Datasheet

PM8903A Device description
Doc ID 024147 Rev 1 15/33
The protection is triggered when the voltage sensed on the FB pin rises over the OVP
threshold (0.72 V typ.) and the device acts as follows:
● HS MOSFET is suddenly forced OFF
● LS MOSFET is turned on (to discharge the output and protect the load) until V
FB
drops
to 0.3 V, it is then turned off (to avoid negative spikes on the output voltage). If V
FB
recrosses OVP rising threshold, LS is turned on again.
This protection state is latched, cycle EN or VCC to recover.
5.3.2 Undervoltage protection
Undervoltage protection is active from the end of soft-start.
If V
FB
falls below the UVP threshold (0.48 V typ.), undervoltage protection is triggered and
the device starts a soft-off sequence (see
Section 5.2.2 ).
This protection state is latched, cycle EN, VCC or VIN to recover.
5.3.3 Feedback disconnection protection
In order to protect the load even if the FB pin is not connected to the PCB, a 100 nA current
is constantly sourced from the FB pin: if the FB pin is left floating, it is internally pulled high
triggering OVP protection and preventing V
OUT
from rising out of control.
Figure 10. FB disconnection
5.3.4 Power Good (PGOOD)
PGOOD is an open drain output, left floating when V
OUT
is in regulation at the programmed
voltage, at the end of soft-start.
PGOOD is forced low, to communicate that the output voltage is no longer in regulation, if
one of the following conditions is verified:
● The voltage of the FB pin exits from the PGOOD window (±20% of V
REF
)
● The device is disabled, EN is forced low
● VCC voltage is below the UVLO threshold
● Any protection is triggered (OVP, UVP, OCP, OTP).
100nA
FB
R
OS
R
FB
V
OUT
720mV
OVP
COMPARATOR