LTC1387
Single 5V RS232/RS485
Multiprotocol Transceiver
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DESCRIPTIO
FEATURES
■
■
■
■
■
■
■
■
■
■
Two RS232 Transceivers or One RS485 Transceiver
Operates from a Single 5V Supply
Guaranteed Receiver Output with Inputs
Floating or Shorted to Ground
Logic Selectable Fast/Slow RS485 Driver Slew Rate
Low Supply Current: 7mA Typical
5µA Supply Current in Shutdown
Self-Testing Capability in Loopback Mode
Separate Driver and Receiver Enable Controls
Driver Maintains High Impedance in Three-State,
Shutdown or with Power Off
Receiver Inputs Can Withstand ±25V
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APPLICATIONS
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■
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Point-of-Sale Terminals
Software Selectable Multiprotocol Interface Ports
Low Power RS485/RS422/RS232/EIA562 Interface
Cable Repeaters
Level Translators
The LTC ®1387 is a low power reconfigurable CMOS bidirectional transceiver. It can be configured as an RS485
differential port or as two RS232 single-ended ports. An
onboard charge pump uses four 0.1µF capacitors to
generate boosted positive and negative supplies, allowing
the RS232 drivers to meet ±5V output swing requirements with only a single 5V supply. A shutdown mode
reduces the ICC supply current to 5µA.
The RS232 transceivers are in full compliance with RS232
specification. The RS485 transceiver is in full compliance
with RS485 and RS422 specifications. The RS485 receiver assumes a known output state when the inputs are
floating or shorted to ground. All interface drivers feature
short-circuit and thermal shutdown protection. An enable
pin allows RS485 driver outputs to be forced into high
impedance which is maintained even when the outputs are
forced beyond supply rails or the power is off. A loop back
mode allows the driver outputs to be connected back to the
receiver inputs for diagnostic self-test.
The LTC1387 is available in 20-pin plastic SSOP and SW
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATI
2
1 20
19
19
20 1
3
LTC1387
LTC1387
2
3
18
VCC2
5V
18
VCC1
5V
RECOUT
17
4
5
120Ω
DR IN
SLEW
DR ENABLE
5V
15
4
5
RS485 INTERFACE
120Ω
6
6
7
14
9
8
12
13
11
10
7
4000-FT 24-GAUGE TWISTED PAIR
17
15
14
5V
5V
5V
5V
8
9
13
12
10
11
RECOUT
DR IN
SLEW
DR ENABLE
5V
ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE
LTC1387 • TA01
1
LTC1387
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RATI GS
W
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W
AXI U
PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltage (VCC) ............................................. 6.5V
Input Voltage
Drivers ................................... – 0.3V to (VCC + 0.3V)
Receivers ............................................. – 25V to 25V
485/232, ON, DXEN
RXEN, SLEW ........................... – 0.3V to (VCC + 0.3V)
Output Voltage
Drivers ................................................. – 18V to 18V
Receivers ............................... – 0.3V to (VCC + 0.3V)
Short-Circuit Duration
Output ........................................................ Indefinite
VDD, VEE, C1+, C1–, C2+, C2 – .......................... 30 sec
Operating Temperature Range
LTC1387C .............................................. 0°C to 70°C
LTC1387I ........................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
