SEMICONDUCTOR DEVICE, STEP-DOWN CHOPPER REGULATOR, AND ELECTRONIC EQUIPMENT

• US 20080084243A1
• Filed: 08/30/2007
• Published: 04/10/2008
• Est. Priority Date: 08/31/2006
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: KANAMORI, Atsushi, Warita, Hirohisa, Kimura, Tadamasa
• Granted Patent: US 7,737,773 B2
• Time in Patent Office: Days
• US Class Current: 327/589
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H03K 17/166 Soft switching
• CPC Class Codes: H03K 2217/0018 Special modifications or use of the back gate voltage of a FET

Abstract

A bootstrap circuit for a step-down chopper regulator IC includes an LDMOS transistor having a gate and a source connected to output terminals of a constant voltage circuit and a drain connected to a leader terminal of a boot voltage, and a bootstrap control circuit that performs control of turning on and off the LDMOS transistor so as to support high-speed oscillation without requiring expensive process and realize a stable step-down chopping action with a wide input voltage range.

Claims

1. A semiconductor device comprising:

a first switching element connected in series between a terminal to which an input voltage is applied and a leader terminal of an output voltage;

a constant voltage circuit that generates a desired constant voltage from the input voltage with reference to a ground voltage;

a bootstrap circuit that receives the constant voltage and generates a boot voltage that is higher than the output voltage;

a first logic generating circuit that generates a first logic signal for performing control of turning on and off the first switching element; and

a first drive circuit that performs control of turning on and off the first switching element by using the boot voltage based on the first logic signal, wherein

the bootstrap circuit includes

an LDMOS transistor having a source connected to an output terminal of the constant voltage circuit and a drain connected to a leader terminal of the boot voltage, and

a bootstrap control circuit that performs control of turning on and off the LDMOS transistor.

2. The semiconductor device according to claim 1, wherein the bootstrap control circuit controls a back gate of the LDMOS transistor so as to control of turning on and off the LDMOS transistor.

3. The semiconductor device according to claim 2, wherein the bootstrap control circuit includes

a first switch connected between the back gate and the source of the LDMOS transistor,

a second switch connected between the back gate and the drain of the LDMOS transistor, and

a boot portion control circuit and a back gate control circuit that perform control of turning on and off the first and the second switch in accordance with the first logic signal.

4. The semiconductor device according to claim 3, wherein the first switch is a P-channel MOS transistor, and the second switch is an N-channel MOS transistor.

5. The semiconductor device according to claim 4, wherein the first and the second switches are middle withstand voltage elements having a withstand voltage in the range within 7-40 volts or high withstand voltage elements having a withstand voltage in the range within 40-60 volts.

6. The semiconductor device according to claim 3, wherein the boot portion control circuit and the back gate control circuit perform control of turning on and off the first and the second switches so as to have a period while both the first and the second switches are turned off.

7. The semiconductor device according to claim 1, wherein the constant voltage is lower than gate withstand voltage of the LDMOS transistor, and a voltage dropped between the gate and the drain of the LDMOS transistor is set to a voltage value lower than withstand voltage of the first drive circuit.

8. The semiconductor device according to claim 2, further comprising a second constant voltage circuit that generates a second constant voltage that is higher than the constant voltage from the input voltage with reference to the ground voltage, wherein the bootstrap control circuit includes

a first switch connected between the back gate and the source of the LDMOS transistor,

a second switch connected between the back gate and the drain of the LDMOS transistor,

a third switch connected between the back gate and the source of the LDMOS transistor,

a fourth switch connected between the gate of the LDMOS transistor and the output terminal of the second constant voltage circuit, and

a boot portion control circuit and a back gate control circuit that perform control of turning on and off the first through the fourth switches based on an output of the first logic generating circuit.

9. The semiconductor device according to claim 8, wherein the second constant voltage is set to gate withstand voltage of the LDMOS transistor.

10. The semiconductor device according to claim 1, further comprising a zener diode having the cathode connected to the output terminal of the constant voltage circuit and the anode connected to the ground.

11. The semiconductor device according to claim 10, wherein the constant voltage is set to a voltage value that is lower than a zener voltage of the zener diode.

12. The semiconductor device according to claim 1, further comprising:

a second switching element connected in series between the leader terminal of the output voltage and the ground terminal;

a second logic generating circuit that generates a second logic signal for performing control of turning on and off the second switching element; and

a second drive circuit that performs control of turning on and off the second switching element based on the second logic signal.

13. The semiconductor device according to claim 12, wherein the bootstrap control circuit controls the back gate of the LDMOS transistor so as to perform the control of turning on and off the LDMOS transistor.

14. The semiconductor device according to claim 13, wherein the bootstrap control circuit includes

a first switch connected between the back gate and the source of the LDMOS transistor,

a second switch connected between the back gate and the drain of the LDMOS transistor, and

a back gate control circuit that performs control of turning on and off the first and the second switches in accordance with the second logic signal.

15. The semiconductor device according to claim 14, wherein the second drive circuit performs control of turning on and off the second switching element based on an output signal of the back gate control circuit.

16. The semiconductor device according to claim 12, wherein the second logic generating circuit generates the second logic signal from an output signal of the first drive circuit.

17. The semiconductor device according to claim 12, wherein the second logic generating circuit generates the second logic signal from the first logic signal.

18. The semiconductor device according to claim 14, wherein the back gate control circuit includes first and second level shifting circuits that shift the second logic signal to a predetermined voltage level so as to generate an on/off signal of the first and the second switches, wherein sizes of transistors that constitute the first and the second level shifting circuits are different so as to have a period while both the first and the second switches are turned off.

19. The semiconductor device according to claim 12, wherein the semiconductor device further includes a current sensing circuit that senses current flowing in the second switching element, wherein the second logic generating circuit generates the second logic signal in accordance with an output signal of the current sensing circuit.

20. The semiconductor device according to claim 12, wherein the second logic generating circuit generates the second logic signal in accordance with the output voltage.

21. A step-down chopper regulator comprising:

a semiconductor device according to claim 1;

a boot capacitor connected externally between the leader terminal of the output voltage and the leader terminal of the boot voltage; and

a smoothing circuit connected externally between the leader terminal of the output voltage and a load, wherein

the step-down chopper regulator step-downs the input voltage and supplies it to the load.

22. An electronic equipment comprising:

a step-down chopper regulator according to claim 21;

and

a load that is supplied with a drive voltage from the step-down chopper regulator.