XRP7724 Datasheet, PDF (22/29 Pages) Exar Corporation – Quad Channel Digital PWM/PFM Programmable Power Management System

XRP7724
Quad Channel Digital PWM/PFM
Programmable Power Management System
SUPPLY_FAULT_EVENT interrupt generated by
the controller. The host then can use anI2C
command to check which channel is at fault.
In addition, OVP fault can be monitored
through GPIO0.
A user can choose one of three options on
how to react to an OVP event: to shutdown
the faulting channel, to shut down faulting
channel and to perform auto-restart of the
channel, or to restart the chip.
as defined in the electrical characteristics.
The maximum value the user can program is
limited by Rdson of the synchronous Power
FET and current monitoring ADC range. For
example, using a synchronous FET with Rdson
of 30mΩ, using the wider ADC range, the
maximum current limit programmed would
be:
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: a channel will share a response to an
OVP or OCP event.
OCP
A user defined OCP fault level is set with 1mA
increments in PA5. PA5 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
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
4 consecutive switching cycles. When the
switching frequency is using the 4x multiplier,
the current is sampled only every other cycle.
As a result it can take as many as 8 switching
cycles for an over current event to be
detected. When operating in 4x mode
inductors with a soft saturation characteristic
are 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 fault can be monitored
through HW Flags on GPIO0. The host can
also monitor OCP warning flag through HW
Flags on GPIO0. The OCP warning level is
calculated by PowerArchitect™ as 85% of the
OCP fault level.
A user can choose one of three options on
how to react to an OCP event: to shutdown
the faulting channel, to shut down faulting
channel and to perform auto-restart of the
channel, or to restart the chip.
The output current reported by the XRP7724
is processed through a 7 sample median filter
in order to reduce noise. The OCP limit is
compared against unfiltered ADC output.
© 2012 Exar Corporation
22/29
Rev. 1.0.1