LINER LTC486

LTC1481
Ultralow Power
RS485 Transceiver
with Shutdown
U
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
DESCRIPTIO
Low Power: ICC = 120µA Max with Driver Disabled
Drivers/Receivers Have ±10kV ESD Protection
1µA Quiescent Current in Shutdown Mode
High Speed: Up to 2.5Mbits/s Data Rate
ICC = 500µA Max with Driver Enabled, No Load
Single 5V Supply
– 7V to 12V Common Mode Range Permits ±7V
Ground Difference Between Devices on the Data Line
Thermal Shutdown Protection
Power Up/Down Glitch-Free Driver Outputs Permit
Live Insertion or Removal of Transceiver
Driver Maintains High Impedance in Three-State
or with the Power Off
Up to 32 Transceivers on the Bus
30ns Typical Driver Propagation Delays
with 5ns Skew
Pin Compatible with the LTC485
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APPLICATIO S
■
■
The driver and receiver feature 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. The receiver has a fail-safe
feature which guarantees a high output state when the
inputs are left open.
The LTC1481 is fully specified over the commercial and
extended industrial temperature range and is available in
8-pin PDIP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Battery-Powered RS485/RS422 Applications
Low Power RS485/RS422 Transceiver
Level Translator
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■
The LTC®1481 is an ultralow power differential line transceiver designed for data transmission standard RS485
applications. It will also meet the requirements of RS422.
The CMOS design offers significant power savings over its
bipolar counterparts without sacrificing ruggedness against
overload or ESD damage. Typical quiescent current is only
80µA while operating and less than 1µA in shutdown.
TYPICAL APPLICATIO
Supply Current vs Temperature
350
R
VCC1
RE1
Rt
DE1
DI1
D
GND1
Rt
RO2
R
THERMAL SHUTDOWN
WITH DRIVER ENABLED
300
VCC2
SUPPLY CURRENT (µA)
RO1
250
DRIVER ENABLED
200
150
100
DRIVER DISABLED
RE2
50
DE2
DI2
D
GND2
LTC1481 • TA01
0
–50 –25
0
25 50 75 100 125 150 175
TEMPERATURE (°C)
1481 TA02
1481fa
1
LTC1481
W W
W
AXI U
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltage (VCC) .............................................. 12V
Control Input Voltage ..................... – 0.5V to VCC + 0.5V
Driver Input Voltage ....................... – 0.5V to VCC + 0.5V
Driver Output Voltage ........................................... ±14V
Receiver Input Voltage .......................................... ±14V
Receiver Output Voltage ................ – 0.5V to VCC + 0.5V
Operating Temperature Range
LTC1481C ....................................... 0°C ≤ TA ≤ 70°C
LTC1481I .................................... – 40°C ≤ TA ≤ 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
TOP VIEW
RO 1
R
RE 2
DE 3
DI 4
D
N8 PACKAGE
8-LEAD PDIP
8
VCC
7
B
6
A
5
GND
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 130°C/ W (N8)
TJMAX = 125°C, θJA = 150°C/ W (S8)
LTC1481CN8
LTC1481IN8
LTC1481CS8
LTC1481IS8
S8 PART MARKING
1481
1481I
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V (Notes 2, 3) unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VOD1
Differential Driver Output Voltage (Unloaded)
IO = 0
●
MIN
VOD2
Differential Driver Output Voltage (with Load)
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
●
●
TYP
2.0
1.5
MAX
UNITS
5
V
5
V
V
0.2
V
∆VOD
Change in Magnitude of Driver Differential Output
Voltage for Complementary Output States
R = 27Ω or R = 50Ω, Figure 1
●
VOC
Driver Common Mode Output Voltage
R = 27Ω or R = 50Ω, Figure 1
●
3
V
∆VOC
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
R = 27Ω or R = 50Ω, Figure 1
●
0.2
V
VIH
Input High Voltage
DE, DI, RE
●
VIL
Input Low Voltage
DE, DI, RE
●
0.8
V
IIN1
Input Current
DE, DI, RE
●
±2
µA
IIN2
Input Current (A, B)
DE = 0, VCC = 0V or 5.25V, VIN = 12V
DE = 0, VCC = 0V or 5.25V, VIN = – 7V
●
●
1.0
– 0.8
mA
mA
VTH
Differential Input Threshold Voltage for Receiver
