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LMR51430: Constant Current LED Driver FB not responding

Nathan Caylor
Prodigy 10 points
Part Number: LMR51430

Tool/software:

I am trying to use an LMR51430 to create a constant current power supply to drive two LEDs in series at 2A of current. I am having trouble getting my circuit to work on a protoboard. As I power the circuit on it seems that the LMR51430 is not regulating the power at all. It will send all of the power from my supply straight to the LEDs without regulating it when the current is above 2A. I have measured my FB voltage across my sense resistor and it is at 0.6V at 2A but as I increase my amperage past 2A on my power supply my FB voltage will get up to as high as 0.9V and the buck does not seem to respond.

Is it possible that I have damaged the chip when soldering it? I have replaced my LMR51430 a few times but I keep getting the same results. 

Vcc: 18V-24V

Iout: 2A (Vout ~ 7V)

  • 0
    TI__Genius 13825 points

    Hello,

    The device is not setup properly. 

    The LMR51430 has an adjustable output which means feedback resistors are required to set the output. FB should be connected to a feedback divider which connects to the output capacitors. Please refer to the Applications Section of the datasheet. In order for the device to function properly, all recommendations in the datasheet must be followed. Here is an example of proper configuration for reference: 

    Layout is also very important for proper performance of these devices. Instead of evaluating on a protoboard, I recommend evaluating your design on the device EVM: https://www.ti.com/product/LMR51430

    Best regards,

    Ridge