TPS40170: Change Frequency Using Switch of Resistor Network on RT Pin

Jack CCY

Part Number: TPS40170

Hi Buddy,

I would like to ask whether I can use a MOSFET as an switch to change the resistor on RT pin to change the frequency of TPS40170 after power good?

Is there any danger of damaging the chip?

Thanks.

Jack

over 8 years ago

0 Arief Hernadi over 8 years ago

TI__Mastermind 23845 points

Hi,

I dont think this will damage the chip. Are you thinking putting an extra resistor in parallel with original RT and use the MOSFET to switch it on?

Thanks
-Arief

0 Jack CCY over 8 years ago in reply to Arief Hernadi

TI__Intellectual 1695 points

Hi Arief,

You are right. I'm going to do in this way. Use PG pin to control the MOSFET to turn on and change the frequency.

So I want to make sure this will not damage the chip by over voltage or current in RT pin.

Thank you.

Jack

0 Arief Hernadi over 8 years ago in reply to Jack CCY

TI__Mastermind 23845 points

Yes, that should be ok. Are you changing frequency for EMI reason?

Thanks
-Arief

0 Alan Martin over 8 years ago in reply to Jack CCY

TI__Expert 4365 points

If you use a small signal MOSFET such as 2N7002 there will be no issue. Note that if there is no gate drive during startup that the MOSFET will be in the OFF state and only one RT will be active. after power comes up the second RT can be placed in parallel which can only raise f(sw) higher than during startup.

0 Jack CCY over 8 years ago in reply to Arief Hernadi

TI__Intellectual 1695 points

OK. Thank you so much. No, I just want to test the possibility of changing frequency after power good.

Best Regards

Jack Chen

0 Jack CCY over 8 years ago in reply to Alan Martin

TI__Intellectual 1695 points

Yes, I just use 2N7002 to do this. Thank you.

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TPS40170: Change Frequency Using Switch of Resistor Network on RT Pin