LM61460-Q1: About high-pass filter in EN/SYNC pin

Albert Sun

Part Number: LM61460-Q1

Hi Team,

I am reading datasheet and found below description. I know CSYNC and RENT//RENB forms a high pass filter. For RENT//RENB=100kOhm and CSYNC=1nF. The crossover frequency is 1.6kHz, meaning that any external clock frequency higher than 1.6kHz will pass to EN/SYNC. However, the minimum possible frequency range is 180kHz. Shall we decrease RENT//RENB resistance so that high pass filter could work better? What is the consideration when designing CSYNC and this high pass filter?

-A

over 1 year ago

0 Andy Chen over 1 year ago

TI__Mastermind 27045 points

Hi Albert,

It depends if the device On/Off control is also applied thru CSYNC, it require 28us longer low state signal to disable the chip, so time constant of CSYNC and RENT//RENB must be much higher than 28us.

If not, then you can use smaller CSYNC, but better too keep the constant of CSYNC and RENT//RENB higher than 1us.

B R

Andy

0 Albert Sun over 1 year ago in reply to Andy Chen

Intellectual 310 points

Hi Andy,

Get it. The datasheet also mentions that external needs to be off until start-up. However, it never mention when after start-up it can be used. What is TI's recommendation? Add CLK after PGOOD=1?

-A

0 Andy Chen over 1 year ago in reply to Albert Sun

TI__Mastermind 27045 points

Hi Albert,

It means the clock must be applied after IC is enabled by EN or VIN, not means the clock should be applied after Vout is ready, add CLK after PWRGD=1 is also OK.

B R
Andy

0 Albert Sun over 1 year ago in reply to Andy Chen

Intellectual 310 points

Hi Andy,

Thank you very much for your help!

-A

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LM61460-Q1: About high-pass filter in EN/SYNC pin