DocID031629 Rev 1

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PM8804

Applications information

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If SS voltage reaches 2.8 V, a slow hiccup is performed sinking 2 µA from SS, and shutting

down the gate driver until the SS capacitor is fully discharged. Then a new soft-start

procedure is performed.

When a severe overcurrent occurs, like a short-circuit of an internal power component, and

350 mV level is reached on CS, the gate driver is instantaneously shut down and a fast

hiccup cycle is performed. When the 10 µA sink current fully discharges the SS capacitor, a

new soft-start procedure with a charging current of 10 µA is performed.

In case of persistent severe overcurrent, the control logic tries 4 cycles of fast hiccup before

definitively shutting down the PWM controller. To restart the device, after removing the

cause of overcurrent, VIN must be lowered to ground and then powered up again.

Figure 6. Short-circuit on the power transformer output

Ch1= SS, Ch2 = VG1, Ch3 =VCS, Ch4 = Vsense

5.7

Output drivers: GAT1 / GAT2 and MODE pin

The PM8804 is integrating two MOSFET drivers with up to 1 A peak sink current capability.

GAT1 is intended for driving the main switching MOSFET, while GAT2 is used for an

auxiliary function, depending on the topology selected: it can be used to drive a gate drive

transformer in synchronous flyback topologies or to control a P-channel MOSFET referred

to PGND in active clamp forward topologies.

The rising edge of GAT2 is anticipated by time period DT with respect to the rising edge of

GAT1, while the falling edge of GAT2 is delayed by the same time period DT with respect to

the falling edge of GAT1 (see Figure 7).

DT can be adjusted from 10 ns to 200 ns to fine tune the relative switching times of the

MOSFETs and to maximize the converter efficiency.