TPS61181A: TPS61181A - ISET Pin

Hi Jose,

Firstly I would like to know when you want to adjust the ISET resistance? Is it adjusted before power on the IC or after?

BR

Patrick

Hi Patrick,

Thnak you for your answer.

I'll try to describe what we want, so that you can advise on the best solution.

The board allows to connect different LED modules, so what we do is connect the LED module we want, and then switch on the board's power supply.

After that, the uP starts working, and communicates with the PC, where we have proprietary windows software that allows us to configure the entire board.

We now want to configure the ISET current as well, depending of the LED module used.

Regarding your question:

If all we have to do is change the state of the EN pin, making a High -> Low -> High sequence, then it's very easy for us, as uP can do this after setting the current ISET.

If we really need to hard power on the TPS61181A, we can design a circuit to control the P Mosfet that we use at the input of the TPS61181A by making a Power OFF -> Power ON to the TPS61181A. The uP could control this circuit to hard power on the TPS61181A after define the ISET.

Finally, there is another alternative, which is to do a Power OFF -> Power On on the power supply to the entire board, which we don't think is a good solution.

In this way we want to find the best solution, with the least number of components, PCB area and cost.

We look forward to your suggestions and comments.

regards

Jose

Hi Jose,

You can adjust the ISET resistor even when TPS61181A is working, but the LED current will have some time to reflect to the target current you want. So maybe you will observe the brightness change process. Could this be accepted?

BR

Patrick

Hi Patrick.

What you suggest is suitable for our application, as the ISET configuration is done at the final assembly stage, while still in the factory.

What do you suggest for setting ISET in a simple way and without high costs?

regards

Jose

Hi Jose,

Seems you need total 3 LED current, right? You can use 3 resistors and 2 transistors/MOSFETs to achieve this. One of the 3 resistors connects to ISET pin and GND directly, and the other 2 resistors could be in series with each transistor and parallel with resistor 1.

BR

Patrick

Hi Patrick,

Thank you for your suggestion, as we have already evaluated it.

It does solve the current problem, but if we want to use a new LED module later on, it may not be flexible enough.

Do you see any possibility of using a digital potentiometer, DAC or other solution that would allow great flexibility in configuring the ISET current in the future?

regards

Jose

Hi Jose,

I didn't saw digital potentiometer used as the ISET resistor before, but theoretically it is a method.

BR

Patrick

Hi Patrick,

So there's nothing better than doing a test.

Can we assume that on the ISET pin the voltage does not rise above 1.253V, and the maximum current is 25uA ?
These were the only specifications we found for the ISET pin.

regards,

Jose

Hi Jose,

Yes. It will be better if you can have a test.

BR

Patrick

Hi Patrick,

Can you please confirm that the values ​​we mentioned in the previous message are correct?

regards

Jose

Hi Jose,

You can consider the ISET pin voltage does not rise above 1.253V, and the maximum current is 31uA (ILED=30mA, KISET=970)

BR

Patrick