about the external CLK input from the LTC1871 SYNC pin(min freqe)

Let me ask you about the external CLK input from the LTC1871 SYNC pin.

Q1 I would like to operate at 25kHz. Is it possible to use it with an external CLK?
(Internal CLK was from 50KHz or higher)

Q2 If Q1 is OK, should I pull down the FREQ terminal appropriately?