TPS922051: TPS922051D1DSGREVM

John Ivanov

Prodigy 10 points

Part Number: TPS922051

Tool/software:

I have 2 new TPS922051D1DSGREVM boards and they are not diming an LED load for me.

The test set up is as indicated in the product manual:

24 Vdc is powering the board at J1.
A lab supply is providing a square wave at TP5(+), and TP2(-). This is verified by an oscilloscope to be:
- 1kHz
- Amplitude form 0Vdc to 4.24Vdc
- And an adjustable duty cycle of this signal between 20% to 80%
An LED board is the load at J2:
- It is drawing 50mA and lighting up
- Varying the above duty cycle does not vary the brightness of the LED board. The Voltage to the LED board stays at a solid 24Vdc.

I have tried the above set up on both boards and neither one works.

Why doesn’t the LED brightness dim?

Thanks, John

3 months ago

0 Lucia Gao 3 months ago

TI__Mastermind 31901 points

Hi John,

Let me check and get back to you soon. Thank you!

BRs

Lucia

0 Lucia Gao 3 months ago in reply to Lucia Gao

TI__Mastermind 31901 points

Hi John,

Thanks for reaching out! Could you pls first take a photo of the EVM board and share with me? And if you just use a DC power supply as 3.3V DC for DIM pin, will it work with constant current?

Thank you!

BRs

Lucia

0 John Ivanov 3 months ago in reply to Lucia Gao

Prodigy 10 points

0 Lucia Gao 3 months ago in reply to John Ivanov

TI__Mastermind 31901 points

Hi John,

Thank you for your feedback!

There is no problem of the connection. Just want to check the photo of the real board. And not sure when you give a DC power supply, will the LED work good.

Thank you!

BRs

Lucia

0 John Ivanov 3 months ago in reply to Lucia Gao

Prodigy 10 points

Hi Lucia,

I noticed that the output of the board floats at 6.4Vdc and the LED load does not light up if there is no connection to TP5 and TP2. If I apply 3.3Vdc to TP5 and TP2 the LED load goes to full brightness and J2 has 24Vdc on it. I am working on getting you a photo of that now.

Thanks,

John

0 John Ivanov 3 months ago in reply to John Ivanov

Prodigy 10 points

...

0 John Ivanov 3 months ago in reply to John Ivanov

Prodigy 10 points

0 Lucia Gao 3 months ago in reply to John Ivanov

TI__Mastermind 31901 points

Hi John,

Thank you for your feedback. And yes, it's a normal behavior. For TPS922051D1, when DIM is floating, the device will not switching. You'll need to apply a DC/PWM signal for DIM pin.

Thank you!

BRs

Lucia

0 John Ivanov 3 months ago in reply to Lucia Gao

Prodigy 10 points

Hi Lucia,

Thank you for confirming the behavior of the board. I have another question about this board: Is there an LED Load Specification ? My LED Load only needs 50mA at 24Vdc. ...

0 Lucia Gao 3 months ago in reply to John Ivanov

TI__Mastermind 31901 points

Hi John,

Pls set the current of the LED driver in order not to damage your LED load. Thank you!

BRs

Lucia

0 Lucia Gao 3 months ago in reply to Lucia Gao

TI__Mastermind 31901 points

Hi John,

Kindly let us know any further support need from our side. Thank you!

BRs

Lucia

0 John Ivanov 3 months ago in reply to Lucia Gao

Prodigy 10 points

Hi Lucia,

None of the suggestions made either of our 2 boards work.

Can I return them to TI?

John

0 Lucia Gao 3 months ago in reply to John Ivanov

TI__Mastermind 31901 points

Hi John,

From my understanding, with TP5 and TP2 connected with 3.3Vdc, the LED load will go to full brightness which means that it can work. And you also said none of the suggestion make your board work. Could you pls let us know your problem? Thank you!

John Ivanov said:
I noticed that the output of the board floats at 6.4Vdc and the LED load does not light up if there is no connection to TP5 and TP2. If I apply 3.3Vdc to TP5 and TP2 the LED load goes to full brightness and J2 has 24Vdc on it.

Thank you!

BRs

Lucia

0 John Ivanov 3 months ago in reply to Lucia Gao

Prodigy 10 points

Hi Lucia,

I understand that with a 3.3Vdc input I am getting a full brightness. The problem is that the diming function does not work.

0 Lucia Gao 3 months ago in reply to John Ivanov

TI__Mastermind 31901 points

Hi John,

Thank you for the feedback.

Firstly, with DIM always pull high, the LED load will go to full brightness.

Then, pls try with for example 1kHz PWM signal and pls help capture the waveform of DIM pin, SW pin and ILED(LED current) so that we can check why PMW dimming not working with current setup.

Thank you!

BRs

Lucia

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TPS922051: TPS922051D1DSGREVM