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ADM4073F RS + / RS- Leakage problem

Dear Sir,

I use the ADM4073FWRJZ-REEL7 for the current sense. Independent 3.3V as power supply. RS + / RS- / OUT unconnected. But I use a multimeter to measure RS + / RS-. It can measure 1.71V at RS +. The RS- can measure up to 1.9V. Is this normal?

Thanks.

Andy Yang.

Parents
  • Hi Andy Yang,

    To avoid misunderstandings, please share the electrical diagram that corresponds to the measurement conditions.

    Regards,

    Kirill

  • Dear Kirill,

    Only connect Vcc and GND. Then use a multimeter to measure RS + / RS-.

    Thanks & best regards.

    Andy Yang.

  • Hi Andy Yang,

    In fact, you are not measuring a leak, but something similar to the input bias current. I assume that you are using a typical multimeter with an input resistance of 1 or 10 MOhm. You can see the voltage drop on the input resistance of the multimeter, which is created by the input currents of the RS+/RS-pins. These currents are in the microampere range.

    I don't see anything strange here. But don't forget that your measurements are very different from normal operating conditions. Can you clarify what you wanted to measure?

    Regards,

    Kirill

  • Dear Kirill,

    The schematic is as follows. When the system enters the Standby mode,  the PSU does not supply 12V / 5V / 3.3V. The 3V3SB continues to supply power. Use a multimeter to measure the voltage at each group of RS + / RS- (12V / 5V / 3.3V). It can be measured to 1 .xV voltage. The same is true when measuring with an oscilloscope or ATE.

    Thanks and best regards.

    Andy Yang.

  • Hi Andy Yang,

    Let me summarize what you said. Your current-sense amplifiers are located on the PSU Board, and the current-measuring resistors are always connected to the RS+/RS- pins. You measure the voltage at the RS+/RS- pins relative to the ground, but in fact, you measure the voltage at the left and right ends of the current-measuring resistors, respectively. But the main thing is not even the voltage on the pins RS+ / RS- in itself, but the voltage difference between the pins. This means that current flows through the current-measuring resistor, and, given your numerical results, the current flows from the load. And the value of this current is large, the device in the SOT23 case can not create such a current.

    It seems that you are looking for a problem in the wrong place

    Regards,

    Kirill

  • Hi Kirill,

    Good day, I'm Andy's colleague, please allow me to complement this application scenario. 

    In the experiment, there's no voltage and load supplied on current-measuring resistors path. (only voltage voltage is supplied to ADM4073's Vcc.)

    We can measure RS+ and RS- compare to ground, we both can measure the voltage around 1.xV even if we disconnect RS+/RS- with current-measuring resistors.

    I hope these information can help you understand the issue we have, thank you!

    Henry

  • Hi Henry,

    Okay, but first tell me why you're taking these measurements. Your PSU is not working properly and you are looking for a reason?

    Also, what measurement results do you expect? In other words, what voltages do you think should be on the RS+/RS- pins ?

    Because I don't really understand what problems you have

    Regards,

    Kirill

  • Dear Kirill,

    Let me correct it, the system should enter the shutdown mode, not standby mode. The customer uses the x86 platform. In the S5 shutdown mode, only Standby power 5V / 3.3V should be powered. + 12V / 5V / 3.3V / -12V should be no Power 0V status.
    When the system enters the shutdown mode, ADM4073F is still powered by Standby 3.3V. Measure RS + / RS- to ground. The two pins will measure almost the same voltage of 1.xV. This voltage will let the system determine that it is not in S5 Mode. The ATE test will also be determined to fail. There is no issue when the customer test Intel original platform (Intel original platform use Maxim solution).
    Disconnect the RS + / RS- of the ADM4073F from the surrounding area. It is not connected to current-measuring resistors. RS + / RS- can measure 2 different voltages, 1.90V and 1.71V. How to fix this problem? My customer needs to provide the first version PCB for the end customer test this week.

    Thanks and best regards.

    Andy Yang.

  • Hi Andy Yang,

    As far as I understand, in the shutdown mode, the power lines become "high-resistance" and ADM4073 can create voltage on these lines, which is perceived by the system as an abnormal state. Am I right?

    Find out what current can flow from the RS pins to the ground. Just measure this with a multimeter between each RS pin and the ground. It is these currents that create a voltage of more than 1 V on the power lines.

    If the system is able to detect the voltage on the power lines in shutdown mode, then there must be some threshold level above which the system diagnoses an error. Can you figure out this level?

    I hope this info will help find a good solution

    Regards,

    Kirill

  • Dear Kirill,

    My customer's RD thinks that at least 5V power line should be lower than 1.5V. The 3.3V power line should be lower than 0.99V. But the RD Leader thinks that all (including the 12V power line) should be lower than 0.3V. We first meet the requirements of RD. But need to explain why these voltages are generated. Our solution to reduce these voltages is no problem. It will not affect the accuracy and precision of normal current detection. My customer also needs to explain to the end customers to let them accept this solution.

    Thanks and best regards.

    Andy Yang.

  • Hi Andy Yang,

    I think it has to do with the fact that this amplifier is not truly isolated amplifier. As you can see from the simplified internal circuit, current is consumed from the power line for feedback operation. I am sure that the effect you get is inevitable with this particular amplifier due to its internal structure.

    The most logical solution would be to turn off the supply voltage of all ADM4073. This can become an analog of sleep mode as in many other analog ICs, in which the influence of the amplifier itself on the external circuits is minimal.

    Regards,

    Kirill

  • Dear Kirill,

    Will the -IN / + IN of LT6106 have the problem of leakage voltage?
    If LT6106 is used to replace ADM4073F, can this phenomenon be improved?

    Thanks and best regards.

    Andy Yang.

Reply Children
  • Hi Andy Yang,

    Sorry for the delay. Unfortunately, I can't give an exact answer. These amps seem similar in nature when compared to their data sheets. I don't think you can solve the problem by directly replacing one with the other. But I have noticed that the supply voltage range of these devices far exceeds the voltage on the power lines of your system. Can you connect the supply of a current-sense amplifier directly to the power line? This may solve your problem, because without power supply, the amplifier will not be able to affect the operation of the system.

    Regards,

    Kirill