TPS61161: Dimming control

Steve Jarvis

Part Number: TPS61161
Other Parts Discussed in Thread: TPS61160,

Tool/software:

Hi,

I was going to include a schematic but there seem to be no way to attach any file or image? If I click on insert Insert -> Image/video/file the only thing you can add is a link? How bizarre and absurd is that? Am I missing something?

About this post, some questions about the TPS61161 and TPS61160. I need to make sure that the brightness is 100% when the system boots (i.e. before the micro can control the CTRL pin).

1. How do I configure the hardware to ensure that is so? Do I just place a pull-up on the CTRL pin to 5V? Does that ensure that Vfb value is set to a specific value by default? If so, is such value 200mV?

2.the dimming of the TPS61161 and TPS61160 be controlled exclusively from a digital pin from a 3V3 micro even if Vin is 5V correct?

3. Table 6.5 page 6 it says "CTRL pull down resistor" and it provides a value up to 1.6K. But the resistor is not shown or mentioned anywhere in the datasheet. And Figure 13 (and also the internal block diagram) shows there is no resistor. Which resistor is "CTRL pull down resistor" referring to? Is that mentioned because any pullup added externally on CTRL pin needs to be within a certain range perhaps?

4. dimming can be controlled exclusively with PWM on the CTRL pin instead of the 1-wire commands, correct?

5. If yes, why is there also the much more complex RC dimming on the FB pin as mentioned in "7.4.4 External PWM Dimming"? It seems to only take more components and no advantage...

Thank you

10 months ago

0 Patrick Yao 10 months ago

TI__Mastermind 34710 points

Hi Steve,

1. Yes, you can add a pull-up resistor before you apply PWM or one-wire code.

2. Yes

3. This is an internal resistor.

4. Either PWM or 1-wire could control the brightness. But you can only use one of them in the same time.

5. The external components are used to avoid the input PWM frequency limit. CTRL pin requires the PWM frequency to be within 5kHz to 100kHz.

Patrick

0 Steve Jarvis 9 months ago in reply to Patrick Yao

Intellectual 600 points

Thank you

about point 3, as mentioned, there is no sign of any internal resistors anywhere else in the datasheet (which there would normally be). For my understanding and peace of mind, could you please explain how you can be sure about it?

1.6K is a very strong pull down, which when you add a pullup it needs to be very strong which causes relatively large continuous current flowing from VDD to GND for no reason.

For that same reason, all the pulldowns inside ICs are generally 10K to 100K.

If you could explain why you are so certain it would be very much appreciated.

Thank you