The MAX13362 is a 24-channel automotive switch monitor. To avoid the necessity of adding numerous external components, which would increase the application cost and possibly make reliable contact-resistance measurement more difficult, the MAX13362 was carefully designed to be robust. The device monitors the status of 24 remote switches in an automobile while withstanding automotive transients and performing well during the many anomalous automotive test conditions. Since the device interfaces to remote switches in the vehicle, it is directly subjected to all the transients observed in the wiring harness of an automobile.

This article documents how the MAX13362 reacts in many circumstances encountered during automotive ECU-level testing. The situations described here are presented in the following sections:

1. Lost Ground/Power Connections
2. Reverse-Battery Condition
3. Ground and Power-Supply Shifts

The MAX13362 was connected to two external battery-connected switches and two external ground-connected switches. The MAX15007 linear regulator provided a regulated voltage for the digital portion of the IC and for the local microcontroller. The pins connected to ground-connected switches were bypassed with 47nF capacitors to ground. Inputs connected to battery-connected switches had an additional series resistance of 100W, necessary to limit input current during the harsher transients on the battery line. The microcontroller used to read and write SPI information was a MAXQ2000 running on a 3.3V supply. The switches SGND and SVS served to disconnect the corresponding MAX13362 pins during testing. The voltage sources VSB and VSG allowed the shifting of the battery voltage and ground, respectively. During testing special attention was paid to:

1) possible undesired leakage currents due to voltage differences;
2) whether SPI communication was possible;
3) whether switch status was reported correctly or incorrectly. All tests were conducted with a battery voltage of 14V.

See the datasheet: MAX13362 24-Channel Automotive Switch Monitor

Read more: http://pdfserv.maxim-ic.com/en/an/AN4353.pdf