Programmable Electronic Load - ADC and DAC BoosterPack test

WIP

This blog documents the characteristics of the DAC/ADC BoosterPack of the electronic load that Robert Peter Oakes, jc2048 and Jan Cumps are designing.

We have the same DAC/ADC BoosterPacks so we can compare the measurements of each ADC and DAC channel. Check the main document for anything related to hardware and firmware.

Test Setup

Peter has created a GUI that we can use to shoot SCPI commands. We can control the DACs and read the ADCs.

Measurements are performed with and without the power driver BoosterPack installed. We'll use 5V to power the DACs and ADCs in both situations.

P1 and P2 on the bottom of the DAC/ADC BoosterPack have to be open. Else you'll inject 5V onto the LaunchPad 3V3 rail and you'll damage components.

It's not critical if you switch on the power supply before or after you connect the LaunchPad to your computer. The circuits are isolated.

All measurements use P3.10 as GND reference and P3.1 as reference voltage.

Setup without the power driver BoosterPack:

Mount the DAC/ADC BoosterPack on the LaunchPad.

Use a +5V power supply. It should be a decent one, current is approximately 5 mA.

Connect with DAC/ADC BoosterPack P4.2 and with P4.1.

Setup with the power driver BoosterPack:

Mount the DAC/ADC BoosterPack on the LaunchPad and the Power Driver BoosterPack on top of that.

On the Power Driver BoosterPack, bridge pins P2.4, P2.5 and P2.6 to tie both opamp inputs of opamp 3D to ground.

Use a +12V power supply. It should be a decent one, current is approximately 50 mA.

Connect with Power Driver BoosterPack P1.1 and with P1.2.

Measurements

In the table, the first column shows what we're measuring, the second column the SCPI command to execute with Peter's GUI.

The next columns are the measurements for Peter, Jon or Jan with and without the Power Driver BoosterPack.

The last column is for comments. We can indicate odds, errors, learnings.

Data Point	SCPI	Without	Without	Without	With	Measurement method
		Jon	Peter	Jan
Supply	N/A			4.989 V	11.88 V	DMM
DAC/ADC V+	N/A			4.989 V	5.035 V	DMM
VREF	N/A			2.046 V	2.046 V	DMM
ADC A GND	DEVE:ADC1?			2		SCPI output
ADC A VREF	DEVE:ADC1?			10918		SCPI output
ADC A	DEVE:ADC1?				1138	SCPI output
ADC B GND	DEVE:ADC2?			12		SCPI output
ADC B VREF	DEVE:ADC2?			10920		SCPI output
ADC B	DEVE:ADC2?				1	SCPI output
ADC C GND	DEVE:ADC3?			2	2	SCPI output
ADC C VREF	DEVE:ADC3?			10920	10919	SCPI output
ADC C	DEVE:ADC3?				26868	SCPI output
ADC D GND	DEVE:ADC4?			8	3	SCPI output
ADC D VREF	DEVE:ADC4?			10919	10919	SCPI output
DAC A 0	DEVE:DAC1 0			0.000 V	0.001 V	DMM
DAC A max	DEVE:DAC1 65535			2.040 V	2.040 V	DMM
DAC B 0	DEVE:DAC2 0			0.005 V	0.005 V	DMM
DAC B max	DEVE:DAC2 65535			2.046 V	2.046 V	DMM
DAC C 0	DEVE:DAC3 0			0.000 V	0.000 V	DMM
DAC C max	DEVE:DAC3 65535			2.039 V V	2.039 V	DMM
DAC D 0	DEVE:DAC4 0			0.000 V	0.000 V	DMM
DAC D max	DEVE:DAC4 65535			2.039 V	2.039 V	DMM

To resolve
With the power driver installed, ADC C and D act strange (probably also A and B, but I didn't inject a voltage in them because they are connected to opamp pins). In particular strange for ADC D, because that one isn't routed. Strange. I will try to decrease the frequency of the sample speed and the i²c speed to see if it's related to that ... Follow up: the cause is that OPAMP 3C injects -0.8V into ADC A. All measurements are off when that happens. As soon as I force ADC A positive (by tying it to ground or a positive voltage) all measurements are correct.

To resolve

With the power driver installed, ADC C and D act strange (probably also A and B, but I didn't inject a voltage in them because they are connected to opamp pins).

In particular strange for ADC D, because that one isn't routed. Strange.

I will try to decrease the frequency of the sample speed and the i²c speed to see if it's related to that ...

Follow up: the cause is that OPAMP 3C injects -0.8V into ADC A. All measurements are off when that happens. As soon as I force ADC A positive (by tying it to ground or a positive voltage) all measurements are correct.

We have a separate document to analyse the summing node at zero.

Top Comments

Parents

shabaz over 7 years ago

Hi Jan,

I was wondering, what are the expected values, is it reading a value representing 1.602V when it should read a value representing 2.048V?
I'm wondering if it could be due to conversion time (i.e. once the ADC has been requested to perform the conversion, the delay until the conversion result is read may be too short in the code currently). Could that be likely, or is the delay quite long for the tests you did?
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Jan Cumps over 7 years ago in reply to shabaz

yes, Shabaz, I have a controlled value of 2.040 V. Once I mount my additional driver board (self-designed so many things can be wrong ) the ADC says it’s 1.6 V. I checked signals with my scope to see if there isn’t noise or oscillation.

I will give each of the 4 ADC units a little more time to see if this resolves my issue ...
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Jan Cumps over 7 years ago in reply to shabaz

yes, Shabaz, I have a controlled value of 2.040 V. Once I mount my additional driver board (self-designed so many things can be wrong ) the ADC says it’s 1.6 V. I checked signals with my scope to see if there isn’t noise or oscillation.

I will give each of the 4 ADC units a little more time to see if this resolves my issue ...
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Jan Cumps over 7 years ago in reply to Jan Cumps

there’s also an additional i2c device on that driver board that I haven’t programmed yet. that could also be a source of issues. it’s sharing the lines with the ADC and DAC ic.
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