L7980 / L7981 Sync pin capacitance?

[MElle.1]

I'm building a power supply and hoping to use 3 or 4 of the L7981 chips. I'd like to synchronize them using a single MEMS oscillator IC but need to make sure I don't need a clock splitter / buffer. As far as I can tell, the datasheet does not mention the equivalent input resistance or capacitance on the SYNC pin. Does anyone have that information or know where to find it?

[Peter BENSCH]

The datasheet of the L7981 give some hints regarding this topic:

Connecting together the SYNCH pin of two devices, the one with higher frequency works as master and the other one as slave [...]

In Table 4, the sink current of the SYNCH pin is also given as 0.7 to 0.9mA at Vsynch=2.9V.

Please also read section 5.1 and especially the note:

The device can be synchronized to work at higher frequency feeding an external clock signal. The synchronization changes the sawtooth amplitude, changing the PWM gain (Figure 5.c). This changing has to be taken into account when the loop stability is studied.

To minimize the change of the PWM gain, the free running frequency should be set (with a resistor on the FSW pin) only slightly lower than the external clock frequency. This preadjusting of the frequency will change the sawtooth slope in order to get negligible the truncation of sawtooth, due to the external synchronization.

Regards

/Peter