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Q: In PWM dimming mode, is it OK to use frequencies outside the specified range for the PWM input signal on the CTRL pin of the TPS61160, TPS61161 and TPS61165?
It is not recommended to input PWM signals outside the recommended frequency range.
For PWM signal frequencies slower than 200 Hz (1/(2*toff=2.5ms)) and D<50%, the IC will alternate between being enabled and disabled and so will struggle to reach current regulation after soft start.
For PWM signal frequencies between 1kHz (1/tes_win=1ms) and 2.8kHz (1/(tes_delay=100us+tes_detect=260us)), certain duty cycles could result in the TPS61160, TPS61161 and TPS61165 ICs entering EasyScale mode. The TPS61160A and TPS61161A have EasyScale mode disabled.
For PWM signal frequencies between 200Hz and 5KHz, assuming the IC does not enter EasyScale mode, the internal chopper circuit produces a PWM signal with average voltage equal to D*0.2V. However, the chopper's RC filter roll-off point is too high in frequency to effectively filter the PWM signal. So the reference voltage seen by the error amplifier has signficant ripple voltage which has been known to cause the control loop to go unstable. This ripple voltage propagates through to the output voltage and current.
For PWM signal frequencies above 100kHz, the chopper circuit's FETs actually have a turn on/off time of several hundred nanosecond so the chopper could potentially operate normally but we have not tested such operation.
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