XRP7724 Datasheet, PDF (23/29 Pages) Exar Corporation – Quad Channel Digital PWM/PFM Programmable Power Management System

XRP7724
Quad Channel Digital PWM/PFM
Programmable Power Management System
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
OCP or OVP event.
Start-up Time-out Fault
A channel will be at Start-up Time-out Fault if
it does not come-up in a time period specified
in the “Startup Timeout” box. In addition, a
channel is at Start-up Timeout Fault if in pre-
bias configuration voltage is a defined value
too close to the target.
When 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.
LDO5 OCP
When current is drawn from LDO5 exceeds
LDO5 current limit the controller gets reset.
LDO3.3 OCP
When current drawn from LDO3.3 exceeds
LDO3.3 current limit the regulator gets shut
down, a fault is generated, and the host will
be notified by the SUPPLY_FAULT_EVENT
interrupt generated by the controller. The
host then can through an I2C command
check which channel/regulator is at fault.
Once the fault condition is removed, the host
needs to turn the regulator on again.
V5EXT SWITCHOVER
The V5EXT gives a user an opportunity to
supply an external 5 Volt rail to the controller
in order to reduce the controller’s power
dissipation. The 5 Volt rail can be an
independent power rail present in a system or
any of 7724 channels regulated to 5 Volts (in
the PFM mode in particular) and routed back
to the V5EXT pin. It is important to mention
that voltage to Vcc must be applied all the
time even after the switchover in which case
the current drawn from Vcc supply will be
minimal.
If the function not used, we recommend the
pin to be either grounded or left floating in
conjunction with making sure the function
gets disabled through register settings.
V5EXT switchover control
The function is enabled in PA5. The
switchover thresholds are programmable in
50mV steps with a total range of 200mV.
Hysteresis to go in-out is 150mV. LDO5
automatically turns off when the external
voltage is switched in and turns on when the
external voltage drops below the lower
threshold.
When the controller switches over to the
V5EXT rail, the V5EXT_RISE interrupt is
generated to inform the host. Similarly, when
the controller switches out, the V5EXT_FALL
interrupt gets generated.
EXTERNAL CLOCK SYNCHRONIZATION
XRP7724 can be run off an external clock
available in the system or another XRP7724.
The external clock must be in the ranges of
10.9MHz to 14.7MHz or 21.8MHz to 29.6MHz.
Locking to the external clock is done through
an internal Phase Lock Loop (PLL) which
requires an external loop capacitor of 2.2nF to
© 2012 Exar Corporation
23/29
Rev. 1.0.1