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LM3429: Low Power mode

Part Number: LM3429
Other Parts Discussed in Thread: LM3421

Dear Sir or Madam,

 

I am designing a buck-boost LED driver using the LM3429. PWM is used. Design is similar to the evaluation board. However, we would like to enter a low power state when LED is turned off (nDIM held high). What would the typical power consumption be in this case? There is the Quiescent current stated in the datasheet of typically 1.6 mA and also the OVLO and UVLO circuitry that takes some current, but is this enough to esitmate current consumption in this state? Will the device enter some low power state when nDIM is not active?

 

Instead I was thinking of using the LM3421 that has EN and RPD pins. However the datasheet shows a more complex way of connecting DDRV pin to an external FET handling PWM functionality. As I want to keep complexity down, is it possible to run PWM on the LM3421 in the same way as the LM3429 does, that is, without the FET connected to DDRV pin, and just feeding PWM to the nDIM pin? What would the drawbacks be?

 

Best regards,

 

Per

  • Hello,

    The LM3429 does not enter a low power state with nDIM low so a valid current consumption would be the resistor dividers and the Iq (static) of the device.

    The LM3421 is basically the same device with some added features. If you do not want to use the dimming FET you can omit all of that circuitry and just drive nDIM like you would with the LM3429. The only drawback is the speed of the edges, but it will still be just as fast as the LM3429 given the same component values and operating parameters. The external FET is only needed if you really need high contrast ratios at higher frequencies than you can get without it.

    Regards,

    Clint