– 7V ≤ VCM ≤ 12V
●
0.2
V
∆VTH
Receiver Input Hysteresis
VCM = 0V
●
VOH
Receiver Output High Voltage
IO = – 4mA, VID = 200mV
●
VOL
Receiver Output Low Voltage
IO = 4mA, VID = – 200mV
●
0.4
V
IOZR
Three-State (High Impedance) Output
Current at Receiver
VCC = Max, 0.4V ≤ VO ≤ 2.4V
●
±1
µA
RIN
Receiver Input Resistance
– 7V ≤ VCM ≤ 12V
●
ICC
Supply Current
No Load, Output Enabled
No Load, Output Disabled
●
●
ISHDN
Supply Current in Shutdown Mode
DE = 0, RE = VCC
IOSD1
Driver Short-Circuit Current, VOUT = HIGH
– 7V ≤ VO ≤ 12V
●
IOSD2
Driver Short-Circuit Current, VOUT = LOW
– 7V ≤ VO ≤ 12V
IOSR
Receiver Short-Circuit Current
0V ≤ VO ≤ VCC
2
V
– 0.2
45
mV
3.5
V
12
kΩ
300
80
500
120
µA
µA
1
10
µA
35
250
mA
●
35
250
mA
●
7
85
mA
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2
LTC1481
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SWITCHI G CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V (Notes 2, 3) unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
tPLH
Driver Input to Output
tPHL
Driver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 3, 5)
tSKEW
Driver Output to Output
●
tr, tf
Driver Rise or Fall Time
●
tZH
Driver Enable to Output High
CL = 100pF (Figures 4, 6), S2 Closed
tZL
Driver Enable to Output Low
tLZ
Driver Disable Time from Low
tHZ
tPLH
tPHL
Receiver Input to Output
tSKD
tPLH – tPHL Differential Receiver Skew
tZL
Receiver Enable to Output Low
tZH
Receiver Enable to Output High
tLZ
tHZ
fMAX
Maximum Data Rate
●
2.5
tSHDN
Time to Shutdown
DE = 0, RE =
●
50
tZH(SHDN)
Driver Enable from Shutdown to Output High
CL = 100pF (Figures 4, 6), S2 Closed
tZL(SHDN)
Driver Enable from Shutdown to Output Low
tZH(SHDN)
Receiver Enable from Shutdown to Output High
tZL(SHDN)
Receiver Enable from Shutdown to Output Low
UNITS
●
10
30
60
ns
●
10
30
60
ns
5
10
ns
3
15
40
ns
●
40
70
ns
CL = 100pF (Figures 4, 6), S1 Closed
●
40
70
ns
CL = 15pF (Figures 4, 6), S1 Closed
●
40
70
ns
Driver Disable Time from High
CL = 15pF (Figures 4, 6), S2 Closed
●
40
70
ns
Receiver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 3, 7)
●
30
140
200
ns
●
30
140
200
ns
●
13
CRL = 15pF (Figures 2, 8), S1 Closed
●
20
50
ns
CRL = 15pF (Figures 2, 8), S2 Closed
●
20
50
ns
Receiver Disable from Low
CRL = 15pF (Figures 2, 8), S1 Closed
●
20
50
ns
Receiver Disable from High
CRL = 15pF (Figures 2, 8), S2 Closed
●
20
50
ns
200
600
ns
●
40
100
ns
CL = 100pF (Figures 4, 6), S1 Closed
●
40
100
ns
CL = 15pF (Figures 2, 8), S2 Closed
●
3500
ns
CL = 15pF (Figures 2, 8), S1 Closed
●
3500
ns
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
ns
Mbits/s
Note 3: All typicals are given for VCC = 5V and TA = 25°C.
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TYPICAL PERFOR A CE CHARACTERISTICS
Driver Differential Output Voltage
vs Temperature
Driver Differential Output Voltage
vs Output Current
2.5
TA = 25°C
DIFFERENTIAL VOLTAGE (V)
OUTPUT CURRENT (mA)
60
50
40
30
20
10
0
1
2
4
3
OUTPUT VOLTAGE (V)
5
1481 G01
TA = 25°C
60
2.3
2.2
2.1
2.0
1.9
1.8
50
40
30
20
1.7
10
1.6
0
70
RL = 54Ω
2.4
OUTPUT CURRENT (mA)
70
Driver Output Low Voltage
vs Output Current
1.5
–50 –25
50
0
75
25
TEMPERATURE (°C)
100
125
0
0
1
2
3
4
OUTPUT VOLTAGE (V)
1481 G02
1481 G03
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3
LTC1481
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TYPICAL PERFOR A CE CHARACTERISTICS
Receiver tPLH – tPHL vs
Temperature
Driver Output High Voltage
vs Output Current
0
TA = 25°C
3.0
12
2.5
–20
10
–40
–50
2.0
TIME (ns)
–30
TIME (ns)
OUTPUT CURRENT (mA)
–10
Driver Skew vs Temperature
14
8
6
–60
1.5
1.0
4
–70
0.5
2
–80
–90
0
1
2
3
OUTPUT VOLTAGE (V)
0
–50 –25
5
4
50
25
75
0
TEMPERATURE (°C)
1481 G04
100
0
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
100
125
1481 G05
1481 G05
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PI FU CTIO S
RO (Pin 1): Receiver Output. If the receiver output is
enabled (RE low), then if A > B by 200mV, RO will be high.
