PM8903

Device description

Doc ID 022748 Rev 1

17/34

5.4

Overcurrent protection

Overcurrent protection is active as soon as the device is enabled and both VCC and VIN

voltages are above the respective UVLO levels.

The overcurrent function protects the converter from a shorted output or overload by

sensing the output current information across the integrated MOSFETs as follows:

●

During normal operation the output current information is monitored reading the current

flowing in the HS MOSFET

●

When the converter is working with an ON time lower than 130 ns (typ.) the current is

monitored reading the current flowing in the LS MOSFET

If the monitored current information is bigger than the overcurrent thresholds, an overcurrent

event is detected.

For maximum safety and load protection, the PM8903 implements a dual level overcurrent

protection system.

●

First level threshold

During a switching cycle, if the monitored current information exceeds a 4.6 A (typ.)

threshold, first level overcurrent is detected: the HS MOSFET is turned off and the LS

MOSFET is turned on until the next cycle. If four first level OC events are detected in

four consecutive switching cycles, overcurrent protection is triggered.

●

Second level threshold

If the monitored current information exceeds the 5.2 A (typ.) threshold, overcurrent

protection is triggered immediately.

When overcurrent protection is triggered, the device suddenly turns off the HS and keeps

the LS turned on until the output current drops to 600 mA, then the device turns off both LS

and HS MOSFETs in a latched condition; cycle EN or VCC to recover.

5.5

Overtemperature protection

It is recommended that the device never exceeds the maximum allowable junction

temperature. This temperature increase is mainly caused by the total power dissipated from

the integrated power MOSFETs.

To avoid any damage to the device when reaching high temperature, the PM8903

implements a thermal shutdown feature: when the junction temperature reaches 140 °C the

device turns off both MOSFETs.

When the junction temperature drops to 100 °C, the device restarts with a new soft-start

sequence.

5.6

Synchronization

Synchronization of two PM8903s is enabled simply connecting the SYNCH pins of the two

devices together. No synchronization is implemented if the SYNCH pin is left floating.

When synchronization is enabled, the first device must be configured as a master and the

second device must be configured as a slave. Connect a resistor between the PSKIP/MS

pin and ground, and select the resistor value according to

Table 7, to program the IC to be

master or slave.