125 kbps with AMIS-4168x

AND8365/D
125 kbps with AMIS-4168x
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APPLICATION NOTE
Introduction
Question
program the CAN−controller in such a way that the
propagation segment of a bit time accounts for two
maximum propagation delays to ensure correct function of
the bus during arbitration and acknowledgment. In our
example, the propagation segment shall be at least 3.11 ms
long.
If for instance the bit time is divided in 16 time quanta (tq),
tq will be 0.5 ms and the Prop_Seg has to be set to 7 tq =
3.5 ms. By applying this CAN−controller setting, it’s
ensured that the bus signal will be sampled correctly in all
situations.
“Is it possible to drive 125kB with the AMIS−41682?”
Please consider all possible CAN bit timings (TSEG1,
TSEG2, SJW), a capacitive load at each can pin about
300 pF and l = 20m line (5 ns/m) length. Please investigate
different communication scenarios (e.g. arbitration).
Conclusion
The maximum propagation delay measured at 125 kB is
1.555 ms. This is for 270 pF capacitive load and a bus length
of 20m. When using the AMIS−41682, the user has to
Bit time (8 ms)
tq
Sync
_Seg
Prop
_Seg
Phase
_Seg1
Phase
_Seg2
Sample Point
Figure 1. Example of CAN−Controller Setting Suitable for 125kB Operation with AMIS−4168x
• Oscilloscope type: Agillent Infiniium 600 MHz,
Overall, it is not a problem to drive 125 kB with the
AMIS−41682.
4 GSa/s
• Power supply: Thurlby Thandar Instruments
Performed Measurements
Propagation delay between Tx_1 and Rx_1 (transceiver
1) and Tx_1 and Rx_2 (receive transceiver 2) for different
cable length, and CANL/CANH termination of 220 W.
Used equipment:
• Oscillator type: Hewlett−Packard 3310A Function
Generator; frequency 62.5 kHz (tbit = 8 ms)
© Semiconductor Components Industries, LLC, 2009
January, 2009 − Rev. 0
•
PL310QMD
Cable: Alcatel TIA/EIA 568−B.2 Category 5e; 100 W;
propagation delay: 570 ns/100m at 1 MHz
The circuit shown in was Figure 2 used for the
measurement.
1
Publication Order Number:
AND8365/D
AND8365/D
1N4004
10mF
50V
+
+5V
Tx_1
10 kohm
10 kohm
10 kohm
L = 0m / 20m
WAKE
MP3
220 ohm
CANL_1
CANH_1
220 ohm
C1
MP4
C2
2 x 270 pF
220 ohm
220 ohm
C1
+5V
10 nF
C2
VBAT INH VCC
1
10
7 14
RTL 9
6 EN
4 ERR
CANL 12
5 STB
AMIS−41682
CANH 11
3 RxD
RTH 8
2 x 270 pF
100 kohm
MP5
Rx_2
2 TxD
13
GND
10 kohm
Rx_1
10 kohm
VCC INH VBAT
WAKE
10
1
14 7
9
EN 6
RTL
ERR 4
12 CANL
STB 5
AMIS−41682
11 CANH
RxD 3
TxD 2
8 RTH
13
GND
100 kohm 100 kohm
+5V
10 kohm
MP1
33 kohm
10 kohm
10 kohm
10 nF
10 nF
33 kohm
10 kohm
+5V
10 nF
10 kohm
+12V
Tx_2
100 kohm
MP2
Figure 2. Measurement Set−Up
Measurements Results
Propagation delay (see data sheet) L −> H and H −> L for different bus configurations.
Tbit = 8 ms
Tamb = 25°C
Table 1. MEASURED PROPAGATION DELAYS
Symbol
Parameter
Value
Comment
C1 = C2 = 270 pF
L = 0m
1.041 ms
See Figure 3
Propagation delay Tx_1 to Rx_1 low
C1 = C2 = 270 pF
L = 0m
1.107 ms
See Figure 4
tPD(H)
Propagation delay Tx_1 to Rx_2 high
C1 = C2 = 270 pF
L = 0m
1.051 ms
See Figure 5
tPD(L)
Propagation delay Tx_1 to Rx_2 low
C1 = C2 = 270 pF
L = 0m
1.110 ms
See Figure 6
tPD(H)
Propagation delay Tx_1 to Rx_1 high
C1 = C2 = 270 pF
L = 20m
1.536 ms
See Figure 7
tPD(L)
Propagation delay Tx_1 to Rx_1 low
C1 = C2 = 270 pF
L = 20m
1.176 ms
See Figure 8
tPD(H)
Propagation delay Tx_1 to Rx_2 high
C1 = C2 = 270 pF
L = 20m
1.555 ms
See Figure 9
tPD(L)
Propagation delay Tx_1 to Rx_2 low
C1 = C2 = 270 pF
L = 20m
1.244 ms
See Figure 10
tPD(H)
Propagation delay Tx_1 to Rx_1 high
tPD(L)
Condition
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AND8365/D
Measurements Cable Length 0m
Figure 3. Propagation Delay tPD(H) Between Tx_1 and Rx_1 at 125kB and Cable Length 0m = 1.041 ms
Figure 4. Propagation Delay tPD(L) Between Tx_1 and Rx_1 at 125kB and Cable Length 0m = 1.107 ms
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AND8365/D
Figure 5. Propagation Delay tPD(H) Between Tx_1 and Rx_2 at 125kB and Cable Length 0m = 1.051 ms
Figure 6. Propagation Delay tPD(L) Between Tx_1 and Rx_2 at 125kB and Cable Length 0m = 1.110 ms
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AND8365/D
Measurements Cable Length 20m
Figure 7. Propagation Delay tPD(H) Between Tx_1 and Rx_1 at 125kB and Cable Length 20m = 1.536 ms
Figure 8. Propagation Delay tPD(L) Between Tx_1 and Rx_1 at 125kB and Cable Length 20m = 1.176 ms
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AND8365/D
Figure 9. Propagation Delay tPD(H) Between Tx_1 and Rx_2 at 125kB and Cable Length 20m = 1.555 ms
Figure 10. Propagation Delay tPD(L) Between Tx_1 and Rx_2 at 125kB and Cable Length 20m = 1.244 ms
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