TPS61169: SW output keeps high voltage at 5V when PWM dimming control is 20kHZ,50% duty cycle

Zoe Yang

Part Number: TPS61169

Hi team, when using TPS61169 , my customer has some problem when debugging at above working conditions. The CTRL=200kHz, duty cycle=50%. VBAT=5V, but the SW output is always 5V high level. FB pin was measured as 4.3V.The external circuit is shown below. And first waveform is SW. Second is CTRL. Can you please help find what is wrong with current configuration? Thanks!

6 months ago

+1 Patrick Yao 6 months ago

TI__Mastermind 25000 points

Hi Zoe,

Could you please double confirm that the CTRL is 200kHz? The recommended PWM input frequency range is 5kHz~100kHz instead.

And what are the parameters of R6, R7, R8, R10 and C20?

Patrick

0 Zoe Yang 6 months ago in reply to Patrick Yao

TI__Intellectual 2210 points

custimer modified 20K ，still don't work. Can you help check attached parameters?

0 Patrick Yao 6 months ago in reply to Zoe Yang

TI__Mastermind 25000 points

Hi Zoe,

Will remove the 499ohm resistor do any help?

Patrick

0 Zoe Yang 6 months ago in reply to Patrick Yao

TI__Intellectual 2210 points

Hi Patrick,

Currently the output of SW is much more stable now under attached schematic. But the duty cycle is large or small now and then. How to output a stable duty cycle?

0 Patrick Yao 6 months ago in reply to Zoe Yang

TI__Mastermind 25000 points

Hi Zoe,

This looks like a DCM operation, so the duty cycle will not be stable. With larger load will lead the IC in CCM mode and will get a stable duty cycle.

Patrick

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TPS61169: SW output keeps high voltage at 5V when PWM dimming control is 20kHZ,50% duty cycle