XRP7704 Datasheet, PDF (24/31 Pages) Exar Corporation – Quad-Output Digital PWM Buck Controller

REV 1.1.0
XRP7704
Quad-Output Digital PWM Buck Controller
Frequency Synchronization Function and External Clock
The user of the XRP7704 can choose to use an external source as the primary clock for the XRP7704. This
function can be configured using the SET_SYNC_MODE_CONFIG register. This register sets the operation of the
XRP7704 when an external clock is required. By selecting the appropriate bit combination the user can configure
the IC to function as a master or a slave when two or more XRP7704s are used to convert power in a system.
Automatic clock selection is also provided to allow operation even if the external clock fails by switching the IC
back to an internal clock.
External Clock Synchronization
Even when configured to use an external clock, the chip initially powers up with its internal clock. The user can
set the percent target that the frequency detector will use when comparing the internal clock with the clock
frequency input on the GPIO pin. If the external clock frequency is detected to be within the window specified by
the user, then a switchover will occur to the external clock. If the IC does not find a clock in the specified
frequency target range then the external clock will not be used and the IC will run on the internal clock that was
specified by the user. If the external clock fails the user can chose to have the internal clock take over, using the
automatic switch back mode in the SET_SYNC_MODE_CONFIG register.
CLK_IN
GPIO1
XRP7704
Configured for
external clock use
XRP7704 Configured For External Clock Use
Synchronized Operation as a Master and Slave Unit
Two XRP7704s can be synchronized together. This Master-Slave configuration is described below.
Master
When the XRP7704 powers up as a master unit after the internal configuration memory is loaded the unit will
send CLK_OUT and SYNC_OUT signals to the slave on the preconfigured GPIO pins
Slave
When powering in sync mode the slave unit will initially power up with its internal clock to transfer the
configuration memory. Once this transfer occurs, then the unit is set to function as a slave unit. In turn the unit will
take the external clock provided by the master to run as its main internal clock.
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