TPS92513: TPS92513DGQT

Hi,

Our expert will reply you today.

Hi Kiran,

I take a quick look over your schematic and do not see an obvious mistake. Just to double check - Are C23 and C18 open (not component is installed)?

kiran surve said:

We are facing LED failures for which we SUSPECT the IC TPS92513 during OFF to ON condition give instantaneous peak current on output which opens the LED.

Please try capturing the LED current waveform and kindly share the oscilloscope capture. Thanks.

Best Regards,

Steven

C23 and C18 are not installed.

Please find oscilloscope current waveforms taken across parallel combination of resistors R136 & R137.

PWM is set at 50%, 75% and 100%.

Best Regards,

KIRAN SURVE

Hi, Kiran

our expert will reply you late.

Hi Kiran,

I check the oscilloscope captures you shared but do not see any abnormal behavior.

Could you directly measure the LED current? The voltage across the current sense resistor (parallel combination of resistors R136 & R137) only reflects the inductor current but not reflects the LED current.

One thing to check - Does the LED failure happen for all devices? Or does it happen occasionally? (What is the failure rate?)

Best Regards,

Steven

Hi Steven,

Thanks for the reply.

The measured LED current is 710mA when measure keeping current meter in series of LED.

The LED failures are not for all the devices. It happens occasionally. The Failure rate is 5%.

Best Regards,

KIRAN SURVE

Hi Kiran,

I would recommend you use a current probe to measure the instantaneous current across the LED and check if there is any spike on the current waveform. Measuring the average (or RMS) current with the current meter may not show if there is any spike that may cause damage to the LED.

Also, please check if the LED has a good heat dissipation condition and does not get damaged due to overheat.

Best Regards,

Steven

Hi,

I do not have current probe. I added 0.22ohms resistor in series of LED and measured voltage drop across 0.22R on oscilloscope.

Please find voltage drop pic measured across 0.22R resistor. I did not found any instantaneous changes in the voltage drop across the resistor.

Pic 1 - 25% PWM

Pic 2 - 50% PWM

Pic 3 - 100% PWM

Best Regards,

KIRAN SURVE

Hi, 

Added pic for PWM change over from 0% to 100% measure Vdrop across 0.22R resistor connected in series of LED.

Regards,

KIRAN SURVE

Hi Kiran,

I am currently out of office for Chinese New Year Holiday. I will reply to you on Feb.8 when I am back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Kiran,

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

Best Regards,

Steven