SAP5SD-A-G1-T Datasheet, PDF (31/63 Pages) List of Unclassifed Manufacturers – Universal Actuator-Sensor Interface IC

SAP5S / SAP51
Universal Actuator-Sensor Interface IC
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 sin²-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
V_SIG
AC signal peak-peak amplitude (between LTGP and LTGN)
V_LSIGon Receiver comparator threshold level (refer to Figure 5)
Min Max Unit
Note
3
8
V
45
55
%
Related to
amplitude of
1st pulse
DC level
V_LSIGon = (0.45 ... 0.55) * V_SIG / 2
The IC determines the
amplitude of the first
negative pulse of the
AS-i telegram. This
amplitude is asserted
to be V_SIG / 2.
V_LSIGon
First negative
pulse of the
AS-i telegram
V_SIG / 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 sin²-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
I_SIG
Modulated transmitter peak current swing (between LTGP and 55 68 mA
LTGN)
Data Sheet
July 17, 2012
© 2012 Zentrum Mikroelektronik Dresden AG — Rev. 3.1
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