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ABSOLUTE
ORDER PART
NUMBER
TOP VIEW
C1+ 1
20 C2 +
C1–
2
19 C2 –
VDD 3
18 VCC
LTC1387CG
LTC1387CSW
LTC1387IG
LTC1387ISW
A 4
17 RA
B 5
16 RB
Y 6
15 DY
Z 7
14 DZ/SLEW
485/232 8
13 ON
DXEN 9
12 RXEN
GND 10
G PACKAGE
20-LEAD PLASTIC SSOP
11 VEE
SW PACKAGE
20-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 120°C/W (G)
TJMAX = 125°C, θJA = 75°C/W (SW)
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RS485 Driver (485/232 = High, ON = DXEN = High)
VOD1
Differential Driver Output Voltage (Unloaded)
IO = 0
●
VOD2
Differential Driver Output Voltage (With Load)
Figure 1, R = 50Ω (RS422)
Figure 1, R = 27Ω (RS485)
●
●
6
V
6
6
V
V
∆VOD
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
Figure 1, R = 27Ω or R = 50Ω
●
0.2
V
VOC
Driver Common Mode Output Voltage
Figure 1, R = 27Ω or R = 50Ω
●
3
V
∆VOC
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary Output States
Figure 1, R = 27Ω or R = 50Ω
●
0.2
V
IOSD
Driver Short-Circuit Current
VO = – 7V, 12V; VO = High
VO = – 7V, 12V; VO = Low (Note 4)
●
●
250
250
mA
mA
IOZD
Three-State Output Current (Y, Z)
– 7V ≤ VO ≤ 12V
500
µA
2.0
1.5
35
10
±5
RS232 Driver (485/232 = Low, ON = DXEN = High)
VO
Output Voltage Swing
Figure 4, RL = 3k, Positive
Figure 4, RL = 3k, Negative
●
●
IOSD
Output Short-Circuit Current
VO = 0V
●
5
–5
6.5
– 6.5
±17
V
V
±60
mA
Driver Inputs and Control Inputs
VIH
Input High Voltage
DY, DZ, DXEN, RXEN, ON, 485/232, SLEW
●
VIL
Input Low Voltage
DY, DZ, DXEN, RXEN, ON, 485/232, SLEW
●
IIN
Input Current
DY, DZ, DXEN, RXEN, ON, 485/232
SLEW (Note 5)
●
●
2
2
V
±0.1
5
0.8
V
±10
15
µA
µA
LTC1387
DC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RS485 Receiver (485/232 = High, ON = RXEN = High)
VTH
Differential Input Threshold Voltage
– 7V ≤ VCM ≤ 12V
∆VTH
Input Hysteresis
VCM = 0V
IIN
Input Current (A, B)
VIN = 12V
VIN = – 7V
●
●
– 0.8
– 7V ≤ VIN ≤ 12V
●
12
Input Low Threshold
Input High Threshold
●
●
0.8
RIN
Input Resistance
●
– 0.20
0.20
40
V
mV
1
24
mA
mA
kΩ
RS232 Receiver (485/232 = Low, ON = RXEN = High)
VTH
Receiver Input Voltage Threshold
∆VTH
Receiver Input Hysteresis
RIN
Receiver Input Resistance
2.4
0.6
VIN = ±10V
3
5
3.5
4.6
V
V
V
7
kΩ
Receiver Output (ON = RXEN = High)
VOH
Receiver Output High Voltage
IO = – 3mA, VIN = 0V, 485/232 = Low
●
VOL
IOSR
Receiver Output Low Voltage
IO = 3mA, VIN = 3V, 485/232 = Low
●
Short-Circuit Current
0V ≤ VO ≤ VCC
●
IOZR
Three-State Output Current
RXEN = 0V
●
0.2
7
±0.1
V
0.4
V
85
mA
±10
µA
Power Supply Generator
VDD
VDD Output Voltage
No Load, ON = DXEN = RXEN = High
IDD = – 5mA, ON = DXEN = RXEN = High
VEE
VEE Output Voltage
No Load, ON = DXEN = RXEN = High
IEE = 5mA, ON = DXEN = RXEN = High
8
7
V
V
– 7.7
– 7.0
V
V
Power Supply
ICC
VCC Supply Current
No Load, ON = DXEN = RXEN = High
Shutdown, ON = DXEN = RXEN = 0V
●
●
7
5
25
100
mA
µA
TYP
MAX
UNITS
AC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
RS232 Mode (ON = DXEN = RXEN = High, 485/232 = Low)
SR
Slew Rate
Figure 4, RL = 3k, CL = 15pF
Figure 4, RL = 3k, CL = 1000pF
●
●
4
0.22
30
V/µs
V/µs
1.9
3.1
µs
tT
Transition Time
Figure 4, RL = 3k, CL = 2500pF
●
tPLH
Driver Input to Output
Figures 4, 10, RL = 3k, CL = 15pF
●
0.6
4
µs
tPHL
Driver Input to Output
Figures 4, 10, RL = 3k, CL = 15pF
●
0.6
4
µs
tPLH
Receiver Input to Output
Figures 5, 11
●
0.3
6
µs
tPHL
Receiver Input to Output
Figures 5, 11
●
0.4
6
µs
RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)
