TPS61170: Problem with PWM

Elisha Tarroza71

Part Number: TPS61170

Hello,

The customer is having problems with PWM of TPS61170. Please see details below:

1) PWM duty cycle = 100%, with or without load, it works fine
2) PWN = variable, without load, the output voltage changes as expected
3) PWN = variable, WITH load, everything drops out
So it seems I have the chip set up OK, the PWM is working (i've looked at oscilloscope), it just shuts down or something when I make PWM anything other than 1
(Schematic diagram attached) - generated using Webench tool. Everything is identical to this circuit, except I connected CNTRL to PWM.

Thanks!

over 6 years ago

0 Minqiu Xie over 6 years ago

TI__Mastermind 21565 points

Hi Elisha:

May you help to clarify the Vin range, Vout range and the load condition?

And what's the amplitude and frequency of the PWM signal?

0 Minqiu Xie over 6 years ago in reply to Minqiu Xie

TI__Mastermind 21565 points

Hi Elisha:

And one more question, have you tried enlarger the load from zero to target?

As you mentioned, it worked well with no load but failed with load. May you help to find the fault point with adjustment load/resistance?

0 Julien Caubel over 6 years ago in reply to Minqiu Xie

Prodigy 10 points

Hi Minqiu Xie,

Please find responses to your questions below:

1) Vin = 6.5 to 7.4 V (from 2 cell LiPo Battery)

2) Vout = 12 to 21 V (set to 21 V using resistors, and we want to PWM that down)

3) Iout =< 115 mA

4) PWM freq = 10 kHz

5) PWM amplitude = 3.3 V.

We've tried modulating all these parameters, with no luck. For example, we've tried a range of PWM freqs at both 3.3 and 5 V. We've also tried messing with input voltage, and load. With loads as low as one 10 kOhm resistor (so its as simple as can be), the Vout still drops out. Vin also has no effect. It drives our actual load just fine at PWM duty = 100% (Vout = 21 V).

Best,

- Julien

0 Minqiu Xie over 6 years ago in reply to Julien Caubel

TI__Mastermind 21565 points

Hi Julien:

May you share schematic and the layout for us? And the waveform for the normal operation and fail. Thank you~

0 Minqiu Xie over 6 years ago in reply to Minqiu Xie

TI__Mastermind 21565 points

Hi Julien:

I closed the thread assuming that you had solved the issue. if not, just reply below

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TPS61170: Problem with PWM