Datasheet

Device description PM8903A
16/33 Doc ID 024147 Rev 1
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 PM8903A 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 PM8903A
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 PM8903As 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
Tabl e 7 , to program the IC to be
master or slave.