TPS61193-Q1: TPS61193

lfcchen

Part Number: TPS61193-Q1

Dear TI team：

Because of the minimum brightness requirement in night mode, the Riset resistor of our backlight circuit uses a 196K ohm resistor。

But spec required for normal operation, resistor value from 24 kΩ to 129 kΩ must be connected between this pin and ground。

I would like to consult if there is any risk of Riset exceeding 129K ohms。

The following is the schematic diagram of our backlight circuit，thanks！

over 3 years ago

0 Charles-Chen over 3 years ago

TI__Genius 11836 points

Hi Ifcchen,

1. Is there any concern to use PWM dimming?

2. If you use the resistor of Iset pin over the spec, the accuracy may be reduced.

0 lfcchen over 3 years ago in reply to Charles-Chen

Prodigy 100 points

Hi Charles：

1. At present, no dimming problem is found. Will this resistor out of range be affecting PWM dimming?

2. Will it only affect the accuracy of the current？RISET = 2342 / (IOUT ± 2.5) ，Is this formula still valid when the resistance is 196kΩ？

3. Any other risks? For example, whether it will damage the chip, etc

Thanks！

0 Charles-Chen over 3 years ago in reply to lfcchen

TI__Genius 11836 points

Hi Ifcchen,

1.Do you use PWM dimming now?

2. You can use it to estimate the current but the accuracy is reduced.

2.The risk can be identified now is accuracy.

0 lfcchen over 3 years ago in reply to Charles-Chen

Prodigy 100 points

Hi Charles：

1. We are using PWM dimming now. The Riset resistor only limits the maximum current, and has little to do with adjusting the PWM duty cycle.

2. Does that mean that RISET is out of scope and there are no other potential risks, right?

Thank You！

0 Charles-Chen over 3 years ago in reply to lfcchen

TI__Genius 11836 points

Hi Ifcchen,

The risk can be identify now is just accuracy. However, we don't recommended to do so since it is over spec and I suggest that do more test as you can to verify it. Since you can use PWM dimming, why you can't set a smaller Iset resistor and use PWM dimming to achieve low brightness?

0 lfcchen over 3 years ago in reply to Charles-Chen

Prodigy 100 points

Hi Charles：

Do more tests refer to the brightness test of more samples? What other tests need to be done? Please point it out, thank you.

Choose a resistance within 129K, the duty cycle is adjusted to the minimum and the minimum brightness is not met, so we chose a 196K resistor.

Thanks！

0 Charles-Chen over 3 years ago in reply to lfcchen

TI__Genius 11836 points

Hi Ifcchen,

For example, checking whether dimming problem exists for more samples as the same as you mentioned previously.

In my opinion, it just affects the accuracy although it is over spec. But we don't have data for it.

0 lfcchen over 3 years ago in reply to Charles-Chen

Prodigy 100 points

Hi Charles：

The following picture shows the data of the two prototypes. The brightness values of the daytime mode and the night mode are measured. Is the

dimming of the night mode normal from the data?

Thanks

0 Charles-Chen over 3 years ago in reply to lfcchen

TI__Genius 11836 points

Hi Ifcchen,

I think the judgement depends on the accuracy of your system requirement.

Power management

Power management forum

TPS61193-Q1: TPS61193