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Automotive back light LED driver

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: LM3431-Q1, LP8860-Q1, LM3410-Q1, LM3410, LM3423-Q1, TPS92601-Q1, LM3423, TPS92691

Hello,

Are there any suitable device for the following specification?
I think that LP8860-Q1, LM3431-Q1, LM3410-Q1 are similar with required specifications but not satisfied all requirement.

<Required Specification>
Vin : 3.3V or 5V (not fixed)
LED : 2S,1P
Vf : 3.3V (Vout=6.6V)
Iout : 400mA (device requirement is 500mA)
Dimming : Analog and PWM
PWM Dimming ratio : 1000:1

Best Regards,
Ryuji Asaka 

  • 0
    TI__Mastermind 25500 points

    Finding an automotive qualified device that operates down to 3.3V is difficult since most of them are higher voltage to satisfy load dump requirements. As you found the LM3410 could do it but it lacks analog dimming. If the input could be fixed at 5V then you would have more options such as the LM3424Q or the TPS92690Q which has a much easier analog dimming function. There are other LM342x Q-grade devices but most of them add some complexity. It also depends on how fast of PWM dimming frequency you need whether or not you could make 1000:1.

  • 0 in reply to Clinton Jensen
    Guru 20090 points
    Hello Clinton san,

    Thank you for the reply.
    Since the customer required Fault Diagnostics function, I promote the TPS92601-Q1 , LP8860-Q1 and LM3423-Q1.
    Could you please let me know the how to calculate dimming ratio ? If there is any application note, please let me know.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Mastermind 25500 points

    I am only familiar with the LM3423 device out of those, but either way the dimming ratio will depend on the operating points (input and output voltage along with LED current), component values (particularly output capacitor and inductor), and the dynamic resistance of the LED load. Basically these all determine your rise and fall times and therefore the minimum pulse width that still gives you acceptable linearity. In the case of the LM3423 it can drive a series dimming FET which prevents the output capacitor from discharging much when the LEDs are off, so the rise and fall times are very fast. 1000:1 or better is easily achievable at lower PWM frequencies (up to say 1kHz, the lower the frequency the better you can get though). So it depends on a lot of things and in the end should be bench tested to see actual rise and fall times. Another option that is a newer and higher performance device if you are interested is the Q grade version of the TPS92691 which also has a series disconnect FET and fault monitoring.