TPS61500: Pure PWM Dimming Method

Sarah Cratem

Part Number: TPS61500

Hi team,

I’m looking Figure 11 Pure PWM Dimming Method.

It looks like the PWM signal is applied both to the MOSFETs that control the current driving the LEDs as well as the Enable pin of the TPS61500.

Why drive the EN pin with PWM in addition to PWM’ing the MOSFET control for the LEDs? Doesn’t this enable/disable the device? Does the TPS61500 react (start-up and shut-down speeds) fast enough and cleanly enough for this to really be viable? What about delays caused by the reactive elements (L’s & C’s) charge/discharge times?

I've seen many posts on E2E discussing the PWM mode but none that really answer these questions.

Thanks,
Sarah

over 4 years ago

0 Frank Qiu over 4 years ago

TI__Genius 15776 points

Hi hardy， please help in this case.

+1 Hardy Wu over 4 years ago

TI__Genius 12915 points

Hi Sarah,

For the reason why TPS61500 need to also be driven with PWM is because of the over voltage protection. If TPS61500 keep enable when cut off LEDs, OVP would be triggered and shut down the device. Your concern for device set up time is right. Usually there need around 10us for internal loop stablish. That is why the recommended PWM frequency for PWM dimming method is below 1kHz.

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TPS61500: Pure PWM Dimming Method