TPS61194-Q1: Analog dimming

tateo yamashiro

Part Number: TPS61194-Q1
Other Parts Discussed in Thread: LP8860-Q1

Hi,

We got a question from the customer about TPS61194-Q1.
Could you help us?

[Question]
Is there any method of analog dimming? If you have the recommended circuit, could you provide application note? They assume that if DC voltage is inputted to ISET pin, it might work.

Best Regards,
tateo

over 7 years ago

0 Sung Ho Yoon over 7 years ago

TI__Expert 4565 points

Hi Yamashiro-san,

Putting DC voltage to Iset pin won't work. Iset input is ADC input to detect sink current through this pin, and voltage at this pin is fixed to ~1.2V.

So, sink current will vary with Riset values from 50uA to ~0uA while DC voltage stays same.

If customer needs current dimming or even more advanced hybrid dimming, I recommend using LP8860-Q1.

Thanks,

0 tateo yamashiro over 7 years ago in reply to Sung Ho Yoon

Guru 10890 points

Hi, Thank you for your quick reply. They have additional question. If DC voltage is inputted to ISET resistor, it is considered that ISET current vary as following equation.

ISET current = (1.2V - DC voltage) / Riset

They are thinking that if LED current is related to ISET current, it might work. Could you please check their opinion?

Best Regards,
tateo

0 Sung Ho Yoon over 7 years ago in reply to tateo yamashiro

TI__Expert 4565 points

Hi Yamashiro-san,

Yes, this method will work. If there is current flow from Iset pin to GND, LED current will be controlled by that.

External voltage range can be 0~1.2V. One thing is that regulating this external DC will be very important to keep stable LED current. Any fluctuation or noise will affect LED current dynamically. If this LED current fluctuation is not an issue for the apps, it can be used in this way.

Thanks,

0 tateo yamashiro over 7 years ago in reply to Sung Ho Yoon

Guru 10890 points

Hi, Thank you for your feedback. Let me make sure about one thing. Could you provide the equation to estimate LED current in this method? We would like to know the ratio of ISET current to LED current.

Best Regards,
tateo

0 Sung Ho Yoon over 7 years ago in reply to tateo yamashiro

TI__Expert 4565 points

Riset calc.xlsxHi Yamashiro-san,

I've made calculation tool and attached here.

Hope this helps,

0 tateo yamashiro over 7 years ago in reply to Sung Ho Yoon

Guru 10890 points

Hi, Thank you for your support. I checked your file. So I have a question. Your equation used 1.21V for Iset voltage. I think it is 1.2V. Which is correct?

Best Regards,
tateo

0 Sung Ho Yoon over 7 years ago in reply to tateo yamashiro

TI__Expert 4565 points

1.21V is more accurate value, but you can also use 1.2V which is abbreviated value. Thanks,

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TPS61194-Q1: Analog dimming