Under voltage lock-out circuit

1. An electronic circuit comprising:

a GaN FET power switch; and

a driver for the GaN FET power switch, the driver including:

a reference device for generating a reference voltage,

a GaN-based under-voltage detector having a first input terminal receiving a supply voltage, a second input terminal for receiving a voltage at ground potential, a third input terminal receiving the reference voltage, and an output terminal, wherein the reference voltage is referred to the supply voltage, and wherein the GaN-based under-voltage detector outputs an under voltage lock-out signal when the supply voltage is below a low-to-high threshold value, and does not output the under voltage lock-out signal when the supply voltage is above the low-to-high threshold value, and

a pulse stretcher having an input terminal coupled to the output terminal of the GaN-based under-voltage detector, and an output terminal for outputting a stretched under voltage lock-out signal for a predetermined amount of time after the supply voltage first rises above the low-to-high threshold value, the pulse stretcher comprising:

a first transistor having a drain, a source coupled to ground potential, and a gate coupled to the input terminal of the pulse stretcher,

a first resistor coupled between the supply voltage and the drain of the first transistor,

a second resistor having one end coupled to the drain of the first transistor,

a first capacitor coupled between another end of the second resistor and ground potential,

a first diode having an anode coupled to the other end of the second resistor, a third resistor having one end coupled to a cathode of the first diode,

a second capacitor coupled between another end of the third resistor and ground potential,

a second diode having an anode coupled to another end of the third resistor,

a third diode having an anode coupled to a cathode of the second diode and a cathode coupled to ground potential,

a second transistor having a drain coupled to the other end of the third resistor, a source coupled to ground potential, and a gate coupled to the input terminal of the pulse stretcher,

a third transistor having a drain, a gate coupled to the other end of the third resistor, and a source coupled to ground potential, and

a fourth resistor coupled between the supply voltage and the drain of the third transistor,

wherein the stretched under voltage lock-out signal is produced at the drain of the third transistor.

2. The electronic circuit of claim 1 , wherein the reference device is fabricated using a silicon process.

3. The electronic circuit of claim 2 , wherein the reference device is a Zener diode.

4. The electronic circuit of claim 1 , wherein the predetermined amount of time is a function of ramp rate of the supply voltage.

5. The electronic circuit of claim 4 , wherein the predetermined amount of time increases as the ramp rate of the supply voltage decreases.

6. The electronic circuit of claim 1 , wherein the low-to-high threshold value is independent of threshold voltage of GaN devices of the GaN-based under-voltage detector.

7. An integrated circuit, comprising:

a substrate;

a GaN FET power switch disposed on the substrate; and

a GaN-based driver disposed on the substrate and coupled to the GaN FET power switch, the GaN-based driver having an input terminal for receiving a supply voltage, the GaN-based driver including:

an under-voltage detector comprising:

a first GaN transistor having source and gate coupled to the input terminal and a drain coupled to ground through first and second resistors connected in series and having a node therebetween,

a second GaN transistor having a gate coupled to the node,

a third resistor having one end coupled to the input terminal and another end coupled to a drain of the second GaN transistor,

a third GaN transistor having a gate coupled to the node and a source coupled to ground,

a fourth resistor coupled between a source of the second GaN transistor and a drain of the third GaN transistor,

a fourth GaN transistor having a gate coupled to the other end of the third resistor, a source coupled to the source of the second GaN transistor, and a drain coupled to the drain of the first GaN transistor through a fifth resistor, and

an output terminal at the drain of the second transistor for generating an under voltage lock-out signal,

wherein the under-voltage detector outputs the under voltage lock-out signal when the supply voltage is below a low-to-high threshold value, and does not output the under voltage lock-out signal when the supply voltage is above the low-to-high threshold value, and

a pulse stretcher having an input terminal coupled to the output terminal of the under-voltage detector and an output terminal for outputting a stretched under voltage lock-out signal for a predetermined amount of time after the supply voltage rises above the low-to-high threshold value.

8. The integrated circuit of claim 7 , wherein a minimum low-to-high threshold value is greater than 2 times threshold voltage of fabrication process of the GaN-based driver.

9. The integrated circuit of claim 8 , wherein the minimum low-to-high threshold value tracks the threshold voltage of the fabrication process of the GaN-based driver.

10. The integrated circuit of claim 7 , wherein the predetermined amount of time is a function of ramp rate of the supply voltage.

11. The integrated circuit of claim 10 , wherein the predetermined amount of time increases as the ramp rate of the supply voltage decreases.

12. The electronic circuit of claim 1 , wherein the pulse stretcher is totally GaN-based.

13. The electronic circuit of claim 12 , wherein each transistor is a N-channel enhancement-mode GaN high-electron-mobility transistor.

14. The integrated circuit of claim 7 , wherein all the resistors are GaN-based.