19. ISRC - Current Source
19.1 Features
●
●
100µA constant current source
±6% absolute accuracy
The ATmega16/32/64/M1/C1 features a 100µA ±5% current source. After RESET or up on request, the current is flowing
through an external resistor. The voltage can be measured on the dedicated pin shared with the ADC. Using a resistor in
series with a ≤≤ 0.5% tolerance is recommended. To protect the device against big values, the ADC must be configured with
AVcc as internal reference to perform the first measurement. Afterwards, another internal reference can be chosen
according to the previous measured value to refine the result.
When ISRCEN bit is set, the ISRC pin sources 100µA. Otherwise this pin keeps its initial function.
Figure 19-1. Current Source Block Diagram
AVCC
100μA
ISRCEN
AREF/ISRC
AREF Internal Circuit
AREFEN
External
Resistor
ADC Input
19.2 Typical Applications
19.2.1 LIN Current Source
During the configuration of a LIN node in a cluster, it may be necessary to attribute dynamically an unique physical address
to every cluster node. The way to do it is not described in the LIN protocol.
The Current Source offers an excellent solution to associate a physical address to the application supported by the LIN
node. A full dynamic node configuration can be used to set-up the LIN nodes in a cluster.
ATmega16/32/64/M1/C1 proposes to have an external resistor used in conjunction with the current source. The device
measures the voltage to the boundaries of the resistance via the analog to digital converter. The resulting voltage defines the
physical address that the communication handler will use when the node will participate in LIN communication.
In automotive applications, distributed voltages are very disturbed. The internal Current Source solution of
ATmega16/32/64/M1/C1 immunizes the address detection against any kind of voltage variations.
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ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
