Boost inductor recirculation protection based on switch node detection method

1. A method of operating a switch mode power supply (SMPS), the method comprising:

following an initial startup of the SMPS, sensing an input voltage (V IN ) coupled through a boost-inductor to a switch pin (BSW-pin) of a primary integrated circuit (IC) in the SMPS by isolating a DC component (V DC_BSW ) of a switching voltage (V BSW ) coupled to the BSW-pin;

checking if V IN is greater than or equal to a minimum input voltage (V IN_MIN ) by comparing V DC_BSW to a starting reference voltage (V REF_START ) in the primary IC; and

if V DC_BSW is greater than or equal to V REF_START :

operating a boost-converter to turn on boost-mode by cycling a boost-switch in the primary IC through which the BSW-pin is coupled to ground on and off to alternately store and discharge energy in the boost-inductor; and

boosting a supply voltage (Vcc) to a Vcc-pin of the primary IC coupled to the BSW-pin and boost-inductor through a rectifier and to ground though a capacitor on which Vcc is generated.

2. The method of claim 1 wherein if V IN is not greater than or equal to V IN_MIN the method comprises confirming the boost-mode is turned off by operating the boost-converter to turn off the boost-switch, while powering the primary IC with a startup circuit, and repeating checking if V IN is greater than or equal to V IN_MIN .

3. The method of claim 1 further comprising after turning on boost-mode checking if V IN is greater than or equal to a maximum input voltage (V IN_MAX ) by comparing V DC_BSW to a reference voltage (V REF ) in the primary IC, where V REF is greater than V REF_START , and if V DC_BSW is greater than or equal to V REF , the method further comprises operating the boost-converter to turn off boost-mode by turning off and ceasing to cycle the boost-switch on and off.

4. The method of claim 3 further comprising after turning off boost-mode, checking if V IN has decreased to less than or equal to a V IN under voltage level (V IN_UV ), and if V IN has decreased to less than or equal V IN_UV , the method further comprises checking if V IN is greater than or equal V IN_MIN , and if V IN is greater than or equal V IN_MIN turning boost-mode back on by resuming cycling the boost-switch on and off.

5. The method of claim 4 wherein checking to determine if V IN has decreased to less than or equal to V IN_UV comprises comparing V DC_BSW to V REF and determining if V DC_BSW is more than an offset voltage (V OFF ) below V REF .

6. The method of claim 5 wherein if V IN has not decreased to less than or equal V IN_UV the method further comprises repeating checking to determine if V IN has decreased to less than or equal to V IN_UV .

7. The method of claim 5 wherein comparing V DC_BSW to V REF comprises coupling V DC_BSW to an inverting input of a comparator in the primary IC while coupling V REF to a non-inverting input of the comparator, and wherein the V OFF is provided by a hysteresis of the comparator implemented by a positive feedback loop from an output of the comparator to the non-inverting input.

8. The method of claim 1 wherein comparing V DC_BSW to V REF_START comprises comparing V DC_BSW to V REF_START using a comparator in the primary IC, and wherein isolating V DC_BSW comprises dividing and filtering V BSW using a voltage divider and a low pass filter in the primary IC through which the BSW-pin is coupled to an input of the comparator.

9. A boost-converter comprising:

a boost-inductor coupled between a voltage input and a boost-switch pin (BSW-pin) of a primary integrated circuit (IC) in a switch mode power supply (SMPS), the boost-inductor operable to receive an input voltage (V IN ) and couple a switching voltage (V BSW ) to the BSW-pin;

a voltage supply-pin (Vcc-pin) in the primary IC coupled to the BSW-pin and the boost-inductor through a diode, the Vcc-pin further coupled to ground through a capacitor to generate a supply voltage (Vcc) on the Vcc-pin; and

a boost-circuit in the primary IC coupled to the BSW-pin, and including a controller coupled to a boost-switch through which the BSW-pin is coupled to ground, the controller operable to turn on boost-mode by cycling the boost-switch on and off to alternately store energy in and discharge the boost-inductor boosting Vcc,

wherein the boost-circuit is further operable to sense V IN , determine if V IN is greater than or equal to a maximum input voltage (V IN_MAX ), and if V IN is greater than or equal to V IN_MAX to protect the boost-inductor from damage due to current runaway by turning off boost-mode by turning off and ceasing to cycle the boost-switch.

10. The boost-converter of claim 9 wherein the boost-circuit further includes a comparator having an inverting input coupled to the BSW-pin through an internal voltage divider and a low pass filter, and a first non-inverting input coupled to an internal reference voltage (V REF ), and wherein the boost-circuit is operable to determine if V IN is greater than or equal to V IN_MAX by isolating a DC component (V DC_BSW ) of a switching voltage (V BSW ) on the BSW-pin by dividing and filtering V BSW using the voltage divider and low pass filter, and to compare V DC_BSW to V REF using the comparator.