If A < B by 200mV, then RO will be low.
RE (Pin 2): Receiver Output Enable. A low enables the
receiver output, RO. A high input forces the receiver
output into a high impedance state.
DE (Pin 3): Driver Outputs Enable. A high on DE enables
the driver output. A, B and the chip will function as a line
driver. A low input will force the driver outputs into a high
impedance state and the chip will function as a line
receiver. If RE is high and DE is low, the part will enter a low
power (1µA) shutdown state.
DI (Pin 4): Driver Input. If the driver outputs are enabled
(DE high) then a low on DI forces the outputs A low and B
high. A high on DI with the driver outputs enabled will force
A high and B low.
GND (Pin 5): Ground.
A (Pin 6): Driver Output/Receiver Input.
B (Pin 7): Driver Output/Receiver Input.
VCC (Pin 8): Positive Supply. 4.75V < VCC < 5.25V.
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FU CTIO TABLES
LTC1481 Receiving
LTC1481 Transmitting
INPUTS
INPUTS
OUTPUTS
OUTPUTS
RE
DE
DI
B
A
RE
DE
A–B
RO
X
1
1
0
1
0
0
≥ 0.2V
1
0
≤ – 0.2V
0
X
1
0
1
0
0
0
0
X
Z
Z
0
0
Inputs Open
1
1
0
X
Z*
Z*
1
0
X
Z*
*Shutdown mode for LTC1481
*Shutdown mode for LTC1481
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4
LTC1481
TEST CIRCUITS
A
R
VOD
1k
VCC
VOC
R
S1
TEST POINT
RECEIVER
OUTPUT
1k
CRL
S2
B
LTC1481 • F01
LTC1481 • F02
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
3V
DE
A
DI
CL1
S1
VCC
RO
RDIFF
B
A
B
CL2
15pF
RE
500Ω
OUTPUT
UNDER TEST
S2
CL
LTC1481 • F03
LTC1481 • F04
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load
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SWITCHI G TI E WAVEFOR S
3V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
DI
1.5V
0V
t PLH
1/2 VO
t PHL
B
VO
A
VO
0V
–VO
tSKEW
1/2 VO
t SKEW
90%
90%
10%
VDIFF = V(A) – V(B)
10%
tr
LTC1481 • F05
tf
Figure 5. Driver Propagation Delays
3V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
1.5V
DE
1.5V
0V
5V
A, B
t ZL(SHDN), t ZL
2.3V
OUTPUT NORMALLY LOW
0.5V
2.3V
OUTPUT NORMALLY HIGH
0.5V
VOL
VOH
A, B
t LZ
0V
t ZH(SHDN), t ZH
t HZ
LTC1481 • F06
Figure 6. Driver Enable and Disable Times
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LTC1481
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SWITCHI G TI E WAVEFOR S
VOH
1.5V
RO
1.5V
OUTPUT
VOL
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
t PHL
VOD2
A–B
–VOD2
0V
t PLH
0V
INPUT
LTC1481 • F07
Figure 7. Receiver Propagation Delays
3V
1.5V
RE
t ZL(SHDN), tZL
5V
RO
RO
1.5V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
0V
t LZ
1.5V
OUTPUT NORMALLY LOW
0.5V
1.5V
OUTPUT NORMALLY HIGH
0.5V
0V
t ZH(SHDN), tZH
t HZ
LTC1481 • F08
Figure 8. Receiver Enable and Disable Times
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APPLICATIO S I FOR ATIO
Basic Theory of Operation
Traditionally, RS485 transceivers have been designed
using bipolar technology because the common mode
range of the device must extend beyond the supplies and
the device must be immune to ESD damage and latch-up.
Unfortunately, most bipolar devices draw a large amount
of supply current, which is unacceptable for the numerous
applications that require low power consumption. The
LTC1481 is a CMOS RS485/RS422 transceiver which
features ultralow power consumption without sacrificing
ESD and latch-up immunity.
The LTC1481 uses a proprietary driver output stage,
which allows a common mode range that extends beyond
the power supplies while virtually eliminating latch-up and
providing excellent ESD protection. Figure 9 shows the
LTC1481 output stage while Figure 10 shows a conventional CMOS output stage.
When the conventional CMOS output stage of Figure 10
enters a high impedance state, both the P-channel (P1)
and the N-channel (N1) are turned off. If the output is then
driven above VCC or below ground, the P+/N -well diode
(D1) or the N+/P-substrate diode (D2) respectively will
turn on and clamp the output to the supply. Thus, the
output stage is no longer in a high impedance state and is
not able to meet the RS485 common mode range requirement. In addition, the large amount of current flowing
through either diode will induce the well-known CMOS
latch-up condition, which could destroy the device.
