SN75HVD08 Datasheet, PDF (12/17 Pages) Texas Instruments – WIDE SUPPLY RANGE RS-485 TRANSCEIVER

SN75HVD08, SN65HVD08
SLLS550C – NOVEMBER 2002 – REVISED JULY 2006
Opto
Isolators
SN65HVD08
Local Power
Source
Rest of
Board
Opto
Isolators
Local Power
Source
Rest of
Board
Figure 17. Distribution of Isolated Power
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The features of the SN65HVD08 are particularly
good for the application of Figure 17. Due to added
supply source impedance, the low quiescent current
requirements and wide supply voltage tolerance
allow for the poorer load regulation.
AN OPTO ALTERNATIVE
The ISO150 is a two-channel, galvanically isolated
data coupler capable of data rates of 80 Mbps. Each
channel can be individually programmed to transmit
data in either direction.
Data is transmitted across the isolation barrier by
coupling complementary pulses through high-voltage
0.4-pF capacitors. Receiver circuitry restores the
pulses to standard logic levels. Differential signal
transmission rejects isolation-mode voltage
transients up to 1.6 kV/ms.
ISO150 avoids the problems commonly associated
with opto-couplers. Optically-isolated couplers
require high current pulses and allowance must be
made for LED aging. The ISO150's Bi-CMOS
circuitry operates at 25 mW per channel with supply
voltage range matching that of the SN65HVD08 of 3
V to 5.5 V.
Figure 18 shows a typical circuit.
–5 V
+5 V
SN65HVD08
Data
(I/O)
D2A R/T_2A GA
ISO150 VSB R/T_2B D2B
Channel 1
D
DE
RE
A
Bus
B
Side A
R
Side B
DE/RE
D1A R/T1A VSA
Channel 2
GA R/T1B D1B
+5 V
“1”
+5 V
Figure 18. Isolated RS-485 Interface
12
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