PMO)
The parasitic PNP transistor 30 in the vertical direction from the drain of S) to the P-type substrate PSUB is also turned on, and a through current flows from the lithium ion battery 6 to the ground (0 V point).

By setting the on-resistance of MP1 (PMOS) to zero as much as possible, the parasitic PNP transistor 3
It seems that the base current for turning on 0 does not flow, but during DC operation, even if there is no problem, the power is turned on / off.
In the transient state at the time of turning off, the forward current of the diode is dominant until the channel current of MP1 (PMOS) flows.
Through current will flow.

Therefore, in FIGS. 3 and 4, which are embodiments of the present invention, in order to eliminate the problem caused by the parasitic element, the bulk of the MP1 (PMOS) and the output terminal of the lithium ion battery 6 are removed. Between the diode-connected M
N1 (NMOS) is connected. That is, MP1
(PMOS) bulk with diode-connected MN1
By connecting to the lithium ion battery 6 via (NMOS), it is possible to eliminate the ON of the parasitic PNP transistor and eliminate the through current. The reason is as follows.

In the circuits shown in FIGS. 3 and 4, when the lithium ion battery 6 and the external power supply 8 are both connected, MP1 (PMOS) is turned off and no channel current flows. At this time, the PN diode between the drain of MP1 and the bulk (N well) is forward biased,
Since the end of the N well (the left side in FIG. 4) is a diode connection of MN1 (NMOS), the PN to be flown is set.
The diode current is then blocked. Therefore, the parasitic PNP transistor 30, the parasitic PNP transistor 5
Since no base current for turning on 0 is generated, a backflow current from the external power supply 8 to the lithium ion battery 6 is also prevented, and no through current due to the parasitic PNP transistor 30 is generated.

Next, when the external power supply 8 is disconnected and a drive current is supplied to the node 1 only from the lithium ion battery 6, MP1 (PMOS) is turned on and a channel current flows. Also, the bulk of this MP1 (PMOS)
Since it is connected to the lithium ion battery 6 via the diode connection of MN1 (NMOS), the parasitic PNP transistor 30 does not turn on.

The above description is based on the premise that an integrated circuit is formed by a CMOS process.
If it is composed of transistors, MP1 (P
MOS) and MN1 (NMOS) need not be combined, and only MP1 (PMOS) is used as shown in FIG.
In addition, a configuration may be adopted in which the bulk of MP1 (PMOS) is connected to the node 1 side.

[0029]

As described above, according to the present invention, it is possible to realize a power supply switching circuit using a CMOS process, which functions to prevent backflow between power supplies and eliminates an extra voltage drop.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventionally known power supply switching circuit.

FIG. 2 is a circuit diagram showing a state in which the backflow prevention diode shown in FIG. 1 is replaced with a diode-connected NMOS.

FIG. 3 is a circuit diagram showing a power supply switching circuit to which the present invention is applied.

FIG. 4 is a sectional configuration diagram of the circuit shown in FIG. 3;

FIG. 5 is an auxiliary diagram for explaining the operation of FIGS. 3 and 4;

FIG. 6 is an auxiliary diagram for explaining the operation of FIGS. 3 and 4;

[Explanation of symbols]

 2 Reference voltage generation circuit 4 Power supply rise monitoring circuit 6 Lithium ion battery 8 External power supply

Claims (3)

[Claims] 1. A power supply switching circuit for disconnecting an internal power supply so that power is supplied from the external power supply to the device when the external power supply is connected to a device operated by the internal power supply. A P-type MOS transistor connected to the device; connection means for turning off the P-type MOS transistor in response to connection of the external power supply; a bulk of the P-type MOS transistor and an output of the internal power supply N-type M in diode connection form connected between terminals
A power supply switching circuit, comprising: an OS transistor. 2. The power supply switching circuit according to claim 1, wherein said P-type MOS transistor and said N-type MOS transistor are formed on a common P-type substrate. 3. The power supply switching circuit according to claim 1, wherein said connection means outputs an output voltage of said external power supply to said P-type power supply.
A power supply switching circuit, which is applied to a gate of an OS transistor.