TPS61500: PWM Frequency outside of recommended range

Tajbid Rahman

Part Number: TPS61500
Other Parts Discussed in Thread: LM3643, LM36010, LM3644

Hello,

I am considering using the TPS61500 for driving a couple of high power IR LEDs. I want to keep these LEDs on for 14 ms. As such, I am thinking of applying a 30 Hz PWM signal but as per the datasheet, the minimum recommended PWM frequency is 200 Hz. So, can I not use the TPS61500 as my LED driver? Also, if you have any other recommendations for keeping these LEDs on for 14 ms, that would be great. Thank you.

Sincerely,

Tajbid Rahman

over 5 years ago

0 Sean Zhou over 5 years ago

TI__Mastermind 22745 points

Hi Tajbid,

We don't suggest to dimming our of our spec frequency. So could you share me your detail specs, such as Vin, Iout, Vout and dimming method. Since we have some flash led drivers that may help you a lot. You can check LM3643/LM3644/LM36010. That should help you a lot.

Regards

Sean

0 Tajbid Rahman over 5 years ago in reply to Sean Zhou

Prodigy 70 points

I have a Vin of 5V, Vout of max 14V. Iout is around 400 mA. I want to use true PWM dimming. As such, I want to input a 30 Hz signal into the input signal of the TPS61500 and keep the signal high for 14 ms. This means that the LED will be lit for 14 ms and then shut off. It seems that the lowest possible frequency is 200 Hz on the datasheet but is 30 Hz doable? Please let me know. Thank you.

Sincerely,

Tajbid Rahman

0 Sean Zhou over 5 years ago in reply to Tajbid Rahman

TI__Mastermind 22745 points

Hi Tajbid,

Technically saying, it should support 30Hz dimming frequency, But I need to check with our designer and I will reply to you later.

Regards

Sean

0 Sean Zhou over 5 years ago in reply to Tajbid Rahman

TI__Mastermind 22745 points

Hi Tajbid,

I have tried with TPS61500 with 30hz PWM dimming, it can support for 30Hz, 14ms on time dimming as below:

Regards

Sean

0 Tajbid Rahman over 5 years ago in reply to Sean Zhou

Prodigy 70 points

Hello Sean,

Thank you for your help. This is really helpful. My last question would be about the ramp up time to max output current. Would it be possible to share your schematics for this test? For my application, I need a fast response similar to the ones you have posted. Thanks for the help again.

Sincerely,

Tajbid Rahman

0 Sean Zhou over 5 years ago in reply to Tajbid Rahman

TI__Mastermind 22745 points

Hi Tajbid,

I just used the TPS61500EVM and you can request the EVM from this website:

http://www.ti.com/tool/TPS61500EVM-369?keyMatch=tps61500&tisearch=Search-EN-Everything

And I have removed the C7 and changed the C6 from 0.1uF to 47nF. Then I get the waveform as above.

Regards

Sean

0 Tajbid Rahman over 5 years ago in reply to Sean Zhou

Prodigy 70 points

Hello Sean,

Thank you. This helped me resolve the issue.

Sincerely,

Tajbid Rahman

0 Sean Zhou over 5 years ago in reply to Tajbid Rahman

TI__Mastermind 22745 points

Hi Tajbid,

Can you share me what's the detail application? Why you need such low dimming frequency? Recently I have received several support about similiar question, I'd like to ask about the detail application and specs. Thanks.

Regards

Sean

0 Tajbid Rahman over 5 years ago in reply to Sean Zhou

Prodigy 70 points

Hello Sean,

I am planning to use the TPS61500PWP to power some high power IR LEDs. A low dimming frequency was necessary because I want the LEDs to flash for a small amount of time. The use case is an illumination system. Like we talked about, the illumination window of 14 ms was critical and so the Iout ramp time and response was very critical. I am planning to take a 5V input and then output about 13 V and 800 mA, set by the sense resistor. Hope that helps. Thanks again for the help.

Sincerely,

Tajbid Rahman

0 Sean Zhou over 5 years ago in reply to Tajbid Rahman

TI__Mastermind 22745 points

Hi Tajbid,

Yes, I understand that 14ms window time is critical, But as I know if 14ms window time is fixed, so how about the dimming frequency? 30Hz is another critical spec? Since f=50Hz can also provide 14ms window time. Thanks for explanation.

Regards

Sean

0 Tajbid Rahman over 5 years ago in reply to Sean Zhou

Prodigy 70 points

Hello Sean,

Sorry I should have mentioned that. 30 Hz was another critical spec for the overall system. I could have made 50 Hz work perhaps but ideally, 30 Hz was what I was looking for. Thanks.

Sincerely,

Tajbid Rahman

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TPS61500: PWM Frequency outside of recommended range