I am integrating a variable reluctance sensor into my project. These take the the signals produced by inductive pickups and convert them into nice square signals that a processor can use. Quite often, the voltages produced by inductive pick ups can be very large (> 100 volts). Becase of this, most of these sensor inputs are rated over 100V (see the LM1815 or the NCV1124). However, one sensor IC, the MAX9926, appears to have inputs that are limited to Vcc. This doesn't make sense to me. Am I reading the datasheet wrong or do they expect you to take care of clipping the voltage before the IC input?
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The current on the input pins is rated +/- 40 mA. The data sheet shows 10K resistors in series with the input. So if the input is 100V the current into the chip would be 10 mA. Internal protection diodes clamp the input to VCC + diode drop. If input is really 100V I would attenuate it with resistor divider or external clamp to be safe.
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\$\begingroup\$ But it also says that maximum rating is .-0.3V to (VCC + 0.3V) and those resistors are after the diodes. I imagine that you might send more than 40mA through those diodes at 100V? \$\endgroup\$ Commented Aug 16, 2018 at 20:19
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\$\begingroup\$ Maybe I could put a 10k resistor in series with the input? That would limit the current through that dodie and limit the voltage at the pin to vcc. \$\endgroup\$ Commented Aug 16, 2018 at 20:25
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\$\begingroup\$ Yes the data sheet shows 10K resistor in series with input \$\endgroup\$– EE_socalCommented Aug 16, 2018 at 20:50