UM3352E_15 Datasheet, PDF (8/13 Pages) Union Semiconductor, Inc. – ESD-Protected, Slew-Rate-Limited, Fail-Safe, True RS-485 Transceivers

UM3352E
5V
DI 0V
B
A
VO
1.5V
tDPLH
VO
90%
1/2VO
VDIFF 0V
10%
-VO
tDR
VDIFF = VA - VB
t SKEW=|t DPLH-t DPHL|
1.5V
tDPHL
1/2VO
90%
10%
tDF
Figure 7. Driver Propagation Delays
VOH
RO
VOL
A 1V
B -1V
1.5V
tRPHL
OUTPUT
INPUT
1.5V
tRPLH
Figure 9. Receiver Propagation Delays
5V
DE 0V
B VOH
1.5V
VOL
VOH
A VOL
tDZL(SHDN), tDZL
2.3V
tDLZ
Output Normally Low
Output Normally High
2.3V
tDZH(SHDN), tDZH
tDHZ
1.5V
VOL+0.5V
VOH-0.5V
Figure 8. Driver Enable and Disable Times
5V
RE
0V
VOH
1.5V
RO
VOL
tRZL(SHDN), tRZL
1.5V Output Normally Low
Output Normally High
1.5V
tRZH(SHDN), tRZH
1.5V
tRLZ
VOL+0.5V
VOH-0.5V
tRHZ
Figure 10. Receiver Enable and Disable Times
Detail Description
The UM3352E high-speed transceivers for RS-485 communication contain one driver and one
receiver. The device features fail-safe circuitry, which guarantees a logic-high receiver output when
the receiver input is open or shorted, or when it is connected to a terminated transmission line with
all drivers disabled. The UM3352E features reduced slew-rate driver that minimizes EMI and
reduces reflections caused by improperly terminated cables, allowing error-free data transmission up
to 500kbps. It operates from a single +5V supply. Drivers are output short-circuit current limited.
Thermal shutdown circuitry protects drivers against excessive power dissipation. When activated,
the thermal shutdown circuitry places the driver outputs into a high impedance state.
Fail-Safe
The UM3352E guarantees a logic-high receiver output when the receiver inputs are shorted or open,
or when they are connected to a terminated transmission line with all drivers disabled. This is done
by setting the receiver threshold between -50mV and -200mV. If the differential receiver input
voltage (A-B) is greater than or equal to -50mV, RO is logic high. If A-B is less than or equal to
-200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the
receiver’s differential input voltage is pulled to 0V by the termination. With the receiver thresholds
of the UM3352E, this results in a logic high with a 50mV minimum noise margin. Unlike previous
fail-safe devices, the -50mV to -200mV threshold complies with the ±200mV EIA/TIA-485
standard.
__________________________________________________________________________
http://www.union-ic.com Rev.07 Sep.2015
8/13