t PLH
Driver Input to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
15
40
70
ns
t PHL
Driver Input to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
15
40
70
ns
tSKEW
Driver Output to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
5
15
ns
tr, tf
Driver Rise or Fall Time
Figures 2, 7, RL = 54Ω, CL = 100pF
●
15
40
ns
3
3
LTC1387
AC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High)
tZL
Driver Enable to Output Low
Figures 3, 8, CL = 100pF, S1 Closed
●
50
90
ns
tZH
tLZ
Driver Enable to Output High
Figures 3, 8, CL = 100pF, S2 Closed
●
50
90
ns
Driver Disable from Low
Figures 3, 8, CL = 15pF, S1 Closed
●
50
90
ns
tHZ
Driver Disable from High
Figures 3, 8, CL = 15pF, S2 Closed
●
60
90
ns
RS485 Mode (Slow Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = Low)
t PLH
Driver Input to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
100
700
1500
ns
t PHL
Driver Input to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
100
700
1500
ns
tSKEW
Driver Output to Output
Figures 2, 7, RL = 54Ω, CL = 100pF
●
200
750
ns
tr, tf
Driver Rise or Fall Time
Figures 2, 7, RL = 54Ω, CL = 100pF
●
150
300
1500
ns
tZL
Driver Enable to Output Low
Figures 3, 8, CL = 100pF, S1 Closed
●
600
1500
ns
tZH
Driver Enable to Output High
Figures 3, 8, CL = 100pF, S2 Closed
●
600
1500
ns
tLZ
Driver Disable from Low
Figures 3, 8, CL = 15pF, S1 Closed
●
100
200
ns
tHZ
Driver Disable from High
Figures 3, 8, CL = 15pF, S2 Closed
●
100
200
ns
RS485 Mode (ON = RXEN = High, 485/232 = High)
t PLH
Receiver Input to Output
Figures 2, 9, RL = 54Ω, CL = 100pF
●
20
70
140
ns
t PHL
Receiver Input to Output
Figures 2, 9, RL = 54Ω, CL = 100pF
●
20
70
140
ns
tSKEW
Differential Receiver Skew, tPLH – tPHL
Figures 2, 9, RL = 54Ω, CL = 100pF
10
ns
Receiver Output Enable/Disable (ON = High)
tZL
Receiver Enable to Output Low
Figures 6, 12, CL = 15pF, S1 Closed
●
40
90
ns
tZH
tLZ
Receiver Enable to Output High
Figures 6, 12, CL = 15pF, S2 Closed
●
40
90
ns
Receiver Disable from Low
Figures 6, 12, CL = 15pF, S1 Closed
●
40
90
ns
tHZ
Receiver Disable from High
Figures 6, 12, CL = 15pF, S2 Closed
●
40
90
ns
The ● denotes specifications which apply over the full operating
temperature range.
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.
Note 3: All typicals are given at VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF
and TA = 25°C.
Note 4: Short-circuit current for RS485 driver output low state folds back
above VCC. Peak current occurs around VO = 3V.
Note 5: SLEW includes an internal pull-up in RS485 mode.
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PIN FUNCTIONS
C1+ (Pin 1): Commutating Capacitor C1 Positive Terminal.
Requires an external 0.1µF capacitor between Pins 1 and 2.
C1– (Pin 2): Commutating Capacitor C1 Negative Terminal.
VDD (Pin 3): Charge Pump Positive Supply Output.
Requires an external 0.1µF capacitor to ground.
A (Pin 4): Receiver Input A. Inverting input of RS232
receiver A in RS232 mode; inverting RS485 receiver input
in RS485 mode.
4
B (Pin 5): Receiver Input B. Inverting input of RS232
receiver B in RS232 mode; noninverting RS485 receiver
input in RS485 mode.
Y (Pin 6): Driver Output Y. Inverting RS232 driver Y output
in RS232 mode; inverting RS485 driver output in RS485
mode.
Z (Pin 7): Driver Output Z. Inverting RS232 driver Z output
in RS232 mode; noninverting RS485 driver output in
RS485 mode.
