Datasheet
MAX3157
High CMRR RS-485 Transceiver
with ±50V Isolation
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Pin Description
PIN
SSOP
PDIP
NAME FUNCTION
12 RO
Receiver Output. When RE is low and A - B > -50mV, RO will be high; if A - B ≤ -200mV,
RO will be low.
23 RE Receiver Output Enable. Drive RE low to enable RO.
3 4 DE Driver Output Enable. Drive DE high to enable driver outputs.
45 DI
Driver Input. With DE high, a low on DI forces the noninverting output low and the inverting
output high; with DI high, outputs reverse.
5 6 C1LO Connect to the negative terminal of C1 (0.047µF, 50V).
6, 7,
12, 22,
23
1, 12,
14, 15,
28
N.C. No Connection
8 7 C1HI Connect to the positive terminal of C1 (0.047µF, 50V).
9 8 ISOVCC
Internally generated power-supply voltage, referenced to the cable ground (ISOCOM).
Connect a 1µF capacitor to ISOCOM.
10 9 H/F
Half/Full-Duplex Selector Pin. Leave open, or connect to ISOCOM to select Full Duplex, or
connect to ISOVCC to select Half Duplex.
11 10 ZR
Connect to ISOCOM for a 1.5kΩ input impedance on Z. Leave open for a 12kΩ input
impedance on Z.
13 11 YR
Connect to ISOCOM for a 1.5kΩ input impedance on Y. Leave open for a 12kΩ input
impedance on Y.
14 13
ISOCOM
Cable Ground
15 16 Z Inverting Driver Output (and Inverting Receiver Input in Half-Duplex Mode)
16 17 Y Noninverting Driver Output (and Noninverting Receiver Input in Half-Duplex Mode)
17 18 B Inverting Receiver Input in Full-Duplex Mode
18 19 A Noninverting Receiver Input in Full-Duplex Mode
19 20 BR
Connect to ISOCOM for a 1.5kΩ input impedance on B. Leave open for a 12kΩ input
impedance on B.
20 21 AR
Connect to ISOCOM for a 1.5kΩ input impedance on A. Leave open for a 12kΩ input
impedance on A.
21 22 C2HI Connect to the positive terminal of C2 (0.047µF, 50V).
24 23 C2LO Connect to the negative terminal of C2 (0.047µF, 50V).
25 24 GND Ground
26 25 TXP
Transmitter Phase. Leave open, or connect to GND for normal transmitter polarity, or connect
to V
CC
to invert the transmitter polarity.
27 26 RXP
Receiver Phase. Leave open, or connect to GND for normal receiver polarity, or connect to
V
CC
to invert the receiver polarity.
28 27 V
CC
+4.75V to +5.25V Positive Supply. Connect a 0.1µF capacitor to GND.