LTC486
Quad Low Power
RS485 Driver
FEATURES
■
■
■
■
■
■
■
■
■
DESCRIPTIO
Very Low Power: I
CC
= 110µA Typ
Designed for RS485 or RS422 Applications
Single 5V Supply
– 7V to 12V Bus Common-Mode Range Permits
±
7V GND Difference Between Devices on the Bus
Thermal Shutdown Protection
Power-Up/Down Glitch-Free Driver Outputs Permit
Live Insertion/Removal of Package
Driver Maintains High Impedance in Three-State or
with the Power Off
28ns Typical Driver Propagation Delays
with 5ns Skew
Pin Compatible with the SN75172, DS96172,
µA96172,
and DS96F172
The LTC486 is a low power differential bus/line driver
designed for multipoint data transmission standard RS485
applications with extended common-mode range (12V to
–7V). It also meets RS422 requirements.
The CMOS design offers significant power savings over its
bipolar counterpart without sacrificing ruggedness against
overload or ESD damage.
The driver features three-state outputs, with the driver
outputs maintaining high impedance over the entire
common-mode range. Excessive power dissipation caused
by bus contention or faults is prevented by a thermal
shutdown circuit which forces the driver outputs into a
high impedance state.
Both AC and DC specifications are guaranteed from 0°C to
70°C (Commercial), – 40°C to 85°C (Industrial), over the
4.75V to 5.25V supply voltage range.
APPLICATI
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■
S
Low Power RS485/RS422 Drivers
Level Translator
TYPICAL APPLICATI
CABLE LENGTH (FT)
EN
EN
4
DI
1
DRIVER
12
1/4 LTC486
EN
120Ω
4000 FT BELDEN 9841
120Ω
2
4
RECEIVER
3
RO
1
1/4 LTC488
LTC486 • TA01
U
RS485 Cable Length Specification*
10k
1k
100
10
10k
100k
1M
2.5M
10M
DATA RATE (bps)
LTC486 • TA09
UO
UO
* APPLIES FOR 24 GAUGE, POLYETHYLENE
DIELECTRIC TWISTED PAIR
1
LTC486
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
DI1
DO1A
DO1B
EN
DO2B
DO2A
DI2
GND
1
2
3
4
5
6
7
8
16 V
CC
15
DI4
14 DO4A
13 DO4B
12 EN
11 DO3B
10 DO3A
9
DI3
Supply Voltage (V
CC
) ............................................... 12V
Control Input Voltages .................... – 0.5V to V
CC
+ 0.5V
Driver Input Voltages ...................... – 0.5V to V
CC
+ 0.5V
Driver Output Voltages .........................................
±
14V
Control Input Currents .......................................
±
25mA
Driver Input Currents .........................................
±
25mA
Operating Temperature Range
LTC486C ................................................ 0°C to 70°C
LTC486I ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LTC486CN
LTC486CSW
LTC486IN
LTC486ISW
N PACKAGE
S PACKAGE
16-LEAD PLASTIC DIP
16-LEAD PLASTIC SOL
T
JMAX
= 125°C,
θ
JA
= 70°C/W (N)
T
JMAX
= 150°C,
θ
JA
= 95°C/W (S)