LTC1387
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PI FU CTIO S
485/232 (Pin 8): Interface Mode Select Input. A low logic
input enables two RS232 drivers and two RS232 receivers. A high input enables the RS485 driver and the RS485
receiver.
DXEN (Pin 9): Driver Enable Input. A high logic input
enables the drivers and a low logic input disables the
drivers. When disabled, all driver outputs are in high
impedance
GND (Pin 10): Ground.
VEE (Pin 11): Charge Pump Negative Supply Output.
Requires an external 0.1µF capacitor to ground.
RXEN (Pin 12): Receiver Enable Input. A high logic input
enables the receivers and a low logic input disables the
receivers. When disabled, all receiver outputs are in high
impedance.
ON (Pin 13): A high logic level at ON input keeps the charge
pump active regardless of the state of the DXEN and RXEN
inputs. When the charge pump is active, the drivers and
receivers can be enabled or disabled without waiting for
charge pump stabilization time (typically 100µs with 0.1µF
capacitors). A low logic state at the ON, DXEN and RXEN
inputs will put the transceiver and charge pump in shutdown mode and reduces ICC to 5µA. Whenever the transceiver is activated from shutdown, the charge pump
should be allowed to stabilize before data transmission.
When DXEN and RXEN are high and ON is low, the charge
pump, drivers and receivers are all active and the driver
outputs are internally looped back to the inputs of the
receiver. The three control inputs ON, DXEN and RXEN can
be configured for one-, two- or three-wire control: onewire mode – all three inputs connected together; two-wire
mode – inputs ON and RXEN connected to one wire, DXEN
a separate wire; three-wire mode – separate wires to each
input. See the Function Tables.
DZ/SLEW (Pin 14): Driver Z or Slew Input. In RS232
mode, this pin is the driver Z input. In RS485 mode, this
pin controls the slew rate of the RS485 driver. With the
SLEW pin high, the RS485 driver runs at maximum (fast)
slew rate and can transmit signals up to 5MBd. With the
SLEW pin low, the RS485 driver runs with reduced (slow)
slew rate to control reflections with improperly terminated
cables. In slow mode, the RS485 driver can support data
rates up to 150kBd. This SLEW pin has internal 5µA pullup during RS485 mode.
DY (Pin 15): Driver Y Input. Input Y in RS232 mode; the
differential driver input in RS485 mode.
RB (Pin 16): Receiver B Output. Output B in RS232 mode;
output is high impedance in RS485 mode.
RA (Pin 17): Receiver A Output. Output A in RS232 mode;
the differential receiver output in RS485 mode.
VCC (Pin 18): Positive Supply. 4.75V ≤ VCC ≤ 5.25V.
Requires an external 0.1µF bypass capacitor to ground.
C2 – (Pin 19): Commutating Capacitor C2 Negative Terminal. Requires an external 0.1µF capacitor between Pins 19
and 20.
C2 + (Pin 20): Commutating Capacitor C2 Positive
Terminal.
5
LTC1387
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FU CTIO TABLES
Select Modes
SELECT INPUTS
ON
RXEN DXEN
RECEIVER
485/232 RXA
DRIVER
RXB
DXY
DXZ
CHARGE PUMP LOOPBACK
COMMENTS
1
0
0
0
Z
Z
Z
Z
ON
OFF
RS232 Mode, DX and RX Off
1
0
1
0
Z
Z
ON
ON
ON
OFF
RS232 Mode, DXY and DXZ On, RX Off
1
1
0
0
