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TPS54200: TPS54200DDC IR LED Current Driving Issue with 5V and 12V Vin

shailesh Kuthe
Prodigy 30 points
Part Number: TPS54200

We are using fallowing TPS54200DDC IR LED driver ckt in our existing Two Designs.

 

CKT USED is both the design is same.

PWM frequency and Voltage (0-1.8V) is also same.

 

Designs 1:

VIN => 12 V

Observation: here the peak Voltage across  is 100 mV which is  as per the datasheet 8.4.4 PWM Dimming-Mode Operation.

Waveform: Measurement across RSENSE(R123-100 mE)

 

Design 2:

VIN => 5V

Observation:  the peak Voltage across RSENSE should be 100 mV as per the datasheet 8.4.4 PWM Dimming-Mode Operation.

Waveform: Measurement across RSENSE(R123-100 mE)

 

 

Queries:

  1. Why TPS54200DDC is behaving differently with different input voltages as the operating voltage is 4.5 to 28V.
  2. What will be the limitation if its working with 5V.
  • 0
    TI__Genius 15335 points

    Hi Shailesh,

    So you are using PWM dimming. Right?

    If this is the case, then please noticed that due to the limited control-loop response, to get a relatively linear dimming performance, the suggested PWM signal frequency should be less than 1 kHz. From the oscilloscope capture, it looks like your PWM frequency is around 25 kHz.

    Please reduce your PWM frequency and have another try.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 30 points

    Hi Steven,

    Please find attached waveform with PWM frequency of approx. 900Hz and duty cycle of 20%.

    Is the above behavior expected at IR LED sense Resistor RSENSE(R123-100 mE) is expected ?

  • 0 in reply to shailesh Kuthe
    TI__Genius 15335 points

    Hi Shailesh,

    I do not think this is a normal behavior.

    • Please enlarge your C128 and see if this helps. Please follow the guidance in Section 9.2.1.2.4 FB Pin RC Filter Selection from the datasheet.
    • How many IR LEDs are you drive? In series?

    Best Regards,

    Steven