ATtiny167-ESSZ datasheet(188/282 Pages) ATMEL

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188

7728D–AVR–07/09

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

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