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REG103: REG103 neg ouput

Part Number: REG103
Other Parts Discussed in Thread: TPS7A90, TL5209, LP2989

Dears,

I am now using the REG103. There has a problems.

The problem is when the first I turn on the board, the LDO has correct output 5V.  Then I turned the board for 1 minute, turn on again. The output of LDO has been set to -1.1V.

The load of this LDO is a amplifier.The test output current of LDO is 92mA. I float the load then the output is OK. 

The following picture shown the schematic of my  circuit. The higher channel connect to the amp which has this problem.

The lower one connect to the ADC which works OK.

Two way to recurrent the error.

1. I use heat gun to blow the LDO when is setup (no load). The output is the same as LDO error output -1.1V.

2. Out 5V sine way at the first AMP input port. 

Is that kind of protection method to set LDO to -1.1V ??

Any suggestion? 


  • Hi Zhengqing,

    This is actually a common issue with older LDOs in applications that require a positive and negative rail. If the negative rail starts up first, the output of the positive LDO is pulled negative through leakage paths in the load. Due to the foldback current limit of REG103, the LDO is not able to startup.

    It is recommended that in any dual rail system the positive voltage be enabled first; however, some newer generation LDOs have been designed so that they can startup from a fault condition of a negative bias on the output. Please consider TPS7A90. This newer generation LDO still has a foldback current limit; however, the current limit circuitry has been designed to allow for startup from a negative bias.

    Very Respectfully,
    Ryan
  • Dears,

    Any Pin2Pin suggestion?

  • Hi Zhengqing,

    I would like to recommend TL5209, and LP2989 as P2P solutions for REG103.

    Best Regards,
    Wilson