Datasheet

188
7728G–AVR–06/10
ATtiny87/ATtiny167
16. ISRC - Current Source
16.1 Features
• 100µA Constant current source
• ±10% Absolute Accuracy
The ATtiny87/167 features a 100µA ±10% Current Source. Up on request, the current is flow-
ing through an external resistor. The voltage can be measured on the dedicated pin shared
with the ADC. Using a resistor in serie 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 per-
form 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 16-1. Current Source Block Diagram
16.2 Typical applications
16.2.1 LIN Current Source
During the configuration of a LIN node in a cluster, it may be necessary to attribute dynami-
cally 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 applica-
tion supported by the LIN node. A full dynamic node configuration can be used to set-up the
LIN nodes in a cluster.
ATtiny87/167 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.
AVCC
ADC Input
External
Resistor
ISRCEN
ADCn/ ISRC
100 uA