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ASI4U / ASI4U-E / ASI4U-F Datasheet

January 26, 2016

4.3.2.

AC Current Input Mode

The IRD input allows direct connection of a photodiode (referenced to 0V pin) and senses the generated photo

current. A valid input signal must have a specified current amplitude (range) and must not exceed a specified

offset current value, which are given in Figure 4.2 and Table 4.3

In contrast to A²SI versions, the IRD input of the ASI4U/ASI4U-E/ASI4U-F covers the entire input current range by

a single amplifying stage with continuous (logarithmical) gain adaptation. This avoids cyclical gain switching, and

the IC can react more safely and without delay on different input signal amplitudes.

Table 4.3

IRD AC Current Input Parameters

PARAMETER

SYMBOL

CONDITIONS

MIN

MAX

UNIT

Input current offset

IIRD_Offset

µA

Input current amplitude

IIRD_Amplitude

100

µA

Figure 4.2

Addressing Channel Input (IRD), Photo-Current Waveforms

The TEMIC TEMD5000 photodiode is suggested for optimal performance.

4.3.3.

CMOS Input Mode

In addition to the AC Current Input Mode, the IRD input can also operate in CMOS Input Mode. Mode switching is

only possible as long as the IC has not already locked to the Addressing Channel by reception of a Magic

Sequence. The input mode that led to the activation of the Addressing Channel will remain locked until the

Addressing Channel is deactivated (by an IC reset).

The CMOS Input Mode is entered if the IRD input voltage is above 2.5V (logic HIGH) for more than 7.680ms

(-6.66%). It is exited if the IRD input voltage is below 1.0V (logic LOW) for more than 7.680ms (-6.66%). The

initial input mode after IC initialization is determined at the end of the initialization phase and depends on the

value of the IRD input signal at that time.

MIN

IRD_Amplitude

MAX

I IRD_Amplitude

MAX

IIRD_Offset

Time

IRD

Input

Current

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