Precision low voltage supply system and method with undervoltage lockout capabilities

• US 6,600,639 B1
• Filed: 06/14/2001
• Issued: 07/29/2003
• Est. Priority Date: 06/14/2001
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Teo, Siew Siong, Frank, Richard, Broach, Michael Eugene
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): NGUYEN, THINH T
• Application Number:
  US09/881,933
• Time in Patent Office: 775 Days
• Field of Search: 361/92, 327/79, 327/143, 323/314, 340/663
• US Class Current: 361/92
• CPC Class Codes: G05F 3/247 producing a voltage or current as a predetermined function of the supply voltage
• CPC Class Codes: H02H 3/243 for DC systems

Abstract

An integrated circuit system and method provides a reliable low voltage reference including undervoltage lockout capabilities that prevent a premature or false response. A physical constant trigger circuit initiates a response based upon a physical constant (e.g. a stable point associated with a voltage summation in a transistor circuit with components configured to produce equal and opposite temperature coefficients). A response includes changing polarities of the transistor circuit at a predetermined inflection point. A comparator compares signals from the physical constant trigger circuit and determines when a change occurs in the response. A voltage divider provides a varying voltage to the physical constant trigger and when the voltage level corresponds to the physical constant it is utilized as the reference voltage. An input signal port conveys an input signal to the voltage divider and output port conveys an indication of the response (e.g., a desired reference voltage is available).

Claims

1. A reference voltage identification system comprising:

a physical constant trigger circuit for initiating a response based upon a physical constant requirement;

a comparator coupled to said physical constant trigger circuit, said comparitor for comparing signals from said physical constant trigger circuit and determining when a change occurs in said response;

said comparator coupled to said physical constant trigger;

a voltage divider for providing a varying voltage to the physical constant trigger, said voltage divider coupled to said physical constant trigger;

an input signal port for conveying an input signal to said voltage divider, said input signal port coupled to said voltage divider;

a shutdown component for preventing circuit operation during shutdown mode, said shutdown component is coupled to said input signal port; and

an output for conveying an indication of the response, said output signal port coupled to said comparator.

2. The reference voltage identification system of claim 1 wherein said physical constant trigger circuit includes bipolar devices in which said response initiation comprises changing polarities of signals of said bipolar devices at a predetermined inflection point.

3. The reference voltage identification system of claim 2 wherein said predetermined inflection point corresponds to said physical constant.

4. The reference voltage identification system of claim 1 wherein said comparator compares polarity characteristics of said physical constant trigger circuit and identifies a change in said polarity characteristics.

5. The reference voltage identification system of claim 4 further comprising:

a voltage divider for providing a varying voltage to said physical constant trigger, said voltage divider coupled to said physical constant trigger circuit; and

a lockout circuit for providing a lockout signal before said change in polarities occurs, said lockout circuit coupled to said inputs signal port.

6. The reference voltage identification system of claim 1 said physical constant is associated with a precision reference voltage.

7. A reference voltage identification system comprising:

a physical constant trigger circuit including a plurality of transistors for initiating a response based upon a base emitter voltage associated with the temperature stable point of the transistors;

a comparator coupled to said physical constant trigger circuit, said comparitor for comparing signals from said physical constant trigger circuit and determining when a chance occurs in said response;

said comparitor coupled to said physical constant trigger;

a voltage divider for providing a varying voltage to the physical constant trigger, said voltage divider coupled to said physical constant trigger;

an input signal port for conveying an input signal to said voltage divider, said input signal port coupled to said voltage divider;

a shutdown component for preventing circuit operation during shutdown mode, said shutdown component is coupled to said input signal port; and

an output for conveying an indication of the response, said output signal port coupled to said comparator.

8. The reference voltage identification system of claim 7 wherein the transistors are configure to produce voltages with equal and opposite temperature coefficients.

9. The reference voltage identification system of claim 7 wherein the voltage supplied to the bases of said plurality of transistors determine the respective polarity and direction of currents at the collectors of said plurality of transistors.

10. The reference voltage identification system of claim 7 wherein there is an inflection point voltage associated with the transistor circuit stable point that results in equal collector voltages and currents.

11. The reference voltage identification system of claim 7 wherein collector voltages from said plurality of transistors are fed into said comparator circuit and said comparator detects when the voltages cross polarities.

12. The reference voltage identification system of claim 7 further comprising a lockout circuit for providing a lockout function, said lockout circuit coupled to said voltage divider and said comparator.

13. The reference voltage identification system of claim 11 where said lockout circuit prevents said comparator from incorrectly sensing a predetermined voltage level during a power up process.

14. The reference voltage identification system of claim 11 where said lockout circuit ensures a zero volt output until a predetermined inflection voltage is reached during a sweep up from zero and provides secondary protection against false logic.

15. A reference voltage identification method comprising:

monitoring an incoming signal;

determining when the incoming signal is at a particular voltage level associated with a physical constant;

preventing circuit operation during shutdown mode; and

providing an indication that the particular voltage level is provided.

16. A reference voltage identification method of claim 15 further comprising the step of changing the polarity of a signals when the particular voltage level is provided.

17. A reference voltage identification method of claim 15 wherein a delta voltage base to emitter (VBE) generator is utilized to monitor said incoming signal.

18. A reference voltage identification method of claim 17 wherein said physical constant is a sum of the VBE and delta VBE of the delta VBE associated with a temperature stable point of the delta VBE generator.

19. A reference voltage identification method of claim 15 wherein said indication is associated with a change in polarities of a signal at the collector of a transistor.

20. A reference voltage identification method of claim 15 further comprising the step of preventing a false indication that a reference voltage is available.