AN4218 Datasheet, PDF (16/26 Pages) STMicroelectronics – Hardware design guideline

Application circuits
3
Application circuits
AN4218
3.1
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Reference circuit
A system containing the microcontroller, the power supply generation, physical layer, load
drivers and a measurement unit for permanent enabled battery supply (e.g. KL30) is shown
in Figure 15.
Figure 15. Reference circuit
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3.2
3.2.1
Note:
Implementation suggestions
Besides the above mentioned requirements for the microcontroller power supply generation
special care has to be taken on the following system parts.
Measurement of an permanently enabled power-supply (V_MEASURE)
Since V_MEASURE is permanently supplied, while the supply for the microcontroller system
(V_BAT) can be turned off, it must be made sure, that the power-up functionality of the
microcontroller is not influenced.
Additional the microcontroller pins have to be protected against ISO-pulses, which may
damage the microcontroller. These ISO-transients are defined in ISO 7637-2:2011(E).
The calculations and values used are examples only. For the actual values please refer to
the latest datasheet of the used device.
Calculation of R_V1/2 for ADC
The voltage divider has to be dimensioned such that no overvoltage condition at the analog-
to-digital-convertor (ADC) input can occur. Especially it must be ensured, that the voltage at
the ADC is never higher than at the V_DD, which supplies the ADC pin.
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