The LTC1481 output stage of Figure 9 eliminates these
problems by adding two Schottky diodes, SD3 and SD4.
The Schottky diodes are fabricated by a proprietary modification to the standard N-well CMOS process. When the
output stage is operating normally, the Schottky diodes
are forward biased and have a small voltage drop across
them. When the output is in the high impedance state and
is driven above VCC or below ground, the parasitic diode
D1 or D2 still turns on, but SD3 or SD4 will reverse bias and
prevent current from flowing into the N-well or the substrate. Thus the high impedance state is maintained even
with the output voltage beyond the supplies. With no
minority carrier current flowing into the N-well or substrate, latch-up is virtually eliminated under power-up or
power-down conditions.
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LTC1481
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APPLICATIO S I FOR ATIO
Low Power Operation
VCC
SD3
P1
D1
OUTPUT
LOGIC
SD4
N1
D2
ESD
Shutdown Mode
LTC1481 • F09
Figure 9. LTC1481 Output Stage
VCC
P1
D1
OUTPUT
LOGIC
N1
The LTC1481 is designed to operate with a quiescent
current of 120µA max. With the driver in three-state, ICC
will drop to this 120µA level. With the driver enabled there
will be additional current drawn by the internal 12k resistor. Under normal operating conditions this additional
current is overshadowed by the current drawn by the
external bus impedance.
D2
Both the receiver output (RO) and the driver outputs (A, B)
can be placed in three-state mode by bringing RE high and
DE low respectively. In addition, the LTC1481 will enter
shutdown mode when RE is high and DE is low.
In shutdown the LTC1481 typically draws only 1µA of
supply current. In order to guarantee that the part goes
into shutdown, DE must be low and RE must be high for
at least 600ns simultaneously. If this time duration is less
than 50ns the part will not enter shutdown mode. Toggling
either RE or DE will wake the LTC1481 back up within
3.5µs.
Propagation Delay
Many digital encoding schemes are dependent upon the
difference in the propagation delay times of the driver and
receiver. Figure 11 shows the test circuit for the LTC1481
propagation delay.
LTC1481 • F10
Figure 10. Conventional CMOS Output Stage
The LTC1481 output stage will maintain a high impedance
state until the breakdown of the N-channel or P-channel is
reached when going positive or negative respectively. The
output will be clamped to either VCC or ground by a Zener
voltage plus a Schottky diode drop, but this voltage is well
beyond the RS485 operating range. Because the ESD
injected current in the N-well or substrate consists of
majority carriers, latch-up is prevented by careful layout
techniques. An ESD cell protects output against multiple
10kV human body model ESD strikes.
The receiver delay times are:
tPLH – tPHL = 13ns Typ, VCC = 5V
The drivers skew times are:
Skew = 5ns Typ, VCC = 5V
10ns Max, VCC = 5V, TA = – 40°C to 85°C
100pF
TTL IN
t r, t f < 6ns
D
R
54Ω
R
RECEIVER
OUT
LTC1481 • F11
100pF
Figure 11. Receiver Propagation Delay Test Circuit
1481fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights.
7
LTC1481
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PACKAGE DESCRIPTIO
N8 Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.300 – .325
(7.620 – 8.255)
(
+0.889
8.255
–0.381
.130 ± .005
(3.302 ± 0.127)
.045 – .065
(1.143 – 1.651)
.065
(1.651)
TYP
.008 – .015
(0.203 – 0.381)
+.035
.325 –.015
.400*
(10.160)
MAX
)
8
7
6
1
2
3
5
.255 ± .015*
(6.477 ± 0.381)
.120
(3.048) .020
MIN (0.508)
MIN
.018 ± .003
.100
(2.54)
BSC
4
N8 1002
(0.457 ± 0.076)
NOTE:
1. DIMENSIONS ARE
INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.010 – .020
× 45°
(0.254 – 0.508)
.004 – .010
(0.101 – 0.254)
.053 – .069
(1.346 – 1.752)
.008 – .010
(0.203 – 0.254)
NOTE:
1. DIMENSIONS IN
7
6
.045 ±.005
5
.050 BSC
N
N
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
8
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
.050
(1.270)
BSC
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.245
MIN
.160 ±.005
N/2
1
SO8 0502
1
2
3
4
.030 ±.005
TYP
2
3
N/2
RECOMMENDED SOLDER PAD LAYOUT
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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Quad RS485 Driver
Fits 75172 Pinout, Only 110µA IQ
LTC488
Quad RS485 Receiver
Fits 75173 Pinout, Only 7µA IQ
LTC490
Full Duplex RS485 Transceiver
Fits 75179 Pinout, Only 300µA IQ
LTC1485
Differential Bus Transceiver
Fits 75176A Pinout, Only 1.7mA IQ
1481fa
8
Linear Technology Corporation
LT/TP 0303 1K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 1994