ON
ON
Z
Z
ON
OFF
RS232 Mode, DX Off, RXA and RXB On
1
1
1
0
ON
ON
ON
ON
ON
OFF
RS232 Mode, DXY and DXZ On,
RXA and RXB On
0
0
1
0
Z
Z
ON
Z
ON
OFF
RS232 Mode, DXY On, DXZ Off, RX Off
0
1
0
0
Z
ON
ON
Z
ON
OFF
RS232 Mode, DXY On,
DXZ Off, RXA Off, RXB On
0
1
1
0
ON
ON
ON
ON
ON
ON
RS232 Loopback Mode, DXY and DXZ On,
RXA and RXB On
0
0
0
X
Z
Z
Z
Z
OFF
OFF
Shutdown, RS485 RIN
1
0
0
1
Z
Z
Z
Z
ON
OFF
RS485 Mode, DX and RX Off
X
0
1
1
Z
Z
ON
ON
ON
OFF
RS485 Mode, DX On, RX Off
X
1
0
1
ON
Z
Z
Z
ON
OFF
RS485 Mode, DX Off, RX On
1
1
1
1
ON
Z
ON
ON
ON
OFF
RS485 Mode, DX On, RX On
0
1
1
1
ON
Z
ON
ON
ON
ON
RS485 Loopback Mode, DX On, RX On
RS485 Driver Slew Rate
RS232 Driver Mode
SELECTED
INPUTS
485/232
D
CONDITIONS
OUTPUTS
Y, Z
DXEN
INPUTS
485/232
SLEW
OUTPUTS
SLEW RATE
YES
0
0
No Fault
1
1
1
0
Slow
1
1
Fast
1
X
Z
YES
0
1
No Fault
0
1
YES
0
X
Thermal Fault
Z
0
NO
0
X
X
Z
RS485 Driver Mode
DXEN
INPUTS
485/232
D
CONDITIONS
1
1
0
No Fault
0
1
RS232 Receiver Mode
OUTPUTS
Z
Y
SELECTED
INPUTS
485/232
A, B
OUTPUTS
RA, RB
YES
0
0
1
1
1
1
No Fault
1
0
1
X
Thermal Fault
Z
Z
1
X
X
Z
Z
YES
0
1
0
1
YES
0
Inputs Open
1
0
NO
0
X
Z
RS485 Receiver Mode
RXEN
6
INPUTS
485/232
B–A
OUTPUTS
RA
RB
1
1
< – 0.2V
0
Z
1
1
> 0.2V
1
Z
1
1
Inputs Open
or Shorted to Ground
1
Z
0
1
X
Z
Z
LTC1387
W
BLOCK DIAGRAM
RS232 MODE
WITHOUT LOOPBACK
1
20
C1
VDD
A
B
Y
Z
485/232
DXEN
GND
2
19
3
18
4
17
5
16
6
15
7
14
8
13
9
12
10
11
RS485 MODE
WITHOUT LOOPBACK
1
20
C2 C1
VCC
RA
RB
DY
DZ
ON
VDD
2
19
3
18
17
4
A
5
B
15
6
Y
DXEN
GND
VCC
VDD
8
13
9
12
10
11
RS485 MODE
WITH LOOPBACK
20
2
19
3
18
RA
17
16
RB
DY
Y
14
485/232*
VEE
1
C2 C1
7
Z
RXEN
16
RS232 MODE
WITH LOOPBACK
Z
SLEW
ON
RXEN
485/232
DXEN*
VEE
GND
6
15
7
14
8
13
9
12
10
11
C2 C1
VCC
VDD
1
20
2
19
3
18
17
RA
16
RB
DY
DZ
15
Y
Z
ON 485/232*
RXEN*
VEE
DXEN*
GND
6
7
14
8
13
9
12
10
11
*485/232, DXEN, RXEN = VCC
C2
VCC
RA
RB
DY
SLEW
ON
RXEN*
VEE
LTC1387 • BD
TEST CIRCUITS
VCC
Y
R
SLEW
D
VOD
Y
CL
B
R
500Ω
DR OUT
VOC
Z
A
RL
Z
R
S1
CL
15pF
485 = 3V, DXEN = 3V, RXEN = 3V
LTC1387 • F02
LTC1387 • F01
Figure 1. RS485 Driver
Test Load
CL
Figure 2. RS485 Driver/Receiver
Timing Test Circuit
S2
LTC1387 • F03
Figure 3. RS485 Driver Output
Enable/Disable Timing Test Load
VCC
S1
D
Y, Z
D
CL
232 = 0V, DXEN = 3V
Figure 4. RS232 Driver
Timing Test Circuit
Y, Z
A, B
RECEIVER
OUT
R
RL
15pF
1k
CL
S2
LTC1387 • F05
LTC1387 • F04
232 = 0V, DXEN = 3V, RXEN = 3V
Figure 5. RS232 Receiver
Timing Test Circuit
LTC1387 • F06
Figure 6. Receiver Output
Enable/Disable Timing Test Load
7
LTC1387
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SWITCHI G WAVEFOR S
f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE)
f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE)
3V
1.5V
D
1.5V
0V
tPLH
tPHL
VO
90%
Z–Y
50%
10%
–VO
VDIFF = V(A) – V(B)
90%
50%
10%
1/2 VO
tr
tf
Y
VO
Z
tSKEW
tSKEW
LTC1387 • F07
Figure 7. RS485 Driver Propagation Delays
f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE)
f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE)
3V
1.5V
DXEN
1.5V
0V
tZL
tLZ
5V
Y, Z
2.3V
OUTPUT NORMALLY LOW
VOL
tZH
OUTPUT NORMALLY HIGH
VOH
0.5V
tHZ
0.5V
2.3V
Z, Y
0V
LTC1387 • F08
Figure 8. RS485 Driver Enable and Disable Times
VOD2
0V
B–A
f = 1MHz: t r ≤ 10ns: t f ≤ 10ns
