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LM3478: LM3478

Vijay DALMET
Prodigy 140 points
Part Number: LM3478
Other Parts Discussed in Thread: BQ24630

We have been using LM3478 to charge a LFP battery. We are using a micro-controller in our design ans hence not using dedicated battery charger to save cost and as micro-controller provides better management. We used Webench design to get the voltage output of 18.1 Volts and current limit of 1.2 Amps. The input voltage ranges from 10 Volts to 16 volts (Automotive nominal 12V range).

Schematics and PCB layout attached. The global label "Charge_Enable" is controlled (connected to GND) by a micro-controller.

Everything works fine in our circuit except the current limit. The circuit supplies as much current as the load wants without limiting the current.

What could be the issue? Do we need to use an external current limiter?

  • 0
    TI__Guru 73830 points
    Hi Vijay,

    Thank you for considering the LM3478 in your design. What is the Vout condition when you see the current limit is not functioning? Is it when your output voltage is held lower by the load side battery than the input charging battery voltage? If it is, then you are facing the fundamental drawback of the boost converter topology--not able to limit the over current when Vout < Vin.

    Can you send us a SW node voltage waveform when this happens for a double check?

    Thanks,
    Youhao Xi, System and Applications Engineering, APP-BMC-BCS, TI
  • 0 in reply to Youhao Xi
    Prodigy 140 points

    Hi Youhao Xi,

    Thanks for the quick reply and looks like we are facing the drawback of the boost converter you mentioned.  Our load side battery voltage is much lower (10V to 16.5V) than the LM3478 output (18.1V).

    Does TI have any other component or IC to overcome this problem?

    Again, we are not looking into BQ24630 kind of solution as it costs more and we are using micro-controller to manage the battery charging.

    Thanks.

    Vijay