ISL3170E_08 Datasheet, PDF (12/19 Pages) Intersil Corporation – RS-485/RS-422 Transceivers

ISL3170E, ISL3171E, ISL3172E, ISL3173E, ISL3174E, ISL3175E, ISL3176E, ISL3177E, ISL3178E
Built-In Driver Overload Protection
As stated previously, the RS-485 spec requires that drivers
survive worst case bus contentions undamaged. These
devices meet this requirement via driver output short circuit
current limits, and on-chip thermal shutdown circuitry.
The driver output stages incorporate short circuit current
limiting circuitry which ensures that the output current never
exceeds the RS-485 spec, even at the common mode
voltage range extremes. Additionally, these devices utilize a
foldback circuit which reduces the short circuit current, and
thus the power dissipation, whenever the contending voltage
exceeds either supply.
In the event of a major short circuit condition, devices also
include a thermal shutdown feature that disables the drivers
whenever the die temperature becomes excessive. This
eliminates the power dissipation, allowing the die to cool. The
drivers automatically re-enable after the die temperature
drops about 15°. If the contention persists, the thermal
shutdown/re-enable cycle repeats until the fault is cleared.
Receivers stay operational during thermal shutdown.
Low Power Shutdown Mode
These CMOS transceivers all use a fraction of the power
required by their bipolar counterparts, but some also include
a shutdown feature that reduces the already low quiescent
I_CC to a 10nA trickle. These devices enter shutdown
whenever the receiver and driver are simultaneously
disabled (RE = V_CC and DE = GND) for a period of at least
600ns. Disabling both the driver and the receiver for less
than 50ns guarantees that the transceiver will not enter
shutdown.
Note that receiver and driver enable times increase when the
transceiver enables from shutdown. Refer to Notes 7 through
11, at the end of the “Electrical Specification table” on page 8,
for more information.
Typical Performance Curves V_CC = 3.3V, T_A = +25°C; Unless Otherwise Specified
120
2.35
2.30
100
2.25
R_DIFF = 100Ω
80
2.20
2.15
60
2.10
2.05
40
2.00
20
1.95
R_DIFF = 54Ω
1.90
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL OUTPUT VOLTAGE (V)
FIGURE 7. DRIVER OUTPUT CURRENT vs DIFFERENTIAL
OUTPUT VOLTAGE
1.85
-40 -25
0
25
50
75 85
TEMPERATURE (°C)
FIGURE 8. DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs
TEMPERATURE
200
ISL3176E/77E/78E
150
Y OR Z = LOW
ISL3170E THRU ISL3175E
100
50
0
-50
-100
ISL317XE
Y OR Z = HIGH
-150
-7 -6 -4 -2
0
2
4
6
OUTPUT VOLTAGE (V)
8 10 12
FIGURE 9. DRIVER OUTPUT CURRENT vs SHORT CIRCUIT
VOLTAGE
0.52
ISL3172E/75E/78E, DE = V_CC, RE = X
0.51
0.50
ISL3170E/73E/76E, DE = X, RE = 0V; ISL3171E/74E/77E
0.49
0.48
0.47
ISL3172E/75E/78E, DE = 0V, RE = 0V
0.46
-40 -25
0
25
50
75 85
TEMPERATURE (°C)
FIGURE 10. SUPPLY CURRENT vs TEMPERATURE
12
FN6307.4
June 10, 2008