Dear costumer support,
We would like to use the INA199A3 type IC product to measure the power consumption of circuits, but we have several issues regarding the application of this product.
To describe the problem I have attached a drawing of the circuit, and also a part of the PCB near the IC.
Two kind of applications can be found on the drawing of the same PCB:
1st application:
a, at first we connected the shunt resistor with (R125, R127) series resistors to the IC’s inputs, (the shunt resistor is the PCB’s 18mm long, 2,5mm wide 18um thick copper foil/film, approx. 7mΩ).
The series resistor’s value was 5R1/1206/1%.
80% of the circuits have had serious problems during operation:
most of the outputs had the IC’s supply voltage, the rest had either 0V or set in between 0 and 5V, by having 0mA shunt current (the consumer circuit has been disconnected), however the 0V outputs’ error was that even significant current (1A) couldn’t cause voltage output.
The rest (20%) worked more or less correctly.
We have tried to assimetrically adjusting the series resistors (0R to 5R1), most of the time the output range of the IC „could be adjusted” to be in useable range – but this is not normal operation, and there have been cases when even the short-circuiting of the IC inputs had no effect on the output.
The IC’s supply voltage is provided by LM2594M-5V, this supply voltage is filtered with several 10u capacitors on the panel’s conductive foil. We have tried to increase the capacity, but that also hadn’t changed things.
We have tried replacing the IC in the malfunctioning circuits, the operation changed considerably ever, and improved in many cases.
These observations are based on the testing of 15 boards’, including 60 circuits (4 measuring circuits / PCB).
PCB board there wasn’t any correlation statistically between the different circuits’ position and behaviour
b, In the next step we left out the series resistors completely, and replaced it with short circuit.
The percentage of faulty operation has been lowered to 35%.
During the test of 20 boards, we haven’t found any which had +supply voltage on its output while having 0A shunt current, however in some cases it stayed at approx. 500mV, and there have been some which haven’t increased their output even at 1A shunt current.
IC replacement solved the problem in 90% of the cases, and it changed the values in the rest of the cases.
We have tried to increase the IC’s reference input with a resistor divider to 400mV in a circuit which had 0V output, this resulted in the output having 400mV as well, and it reacted with a proportionate change in the shunt current output.
2nd application:
In this case the IC reference level has been increased to 2,7V with a resistor divider,
which was ok for those circuits which worked, the output was also 2,7V while having 0A shunt current.
The rate of malfunctioning was 40%. In this case we observed the following errors during operation, the output didn’t align with the reference level, and/or from the inputs even if only one had potential (battery) on it the output still changed, however the shunt hasn’t had any current, current should have been only on the IC inputs , but because of the shunt this had to arise on the other input as well, so difference should not occur.
The shorting of the series resistors resulted in significant improvement in this case also, but the symptoms have stayed, which changed after IC replacement or –most of the time- improved.
Please inform me if you know about any manufacturing defect concerning the above mentioned IC, or if we are applying/using the IC wrongly.
Thank you in advance!
Best Regards,
J. Botyanszki
