SAP5SD-B-G1-R datasheet(31/63 Pages) ETC2

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SAP5S / SAP51

Universal Actuator-Sensor Interface IC

Data Sheet

July 17, 2012

the prior written consent of the copyright owner. The information furnished in this publication is PRELIMINARY and subject to

changes without notice.

31 of 62

4.5. AS-i Receiver

The receiver detects (telegram) signals at the AS-i line, converts them to digital pulses and forwards them to

the UART for further processing. The receiver is internally connected between the LTGP and LTGN pins.

Functional, the receiver removes the DC value of the input signal, band-pass filters the AC signal and extracts

the digital output signals from the sin

2-shaped input pulses by a set of comparators. The amplitude of the first

pulse determines the threshold level for all following pulses. This amplitude is digitally filtered to guarantee

stable conditions and to suppress burst spikes. This approach combines a fast adaptation to changing signal

amplitudes with a high detection safety. The comparators are reset after every detection of a telegram pause

at the AS-i line.

When the receiver is turned on, the transmitter is turned off to reduce the power consumption.

Table 18: Receiver Parameters

Symbol

Parameter

Min

Max

Unit

Note

VSIG

AC signal peak-peak amplitude (between LTGP and LTGN)

VLSIGon

Receiver comparator threshold level (refer to Figure 5)

Related to

amplitude of

1st pulse

First negative

pulse of the

AS-i telegram

VLSIGon

VLSIGon = (0.45 ... 0.55) * VSIG / 2

DC level

VSIG / 2

The IC determines the

amplitude of the first

negative pulse of the

AS-i telegram. This

amplitude is asserted

to be VSIG / 2.

Figure 5: Receiver comparator threshold set-up in principle

4.6. AS-i Transmitter

The transmitter draws a modulated current between LTGP and LTGN to generate the communication signals.

The shape of the current corresponds to the integral of a sin

2-function. The transmitter comprises a current

DAC and a high current driver. The driver requires a small bias current to flow. The bias current is ramped up

slowly a certain time before the transmission starts so that any false voltage pulses on the AS-i line are

avoided.

When the transmitter is turned on, the receiver is turned off to reduce the power consumption. The SAP5

comprises a Clock Watchdog that becomes activated once the clock signal is stopped for about 100µs …

150µs. Thus, the transmitter is prevented from being permanently switched on in case the clock signal is

missing.

Table 19: Transmitter Current Amplitude

Symbol

Parameter

Min

Max

Unit

Note

ISIG

Modulated transmitter peak current swing (between LTGP and

LTGN)

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