Startup of switched capacitor step-down power converter
Circuit embodiments for a switched-capacitor power converter, and/or methods of operation of such a converter, that robustly deal with various startup scenarios, are efficient and low cost, and have quick startup times to steady-state converter operation. Embodiments prevent full charge pump capacitor discharge during shutdown of a converter and/or rebalance charge pump capacitors during a startup period before switching operation by discharging and/or precharging the charge pump capacitors. Embodiments may include a dedicated rebalancer circuit that includes a voltage sensing circuit coupled to an output voltage of a converter, and a balance circuit configured to charge or discharge each charge pump capacitor towards a target steady-state multiple of the output voltage of the converter as a function of an output signal from the voltage sensing circuit indicative of the output voltage. Embodiments prevent or limit current in-rush to a converter during a startup state.
1. A switched-capacitor power converter including:
(a) first and second input terminals, and first and second output terminals;
(b) a plurality of series-connected switches connected between the first input terminal and the first output terminal;
(c) a plurality of charge pump capacitors, each connected between corresponding adjacent pairs of the plurality of series-connected switches; and
(d) a controller coupled to the plurality of series-connected switches;
wherein the controller is configured to reduce the rate of charge transfer between the plurality of charge pump capacitors by controlling the ON resistance R ON of the series-connected switches during a pre-switching period of a startup state of the switched-capacitor power converter.
2. The invention of claim 1 , wherein the ON resistance R ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
3. The invention of claim 1 , wherein at least some of the plurality of series-connected switches includes a corresponding auxiliary switch/pathway having a higher ON resistance R ON than the corresponding series-connected switch, and wherein the controller is configured to increase the ON resistance RO N of the series-connected switches Sx by using the auxiliary switches/pathways in lieu of the corresponding switches.
4. The invention of claim 3 , wherein the plurality of series-connected switches are switched at a selected frequency, and the controller is further configured to increase the frequency of switching during the pre-switching period of the startup state of the switched-capacitor power converter.
5. The invention of claim 4 , wherein the increase the frequency of switching is increased for at least one of a second selected duration of time, and/or for a second number of switching cycles, and/or while a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
6. The invention of claim 5 , wherein the ON resistance R ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
7. The invention of claim 1 , wherein the plurality of series-connected switches each comprise a field-effect transistor (FET) having a gate that controls the ON resistance R ON of the FET, each FET configured to have its gate coupled to a source of gate drive voltage, and wherein the controller is configured to increase the ON resistance R ON of the series-connected switches by reducing the gate drive voltage to the respective gates of the FETs.
8. The invention of claim 7 , wherein the plurality of series-connected switches are switched at a selected frequency, and the controller is further configured to increase the frequency of switching during the pre-switching period of the startup state of the switched-capacitor power converter.
9. The invention of claim 8 , wherein the increase the frequency of switching is increased for at least one of a second selected duration of time, and/or for a second number of switching cycles, and/or while a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
10. The invention of claim 9 , wherein the ON resistance R ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
11. The invention of claim 1 , wherein the switched-capacitor power converter is configured as one of a boost power converter, a buck power converter, or a buck-boost power converter.
12. A switched-capacitor power converter including:
(a) first and second input terminals and first and second output terminals;
(b) a disconnect switch coupled to the first input terminal and configured to be coupled to a first voltage source;
(c) a second voltage source coupled to the first and second output terminals, wherein a voltage across the second voltage source is less than a voltage across the first voltage source;
(d) a charge pump coupled between the first and second input terminals and the first and second output terminals, the charge pump including a plurality of charge pump capacitors;
(e) a controller coupled to the disconnect switch;
wherein the controller is configured to open the disconnect switch in a startup mode of operation, thereby disconnecting the first voltage source from the charge pump and enabling operation of the charge pump in a step-up mode of voltage conversion until the plurality of charge pump capacitors are charged to at least a desired voltage, and thereafter to close the disconnect switch, thereby connecting the first voltage source to the charge pump and enabling operation of the charge pump in a step-down mode of voltage conversion.
13. The invention of claim 12 , wherein the controller is configured to close the disconnect switch in a gradual manner to limit a current in-rush to the charge pump.
14. The invention of claim 12 , wherein the controller is configured to provide an intermediate state between operation of the charge pump in the step-up mode and operation of the charge pump in the step-down mode in which charge pump operation is paused and then the disconnect switch is closed.
15. The invention of claim 12 , wherein the disconnect switch provides bi-directional isolation.
16. The invention of claim 12 , wherein the disconnect switch includes two series-connected FET switches having corresponding body diodes configured with opposite polarities.
17. A switched-capacitor power converter including:
(a) first and second input terminals and first and second output terminals, wherein the first and second input terminals are coupled to a first voltage source;
(b) a disconnect switch coupled to the first output terminal and configured to be coupled to a second voltage source;
(c) a charge pump coupled between the first and second input terminals and the first and second output terminals, the charge pump including a plurality of charge pump capaci- tors;
(d) a controller coupled to the disconnect switch;
wherein the controller is configured to open the disconnect switch in a startup mode of operation, thereby disconnecting the second voltage source from the charge pump until the plurality of charge pump capacitors are charged from the first voltage source to at least a desired voltage level, and thereafter to close the disconnect switch, thereby connecting the second voltage source to the charge pump and enabling operation of the charge pump.
18. The invention of claim 17 , wherein the controller is configured to close the disconnect switch in a gradual manner to limit a current in-rush to the charge pump.
19. The invention of claim 17 , wherein the disconnect switch provides bi-directional isolation.
20. The invention of claim 17 , wherein the disconnect switch includes two series-connected FET switches having corresponding body diodes configured with opposite polarities.