Li-ion-compatible fully-integrated hybrid converter
View Patent ↗A DC-DC converter converts voltage from a battery source providing a voltage V in to a lower level. A four-level transistor stack selectively connects an input voltage and flying capacitor voltages to an output inductor. Stress reduction transistors limit the charging of the flying capacitors to V in /3. The stress reduction transistors can also limit switching transistor voltages to V in /3. Freewheel switches can be used to limit ringing in the output inductor.
1. A DC-DC converter for converting voltage from a battery source providing a voltage V in , the converter comprising: integrated capacitors and transistors arranged as a hybrid 4-level buck converter with 4-level transistor stack having a pair of flying capacitors C f1 and C f2 connected thereto, an output inductor connected to a center of the 4-level transistor stack, a pair of series stress reduction transistors, one being between two of the transistors in the 4-level transistor stack and the other being between ground and the 4-level transistor stack, and a parallel stress reduction transistor in parallel with at least a portion of the 4-level transistor stack, wherein the series and parallel stress reduction transistors are arranged to limit voltage on each of the flying capacitors to V in /3.
2. The DC-DC converter of claim 1 , further comprising freewheel switches in parallel with the output inductor.
3. The DC-DC converter of claim 2 , wherein the freewheel switches are sized to turn ON only when current in the output inductor is zero.
4. The DC-DC converter of claim 2 , wherein the flying capacitors C f1 and C f2 and the output inductor are connected to internal nodes of the 4-level transistor stack.
5. The DC-DC converter of claim 2 , comprising drivers to drive the 4-level transistor stack, wherein the flying capacitors C f1 and C f2 are arranged to serve as power rails for the drivers.
6. The DC-DC converter of claim 1 , wherein the 4-level transistor stack and the stress reduction transistors consist of 1.5V transistors, and the converter can block a 2.8-4.2V Li-ion battery voltage range.
7. The DC-DC converter of claim 1 , wherein the flying capacitors C f1 and C f2 are sized according to:
C
v
≥
LI
p
k
2
2
V
i
n
(
1
3
-
C
R
)
Δ
V
max
where I pk is the peak inductor current, CR is the conversion ratio (CR=V out /V in ), and ΔV max is a maximum allowed flying capacitor ripple.
8. The DC-DC converter of claim 1 , wherein ΔV max is ≤100 mV.
9. The DC-DC converter of claim 1 , wherein all transistors and passives are sized such that gate-to-source V gs gate-to-drain V gd and drain-to-source V ds voltages of each transistor in the 4-level transistor stack never exceed V in /3 during charging, discharging, or not connected (NC) operation so that capacitor charges are balanced after a switching cycle.
10. The DC-DC converter of claim 9 , comprising a controller and driver that insure C f1 and C f2 are not shorted during switching transitions.
11. The DC-DC converter of claim 1 , wherein a positive terminal of C f2 and a negative terminal of C f2 (V b2 ) are used as power and ground of drivers that drive middle switches of the 4-level transistor stack.
12. The DC-DC converter of claim 1 , wherein all transistors in the converter are fully depleted silicon-on-insulator body biased transistors.
13. The DC-DC converter of claim 1 , comprising:
a finite state machine that provides signals switching between GND and V in /3 for driving the transistors in the 4-level transistor stack based upon a difference between an output voltage of the converter and a reference voltage;
drivers receiving a signal from the finite state machine and driving transistors in the 4-level transistor stack; and
a level shifter for raising the signals of the finite state aching to signals that switch between 2V in /3 and V in .
14. The DC-DC converter of claim 12 , wherein the battery source is a lithium ion battery.
15. The DC-DC converter of claim 1 , comprising drivers for driving transistors in the 4-level transistor stack, wherein the drivers provide three-level gate signals to middle transistors of the 4-level transistor stack, and wherein the drivers switch between GND, Vi n /3, and 2V in /3.
16. The DC-DC converter of claim 15 , wherein the drivers have circuitry to delay negative edges of the switching of the middle transistors in the 4-level transistor stack with respect to rising edges of top and bottom transistors in the 4-level transistor stack.
17. A DC-DC converter for converting voltage from a battery source providing a voltage V in , the converter comprising:
switching means for selectively connecting an input voltage and flying capacitor voltages to an output inductor;
stress reduction means for limiting the charging of the flying capacitors to V in /3.
18. The DC-DC converter of claim 17 , further comprising ringing reduction means for reducing ringing in the output inductor.
19. The DC-DC converter of claim 17 , comprising means for driving the switching means to limit transistors charging the flying capacitors to V in /3.
20. The DC-DC converter of claim 17 , wherein the stress reduction means limits voltages across transistors of the switching means to V in /3.