ISO224EVM: output error

user3756530

Part Number: ISO224EVM
Other Parts Discussed in Thread: ISO224, OPA277, AMC3330

Now I use iso224evm to test, the front-end uses 100A: 3.53v transformer to sample, and the signal is sampled to ADC through iso224 and opa277 amplification circuit;

The connection is as follows: iso224evm, VDD power supply ± 12V, VDD2 power supply + 5V, vdd1 power supply + 5V / external input + 14V through tps74050 on board. It is found that TP3 output of iso224 output test point is 2.22V DC when there is no output, 50Hz / 560mv signal and 1V signal from transformer output. The input and output waveforms are as follows:

Please help to analyze the reasons?

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Can you post a schematic of the input circuitry? How do you connect the transformer to the input of INA224?

What do you see at TP4?

Kai

0 Alexander Smith over 3 years ago in reply to kai klaas69

TI__Mastermind 47595 points

Hi,

The ISO224 has an internal gain of 1/3 and outputs a differential signal on a common-mode of VDD2/2. From what I see in the waveform captures, the device is working as expected, however the measurement has some noise - most likely due to not using the FSR of the device and the connectors used to measure the signal. If you don't expect the input signal to go beyond +/-1V, I would recommend using a device with a smaller input range, such as the AMC3330.

Please let me know if you have additional questions.

0 user3756530 over 3 years ago in reply to Alexander Smith

Intellectual 940 points

When there is no signal input, 2.22v DC signal is also output, and whether there is VIN output has no change.

0 kai klaas69 over 3 years ago in reply to user3756530

Guru 140200 points

Yes, always. That's why I asked what you see at TP4.

Kai

0 Alexander Smith over 3 years ago in reply to user3756530

TI__Mastermind 47595 points

Hi,

With no input signal, 2.22VDC signal on output is correct.

With an input signal on VIN, there should be a change on the output. Can you please provide a schematic of how the input is connected like Kai asked?

Can you verify the input signal is present on the input with respect to the high side ground?

Amplifiers

Amplifiers forum

ISO224EVM: output error