TPS61196/TPS61199 as a strobing/scanning backlight controller: analog dimming in addition to PWM?

Cirthix

Other Parts Discussed in Thread: TPS61196, TPS61199

In this application, it would be desirable to have different current settings for strobing/scanning than regular PWM.

Scanning/strobing can have a maximum effective duty cycle of 10 or 15%, so the backliight current is often 2-3x the regular mode.

I know that the TPS61196 has a 120mA short-circuit-detection on the Iset pin, so some care would be needed (R2 below), but other than this, can the Iset pin tolerate more than a simple set resistor attached to the pin? Here is what I am considering to get the full 25mA-400mA per channel range:

For this chip, a similar circuit would need to be applied to IFBV (R10 in datasheet).

My questions to you:

Can TPS61196 tolerate this?

Can TPS61199 tolerate this (modified for it's own anti-short protection?)?

Thanks

over 9 years ago

0 Cirthix over 9 years ago

Prodigy 195 points

Hopefully attached this time.

0 Harini Sankabattula over 9 years ago in reply to Cirthix

TI__Intellectual 1780 points

Hi Cirthix,

Thank you for your question.

The max LED current per channel of TPS61199 is 70mA. So, for your application, I'd recommend TPS61196.

From your circuit, it looks like you're trying to adjust voltage at ISET pin. But that node is internally regulated to ~1.229V. Something like below may be a better choice:

Please feel free to let me know if there are any further questions.

Best,
-Harini

0 Cirthix over 9 years ago in reply to Harini Sankabattula

Prodigy 195 points

Sure, if you want to draw the circuit that way.

Will a sizable capacitance (~1uF) or 1% ripple on the voltage source in your diagram cause any instability within the TPS61196?

0 Harini Sankabattula over 9 years ago in reply to Cirthix

TI__Intellectual 1780 points

Hi Cirthix,

Actually what you've is a parallel implementation of the same. It may be better as we need not turn on PWM before enabling the part.

The PWM freq = 10kHz need to be greater than 1/(2*PI*R3*C1) =~ 75ohm. I'd go with your circuit. It should not have any instability issues.

Thank you,
-Harini

0 Cirthix over 9 years ago in reply to Harini Sankabattula

Prodigy 195 points

Just got the board assembled today.

This solution does *not* work past 3/255 dutycycle ADIM at 16KHz. In the 0-3 range here, the current level is controlled.

Will have to investigate further.

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TPS61196/TPS61199 as a strobing/scanning backlight controller: analog dimming in addition to PWM?