XRP7725 Datasheet, PDF (23/34 Pages) Exar Corporation – Power Management System

XRP7725
Intel Node Manager Compatible Programmable
Power Management System
WARNING: Choosing the “Restart Chip”
option during development is NOT
recommended as it makes debug efforts
difficult.
OCP
A user defined OCP fault level is set with 10
mA increments in PA 5.1. PA 5.1 uses
calculations to give the user the approximate
DC output current entered in the current limit
field. However the actual current limit trip
value programmed into the part is limited to
280mV as defined in the electrical
characteristics. The maximum value the user
can program is limited by R_DSON of the
synchronous Power FET and current
monitoring ADC range. For example, using a
synchronous FET with R_DSON of 30mΩ, and the
wider ADC range, the maximum current limit
programmed would be:
280ܸ݉
ݔܽܯ ܲܥܱሺܣሻ ൌ _30݉Ω ൌ 9.33ܣ
In the case of shutting down the faulting
channel and auto-restarting, the user has an
option to specify startup timeout (the time in
which the fault is validated) and hiccup
timeout (the period after which the controller
will try to restart the channel) periods in 1
msec increments with a maximum value of
255 msec.
Note: The Channel Fault Action response is
the same for an OVP or OCP event.
The current is sampled approximately 30ns
before the low side MOSFET turns off, so the
actual measured DC output current in this
example would be 9.33A plus approximately
half the inductor ripple.
An OCP Fault is considered to have occurred
only if the fault threshold has been tripped in
four consecutive switching cycles. When the
switching frequency is set to the 4x multiplier,
the current is sampled only every other cycle.
As a result it can take as many as eight
switching cycles for an over current event to
be detected. When operating in 4x mode an
inductor with a soft saturation characteristic is
recommended.
When the OCP level is reached and the fault is
generated, the host will be notified by the
SUPPLY_FAULT_EVENT interrupt generated by
the controller. The host then can use an I²C
command to check which channel is at fault.
In addition, OCP faults can be monitored
through HW Flags on GPIO0. The host can
also monitor the OCP warning flag through
HW Flags on GPIO0. The OCP warning level is
calculated by PA 5.1 as 85% of the OCP fault
level.
A user can choose one of three options in
response to an OCP event: shut down the
faulting channel, shut down faulting channel
© 2014 Exar Corporation
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Rev. 1.0.0