INPUT
0V
–VOD2
tPLH
OUTPUT
VOH
R
tPHL
1.5V
1.5V
VOL
LTC1387 • F09
Figure 9. RS485 Receiver Propagation Delays
3V
1.5V
1.5V
D
0V
tPHL
tPLH
VO
Y, Z
0V
–VO
Figure 10. RS232 Driver Propagation Delays
8
LTC1387 • F10
0V
LTC1387
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SWITCHI G WAVEFOR S
VIH
1.7V
1.3V
A, B
VIL
tPHL
tPLH
VOH
2.4V
R
LTC1387 • F11
0.8V
VOL
Figure 11. RS232 Receiver Propagation Delays
3V
1.5V
RXEN
f = 1MHz: tr ≤ 10ns: tf ≤ 10ns
1.5V
0V
tZL
tLZ
5V
R
1.5V
OUTPUT NORMALLY LOW
VOL
tZH
OUTPUT NORMALLY HIGH
VOH
0.5V
tHZ
0.5V
1.5V
R
0V
LTC1387 • F12
Figure 12. Receiver Enable and Disable Times
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APPLICATI
S I FOR ATIO
Basic Theory of Operating
The LTC1387 is a single 5V supply, single-port logic
reconfigurable RS485/RS232 transceiver with an onboard
charge pump. The interface port offers a flexible combination of an RS485 driver and an RS485 receiver or two
RS232 drivers and two RS232 receivers. The RS485
transceiver and the RS232 transceivers are designed to
share the same I/O pins. A logic input 485/232 controls the
selection between RS485 and RS232 transceiver modes.
The RS485 transceiver supports both RS485 and RS422
standards, whereas the RS232 transceivers support both
RS232 and EIA562 standards. With four additional control
inputs: ON, DXEN, RXEN and SLEW, the LTC1387 can
easily be reconfigured via software to adapt to various
communication needs including a one-signal-line RS232
I/O mode. Four examples of interface port connections are
shown in Figures 13 through 16.
Both the interface drivers and the receivers feature threestate outputs. Driver outputs are forced into high
impedance when the driver is disabled, in the shutdown
mode or with the power off. The driver outputs can be
forced beyond power supply levels without damage up to
±18V. The receiver inputs can withstand ±25V without
damage. The receiver input resistance is typically 24k in
RS485 mode, shutdown mode or power off but drops to
5k in RS232 mode.
In RS485 mode, the DXEN and RXEN control the threestate outputs of the driver and receiver respectively. The
SLEW input is active during RS485 mode and the logic
level controls the differential driver slew rate. This pin has
an internal 5µA pull-up current source during the RS485
mode. A high logic selects fast differential driver slew rate
and a low logic selects slow slew rate. In slow slew mode,
the maximum signal bandwidth is reduced, minimizing
9
LTC1387
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APPLICATI
S I FOR ATIO
EMI and signal reflection problems. Slow slew rate systems can often use improperly terminated or even
unterminated cables with acceptable results. The RS485
differential input receiver features an offset input threshold of – 80mV at 0V common mode voltage. This allows
the receiver output to have a known High output state
when the inputs are open or shorted. The receiver also
features an input hysteresis of 40mV. The charge pump
can be kept active regardless of the state of DXEN and
RXEN pins by keeping the ON pin High. This improves the
receiver response time by removing the 100µs charge
pump start-up time.
