Fast power-on detect circuit with accurate trip-points
View Patent ↗A power-on reset circuit includes a first PNP transistor having an emitter, a base, and a collector coupled to ground; a second PNP transistor having an emitter coupled to the base of the first transistor, and a base and collector coupled to ground; a third PNP transistor having an emitter, a base coupled to the base of the first transistor, and a collector coupled to ground; a first resistor coupled between VDD and an internal node; a second resistor coupled between VDD and the emitter of the first transistor; a third resistor coupled between the internal node and the emitter of the third transistor; and a comparator having a first input coupled to the internal node and a second input coupled to the emitter of the first transistor for generating a power-on reset signal.
1. A power-on reset circuit comprising:
a first transistor having an emitter, a base, and a collector coupled to a first voltage source;
a second transistor having an emitter coupled to the base of the first transistor, and a base and collector coupled to the first voltage source;
a third transistor having an emitter, a base coupled to the base of the first transistor, and a collector coupled to the first voltage source;
a first resistor coupled between a second voltage source and an internal node;
a second resistor coupled between the second voltage source and the emitter of the first transistor;
a third resistor coupled between the internal node and the emitter of the third transistor; and
a comparator having a first input coupled to the internal node and a second input coupled to the emitter of the first transistor for generating a power-on reset signal in response to a voltage at the first input being greater than a voltage at the second input,
wherein the second transistor is in the current path of the bases of the first and third transistors.
2. The power-on reset circuit of claim 1 wherein the first voltage source comprises VDD and the second voltage source comprises ground.
3. The power-on reset circuit of claim 1 wherein the first voltage source comprises ground and the second voltage source comprises VDD.
4. The power-on reset circuit of claim 1 wherein the first transistor comprises a PNP transistor.
5. The power-on reset circuit of claim 1 wherein the first transistor comprises an NPN transistor.
6. The power-on reset circuit of claim 1 wherein the second transistor comprises a PNP transistor.
7. The power-on reset circuit of claim 1 wherein the second transistor comprises an NPN transistor.
8. The power-on reset circuit of claim 1 wherein the third transistor comprises a PNP transistor.
9. The power-on reset circuit of claim 1 wherein the third transistor comprises an NPN transistor.
10. The power-on reset circuit of claim 1 wherein the first input of the comparator comprises a positive input.
11. The power-on reset circuit of claim 1 wherein the second input of the comparator comprises a negative input.
12. A power-on reset circuit comprising:
a first leg having a first resistor and a first transistor for generating a first voltage;
a second leg having a second resistor, a third resistor, and a second transistor for generating a second voltage;
a diode-connected transistor in the current path of the bases of the first and second transistors; and
a comparator having a first input for receiving the first voltage, a second input for receiving the second voltage, and an output for generating a power-on reset signal in response to a voltage at the first input being greater than a voltage at the second input.
13. A method of generating a power-on reset signal comprising:
providing a first leg having a first resistor and a first transistor for generating a first voltage;
providing a second leg having a second resistor, a third resistor, and a second transistor for generating a second voltage;
providing a diode-connected transistor in the current path of the bases of the first and second transistors; and
providing a comparator having a first input for receiving the first voltage, a second input for receiving the second voltage, and an output for generating the power-on reset signal in response to a voltage at the first input being greater than a voltage at the second input.
14. A power-on reset circuit comprising:
a first transistor having an emitter, a base, and a collector coupled to a first voltage source;
a diode coupled between the base of the first transistor and the first voltage source;
a second transistor having an emitter, a base coupled to the base of the first transistor, and a collector coupled to the first voltage source;
a first resistor coupled between a second voltage source and an internal node;
a second resistor coupled between the second voltage source and the emitter of the first transistor;
a third resistor coupled between the internal node and the emitter of the second transistor; and
a comparator having a first input coupled to the internal node and a second input coupled to the emitter of the first transistor for generating a power-on reset signal in response to a voltage at the first input being greater than a voltage at the second input,
wherein the diode is in the current path of the bases of the first and second transistors.
15. The power-on reset circuit of claim 14 wherein the first voltage source comprises VDD and the second voltage source comprises ground.
16. The power-on reset circuit of claim 14 wherein the first voltage source comprises ground and the second voltage source comprises VDD.
17. The power-on reset circuit of claim 14 wherein the first transistor comprises a PNP transistor.
18. The power-on reset circuit of claim 14 wherein the first transistor comprises an NPN transistor.
19. The power-on reset circuit of claim 14 wherein the second transistor comprises a PNP transistor.
20. The power-on reset circuit of claim 14 wherein the second transistor comprises an NPN transistor.