MAX22088 heating issue

Hi @dzungpv, the first thing I would check is whether the VCC_OUT pin is connected to any external loads. VCC is the LDO output and can supply up to 70mA. Does it connect to some heavy loads?

The second thing is measuring the voltage between HP-HN and compare with the voltage at VRAW. Do you see a typical 1.5V drop between them?

The code marked on the top of the chip indicates the lot/mfg info/date of the part - it is useful in some cases but does not affect the functionality & performance.

Hi, me again. I just received the MAX22088EVKIT, but unfortunately it seem not working. I follow the docs here https://www.analog.com/media/en/technical-documentation/data-sheets/MAX22088EVKIT.pdf and follow 19 steps to get the reference signal, but the board is not working, all led are green, voltage and test point normal but no signal on the H1+ and H1-.

I check the DIN2, there is no signal when I provide ISO_IN 25khz/5v square test signal. Seem the MAX12931BASA is dead. The  MAX12931BASA is not available in my country, so if I try to purchase it, my take more than 1 week to purchase it online.

The kit I purchased from Mouser, it is perfect handle and see no external damage, I don't know why.

Hi there.

I see that you are trying to send data through the isolator and found that DIN2 has no signals. To see whether MAX12931 is truly unfunctional, I recommend measuring the signals at its pins. This way the MAX12931 is isolated from the evkit and the results tell us whether it is defective.

1. Disconnect J4 and J5 such that the rest circuit does not affect MAX12931.
2. Measure the voltage at J2 and J3 to be 5V.
3. Supply your 25kHz input at ISO_IN and measure it at pin3.
4. Measure again on pin6 and match it with your input.

At the meantime, there is also ways to validate the rest of the circuit by sending data from master circuit to remote circuit. This way we don't need to use MAX12931 to test the MAX22088 transceivers.

1. Disconnect J4 and J5 such that the MAX12931 does not affect the rest circuits.
2. Supply your 25kHz at DIN1. Connect J1. As a courtesy check LEDs, test point voltages, etc.
3. Measure the waveform at DOUT1 and H1+ & H1-. It should look like Figure1 in EV kit datasheet. At this moment we know the MAX22088 at master side is functioning.
4. Measure the waveform at DOUT2. Try to use a scope channel on a different ground when doing this step as the remote side has a different ground than master side, particularly when the cable connected two sides is long.

Please let me know if you find anything unclear.

Hi there.

I see that you are trying to send data through the isolator and found that DIN2 has no signals. To see whether MAX12931 is truly unfunctional, I recommend measuring the signals at its pins. This way the MAX12931 is isolated from the evkit and the results tell us whether it is defective.

1. Disconnect J4 and J5 such that the rest circuit does not affect MAX12931.
2. Measure the voltage at J2 and J3 to be 5V.
3. Supply your 25kHz input at ISO_IN and measure it at pin3.
4. Measure again on pin6 and match it with your input.

At the meantime, there is also ways to validate the rest of the circuit by sending data from master circuit to remote circuit. This way we don't need to use MAX12931 to test the MAX22088 transceivers.

1. Disconnect J4 and J5 such that the MAX12931 does not affect the rest circuits.
2. Supply your 25kHz at DIN1. Connect J1. As a courtesy check LEDs, test point voltages, etc.
3. Measure the waveform at DOUT1 and H1+ & H1-. It should look like Figure1 in EV kit datasheet. At this moment we know the MAX22088 at master side is functioning.
4. Measure the waveform at DOUT2. Try to use a scope channel on a different ground when doing this step as the remote side has a different ground than master side, particularly when the cable connected two sides is long.

Please let me know if you find anything unclear.

It is my fault, I use AFG which is peak to peak 5V from -2.5v to +2.5v signal, using the 0v to 5V signal and now the signals like Figure1.

But my design still not working. The idle current of the EVKIT (Remote/device CIRCUIT 2) is 11ma/18V, and active 25ma, My design base on speed of 9.6kbps (difference are just value change in:Table 2. Recommended Component Values for Different Data Rate ) the idle is 25ma and active current is 185ma/18V. I will try to replace the chip to EVKIT to test and report back later.

thanks for the follow up and glad to see you make the EV kit work in your setup.

Hi, The kit work perfect. But with my design for 9.6kbps, the chip still hot, but it can run longer for me, the current now nearly the same with the EVKIT, so if the EVKIT for 57.6kbps the test signal must be change for me, like the test must be device by 57.6/9.6? I follow nearly all the value recommend by the EVKIT documents for the speed 9.6.

Hi, my understanding is that the EV works well in your application with no thermal concern & no abnormal current. Your design still have thermal issue but improving - immediate question: what did you change?

I recommend to do a A-B comparison on the bench between the EV kit & your design. Under the same test condition (data rate, load condition, same equipment, etc) do you observe any significant difference?

the EV kit is designed for 57.6kbps. You can start with this data rate.