Bootstrap capacitor low voltage prevention circuit

• US 6,714,067 B1
• Filed: 06/06/2002
• Issued: 03/30/2004
• Est. Priority Date: 01/18/2001
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Farrenkopf, Douglas Robert
• Primary Examiner(s): Cunningham, Terry D.
• Assistant Examiner(s): Tra, Quan
• Application Number:
  US10/165,218
• Time in Patent Office: 663 Days
• Field of Search: 327/589, 327/108, 327/538, 323/271, 323/225, 323/288, 323/290
• US Class Current: 327/589
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/155 using semiconductor devices only

Abstract

A bootstrap capacitor low voltage prevention circuit and method to control the same is provided. When a low voltage situation is detected the bootstrap capacitor is charged. An over voltage protection circuit is included that prevents the circuit from staying in an over voltage situation for a long period of time.

Claims

1. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a switch connected to an input voltage and coupled to a control logic circuit that produces a switched voltage at a node in response to a signal from the control logic circuit;

the node coupled to a switching regulator circuit that outputs an output voltage and provides a feedback signal coupled to the control logic circuit;

the control logic circuit measuring the voltage across a bootstrap capacitor and controlling operation of the switch by providing the signal based on the measured voltage;

a charging circuit that charges the bootstrap capacitor depending on the state of the switch, the bootstrap capacitor being fully charged when the switched voltage is drained to a predetermined level; and

a temperature shutdown circuit for shutting down the bootstrap capacitor low voltage prevention circuit when a predetermined temperature is reached.

2. The apparatus as in claim 1, wherein the temperature shutdown circuit further comprises:

a temperature sensor to measure temperature;

a comparator to determine when a predetermined temperature has been reached; and

a shutdown circuit for shutting down the circuit when the predetermined temperature has been reached.

3. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a switch connected to an input voltage and coupled to a control logic circuit that produces a switched voltage at a node in response to a signal from the control logic circuit;

the node coupled to a switching regulator circuit that outputs an output voltage and provides a feedback signal coupled to the control logic circuit;

the control logic circuit measuring the voltage across a bootstrap capacitor and controlling operation of the switch by providing the signal based on the measured voltage;

a charging circuit that charges the bootstrap capacitor depending on the state of the switch, the bootstrap capacitor being filly charged when the switched voltage is drained to a predetermined level; and

a switched voltage signal analyzer circuit wherein the switched voltage analyzer circuit further comprises;

a comparator circuit that outputs a comparator signal indicating when the switched input voltage is above or below a predetermined value;

a timer circuit coupled to the output of the comparator circuit that times a period when the comparator signal indicates the switched input voltage is above or below the predetermined value and outputs a time signal based on the timed period; and

a reset circuit coupled to the time signal for resetting the circuit based on the time signal.

4. A method for controlling a bootstrap capacitor low voltage prevention circuit, comprising:

measuring a voltage across a bootstrap capacitor that is coupled between a control logic and a node;

determining when the voltage is too low; and

when it is determined that the voltage is too low;

turning off a driver controlling the charging of the bootstrap capacitor;

activating a switch that is connected between the node and the input voltage in response to the control logic, wherein the voltage at the node corresponds to a switched voltage;

draining the switched voltage to a predetermined level; and

charging the bootstrap capacitor to a predetermined level.

5. The method of claim 4, further comprising determining if the circuit is in an over voltage condition.

6. The method of claim 4, further comprising:

measuring a temperature of the circuit; and

shutting down the circuit when the measured temperature is above a predetermined value.

7. The method of claim 4, further comprising analyzing the switched voltage and resetting the circuit based on the analyzed switched voltage.

8. The method of claim 4, further comprising resetting the circuit when the bootstrap capacitor is charged.

9. The method of claim 4, wherein measuring the voltage across the bootstrap capacitor further comprises:

setting a latch based on the measured voltage; and

turning off the charging circuit when the latch is set.

10. The method as in claim 5, wherein determining if the circuit is in an over voltage condition, further comprises:

determining if the output voltage is above a predetermined value; and

discharging the output voltage when it is determined that the output voltage is above the predetermined value.

11. The method as in claim 7, wherein analyzing the switched voltage and resetting the circuit based on the analyzed switched voltage the switched voltage analyzer circuit further comprises:

indicating when the switched input voltage is above or below a predetermined value;

timing a period of time when the switched input voltage is above or below the predetermined value;

outputting the period of time; and

resetting the circuit based on the period of time.

12. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a means for measuring the voltage across a bootstrap capacitor that is charged according to in input voltage;

a means for determining when the voltage is too low; and

when the voltage is determined to be too low, providing;

a means for turning off a driver controlling the charging of the bootstrap capacitor;

a means for draining a switched voltage to a predetermined level that is connected to the input voltage; and

charging the bootstrap capacitor to a predetermined level.

