LM5176: LM5176+TPS65987D的PDO Feedback resistor problem

Jianping

Intellectual 550 points

Part Number: LM5176
Other Parts Discussed in Thread: TPS65987D

HI,

our TPS65987D的PDO 4pcs only(5 9 15 20V ),but we need 5pcs PDO(5 9 12 15 20V).

like this can't matching the PDO pins one by one.

so Eric(TPS65987D FAE) suggest enter TT Mode (true table) for TPS65987D .

it should be get 7PCS PDO controll pins. but didn't answer us,is it by decorder(3:8) or directly for contact the FB resistor(show as below)

could you help me any sugest about it?

is it by directly (calulation the resistor very difficult for PDO 15V)or decoreder(3:8) method?

thanks!

over 6 years ago

0 Garrett Roecker over 6 years ago

TI__Mastermind 21720 points

Hello,

Thanks for reaching out with your questions.

Just to confirm are you attempting to calculate the resistor value that are required for the output voltages?

Thanks,

Garrett

0 Jianping over 6 years ago in reply to Garrett Roecker

Intellectual 550 points

Hi,Garrett:

Yes, we are need calculation the FB resistor for PDO voltage(special the 15V PDO).
but how to configruation the voltage for the resistor if by upon profile(attached diagram).
could you have any other method for this .

thanks!

0 Youhao Xi over 6 years ago in reply to Jianping

TI__Guru* 78240 points

Hi User,

I am afraid this cannot be done because you have more constrains than variables when you put these in a sets of equations for all the desired voltage settings: two resistors for three arbitrary voltage settings. Mathematically it cannot find a solution. The resolution is to add one more resistor-switch branch to set the 15Vout.

Thanks,
Youhao Xi, Applications Engineering

0 Jianping over 6 years ago in reply to Youhao Xi

Intellectual 550 points

Hi, YouHao:

could you help to me confirm the Rise time for Vin&Vout,

because they aren't clearn value on datasheet(see attached file).

thanks!

0 Garrett Roecker over 6 years ago in reply to Jianping

TI__Mastermind 21720 points

Hi,
The rise time of VIN can be derived from the waveform that was attached. Each horizontal division is 1ms. Based on this the rise time is approximately 1.5ms.
Thanks,
Garrett

0 Jianping over 6 years ago in reply to Garrett Roecker

Intellectual 550 points

Hi,Garrett Roecker:

your meaning said,the the Vout delay time 1.5mS than Vin,is it right?

or base on the attached analysis only

otherwise ,how many time ahead of schedule of Vin than Vout?

could you help to me double check it?

thanks!

0 Garrett Roecker over 6 years ago in reply to Jianping

TI__Mastermind 21720 points

Hello,

I'm not sure I understand you questions. What do you mean by the VIN to VOUT delay time? The output is regulated so the input voltage can vary and the output voltage should be regulated.

If it is easier please contact your FAE (Eric) and have him contact me directly with the questions.

Thanks,

Garrett

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LM5176: LM5176+TPS65987D的PDO Feedback resistor problem