ADP7142(ARDZ-5.0-R7) output out of range, fixed in -0.786v

Hi all, I hope you can help me with the following:

 

I'm testing a dual power supply with the adp7142 for +10v (positive 200mA) and the tps7a30 for -10v (negative 200mA). The source is a pair of 12v batteries in series configuration so the adp7142 is applied with +12v on its input and the tps7a30 is applied with -12v. When both regulators are started through a common switch (nearly at the same time) the output voltages are within range -10.02v and +9.99v respectively. The problem arises when only the positive input is disconnected and then connected back, after this the output of the adp7142 is -0.786v and the sense/adj pin is -0.401v. Also repetitive disconnections and connections won’t fix the problem, the adp7142 output stays at -0.786v. Only by restarting both regulators through the common switch returns the output voltages to the correct values  

 

Here is the schematic for the adp7142:

 

 

Thank you very much

David

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  • 0
    •  Analog Employees 
    on Feb 26, 2018 2:17 PM

    Hi, David.

    I tried to replicate this setup using ADP7142 and ADP7182 as positive and negative LDOs (input voltage (VIN) of ±12V and output voltage (VOUT) of ±10V) and I am NOT experiencing the problem that you've encountered as stated above. ADP7142 VOUT still reaches 10V after VIN is connected and disconnected several times. 

    Having scopeshot of VOUT and board schematics would be helpful too in debugging this issue. Check to see if there is any external pull down current path on VOUT or sense/adj pin to a negative potential when VIN is disconnected that can turn on the protection diodes. I recommend also investigating other paths external to the LDO that could potentially creating this problem.

    Regards,

    Errgy

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  • 0
    •  Analog Employees 
    on Feb 26, 2018 2:17 PM

    Hi, David.

    I tried to replicate this setup using ADP7142 and ADP7182 as positive and negative LDOs (input voltage (VIN) of ±12V and output voltage (VOUT) of ±10V) and I am NOT experiencing the problem that you've encountered as stated above. ADP7142 VOUT still reaches 10V after VIN is connected and disconnected several times. 

    Having scopeshot of VOUT and board schematics would be helpful too in debugging this issue. Check to see if there is any external pull down current path on VOUT or sense/adj pin to a negative potential when VIN is disconnected that can turn on the protection diodes. I recommend also investigating other paths external to the LDO that could potentially creating this problem.

    Regards,

    Errgy

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