11. The boost-converter of claim 10 wherein the boost-circuit is further operable to sense if V IN has decreased to less than or equal to an under voltage level (V IN_UV ) by determining if V DC_BSW is greater than or equal to an offset voltage (V OFF ) below V REF , and if V IN is less than or equal to V IN_UV to sense if V IN is greater than or equal to a minimum input voltage (V IN_MIN ), and if V IN is greater than or equal to V IN_MIN to turn the boost-mode back on by resuming cycling the boost-switch on and off.

12. The boost-converter of claim 11 wherein the V OFF is based on a hysteresis of the comparator implemented by a positive feedback loop from an output of the comparator to the non-inverting input to provide the V OFF .

13. The boost-converter of claim 10 wherein the comparator further comprises a second non-inverting input coupled to a starting reference voltage (V REF_START ), and wherein the boost-circuit is further operable following an initial startup of the SMPS to sense if V IN is greater than or equal to a minimum input voltage (V IN_MIN ), by determining if V DC_BSW is greater than or equal to V REF_START , and to turn on boost-mode by cycling the boost-switch on and off to alternately store and discharge energy in the boost-inductor, boosting Vcc.

14. The boost-converter of claim 9 wherein the SMPS is a universal serial bus power delivery (USB-PD) power supply including a transformer comprising an auxiliary winding, and wherein the boost-inductor is coupled to an output of the auxiliary winding to receive V IN therefrom.

15. A switch mode power supply (SMPS) comprising:

a transformer including a primary side coupled to receive an input voltage and having a power switch (PS) coupled between the input voltage and the primary side, and a secondary side coupled to an output to provide an output voltage thereon;

a primary side controller operable to control the PS, the primary side controller including:

a primary integrated circuit (IC) having a switch pin (BSW-pin) and a voltage supply-pin (Vcc-pin) through which a supply voltage (Vcc) is supplied to power the primary IC; and

a boost-converter comprising:

a boost-inductor coupled between an auxiliary winding in the transformer and the BSW-pin, the boost-inductor operable to receive an input voltage (V IN ) and couple a switching voltage (V BSW ) to the BSW-pin;

a diode through which the Vcc-pin is coupled to the boost-inductor and the BSW-pin;

a capacitor through which the Vcc-pin is coupled to ground to generate Vcc; and

a boost-circuit in the primary IC coupled to the BSW-pin, and including a controller coupled to a boost-switch through which the BSW-pin is coupled to ground, the controller operable to turn on boost-mode by cycling the boost-switch on and off to alternately store energy in and discharge the boost-inductor boosting Vcc,

wherein the boost-circuit is further operable to sense V IN , determine if V IN is greater than or equal to a maximum input voltage (V IN_MAX ), and if V IN is greater than or equal to V IN_MAX to protect the boost-inductor from damage due to current runaway by turning off boost-mode by turning off and ceasing to cycle the boost-switch.

16. The SMPS of claim 15 wherein the boost-circuit further includes a comparator having an inverting input coupled to the BSW-pin through an internal voltage divider and a low pass filter, and a first non-inverting input coupled to an internal reference voltage (V REF ), and wherein the boost-circuit is operable to determine if V IN is greater than or equal to V IN_MAX by isolating a DC component (V DC_BSW ) of a switching voltage (V BSW ) on the BSW-pin by dividing and filtering V BSW using the voltage divider and low pass filter, and to compare V DC_BSW to V REF using the comparator.

17. The SMPS of claim 16 wherein the boost-circuit is further operable to sense if V IN has decreased to less than or equal to an under voltage level (V IN_UV ) by determining if V DC_BSW is greater than or equal to an offset voltage (V OFF ) below V REF , and if V IN is less than or equal to V IN_UV to sense if V IN is greater than or equal to a minimum input voltage (V IN_MIN ), and if V IN is greater than or equal to V IN_MIN to turn the boost-mode back on by resuming cycling the boost-switch on and off.

18. The SMPS of claim 17 wherein the V OFF is based on a hysteresis of the comparator implemented by a positive feedback loop from an output of the comparator to the non-inverting input to provide the V OFF .

19. The SMPS of claim 16 wherein the comparator further comprises a second non-inverting input coupled to a starting reference voltage (V REF_START ), and wherein the boost-circuit is further operable following an initial startup of the SMPS to sense if V IN is greater than or equal to a minimum input voltage (V IN_MIN ), by determining if V DC_BSW is greater than or equal to V REF_START , and to turn on boost-mode by cycling the boost-switch on and off to alternately store and discharge energy in the boost-inductor, boosting Vcc.

20. The SMPS of claim 15 wherein the SMPS is a universal serial bus power delivery (USB-PD) power supply.