Input impedance question
Posted: Sun Feb 22, 2015 1:08 amI am curious as to what a typical analogue input impedance might be, say for an analogue MAP sensor on an M800, and whether this figure is also typical of OE ECU's? Thanks.
From memory, the input impedence of the M800 AV inputs is 100Kohm to gnd, and the AT inputs are 100kohm to ground, with a 1k pullup to 5v, and the LA1s /2s inputs are ~100kohm with a light 33k or so pullup to 5v.
I work in Automotive OEM for a large multinational auto co. and the inputs on OEM ECUs are more tailored to what's connected to them...ie: AV inputs typically 50k-1.0M ohm input impedance, and resistive divider inputs (equiv of AT typeinput) typically 1-20K ohm pullup to 5v, but most commonly 4-15K.
All OEM ecu's will often have additional very light (>50Kohm) pullups and pulldown resistors to assist in diagnosing shorts/open circuits on all inputs (in a similar vein to what the M1 incorporates)
Most OEM voltage output sesnors (eg: tmaps, pressure transducers, etc) are quite comfortable driving into these pullups, and most bosch Tmaps will even drive the 1K pullup on M800 AT inputs
What was the basis of your question??