Tool/software:
Hi,
I am evaluating the TPS922053DRRR; I am using my own circuit. FSET center frequency is configured for about 400KHz (56K-ohms set resistor) and I am testing on about a 18V LED load (Vin more than double). I have I_LED_Full range setup for about 750mA (267m=ohm sense resistor). The ADIM/HD pin is grounded for hybrid dimming, and I am feeding a 1KHz (3V logic) PWM signal to the EN/PWM pin. I can elaborate on other details if needed.
My circuit does not start. I have taken a look at pages 13 and 14 of the datasheet, and I have a particular question regarding the explanation of the startup. The datasheet specifies a "dimming mode start" signal on pages 13 and 14 and describes two scenarios of a startup sequence. My first question has to do with what is meant by this "dimming mode start" signal? In my case, since I am using hybrid dimming, does this mean that the PWM signal provided to the EN/PWM pin should not be sent to the driver IC until 1ms after Vin rises above Vin-min or does this mean that the internal (somewhat abstract) "dimming mode start" state does not occur until 1ms after Vin rises above Vin-min?
In other words, what would happen if a PWM signal (or constant high DC signal) started immediately after the 5us minimum EN startup signal used to trigger the POR? In perhaps, even more clearer words, what would happen if a PWM signal were applied prior to a high POR signal?
I should also mention that with thermal analysis, in my case, I do observe the IC to oscillate to 125C then decrease continuously as it attempts to startup (there is also a bit of audible noise). Perhaps this would suggest thermal foldback is being reached, but I also cannot rule out whether this is being induced by a failed startup or is inducing a failed startup. I mention this merely as extra information in case there are any insights; my main question is above pertaining to understanding the startup procedure described on the datasheet; thanks,
