Author Topic: Current ranger shows higher sleep current  (Read 382 times)

srihari_ue

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Current ranger shows higher sleep current
« on: February 15, 2020, 04:20:03 AM »
Hi,

Current ranger shows higher sleep current (around 33uA) when measuring current in uA range on an Unit under test powered by a Digilent Analog Discovery kit 2 (which has a programmable voltage output and is driven through USB or external power supply). The same setup when using the UUT with a multi meter shows a much lower sleep current (<3uA). The current measurement on the UUT is on the high side, i.e., in series with the power input to the device. The ground from the UUT is not connected to the current ranger setup.

When I try to power the UUT from an external power supply and the current ranger, I do not see this issue.

Could somebody help?

Best Regards,

Srihari


Felix

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Re: Current ranger shows higher sleep current
« Reply #1 on: February 16, 2020, 10:37:46 PM »
I cannot tell is something is not right from the photos.
Maybe a block diagram/schematic of exactly all connections would help me understand better how everything is wired up.

srihari_ue

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Re: Current ranger shows higher sleep current
« Reply #2 on: March 11, 2020, 12:14:40 PM »
Hi Felix,

The higher current issue was due to power supply powering the current ranger, as well as the noise form the Analog Discovery kit's power supply kit output.

Two events happened here that caused a large noise in the readings and thereby push the average DC sleep current a lot higher than it consumed.

1) The earthing noise entered into the measurement system (current ranger) since the current ranger was temporarily powered by an external power supply for our automation test validation. All I had to do was connect the earth terminal on the power supply front panel to the GND on my unit under test (not an ideal way of connecting earth) to actually reference the earth to 0V. Many of the fluctuating noise in my measurement went off.
2) The second AC noise actually came from the Analog Discovery kit's Programmable DC output (either due to stability issues when connecting a load or the USB powering the AD2 was noisy). I put the current ranger to BIAS mode to make bi-directional current measurement and the average current measurement in sleep mode now reduced to under 5uA.

I have a query here. Can I enable both the auto-ranging and BIAS mode together. The manual says these are complementary. But I need them both together, and how could I accomplish this? The reason being that I want to filter out the AC noise that I see in my system for which I need the BIAS mode. Since the noise is random the internal ADC averaging of 1000 samples does not help much here. The auto-ranging is needed because we want to use this system for automation of dynamic current measurements (micro-controller power-up, RF pairing/transmission/reception etc.), and we might even be sampling the analog voltage output from current ranger from an external device.

srihari_ue

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Re: Current ranger shows higher sleep current
« Reply #3 on: March 11, 2020, 12:36:00 PM »
Hi Felix,

I have attached the block diagram.

One more suggestion to all the folks who use the current ranger - I have used ISO7221ADR Opto-Isolator successfully for preventing ground loop issues if you want to data log to USB without any BLuetooth logging module. Just need to connect the Opto-isolator between the current ranger's serial input/output and the USB-UART converter that you are using.

Felix, the opto-isolator and an USB-UART converter IC, if added into a future revision of this module, could be be very helpful if engineers want to directly data log via USB or program without affecting the ADC calibration.

Best Regards,

Srihari S.

Felix

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Re: Current ranger shows higher sleep current
« Reply #4 on: March 11, 2020, 07:59:36 PM »
To integrate these components into the CR means higher cost of mfg and bigger board. Then add the cost of printing a larger box, bigger packaging.
Having made these for some time now that makes no sense, and hence I linked up a no brainer $7 suggested USB isolator which I always use with CR in testing and regular use.