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LM2623EV output shorted?

Johnson Thie
Prodigy 10 points
Other Parts Discussed in Thread: LM2623EV, LM2623

I just bought a LM2623EV evaluation module. The input was connected to a DC PSU at 3 V. I measured the output using a DMM and expected to see 5 V.

When I turned on the PSU, it showed that the module was drawing 1 A. I did not place any load (resistor) across the output. Even when I placed a large resistor (56 kOhm), it still drew 1 A. 

I did continuity test on the pads and could not find any short to ground. 

Note that: the DC PSU is working and is not at fault. I did not modify the board. I tested it out-of-the-box.

Any idea why it was behaving this way?

  • 0
    TI__Expert 4565 points
    Hi,

    I'm not the original application engineer for this, but had same experience for this.
    It seems that LM2623 shutdown output unless Vout level reaches in a given time. So, if power supply ramping is slow and can't help pump Vout enough level, then Vout becomes low and Vin and Vout will be a shorted condition.
    In order to avoid this situation, there can be 2 solutions.
    One is to increase current limit of power supply. I guess your PS current limit was set to 1A now. Current limit required for normal operation will depend on rise time of power supply. The rise time of my PS is ~1ms and needed more than 2.5A limit to make it works correctly.
    Another one is to increase PS rise speed. I've tested this with 1A current limit by plugging PS while it's already on, and EVB worked sine.

    This device is a pretty old design and we don't have original design team in TI any more. So, the answer may not be enough for you. So sorry about it.

    Thanks,