X

0

Q

© 2012 Exar Corporation

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Rev. 1.2.2

appropriate bit combination the user can configure the IC to function as a master or a slave when

two or more XRP7708s 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.

XRP7708

Configured for

external clock use

CLK_IN

GPIO1

Fig. 22:XRP7708 Configured For External Clock Use

Synchronized Operation as a Master and Slave Unit

Two XRP7708s can be synchronized together. This Master-Slave configuration is described below.

•

Master

When the XRP7708 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.

GPIO2

GPIO2

XRP7708

configured

as a master

XRP7708

configured

as a slave

CLK_OUT

SYNC_OUT

SYNC_IN

CLK_IN

GPIO1

GPIO1

Fig. 23: Master/Slave Configuration of the XRP7708