Tool/software:
Dear TI members,
I've tested like below circuits, vin and pwm voltage applying at the same time.
the result is output irled is not turned on. irled is connected serial 4 ea. but it is turned on in case reducing irled 4ea to 2ea.
could you explained why it is ?
Best regards,
Hi Steven,
Please refer to the attached circuits.
I've found below comment in Datasheet.
"Suggested power on sequence is applying Vin at first, then followed by PWM signal "
I think below circuits is applied in this case cause pwm voltage is applied by divided resistor of 12Vin. it is same sequence.
Best regards,
Hi Customer,
I think the problem occurred here was that TPS54200 shutdown and latched during start-up in your case.
Since in real case, VIN ramps to 12V in 'ms' time because of the large input capacitor. In such connection of PWM pin, PWM voltage level reached enable and mode selection threshold when VIN is only raised to around 4V. But the normal operating forward voltage of 4 IR LEDs in series should be 6~8V I believe. So, during VIN rising from 4V to 6~8V, FB will not rise to proper value and TPS54200 would trigger fault condition time counter.
After counting finished, TPS54200 shut down and latched itself.
Could you please change the TPS54200 to TPS54201? In the same case, TPS54201 would not latch itself. Instead, it will retry itself and back to normal operation when VIN rising to proper value in your case.
Best,
John Shen.
