Capacitor balanced driver circuit for dual input charger
A driver circuit includes two high-side switches and a single low-side switch, output inductor, and output capacitor. By having multiple high-side switches, the driver can regulate power from multiple charging devices. The high-side switches share a channel with an input capacitor for that channel and the channels are connected to the low-side switch at a common node. When the capacitor for one of the channels becomes charged quickly, the capacitor of the other channel will balance itself with the charged capacitor. To avoid damaging the high-side switches, a low-impedance bridge and driver circuit is connected between the channels.
1. An apparatus comprising:
a first channel having a first high-side switch having a first terminal configured to receive a first voltage, and a second terminal;
a second channel having a second high-side switch having a first terminal configured to receive a second voltage, and a second terminal coupled to the second terminal of the first high-side switch at a common node; and
a control circuit having a first end coupled to the first terminal of the first high-side switch, a second end coupled to the first terminal of the second high-side switch, and a current path between the first and second ends, the control circuit configured to detect an imbalance between the first voltage and the second voltage, and divert a current from the first high-side switch and the second high-side switch to the current path based on the imbalance.
2. The apparatus of claim 1 , wherein the current path includes:
a first N-type field effect transistor (NFET) having a drain coupled to the first end, a gate, and a source; and
a second NFET having a drain coupled to the second end, a gate, and a source coupled to the source of the first NFET.
3. The apparatus of claim 2 , wherein the control circuit is configured to enable the gate of the first NFET when the first voltage is greater than the second voltage.
4. The apparatus of claim 3 , wherein the second NFET is conductive via a body diode when the first voltage is greater than the second voltage.
5. The apparatus of claim 2 , wherein the control circuit is configured to enable the gate of the second NFET when the second voltage is greater than the first voltage.
6. The apparatus of claim 5 , wherein the first NFET is conductive via a body diode when the second voltage is greater than the first voltage.
7. The apparatus of claim 2 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the first NFET;
a resistor coupled between the anode and the source of the first NFET;
a capacitor coupled between the gate and the source of the first NFET; and
an adjustable current source coupled to the gate of the first NFET, the adjustable current source configured to adjust a charge current to the capacitor based on the imbalance.
8. The apparatus of claim 2 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the second NFET;
a resistor coupled between the anode and the source of the second NFET;
a capacitor coupled between the gate and the source of the second NFET; and
an adjustable current source coupled to the gate of the second NFET, the adjustable current source configured to adjust a charge current to the capacitor based on the imbalance.
9. The apparatus of claim 1 , further comprising:
a single low-side switch having a first terminal coupled to the common node, and a second terminal coupled to a ground terminal.
10. The apparatus of claim 1 , further comprising:
first and second voltage input terminals;
a first input switch coupled between the first voltage input terminal and the first terminal of the first high-side switch; and
a second input switch coupled between the second voltage input terminal and the first terminal of the second high-side switch.
11. A battery charger comprising:
a first input channel having a first high-side switch having a first terminal configured to receive a first voltage, and a second terminal;
a second input channel having a second high-side switch having a first terminal configured to receive a second voltage, and a second terminal coupled to the second terminal of the first high-side switch at a common node;
a first N-type field effect transistor (NFET) having a drain coupled to the first terminal of the first high-side switch, a gate, and a source;
a second NFET having a drain coupled to the first terminal of the second high-side switch, a gate, and a source coupled to the source of the first NFET; and
a control circuit configured to enable the gate of the first NFET when the first voltage is greater than the second voltage, and configured to enable the gate of the second NFET when the second voltage is greater than the first voltage.
12. The battery charger of claim 11 , wherein the second NFET is conductive via a body diode when the first voltage is greater than the second voltage.
13. The battery charger of claim 11 , wherein the first NFET is conductive via a body diode when the second voltage is greater than the first voltage.
14. The battery charger of claim 11 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the first NFET;
a resistor coupled between the anode and the source of the first NFET;
a capacitor coupled between the gate and the source of the first NFET; and
an adjustable current source coupled to the gate of the first NFET, the adjustable current source configured to increase a current to the capacitor when the first voltage is greater than the second voltage.
15. The battery charger of claim 11 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the second NFET;
a resistor coupled between the anode and the source of the second NFET;
a capacitor coupled between the gate and the source of the second NFET; and
an adjustable current source coupled to the gate of the second NFET, the adjustable current source configured to increase a current to the capacitor when the second voltage is greater than the first voltage.
16. A battery charger comprising:
a first input channel having a first voltage input terminal, a first high-side switch, and a first input switch coupled between the first voltage input terminal and the first terminal of the first high-side switch;
a second input channel having a second voltage input terminal, a second high-side switch, and a second input switch coupled between the second voltage input terminal and the first terminal of the second high-side switch;
a first N-type field effect transistor (NFET) having a drain coupled to a first terminal of the first high-side switch, a gate, and a source;
a second NFET having a drain coupled to a first terminal of the second high-side switch, a gate, and a source coupled to the source of the first NFET; and
a control circuit configured to enable the gate of the first NFET when a first voltage of the first terminal of the first high-side switch is greater than a second voltage of the first terminal of the second high-side switch, and configured to enable the gate of the second NFET when the second voltage is greater than the first voltage.
17. The battery charger of claim 16 , wherein the second NFET is conductive via a body diode when the first voltage is greater than the second voltage.
18. The battery charger of claim 16 , wherein the first NFET is conductive via a body diode when the second voltage is greater than the first voltage.
19. The battery charger of claim 16 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the first NFET;
a resistor coupled between the anode and the source of the first NFET;
a capacitor coupled between the gate and the source of the first NFET; and
an adjustable current source coupled to the gate of the first NFET, the adjustable current source configured to increase a current to the capacitor when the first voltage is greater than the second voltage.
20. The battery charger of claim 16 , wherein the control circuit includes:
a diode having an anode, and a cathode coupled to the gate of the second NFET;
a resistor coupled between the anode and the source of the second NFET;
a capacitor coupled between the gate and the source of the second NFET; and
an adjustable current source coupled to the gate of the second NFET, the adjustable current source configured to increase a current to the capacitor when the second voltage is greater than the first voltage.