ATA5279 ATMEL Corporation, ATA5279 Datasheet - Page 19

• Manufacturer Part Number: ATA5279
• Manufacturer: ATMEL Corporation

9125A–RKE–04/08
LF data is transmitted on-off-keyed (OOK). “1” enables the field, whereas “0” disables it. Note
that the field generation strongly depends on the bandwidth (the Q factor) of the coil. If it is too
narrow, the receiver might not be able to decode the data correctly.
path from the modulator stage to the receiver.
Figure 3-13. Example for OOK-data Modulation with ATA5279
Coils with high Q values need more periods to reach the desired field strength and hence appro-
priate detection level thresholds in the receiver. So the Q factor must be adapted in order to
ensure proper data communication. For example, the thresholds here are chosen at 70% of the
required output current for a 0 to 1 and at 30% for a 1 to 0 detection.
The IC supports two data rates: standard, which is 4 kbit/s (or 32 LF periods), and high speed,
rated with 5.7 kbit/s (or 22 LF periods). Note that this refers to the encoded (net) data rate. The
minimum length of an active field (e.g., the time for the first 1 in
standard and 11 LF periods in high speed mode (i.e., gross data rate).
Another aspect of the LF data transmission is that current regulation can only be done roughly,
as the measurement must be interrupted over and over again. At a 0 to 1 transition, the current
measurement will not start until the 5th period, and there will not be any measurement during a
0-transmission. The regulation precision that is achieved during carrier transmission is not valid
here.
As described in
avoid gaps in longer LF telegrams. The following example illustrates this feature.
Assume that following data words have been written into the command buffer via the SPI:
1. Send 2 LF bits (SPI data 00h 05h)
2. Send carrier with a length of 24 data bits (SPI data 98h)
Transmitter Coil Current
Modulator Data
Receiver Data
Section 3.8 “Command Buffer” on page
off
off
1
1
0
0
ATA5279 [Preliminary]
Envelope
1
1
Current
17, data is processed seamlessly to
Receiver
1
1
Figure
Figure 3-13
Detection
3-13), is 16 LF periods in
0
Thresholds
1
1
shows the signal
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