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Automotive battery/ignition monitor

The schematic at the link below is to control the enable pin of LM22680 regulator. It has enable pin pulled up internally, which means it is always ON. This circuit is to pull it to Low to disable. Logic is as follows.

Ignition ON detection threshold is approx 6V at ignition wire and low battery threshold is approx 9V at battery wire.

If (GPIO from MCU is '1' OR Ignition is ON) AND (Battery Voltage is above threshold), ENABLE is left floating to keep LM22680 ON else keep it LOW to disable.

Q1 is ON when battery is above threshold (approx 9V) else OFF. Q2 will be ON when either GPIO OR Ignition is ON. When both Q1 and Q2 ON, Q3 will be OFF leaving Enable floating.(regulator is ON)

Thresholds are not very critical +/- 1V is fine. It works as expected in simulation. Is this fine in automotive environment? Any modifications?

Both Battery and Ignition are reverse polarity, transient and load dump protected. Transients are clamped to 30V. Max continuous voltage is 16V. No 24V jump start protection needed.

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Reply to
bhav.jnk
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egulator. It has enable pin pulled up internally, which means it is always ON. This circuit is to pull it to Low to disable. Logic is as follows.

tery threshold is approx 9V at battery wire.

threshold), ENABLE is left floating to keep LM22680 ON

ON when either GPIO OR Ignition is ON. When both Q1 and Q2 ON, Q3 will be OFF leaving Enable floating.(regulator is ON)

simulation. Is this fine in automotive environment? Any modifications?

Looks weird to me... how did you 'expect' it to work? (Where does the power for Q1 and Q2 come from?)

George H.

rotected. Transients are clamped to 30V. Max continuous voltage is 16V. No

24V jump start protection needed.
Reply to
George Herold

regulator. It has enable pin pulled up internally, which means it is always ON. This circuit is to pull it to Low to disable. Logic is as follows.

threshold is approx 9V at battery wire.

threshold), ENABLE is left floating to keep LM22680 ON

when either GPIO OR Ignition is ON. When both Q1 and Q2 ON, Q3 will be OFF leaving Enable floating.(regulator is ON)

simulation. Is this fine in automotive environment? Any modifications?

Looks ok to me. I think the circuit works ok. The OP is likely asking about special issues from using it in cars. A car electrical system is a tough environment to design electronics for.

Power for the inputs of Q1 and Q2 are provided by their prospective sources, the battery in one case and the MCU in the other. The power for the collector is provided by R22, 100K from the battery.

As long at the transistors are rated for the extreme voltages that may be found. For example, the BE junction of Q1 needs to survive a negative transient through the two 1 kohm resistors. In that case I think D5 is forward biased and R18 won't impact the circuit much. The OP says "Both Battery and Ignition are reverse polarity, transient and load dump protected." Not sure what that implies in terms of the voltages the inputs will then see.

protected. Transients are clamped to 30V. Max continuous voltage is 16V. No 24V jump start protection needed.

--

Rick
Reply to
rickman

0 regulator. It has enable pin pulled up internally, which means it is alwa ys ON. This circuit is to pull it to Low to disable. Logic is as follows.

battery threshold is approx 9V at battery wire.

ove threshold), ENABLE is left floating to keep LM22680 ON

be ON when either GPIO OR Ignition is ON. When both Q1 and Q2 ON, Q3 will be OFF leaving Enable floating.(regulator is ON)

in simulation. Is this fine in automotive environment? Any modifications?

ng

Oops, I missed that, thanks.

George H.

p protected. Transients are clamped to 30V. Max continuous voltage is 16V. No 24V jump start protection needed.

.
Reply to
George Herold

regulator. It has enable pin pulled up internally, which means it is always ON. This circuit is to pull it to Low to disable. Logic is as follows.

battery threshold is approx 9V at battery wire.

threshold), ENABLE is left floating to keep LM22680 ON

ON when either GPIO OR Ignition is ON. When both Q1 and Q2 ON, Q3 will be OFF leaving Enable floating.(regulator is ON)

simulation. Is this fine in automotive environment? Any modifications?

protected. Transients are clamped to 30V. Max continuous voltage is 16V. No 24V jump start protection needed.

Thanks. I said there is a reverse polarity protection diode, TVS diode to clamp the transients to 30V that are not shown in the schematic.

bhav

Reply to
bhav.jnk

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