MCP39F521 Erroneous NAK Response
I am using an MCP39F521 as an active power measurement tool to control the power being delivered to lamp for constant light output regardless of the AC line voltage shifts. I am using a Silicon Labs SI8606 digital isolator between it and my PIC32MX controller, we are getting readings every 250mS from the MCP chip and using the average power readings to modify a phase angle fired output to control the power to the lamp.
This system can work well, for hours up to several days but invariably the MCP chip starts to return a NAK (0x15) instead of the ACK (0x06) and all the data bytes are 0. The only thing that restores it to proper operation is a full power cycle. I have tried resetting the MCP thru the RESET input (pin 10), recycling the power to it (it has an isolated 3.3V DC supply), nothing clears the NAK responses other than a full power off cycle.
In reading the literature I see that the NAK is only mentioned as a response to a calibration command but we never attempt to calibrate the device, we are using the power value as a figure of merit to control against and not as an absolute power measurement.
Has anyone seen anything like this?