TPS92513: weak IR light issue

Hi Henry,

I am currently out of office. I will reply to you on May 6th when I am back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Henry,

May I understand what your input voltage, LED voltage, LED configuration (series / parallel) are?

Best Regards,

Steven

Hi Sir,

Input voltage：5 ~ 5.3V
The series LED voltage：0 ~ 3.1V;  1 of LED voltage is 1.55V; (PDIM duty = 0% ~ 100%)
LED configuration (series / parallel)：2 LEDs of series

Hi Henry,

Steven will give you feedback later.

Hi Henry,

Henry Wang3 said:

BTW, they also try to adjust the PWM frequency down to 100Hz to 1kHz, still can see the weak IR light on the lens. Even do the same test conditions on the TPS92513EVM, also got the same results.

Did the customer modify any components on the EVM? I will try reproducing the phenomenon that the customer observed.

Best Regards,

Steven

Hi Sir,

The customer modified the below components value on the EVM.

R3: 300KOhm

R7: 120KOhm

R8: 2.4Ohm

Hi Henry,

I tried to reproduce the phenomenon on our EVM but failed.

Please let the customer measure the output current waveform and PH node voltage during PDIM = 0V and show me the oscilloscope capture.

Also please check if there are components other than LED on the customer's LED board.

Best Regards,

Steven

Hi Sir,

The customer only used the 5V power supply to test the EVM and let pin PDM shorted to GND.

They does measured the output has 3.7V voltage, please refer to the below figure.

Hi Henry,

1. When open load, please let the customer measure the voltage waveform of LED+ node with an oscilloscope and show me the oscilloscope capture. I am wondering if a ringing happens. (Please refer to Section 9.1.5 Output Protection Clamp (Optional) from the datasheet.)
2. When the LED is connected, please let the customer measure the output current waveform and PH node voltage during PDIM = 0V and show me the oscilloscope capture.

Best Regards,

Steven

Hi Sir,

Please refer to the below figures.

For Q1 and without LED,

Test_A:

1. PDIM = 0
2. PDIM = 1
3. PDIM = 0

Test_B:

1.  PDIM = 1
2.  PDIM = 0
3.  PDIM = 1
4.  PDIM = 0

For Q2, connect the LED,

Hi Henry,

I am currently out of office. I will reply to you next Monday. Thanks for your understanding.

Best Regards,

Steven

Hi Henry,

Based on the last picture you sent to me, the leakage current is 60uA. Am I correct?

I will try to reproduce this condition on our EVM this Wednesday and provide you with the feedback at that time.

Best Regards,

Steven

Hi Henry,

Finally, I reproduced what customer observed - around 50uA leakage current from our EVM with Vin = around 5.42V, load = 1 white LED. I observed that weak light in a dark room. Sorry for missing this point earlier.

However, if you increase the input voltage to a higher value like 10V, this leakage current will not occur.

We need some time to find out what is happening here. Meanwhile, please let the customer try TPS92201, which is designed for low-Vin application. I have tested on TPS92201AEVM with Vin = 5V, load = 1 white LED and no such leakage current is observed when EN pin is logic low.

Best Regards,

Steven