13. The apparatus as in claim 12, further comprising:

a means for determining when an over voltage condition exists within the bootstrap capacitor low voltage prevention circuit; and

a means for determining when the temperature of the bootstrap capacitor low voltage prevention circuit is too high, and when it is determined that the temperature is too high;

a means for shutting down the bootstrap capacitor low voltage prevention circuit.

14. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a switch coupled to an input voltage and produces a switched voltage at a node;

the node coupled to a switching regulator circuit that outputs an output voltage and provides a feedback signal coupled to a control logic circuit;

the control logic circuit measuring the voltage across a bootstrap capacitor and controlling operation of the switch based on the measured voltage;

a charging circuit that charges the bootstrap capacitor depending on the state of the switch, the bootstrap capacitor being fully charged when the switched voltage is drained to a predetermined level; and

a temperature shutdown circuit for shutting down the bootstrap capacitor low voltage prevention circuit when a predetermined temperature is reached.

15. The apparatus as in claim 14, wherein the temperature shutdown circuit further comprises:

a temperature sensor to measure temperature;

a comparator to determine when a predetermined temperature has been reached; and

a shutdown circuit for shutting down the circuit when the predetermined temperature has been reached.

16. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a switch coupled to an input voltage and produces a switched voltage at a node;

the node coupled to a switching regulator circuit that outputs an output voltage and provides feedback signal coupled to a control logic circuit;

the control logic circuit measuring the voltage across a bootstrap capacitor and controlling operation of the switch based on the measured voltage;

a charging circuit that charges the bootstrap capacitor depending on the state of the switch, the bootstrap capacitor being fully charged when the switched voltage is drained to a predetermined level; and

a switched voltage signal analyzer circuit that comprises;

a comparator circuit that outputs a comparator signal indicating when the switched input voltage is above or below a predetermined value;

a timer circuit coupled to the output of the comparator circuit that times a period when the comparator signal indicates the switched input voltage is above or below the predetermined value and outputs a time signal based on the timed period; and

a reset circuit coupled to the time signal for resetting the circuit based on the time signal.

17. A method for controlling a bootstrap capacitor low voltage prevention circuit, comprising:

measuring the voltage across a bootstrap capacitor;

determining when the voltage is too low; and

when it is determined that the voltage is too low;

turning off a driver controlling the charging of the bootstrap capacitor;

draining a switched voltage to a predetermined level;

charging the bootstrap capacitor to a predetermined level;

measuring a temperature of the circuit; and

shutting down the circuit when the measured temperature is above a predetermined value.

18. A method for controlling a bootstrap capacitor low voltage prevention circuit, comprising:

measuring the voltage across a bootstrap capacitor;

determining when the voltage is too low; and

when it is determined that the voltage is too low;

turning off a driver controlling the charging of the bootstrap capacitor;

draining a switched voltage to a predetermined level;

charging the bootstrap capacitor to a predetermined level; and

analyzing the switched voltage and resetting the circuit based on the analyzed switched voltage by indicating when the switched input voltage is above or below a predetermined value, timing a period of time when the switched input voltage is above or below the predetermined value, outputting the period of time, and resetting the circuit based on the period of time.

19. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a means for measuring the voltage across a bootstrap capacitor;

a means for determining when the voltage is too low; and

when the voltage is determined to be too low;

a means for turning off a driver controlling the charging of the bootstrap capacitor;

a means for draining a switched voltage to a predetermined level; and

a means for charging the bootstrap capacitor to a predetermined level;

a means for determining when an over voltage condition exists within the bootstrap capacitor low voltage prevention circuit; and

a means for determining when the temperature of the bootstrap capacitor low voltage prevention circuit is too high and when it is determined that the temperature is too high;

a means for shutting down the bootstrap capacitor low voltage prevention circuit.

20. An apparatus for a bootstrap capacitor low voltage prevention circuit, comprising:

a switch that is operated asynchronously while connected to an input voltage and coupled to a control logic circuit that produces a switched voltage at a node in response to a signal from the control logic circuit;

the node coupled to a switching regulator circuit that outputs an output voltage and provides a feedback signal coupled to the control logic circuit;

the control logic circuit measuring the voltage across a bootstrap capacitor and controlling operation of the switch by providing tee signal based on the measured voltage; and

a charging circuit that charges the bootstrap capacitor depending on the state of the switch, the bootstrap capacitor being filly charged when the switched voltage is drained to a predetermined level and the full charge is sustained for a significant time interval.

21. The apparatus as in claim 20, wherein the circuit utilizes a high-resistance switch within the control logic circuit.