XRP7714_1009 Datasheet, PDF (18/29 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controller

XRP7714
Quad Channel Digital PWM Step Down Controller
Over-Current Fault Handling
When an over-current condition occurs, PWM drivers in the corresponding channels are disabled.
After a 200ms timeout, the controller is re-powered and soft-start is initiated. When the over-
current condition is reached the controller will check the SET_FAULT_RESP_CONFIG_LB and
SET_FAULT_RESP_CONFIG_HB to determine whether there are any “following” channels that need
to be similarly restarted. The controller will also set the fault flags in READ_OVC_FAULT_WARN
register.
Typically the over-current fault threshold would be set to 130-140% of the maximum desirable
output current. This will help avoid any over-current conditions caused by transients that would
shut down the output channel.
CHIP OPERATION AND CONFIGURATION
SOFT-START
The SET_SS_RISE_CHx register is a 16 bit register which specifies the soft-start delay and the
ramp characteristics for a specific channel. This register allows the customer to program the
channel with a 250µs step resolution and up to a maximum 16ms delay.
Bits [15:10] specify the delay after enabling a channel but before outputting pulses; where each bit
represents 250µs steps. Bits [9:0] specify the rise time of the channel; these 10 bits define the
number of microseconds for each 50mV increment to reach the target voltage.
Enable
Signal
Vout
DELAY
Bit [10:15]
RISE TIME
Bit [0:9]
SS_RISE_CHx
REGISTER
Fig. 24: Channel Power Up Sequence
© 2010 Exar Corporation
18/29
Rev. 1.1.4