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

Parents
  • Hi all,
    I have the same problem with this LDO, actually sometimes it does not turn on and gives this -0.7V voltage on its output rail. My setup is the following: I use a bipolar supply from HMP4040 to create a +/-15V that supplies a ADP7142 and a ADP7182 LDO pair which in turn on the output give +/-10.3V. These LDOs supply 4 amplifiers: AD8429,AD8512, and two AD8421ARZs. So they are all connected to these bipolar rails on their output. The enable pins are all fixed to VIN as it is suggested in the datasheet. On their input I have 7u-7u and also on their outputs 4.4u-4.4u.  On the feedback I have R1=75K and R2=10K that create these +/-10.3V.  I use a 5 pin (SOT-23-5) configuration without SS pin.
    When I switch on the supply of the LDOs at the same time, what I observed (see my attached scope shots in the link) is that sometimes the positive LDO (ADP7142) does not turn on and on its output it gives -0.7V, instead the negative LDO (ADP7182) always turn on. When this happen the positive LDO still consumes 14mA and the other negative one that is OK consumes 20.3mA. This happens, when the negative rail comes before the positive rail (see the scope shots). Instead, when the positive rail comes first both LDOs works well (still on the attached scope shots). Additionally I have to say that I have 10K bleeding resistor on the inputs but I think it does not change anything.
    We suspect that since we see -0.7V on its output of the positive LDO, it could be the case that some internal protection turns on suddenly which takes control over the LDO and does not turn it on finally.

    Here is my link to the flies: https://drive.google.com/drive/folders/1Enxx-wdaLROM370Ypi-GBE_udlAhpOAw?usp=sharing

    Thanks in advance for your reply,

    Andras

Reply
  • Hi all,
    I have the same problem with this LDO, actually sometimes it does not turn on and gives this -0.7V voltage on its output rail. My setup is the following: I use a bipolar supply from HMP4040 to create a +/-15V that supplies a ADP7142 and a ADP7182 LDO pair which in turn on the output give +/-10.3V. These LDOs supply 4 amplifiers: AD8429,AD8512, and two AD8421ARZs. So they are all connected to these bipolar rails on their output. The enable pins are all fixed to VIN as it is suggested in the datasheet. On their input I have 7u-7u and also on their outputs 4.4u-4.4u.  On the feedback I have R1=75K and R2=10K that create these +/-10.3V.  I use a 5 pin (SOT-23-5) configuration without SS pin.
    When I switch on the supply of the LDOs at the same time, what I observed (see my attached scope shots in the link) is that sometimes the positive LDO (ADP7142) does not turn on and on its output it gives -0.7V, instead the negative LDO (ADP7182) always turn on. When this happen the positive LDO still consumes 14mA and the other negative one that is OK consumes 20.3mA. This happens, when the negative rail comes before the positive rail (see the scope shots). Instead, when the positive rail comes first both LDOs works well (still on the attached scope shots). Additionally I have to say that I have 10K bleeding resistor on the inputs but I think it does not change anything.
    We suspect that since we see -0.7V on its output of the positive LDO, it could be the case that some internal protection turns on suddenly which takes control over the LDO and does not turn it on finally.

    Here is my link to the flies: https://drive.google.com/drive/folders/1Enxx-wdaLROM370Ypi-GBE_udlAhpOAw?usp=sharing

    Thanks in advance for your reply,

    Andras

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