Consult factory for Military grade parts
DC ELECTRICAL CHARACTERISTICS
V
CC
= 5V
±
5%, 0°C
≤
Temperature
≤
70°C (Commercial), – 40°C
≤
Temperature
≤
85°C (Industrial) (Note 2, 3)
SYMBOL
V
OD1
V
OD2
V
OD
V
OC
❘V
OC
❘
V
IH
V
IL
I
IN1
I
CC
I
OSD1
I
OSD2
I
OZ
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
Driver Common-Mode Output Voltage
Change in Magnitude of Driver Common-Mode
Output Voltage for Complementary Output States
Input High Voltage
Input Low Voltage
Input Current
Supply Current
Driver Short-Circuit Current, V
OUT
= High
Driver Short-Circuit Current, V
OUT
= Low
High Impedance State Output Current
No Load
V
O
= – 7V
V
O
= 12V
V
O
= – 7V to 12V
Output Enabled
Output Disabled
110
110
100
100
±
10
DI, EN, EN
2.0
0.8
±
2
200
200
250
250
±
200
CONDITIONS
I
O
= 0
R = 50Ω; (RS422)
R = 27Ω; (RS485) (Figure 1)
R = 27Ω or R = 50Ω
(Figure 1)
2
1.5
5
0.2
3
0.2
MIN
TYP
MAX
5
UNITS
V
V
V
V
V
V
V
V
µA
µA
µA
mA
mA
µA
SWITCHI G CHARACTERISTICS
SYMBOL
t
PLH
t
PHL
t
SKEW
t
r,
t
f
t
ZH
PARAMETER
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output High
V
CC
= 5V
±
5%, 0°C
≤
Temperature
≤
70°C (Commercial), – 40°C
≤
Temperature
≤
85°C (Industrial) (Note 2, 3)
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 4)
MIN
10
10
5
C
L
= 100pF (Figures 3, 5) S2 Closed
TYP
30
30
5
15
35
MAX
50
50
15
25
70
UNITS
ns
ns
ns
ns
ns
2
U
W
U
U
W W
W
U
LTC486
V
CC
= 5V
±
5%, 0°C
≤
Temperature
≤
70°C (Commercial), – 40°C
≤
Temperature
≤
85°C (Industrial) (Note 2, 3)
SYMBOL
t
ZL
t
LZ
t
HZ
PARAMETER
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
CONDITIONS
C
L
= 100pF (Figures 3, 5) S1 Closed
C
L
= 15pF (Figures 3, 5) S1 Closed
C
L
= 15pF (Figures 3, 5) S2 Closed
MIN
TYP
35
35
35
MAX
70
70
70
UNITS
ns
ns
ns
SWITCHI G CHARACTERISTICS
Note 1:
Absolute maximum ratings are those beyond which the safety of
the device cannot be guaranteed.
Note 2:
All currents into device pins are positive; all currents out of device
SWITCHI G TI E WAVEFOR S
3V
DI
0V
t
PLH
B
V
O
A
V
O
–V
O
1/2 V
O
80%
10%
t
r
3V
EN
0V
t
ZL
5V
A, B
V
OL
V
OH
A, B
0V
t
ZH
t
HZ
LTC486 • TA06
1.5V
t
SKEW
V
DIFF
= V(A) – V(B)
Figure 4. Driver Propagation Delays
1.5V
f = 1MHz : t
r
≤
10ns : t
f
≤
10ns
2.3V
2.3V
Figure 5. Driver Enable and Disable Times
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage
vs Output Current T
A
= 25°C
–96
OUTPUT CURRENT (mA)
64
Driver Differential Output Voltage
vs Output Current T
A
= 25°C
80
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
–72
48
– 48
32
–24
16
0
0
1
2
3
4
LTC486 • TPC01
0
0
1
2
3
4
LTC486• TPC02
OUTPUT VOLTAGE (V)
W
U W
W
U
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 3:
All typicals are given for V
CC
= 5V and temperature = 25°C.
