Hi All,
I'm currently trying out the evaluation kit for the MAX49921 from Maxim, and I'm having a few problems with it. First thing to note is that my board appears to be an issue a board, but all the documentation on the Maxim website is for the issue b variant.
So, the problem I'm having with it, is it seems to be unstable/unreliable when drawing small currents through the shunt resistor. The shunt resistor I'm using is a Murata 3020-01096-0 (1mohm), and I'm using a TTI bench supply to supply power (28V), and a Keysight n6700c dc load mainframe with a 100W module.
As delivered, the device didn't produce an output until 900mA was being drawn through the shunt. Interestingly though, once it was outputting, the current could be stepped down and the device would continue to work down to 10mA.
After some experimentation, I've found adding filtering to the input and output seems to help. The best results I've achieved so far have been with the following values;
R3, R4: 1k6
R7: 200R
C3, C4, C9: 10nF
However, even with filtering, the behaviour starting from a low current still isn't right. The device still won't respond to 10mA, and at 20mA, the device does work however it falls over if the current is increased without turning off the DC load in between. At higher currents, 100mA+, the device continues to work when the current is stepped up.
A couple of other things to note:
The amplifier is being powered at 5V from the second output of the bench supply, and the 0V of both outputs are linked.
When adding filter components, I've cut tracks as necessary to make sure components aren't shorted out.
I'm using screened twisted pair wire (KU05) to connect the board to the shunt resistor.
A link to the datasheet..
https://datasheets.maximintegrated.com/en/ds/MAX49921EVKIT.pdfAny help/ideas would be greatly appreciated, I'm all out of ideas!
Cheers,
Greg