AN2946 datasheet(12/38 Pages) STMICROELECTRONICS

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Hardware design

AN2946

12/38

Doc ID 15473 Rev 2

Figure 10.

Hardware OVP circuit for battery overcharging protection

The schematic of the battery charger is shown in Figure 11 which is based on buck topology.

Q2, D4 are the buck MOSFET and diode, respectively. L2 is the inductor and C13 is the

output capacitor. The charger operates in a continuous current mode so that small output

current ripple is achieved and a small output capacitor can be used. C10 and C11 are used

as a snubber to suppress high voltage spikes.

Since Q2 is floating and high-side transformer T2 is used to drive the MOSFET, the gate

driving circuit is similar to the one shown in Figure 9.

Resistors R9, R17 ~ R20 and R55 are used to sense the charge current to the battery. U3

(TSC101) is the high-side current sensor which amplifies the signal and gives feedback to

the MCU.

P2 is the connector to the battery. One fuse (F1) is in series with the battery to prevent

catastrophic failure. To prevent reverse connection of the battery, one Schottky diode D14 is

added. F1 blows out with D14 if the battery is reversely connected. This helps to protect the

rest of the circuits.

Figure 11.

Battery charger circuit

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