Hello everyone
we are using a TPIC71004 device in an automotive application to cut explosive bolts in an emergency situation. I am working on the software controling the device.
There is a requirement to detect external shotrcuts (e.g. by broken/squeezed wires) of the connections to the explosive squibs to vehicle ground or to the 12V supply.
After some discussion with our hardware department we figured out that the diagnostic mode "Leakage current" (AMX1=0110b) would be used for the "shortcut to ground" test.
Additionally to the settings recommended in the data sheet we set the SHSA source to 1.5 mA for detection of shortcuts to ground.
From the Table 12 and Figure 20 in the datasheet, we assume that the SZSx switch is closed in this diagnostic mode, applying the active measurement current source to both squib wires while preventing the measurement current flowing through the squib.
This works partly. If no shortcut is applied, I get a readout voltage on AMX_OUT pin of ~ 2V. When the shortcut to ground is applied to ZMx pin, the voltage goes down to nearly 0V as expected. When the shortcut to ground is applied to Zx pin, the voltage reduces only by ~ 100mV. I would have expected to go down to 0V as well, as the SZSx switch is closed and both pins (Zx and ZMx) should be equal in this case.
Can anyone please clarify if this approach works at all or if some characteristic of the SZSx switch prevents this ?
With best regards,
Christian
