LT1785 Linear Technology, LT1785 Datasheet - Page 5

• Manufacturer Part Number: LT1785
• Description: 60V Fault Protected RS485/RS422 Transceivers
• Manufacturer: Linear Technology

1mA/DIV
TYPICAL PERFORMANCE CHARACTERISTICS
RO: Receiver Output. TTL level logic output. If the receiver
is active (RE pin low), RO is high if receiver input A B by
200mV. If A
assumes a high impedance output state when RE is high
or the part is powered off. RO is protected from output
shorts from ground to 6V.
RE: Receiver Output Enable. TTL level logic input. A logic
low on RE enables normal operation of the receiver output
RO. A logic high level at RE places the receiver output pin
RO into a high impedance state. If receiver enable RE and
driver enable DE are both in the disable state, the circuit
PIN
– 60V
1000
900
800
700
600
500
400
300
200
100
U
0
–40
Driver Propagation Delay
vs Temperature
LT1785 Input Characteristics
Pins A or B; DE = RE = 0V
FUNCTIONS
–20
U
0
TEMPERATURE ( C)
B by 200mV, then RO will be low. RO
20
V
LH
HL
A,
V
U
40
B
60
W
80
1785/91 G04
1785/91 G07
60V
U
100
1mA/DIV
7
6
5
4
3
2
1
0
– 60V
–40
Supply Current vs Temperature
LT1791 Driver Output Leakage
DE = 0V
RECEIVER ON
DRIVER AND
RECEIVER ONLY
STANDBY
–20
0
TEMPERATURE ( C)
20
V
goes to a low power shutdown state. Placing either RE or
DE into its active state brings the circuit out of shutdown.
Shutdown state is not entered until a 3 s delay after both
RE and DE are disabled, allowing for logic skews in
toggling between transmit and receive modes of opera-
tion. For CAN bus applications, RE should be tied low to
prevent the circuit from entering shutdown.
DE: Driver Output Enable. TTL level logic input. A logic
high on DE enables normal operation of the driver outputs
(Y and Z on LT1791, A and B on LT1785). A logic low level
at DE places the driver output pins into a high impedance
OUT
40
60
80
1785/91 G05
1785/91 G08
100
60V
200 A/DIV
700
600
500
400
300
200
100
– 60V
0
Receiver Propagation Delay
vs Differential Input Voltage
0
LT1791 Receiver Input Current
vs V
LH V
LT1785/LT1785A
LT1791/LT1791A
IN
CM
HL V
1
= 12V
CM
V
IN
= 12V
DIFFERENTIAL (V)
2
V
LH V
IN
HL V
CM
3
CM
= –7V
= –7V
4
1785/91 G06
1785/91 G09
5
60V
5