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LM3414: LM3414 topology question

Kuo Duke
Expert 2040 points
Part Number: LM3414
Other Parts Discussed in Thread: TPS92640

Hi Sir,

 

Looks different vendors have same variable frequency control buck topology LED driver compare LM3414 and one thing different is current sense design on high and low side.

Could you help me to explain current sense design on high / low side advantage and common side effect? Thanks.

 

  • 0
    TI__Expert 3885 points

    Hi Duke,

    For buck topology, with high-side current sense, the LED- (or the cathode of the bottom-most LED in a string) can be connect to ground directly.

    This way, end customer can always assume LED- and ground are connected and no need to do an extra short test.

    With other buck devices such as TPS92640/1, the circuit implementation is different such that it only supports low-side current sense.

    In such case, customer has to connect LED- to a sensing resistor and then ground.

    For floating buck topology like LM3414, it can only use high-side current sense as the LED- is connected to the inductor, rather than ground.

    It will be difficult to get a true low-side current sense with such kind of topology.