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Original question:

LM76003: Connection for NC Pins

LM76003: SYNC input

Andreas Nestler
Intellectual 310 points
Part Number: LM76003

Hello,

we would like to use two (2) Step-down converter build with LM76003 in synchronous interleaved operating mode (same clock 500kHz, 180° phase shift). Some questions regarding implementation:

- According datasheet a termination resistor of 100ohm shall be used. However, this generates a lot of power disssipation. We would like to drive the SYNC input with a CMOS 3.3V logic output or sigle gate LVC logic series (3.3V) respectively. Do you have any recommendation for us regarding need and sizing of the termination resistor RTERM?

- Instead of dedicated external oscillator can we use the SW node of converter 1 (LM76003) and use it via inverter as clock source for second converter (SYNC) input.

- Do you have any reference designs, where SYNC input is used.

Thanks in advance!

Regards, Andreas N.

  • 0
    TI__Guru 57555 points

    Hello

    The termination resistor is only to help prevent reflections, etc.  

    You can drive the SYNC pin with a logic gate.

    If you want to use the SW pin of another device to drive the SYNC pin, you will need

    to consider that the voltage on the SW pin is the full input voltage.  So, you will need 

    some kind of compensated divider.  Also, you will need to run the master device in FPWM mode

    to get a good clean SW waveform to use for the sync signal.

    Thanks