U
f = 1MHz : t
r
<
10ns : t
f
<
10ns
1.5V
t
PHL
1/2 V
O
90%
t
SKEW
20%
t
f
LTC486 • TA05
1.5V
t
LZ
OUTPUT NORMALLY LOW
0.5V
OUTPUT NORMALLY HIGH
0.5V
Driver Output Low Voltage
vs Output Current T
A
= 25°C
60
40
20
0
0
1
2
3
4
LTC486 • TPC03
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3
LTC486
TYPICAL PERFOR A CE CHARACTERISTICS
TTL Input Threshold vs Temperature
1.63
INPUT THRESHOLD VOLTAGE (V)
5
1.61
1.59
TIME (ns)
0
50
100
LTC486 • TPC04
1.57
1.55
–50
Supply Current vs Temperature
130
DIFFERENTIAL VOLTAGE (V)
SUPPLY CURRENT (µA)
120
110
100
90
–50
0
FU CTI
INPUT
DI
H
L
H
L
X
TABLE
ENABLES
OUTPUTS
EN
X
X
L
L
H
OUTA
H
L
H
L
Z
OUTB
L
H
L
H
Z
H: High Level
L: Low Level
X: Irrelevant
Z: High Impedance (Off)
EN
H
H
X
X
L
4
U W
Driver Skew vs Temperature
4
3
2
1
–50
0
50
100
LTC486 • TPC05
TEMPERATURE (°C )
TEMPERATURE (°C )
Driver Differential Output Voltage
vs Temperature R
O
= 54Ω
2.3
2.1
1.9
1.7
50
100
LTC486 • TPC06
1.5
–50
0
50
100
LTC486 • TPC07
TEMPERATURE (°C )
TEMPERATURE (°C )
UO
U
LTC486
PI FU CTI
DI1 (Pin 1):
Driver 1 Input. If Driver 1 is enabled, then a low
on DI1 forces the driver outputs DO1A low and DO1B high.
A high on DI1 with the driver outputs enabled will force
DO1A high and DO1B low.
DO1A (Pin 2):
Driver 1 Output.
DO1B (Pin 3):
Driver 1 Output.
EN (Pin 4):
Driver Outputs Enabled. See Function Table for
details.
DO2B (Pin 5):
Driver 2 Output.
DO2A (Pin 6):
Driver 2 Output.
DI2 (Pin 7):
Driver 2 Input. Refer to DI1.
TEST CIRCUITS
A
R
V
OD
R
B
Figure 1. Driver DC Test Load
APPLICATI
S I FOR ATIO
Typical Application
A typical connection of the LTC486 is shown in Figure 6.
A twisted pair of wires connect up to 32 drivers and
receivers for half duplex data transmission. There are no
restrictions on where the chips are connected to the
wires, and it isn’t necessary to have the chips connected
at the ends. However, the wires must be terminated only
at the ends with a resistor equal to their characteristic
impedance, typically 120Ω. The optional shields around
the twisted pair help reduce unwanted noise, and are
connected to GND at one end.
Thermal Shutdown
The LTC486 has a thermal shutdown feature which pro-
tects the part from excessive power dissipation. If the
outputs of the driver are accidently shorted to a power
U
W
U
UO
UO
U
U
S
GND (Pin 8):
Ground Connection.
DI3 (Pin 9):
Driver 3 Input. Refer to DI1.
DO3A (Pin 10):
Driver 3 Output.
DO3B (Pin 11):
Driver 3 Output.
EN (Pin 12):
Driver Outputs Disabled. See Function Table
for details.
DO4B (Pin 13):
Driver 4 Output.
DO4A (Pin 14):
Driver 4 Output.
DI4 (Pin 15):
Driver 4 Input. Refer to DI1.
V
CC
(Pin 16):
Positive Supply; 4.75V < V
CC
< 5.25V .
EN
CI1
A
DI
DRIVER
B
CI2
LTC486 • TA03
S1
V
CC
OUTPUT
UNDER TEST
500
Ω
R
DIFF
V
OC
C
L
S2
LTC486 • TA04
LTC486 • TA02
EN
Figure 2. Driver Timing Test Circuit
Figure 3. Driver Timing Test Load #2
supply or low impedance source, up to 250mA can flow
through the part. The thermal shutdown circuit disables
the driver outputs when the internal temperature reaches
150°C and turns them back on when the temperature cools
to 130°C. If the outputs of two or more LTC486 drivers are
shorted directly, the driver outputs can not supply enough
current to activate the thermal shutdown. Thus, the ther-
mal shutdown circuit will not prevent contention faults
when two drivers are active on the bus at the same time.
Cable and Data Rate
The transmission line of choice for RS485 applications is
a twisted pair. There are coaxial cables (twinaxial) made for
this purpose that contain straight pairs, but these are less
flexible, more bulky, and more costly than twisted pairs.
Many cable manufacturers offer a broad range of 120Ω
cables designed for RS485 applications.
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