DC-DC converter with reservoir circuitry

1. A DC-DC converter for converting an input voltage at an input node, the converter comprising:

first and second inductor nodes for connection of an inductor therebetween;

first and second flying capacitor nodes for connection of a flying capacitor therebetween;

a first switching network for selectively connecting the first flying capacitor node to each of the input node and the first inductor node;

a second switching network for selectively connecting the second flying capacitor node to each of the input node and a reference voltage node; and

reservoir circuitry, comprising:

first and second reservoir capacitor nodes for connection of a reservoir capacitor therebetween;

a third switching network for selectively connecting the first reservoir capacitor node to each of the first and second flying capacitor nodes;

a fourth switching network for selectively connecting the second reservoir capacitor node to each of the second flying capacitor node and the reference voltage node; and

control circuitry;

wherein during a first phase of a stabilization mode, the control circuitry is operable to control the third and fourth switching networks to connect the reservoir capacitor and the flying capacitor in series; and

wherein during a second phase of the stabilization mode the control circuitry is operable to control the third and fourth switching networks to connect the reservoir capacitor and the flying capacitor in parallel.

2. The DC-DC converter of claim 1 , wherein the control circuitry is configured to control the first and second, switching networks.

3. The DC-DC converter of claim 1 , wherein the control circuitry is operable in a bolster mode to control the third and fourth switching networks to connect the reservoir capacitor in parallel with the flying capacitor for a duration of the bolster mode.

4. The DC-DC converter of claim 3 , wherein connecting the reservoir capacitor in parallel with the flying capacitor comprises:

connecting the first reservoir capacitor node to the first flying capacitor node; and

connecting the second reservoir capacitor node to the second flying capacitor node.

5. The DC-DC converter of claim 1 , wherein during the first phase of the stabilization mode, whilst the reservoir capacitor is connected in series with the flying capacitor, the control circuitry is operable to control the first and second switching networks to:

connect the first flying capacitor node to the input node; and

connect the second flying capacitor node to the first inductor node.

6. The DC-DC converter of claim 1 , wherein during the second phase of the stabilization mode, whilst the reservoir capacitor is connected in parallel with the flying capacitor, the control circuitry is operable to control the first and second switching networks to:

connect the first flying capacitor node to the first inductor node.

7. The DC-DC converter of claim 1 , wherein:

the first switching network comprises:

a first switch coupled between the first flying capacitor node and the input node and a second switch coupled between the first flying capacitor node and the first inductor node;

the second switching network comprises:

a third switch coupled between the second flying capacitor node and the inductor node and a fourth switch coupled between the second flying capacitor node and the reference voltage node;

the third switching network comprises:

a fifth switch coupled between the first reservoir capacitor node and the first flying capacitor node and a sixth switch coupled between the first reservoir capacitor node and the second flying capacitor node; and

the fourth switching network comprises:

a seventh switch coupled between the second reservoir capacitor node and the second flying capacitor node and an eight switch coupled between the second reservoir capacitor node and the reference voltage node.

8. The DC-DC converter of claim 7 , wherein the first, second, third, fourth, fifth, sixth, seventh and eighth switches are MOSFET devices or BJT devices or IGBT devices.

9. The DC-DC converter of claim 1 , further comprising a mode switch coupled between the second reservoir capacitor node and the input node.

10. The DC-DC converter of claim 1 , further comprising the flying capacitor and the reservoir capacitor.

11. The DC-DC converter of claim 1 , further comprising the inductor.

12. An integrated circuit comprising the DC-DC converter of claim 1 .

13. A DC-DC converter for converting an input voltage at an input node, the converter comprising:

first and second inductor nodes for connection of an inductor therebetween;

first and second flying capacitor nodes for connection of a flying capacitor therebetween;

a first switching network for selectively connecting the first flying capacitor node to each of the input node and to the first inductor node;

a second switching network for selectively the second flying capacitor node to the input node and a reference voltage node; and

reservoir circuitry, comprising:

first and second reservoir capacitor nodes for connection of a reservoir capacitor therebetween, the second reservoir capacitor node coupled to the reference voltage;

a reservoir switching network for selectively connecting the first reservoir capacitor node to each of the first flying capacitor node and the second flying capacitor node; and

control circuitry configured, during a boost mode, to control the first switching network, the second switching network and the reservoir switching network:

during a first phase, to connect the second flying capacitor node to the input node and the reference voltage node, and the first flying capacitor node to the input node and the first reservoir capacitor node; and

during a second phase, to connect the first flying capacitor node to the first inductor node, and the second flying capacitor node to the first reservoir capacitor node, wherein:

the first switching network comprises:

a first switch coupled between the first flying capacitor node and the input node and a second switch coupled between the first flying capacitor node and the first inductor node;

the second switching network comprises:

a third switch coupled between the second flying capacitor node and the inductor node and a fourth switch coupled between the second flying capacitor node and the reference voltage node; and

the reservoir switching network comprises:

a fifth switch coupled between the first reservoir capacitor node and the first flying capacitor node and a sixth switch coupled between the second reservoir capacitor node and the second flying capacitor node.

14. A DC-DC converter for converting an input voltage at an input node, the converter comprising:

first and second inductor nodes for connection of an inductor therebetween;

first and second flying capacitor nodes for connection of a flying capacitor therebetween;

a first switching network for selectively connecting the first flying capacitor node to each of the input node and the first inductor node;

a second switching network for selectively connecting the second flying capacitor node to each of the input node and a reference voltage node;

reservoir circuitry, comprising:

first and second reservoir capacitor nodes for connection of a reservoir capacitor therebetween;

a third switching network for selectively connecting the first reservoir capacitor node to each of the first and second flying capacitor nodes;

a fourth switching network for selectively connecting the second reservoir capacitor node to each of the second flying capacitor node and the reference voltage node; and

control circuitry operable in a boost mode,

wherein during a first phase of the boost mode, the control circuitry is operable to control the first and second switching networks and the reservoir circuitry to:

connect the reservoir capacitor and the flying capacitor in parallel; and

connect the input node to the first inductor node,

wherein during a second phase of the boost mode, the control circuitry is operable to control the first and second switching networks and the reservoir circuitry to connect the reservoir capacitor and the flying capacitor in series between the reference voltage node and the first inductor node.

15. A DC-DC converter for converting an input voltage at an input node, the converter comprising:

first and second inductor nodes for connection of an inductor therebetween;

first and second flying capacitor nodes for connection of a flying capacitor therebetween;

a first switching network for selectively connecting the first flying capacitor node to each of the input node and the first inductor node;

a second switching network for selectively connecting the second flying capacitor node to each of the input node and a reference voltage node;

reservoir circuitry, comprising:

first and second reservoir capacitor nodes for connection of a reservoir capacitor therebetween;

a third switching network for selectively connecting the first reservoir capacitor node to each of the first and second flying capacitor nodes;

a fourth switching network for selectively connecting the second reservoir capacitor node to each of the second flying capacitor node and the reference voltage node, wherein:

the first switching network comprises:

a first switch coupled between the first flying capacitor node and the input node and a second switch coupled between the first flying capacitor node and the first inductor node;

the second switching network comprises:

a third switch coupled between the second flying capacitor node and the inductor node and a fourth switch coupled between the second flying capacitor node and the reference voltage node;

the third switching network comprises:

a fifth switch coupled between the first reservoir capacitor node and the first flying capacitor node and a sixth switch coupled between the first reservoir capacitor node and the second flying capacitor node; and

the fourth switching network comprises:

a seventh switch coupled between the second reservoir capacitor node and the second flying capacitor node and an eight switch coupled between the second reservoir capacitor node and the reference voltage node.