Datasheet

provide the same clock to their respective circuits.
Thus, minimal package-to-package skew is critical. The
skew must be kept well below the period of the clock
signal to ensure that all of the circuits on the network
are synchronized.
128 Receivers on the Bus
The standard RS-485 input impedance is 12kW (one-
unit load). The standard RS-485 transmitter can drive
32 unit loads. The MAX3280E/MAX3281E/MAX3283E/
MAX3284E present a 1/4-unit-load input impedance
(48kW), which allows up to 128 receivers on the bus.
Any combination of these RS-485 receivers with a total
of 32 unit loads can be connected to the same bus.
Thermal Protection
The MAX3280E/MAX3281E/MAX3283E/MAX3284E fea-
ture thermal protection. Thermal protection sets the out-
put stage in high-impedance mode when a short circuit
occurs at the output, limiting both the power dissipation
and temperature. The thermal temperature threshold is
+165°C, with a hysteresis of 20°C.
Figure 2. MAX3281E/MAX3283E Receiver Enable/Disable Timing
Figure 1. Receiver Propagation Delay
t
PRZH
OUT
EN
OUT
EN
V
CC
/2
V
CC
/2
V
CC
0
V
OH
0
V
CC
0
V
OH
0
FOR MAX3281E THE ENABLE SIGNAL IS INVERTED.
S1 OPEN
S2 CLOSED
S3 = 1.5V
S1 OPEN
S2 CLOSED
S3 = 1.5V
0.25V
t
PRHZ
t
PRLZ
V
CC
/2
0.25V
OUT
EN
OUT
EN
V
CC
0
V
CC
V
OL
V
CC
0
V
CC
V
OL
S1 CLOSED
S2 OPEN
S3 = -1.5V
S1 CLOSED
S2 OPEN
S3 = -1.5V
t
PRZL
V
CC
/2
V
CC
/2
GENERATOR
1.5V
-1.5V
V
ID R
C
L
1kΩ
S1
V
CC
S2
50Ω
S3
V
CC
/2
V
OH
V
OL
A
B
1V
RO
-1V
f
IN
= 1MHz
t
r
, t
f
3ns
OUTPUT
INPUT
V
CC
/2 V
CC
/2
t
PHL
t
PLH
www.maximintegrated.com
Maxim Integrated │ 7
MAX3280E/MAX3281E/
MAX3283E/MAX3284E
±15kV ESD-Protected 52Mbps, 3V to 5.5V,
SOT23 RS-485/RS-422 True Fail-Safe Receivers
Test Circuits/Timing Diagrams