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SPI Communication fails with ISO7241C but works with ISO7641FC, same circuit?

Prathamesh Dhamanaskar
Prodigy 10 points
Other Parts Discussed in Thread: ISO7641FC, ISO7241C, DAC161S997, ISO7841

Objective: To interface DAC161S997, with Microcontroller C8051F350 through ISO7641FC using SPI Protocol, Which works fine and DAC output is achievable.

Now here is the problem, I have changed ISO7641FC with ISO7241C which has similar pinout and specifications, but with ISO7241C DAC Output is not available somewhere SPI communication fails.

some observation: with DAC161S997 when you send a Command 1 (ex Write Command), on immediate next Command 2(ex Nop Command) you will receive/Read Command 1. Which happens with both ISO7641Fc and ISO7241C.

Now here is other observation, Earlier i was trying to output 4mA on DAC which is to write 0x2AAA value through SPI to DAC butDAC would output 8mA(8.58 to be precise). Now i tried different values 5mA, 6mA .... till 20mA, and i observed after 9mA(0x5ffa) DAC outputs correct current output could be after 8.60mA.


  • 0
    TI__Genius 9965 points
    Although it is hard to debug such an issue remotely, I suggest to check the timing budget of your SPI network. ISO7641FC has faster propagation delays compared to ISO7241C. This could be the reason why ISO7641FC is performing better. We have even a faster device, ISO7841, recently released. You may want to consider it for this design as well.