About LT3952A External PWM Dimming

Hi Kazu,

LT3952A IC does not set limit of frequency/duty cycle range for external PWM dimming. However, with different applications and component selection, the PWM performance varies and has freq/duty limits in order to achieve good ILED waveforms. A good reference is datasheet page 26, 2MHz application can achieve 4000:1 150Hz PWM dimming, with ILED minimum pulse width 1.67us. My rule of thumb is if PWM frequency is 100-1kHz, minimum pulse width is around 5 switching cycles. If your application requirements are beyond the range, I would recommend testing and confirm.

Switching frequency of the circuit does affects (1) and (2). Actually (1) and (2) can be affected many factors like fsw, loop compensation, Cout, length of load cables, etc.

Gengyao

Hi Kazu,

LT3952A IC does not set limit of frequency/duty cycle range for external PWM dimming. However, with different applications and component selection, the PWM performance varies and has freq/duty limits in order to achieve good ILED waveforms. A good reference is datasheet page 26, 2MHz application can achieve 4000:1 150Hz PWM dimming, with ILED minimum pulse width 1.67us. My rule of thumb is if PWM frequency is 100-1kHz, minimum pulse width is around 5 switching cycles. If your application requirements are beyond the range, I would recommend testing and confirm.

Switching frequency of the circuit does affects (1) and (2). Actually (1) and (2) can be affected many factors like fsw, loop compensation, Cout, length of load cables, etc.

Gengyao