TPL1401: using together with TPS61196 for LED current limit instead of Iset resistor

Hi Kirill,

Your image didn't come through. Can you reshare using the "Insert/Edit Media" button (circled in red below). 

However, without seeing your proposal, I believe you can create a circuit similar to this one given in the DAC43401 datasheet using the TPL1401 to complete your goal:

Hi Katlynne,

Thank you for your proposal and I'm sorry I couldn't see my attachment. I hope you would see it in this message.

Here it is: U1 simulates TPL1401 and V1 simulates the voltage output on TPS61196 pin 10 (Iset).

However the question was not addressed for building of current sink using TPL1401, but if it can be used together with TPS61196, more precisely if TPL1401 configured as current sink can be connected to pin 10 (Iset) of TPS61196 to control current settling by f.ex. a microcontroller. This question due to it is not 100% clear to me how TPS61196 Iset circuit is made internally. But I believe as long as only a resistor must be connected to to ground on pin 10, this is a current source output which can be controlled by the circuit above?

Actually I'm 99.9% sure this is a way for dynamic control current settling of LEDs connected to the TPS61196.

Best regards

Kirill Kornuta

Hi Kirill,

I apologize for misunderstanding your question. I have read through the TPS61196 datasheet and there is nothing that leads me to think this wouldn't work as long as the current is in the range of 5mA to 400mA. I am part of the group responsible for the TPL1401, so I am not an expert in the TPS61196. I was looking into older forum posts and I found a similar question to yours where they seem to not recommend the solution:  link here.

I will reach out to the team responsible for the TPS61196 for further comment. 

Hi Kirill,

The engineer responsible for the TPS61196 has let me know that there is an internal current source for detecting the ISET resistor and they don't think using a DAC (or the TPL1401) is a good alternative.

I've asked them to respond here if you have any further questions.

Hi Katlynne,

Thank you for your comments. The link you've send me about controlling TPS61196 Iset and FBP by digipots describe a little bit another situation, where as I understand they want to change the current on the fly by Iset instead or together with PWM dimming.

What I need is to set the current limit before I activate TPS61196 by EN pin, then I will use PWM to dim LEDs and Iset will not be touched. But this is useful feature for us, as we can adapt TPS61196 for different products, which are require different current settling for LEDs.

Furthermore as it is standing in datasheet of TPL1401 it is suitable to various applications to control various devices and as I understand it can be well used to control external current sources like Iset pin 10 of TPS61196. If we looking for the schematic I provided then we can say that MOSFETs drain to source channel due to its properties is a resistor and in this configuration it is a variable resistor controlled by TPL1401 which is in turn connected to the regular resistor of 24.3k. The current source on pin 10 (Iset) of TPS61196 will sense the total resistance created by MOSFET DS channel and the resistor of 24.3k connected to the ground. Thus I can conclude with 99.9% TPS61196 will not see any difference between regular resistors and a combined MOSFET + regular resistor.

The question here rises only because I'm not sure how Iset pin of TPS61196 is build internally, not how to build a variable resistor using TPS61196. If responsible engineer letting us know there is "just" a regular current source, then I'm sure TPS61196 Iset can be controlled using TPL1401, configured as a current source.

Best regards

Kirill Kornuta

Hi Kirill,

I sent another email to the engineer responsible for the TPS61196 but I have not heard back yet. 

I believe you are correct that with this solution, the ISET pin will see the value of the regular resistance + MOSFET resistance which should not be different than just a regular resistor. As you mentioned it is not the same situation as the similar post I shared before where they wanted to directly use a current output DAC, and therefore I have no other information that would disprove your solution. 

I will let you know if I hear anything more from the other team.

Hi Kirill,

TPS61196 detects the ISET voltage though sourcing constant current to external resister. TPL1401 may lead to the internal current source work abnormally.

How about applying MUX to switch resisters? Please let me know if you have any concern.

BR,

Robin

Hi Robin,

Thank you for your reply. I believe I read the same answer for similar question. MUX is not an option, it is better than use regular digipot instead.

But there are some other difficulties using digipot, so still same question. Why do you think the internal current source will work abnormal on TPS61196? The internal current source on Iset and curcuit I posted in the beginning of this thread. They will be set in series, thus the current will be shared.

There are some other thoughts. As I thinking to configure TPS61196 (Iset), then I need to change the values of resistors on FBP and IFBV pins. How they are constructed internally, current source as Iset or different?

I can see IFBV voltage is varies from 0.3 to 1V. Can you provide more detailed description/schematic around these two pins please?

Thank you.

Regards

Kirill

Hi Katlynne,

Thank you for your help I'm now in conversation with Robin.

Best regards

Kirill

Hi Kirill,

You are welcome. Let me know if you need any further help with the TPL1401. I will continue to watch this thread.

Hi Kirill,

For current sink, the resistor of ISET is a feedback resistor, just like the R2 in the above circuit. 

However, the OUT of TPL1401 is connected with BUF. In fact, it's a voltage source. If you connect it with TPS61196 ISET, then ISET voltage is constant, which means TPS61196 current sink feedback is constant. So I think this solution isn't proper. 

As for FBP and IFBV, they are similar with ISET.

We can't provide you more detailed circuit. IFBV can be various since the headroom voltage of current sink varies along with flowing current. The larger current, the higher headroom voltage.

BR,

Robin

Hi Robin,

Thank you for your answers. However, I believe I now realize how pins are constructed internally in TPS61196.

TPL1401 has a FB pin which allow it use in current sink app. Using this configuration I believe I can control all required pins of TPS61196.

Thanks. This thread can now be closed.

Best regards

Kirill Kornuta