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:
first and second input terminals, and first and second output terminals, wherein the first and second input terminals are configured to be coupled to a first voltage source;
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 series-connected switches Sx connected between the first input terminal and the first output terminal and a plurality of charge pump capacitors, each connected between corresponding adjacent pairs of the plurality of series-connected switches;
a regulator circuit coupled to the first and second output terminals and configured to be coupled to a second voltage source; and
a controller coupled to the regulator circuit,
wherein the controller is configured to selectively connect and disconnect the charge pump from the second voltage source.
2. The switched-capacitor power converter of claim 1 , wherein the controller is configured to disable the regulator circuit in a startup mode of operation.
3. The switched-capacitor power converter of claim 2 , wherein disabling the regulator circuit comprises disconnecting the charge pump from the second voltage source.
4. The switched-capacitor power converter of claim 2 , wherein the controller is configured to disable the regulator circuit until the plurality of charge pump capacitors are charged from the first voltage source to at least a predetermined voltage level, and thereafter to enable the regulator circuit, thereby connecting the second voltage source to the charge pump.
5. The switched-capacitor power converter of claim 4 , wherein enabling the regulator circuit comprises connecting the charge pump to the second voltage source.
6. The switched-capacitor power converter of claim 1 , wherein the controller is configured to enable the regulator circuit in a startup mode of operation.
7. The switched-capacitor power converter of claim 6 , wherein the controller is configured to enable the regulator circuit when the series-connected switches Sx begin switching.
8. The switched-capacitor power converter of claim 1 , further comprising an intermediate capacitor coupled to the charge pump and coupled to the first and second output terminals.
9. The switched-capacitor power converter of claim 1 , wherein the regulator circuit comprises an inductor-based switching regulator.
10. A switched-capacitor power converter including:
a charge pump including a plurality of charge pump capacitors;
a first voltage node;
a second voltage node;
at least one disconnect switch coupled between (1) the charge pump and the first voltage node, and/or (2) the charge pump and the second voltage node;
a controller coupled to the disconnect switch;
wherein if the at least one disconnect switch is coupled between the charge pump and the first voltage node, then during startup of the switched-capacitor power converter, the controller is configured to: (1) open the coupled at least one disconnect switch, thereby disconnecting the charge pump from the first voltage node; (2) enable operation of the charge pump until the plurality of charge pump capacitors are charged to at least a desired voltage; and (3) thereafter close the coupled at least one disconnect switch, thereby enabling operation of the charge pump; and
wherein if the at least one disconnect switch is coupled between the charge pump and the second voltage node, then during startup of the switched-capacitor power converter, the controller is configured to: (1) open the coupled at least one disconnect switch, thereby disconnecting the charge pump from the second voltage node until the plurality of charge pump capacitors are charged from the first voltage node to at least a desired voltage level, and (2) thereafter close the coupled at least one disconnect switch, thereby enabling operation of the charge pump.
11. The switched-capacitor power converter of claim 10 , wherein if the at least one disconnect switch is coupled between the charge pump and the first voltage node, then when operation of the charge pump is enabled by the controller after the coupled disconnect switch is opened, the charge pump is configured to operate in a step-up mode of voltage conversion until the plurality of charge pump capacitors are charged to at least a desired voltage.
12. The switched-capacitor power converter of claim 11 , wherein if the at least one disconnect switch is coupled between the charge pump and the first voltage node, when the coupled at least one disconnect switch is closed, the charge pump is configured to operate in a step-down mode of voltage conversion.
13. The switched-capacitor power converter of claim 12 , wherein the controller is configured to provide an intermediate state between operation of the charge pump in a step-up mode and operation of the charge pump in a step-down mode in which charge pump operation is paused and then the at least one disconnect switch is closed.
14. The switched-capacitor power converter of claim 10 , wherein the at least one disconnect switch is configured to provide bidirectional isolation.
15. The switched-capacitor power converter of claim 10 , wherein the at least one disconnect switch includes two series-connected FET switches having corresponding body diodes configured with opposite polarities.
16. A method of limiting in-rush current to a plurality of charge pump capacitors and/or preventing over-stress in a switched-capacitor power converter, each charge pump capacitor being connected between corresponding adjacent pairs of a plurality of series-connected switches Sx, the method comprising:
increasing an ON resistance R ON of the series-connected switches Sx from a first ON resistance value for at least one of:
a first selected duration of time,
a first number of switching cycles, and/or
until a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range; and
decreasing the ON resistance RON of the series-connected switches Sx toward the first ON resistance value.
17. The method of claim 16 , wherein at least some of the plurality of series-connected switches Sx includes a corresponding auxiliary switch/pathway SxA having a higher ON resistance RON than the corresponding switch Sx, wherein increasing the ON resistance R ON of the series-connected switches Sx comprises using the auxiliary switches/pathways SxA in lieu of the corresponding switches Sx.
18. The method of claim 17 , further including increasing the frequency of switching of the series-connected switches Sx for a second selected duration of time and/or a second number of switching cycles and/or until a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
19. The method of claim 16 , wherein the plurality of series-connected switches Sx each comprise a field-effect transistor (FET) having a gate configured to control the ON resistance R ON of the FET, each FET configured to have its gate coupled to a source of gate drive voltage, wherein increasing the ON resistance RON of the series-connected switches Sx comprises reducing the gate drive voltage to the respective gates of the FETs.
20. The method of claim 19 , further including increasing the frequency of switching of the series-connected switches Sx for a second selected duration of time and/or a second number of switching cycles and/or until a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.