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TLC59711 pwm frequency

Godat Yan
Prodigy 20 points
Other Parts Discussed in Thread: TLC59711, SN74LS04

Hi,

I want to make a prototype of LED driver with the TLC 59711 but I can't find the output PWM switching frequency in the data sheet. Is it a constant or can I change it?

Many thanks

Yan

  • 0
    TI__Intellectual 1820 points

    Hello, Yan,

    59711 use internal grayscale clock, which is 10MHz typical. To finish a complete display period(65536 GCLK cycles) , the PWM frequency should be 152Hz typical, you can't change it.
    While, tlc59711 use ES-PWM (128 segments in one display period), thus the measured PWM frequency at output pin will be 152*128=19.5kHz.
    The above calculated PWM frequency is correct when GS>128. When GS<128, the output pin turn-on frequency is not constant since some segments have no chance to turn on yet.
    Since the internal grayscale clock have some variation(minimum 7MHz, maximum 12MHz), then the PWM frequency will also have variation accordingly.

    Best regards

    Mike

  • 0 in reply to Mike(DC/DC) Wang
    Prodigy 20 points

    Hello Mike,

    Thanks for your answer, as expected I measured a 20kHz on each output. For my project I need to drive 12 high current output (4>6A Led), so I try to find a interface between the collector output of TLC59711 and power N mosfet. I've try several options, for example a mosfet driver with internal input  pull-up (fan3226), a logic inverter with pull-up too (SN74LS04). At very low PWM output (0-3% of duty cycle), the mosfet driver could not perform a smooth start; and the inverter solution is influenced by the level of other outputs (think that's because of the current needed by the gate at 20kHz. Have you an idea to better interface TLC outputs and N mosfets while keeping non-inverting signal?

    Thank you and best regard,

    Yan