TPS54200: No dimming mode is not working

Mariselvam M

Prodigy 10 points

Part Number: TPS54200

Hello,

We are validating the TPS54200 in our boards and absorbed the below issue.

Below are the design configurations

Input Voltage - 12V

Output Voltage - 6.1V ( 2 LED in Series 3V per LED)

Output Current - 250mA (400mE used)

IR LED Driver Enable (PWM) - Enabled by Default - Driving with 1.8V pull-up. (No external PWM input - Basically No dimming mode)

For the above configurations, We do not see any output voltage on the driver output. As probed, it is raising to the 6V and dropping to 0V immediately (within a few milliseconds)

If we changed the current limit resistor value to 200mE (500mA current configuration), we can see the output voltage from the driver and it is working.

Please check and let me know your suggestions.

Schematics below

over 1 year ago

0 Steven Li over 1 year ago

TI__Mastermind 18675 points

Hi Mariselvam,

Could you measure the SW pin and inductor current and show me the oscilloscope capture for the 250mA case (for the first milliseconds)?

Mariselvam M said:
For the above configurations, We do not see any output voltage on the driver output. As probed, it is raising to the 6V and dropping to 0V immediately (within a few milliseconds)

Best Regards,

Steven

0 Mariselvam M over 1 year ago in reply to Steven Li

Prodigy 10 points

Hi Steven,

Attached are the captured images.

IR LED - SW Pin.zip

0 Steven Li over 1 year ago in reply to Mariselvam M

TI__Mastermind 18675 points

Hi Mariselvam,

Could you tell me what those curves correspond to?

BR,

Steven

0 Mariselvam M over 1 year ago in reply to Steven Li

Prodigy 10 points

Hi Steve,

Signal name is mentioned in the image itself. Highlighted in yellow color.

0 Steven Li over 1 year ago in reply to Mariselvam M

TI__Mastermind 18675 points

Hi Mariselvam,

Understood. Could you also probe the FB pin during the startup? I am wondering if there is any transient fault condition that triggers the latch-off behavior of TPS54200.

BR,

Steven

0 Mariselvam M over 1 year ago in reply to Steven Li

Prodigy 10 points

Hi Steven,

Attached the captured image for FB pin

FB Pin.zip

0 Steven Li over 1 year ago in reply to Mariselvam M

TI__Mastermind 18675 points

Hi Mariselvam,

Got it. Let me try to re-produce this situation on our EVM.

BR,

Steven

0 Mariselvam M over 1 year ago in reply to Steven Li

Prodigy 10 points

Hi Steven,

Please update

+1 Steven Li over 1 year ago in reply to Mariselvam M

TI__Mastermind 18675 points

Hi Mariselvam,

The C49 (82pF) on your schematic is too small and will make the system prone to instability and make the FB pin very noisy. Please refer to Section 9.2.1.2.4 FB Pin RC Filter Selection from the datasheet to design the FB pin RC filter.

Best Regards,

Steven

0 Mariselvam M over 1 year ago in reply to Steven Li

Prodigy 10 points

Hi Steven,

It started working after changing the RC Filter. Thanks for the support.

0 Steven Li over 1 year ago in reply to Mariselvam M

TI__Mastermind 18675 points

Hi Mariselvam,

You are welcome. I am going to close this thread. Feel free to contact me again if you have any further questions.

Best Regards,

Steven

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TPS54200: No dimming mode is not working