In RS232 mode, the drivers and receivers can be selected
from the Function Tables with control inputs ON, RXEN
and DXEN. The receivers feature a typical 0.6V input
hysteresis.
RS232
RS485
A
INTERFACE
B
A
All the interface driver outputs are fault protected by a
current limiting and thermal shutdown circuit. The thermal
shutdown circuit disables both the RS232 and RS485
driver outputs when the die temperature reaches 150°C.
The thermal shutdown circuit reenables the drivers when
the die temperature cools to 135°C.
A loopback mode enables internal connections from driver
outputs to receiver inputs for self-test. The driver outputs
are not isolated from the external loads during loopback.
The charge pump generates boosted positive voltage VDD
and negative voltage VEE for true RS232 levels from a
single 5V VCC supply. The charge pump requires four
0.1µF capacitors.
LTC1387
RA
RA
RS485
RB
B
Y
DY
RB
DY
DX/RX
DZ/SLEW
Z
ON
DZ
VCC
RXEN
CONTROLLER
RXEN
DXEN
DXEN
485/232
MODE
RS232
TRANSMIT MODE
RS232
RECEIVE MODE
RS485
TRANSMIT MODE
RS485
RECEIVE MODE
SHUTDOWN
MODE
RXEN = 0
RXEN = 1
RXEN = 0
RXEN = 1
RXEN = 0
DXEN = 1
DXEN = 0
DXEN = 1
DXEN = 0
DXEN = 0
MODE = 0
MODE = 0
MODE = 1
MODE = 1
MODE = X
1387 • F13
Figure 13. Half-Duplex RS232 (1-Channel), Half-Duplex RS485
10
LTC1387
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APPLICATI
S I FOR ATIO
LTC1387
RS232
A
INTERFACE
B
RS485
RA
A
TXD
RS232
RA
RS485
RXD
Y
RX
RB
B
RB
DY
CONTROLLER
DY
DX
DZ/SLEW
Z
ON
DZ
VCC
RXEN
DXEN
485/232
RS232
MODE
RS485
TRANSMIT MODE
RS485
RECEIVE MODE
SHUTDOWN
MODE
RXEN
RXEN = 1
RXEN = 0
RXEN = 1
RXEN = 0
DXEN
DXEN = 0
DXEN = 1
DXEN = 0
DXEN = 0
MODE
MODE = 0
MODE = 1
MODE = 1
MODE = 0
1387 • F14
Figure 14. Full-Duplex RS232 (1-Channel), Half-Duplex RS485
LTC1387
RS232
A
RS485
RA
RS485
RS232
RS485
Y
RX
RB
B
B
INTERFACE
Y
RA
A
RXD
DY
RB
CONTROLLER
TXD
DY
RS485
DZ/SLEW
Z
Z
ON
DZ
RXEN
DXEN
485/232
DX
VCC
RS232
MODE
RS485
MODE
SHUTDOWN
MODE
RXEN
RXEN = 1
RXEN = 1
RXEN = 0
DXEN
DXEN = 1
DXEN = 1
DXEN = 0
MODE
MODE = 0
MODE = 1
MODE = X
1387 • F15
Figure 15. Full-Duplex RS232 (1-Channel), Full-Duplex RS485/RS422
LTC1387
RS232
A
INTERFACE
Y
RA
A
RXD
RS232
B
RS485
RA
RS485
RB
B
CTS
RS232
RS485
Y
DY
CONTROLLER
DY
Z
RTS
RS485
RX2
RB
TXD
RS232
RX1
DZ/SLEW
Z
DZ
ON
RXEN
DXEN
485/232
DX1
DX2/SLEW
ON
RXEN
RS232
MODE
RS485
MODE
SHUTDOWN
MODE
ON = 1
ON = 1
ON = 0
RXEN = 1
RXEN = 1
RXEN = 0
DXEN
DXEN = 1
DXEN = 1
DXEN = 0
MODE
MODE = 0
MODE = 1
MODE = X
1387 • F16
Figure 16. Full-Duplex RS232 (2-Channel), Full-Duplex RS485/RS422 with SLEW Control
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 its circuits as described herein will not infringe on existing patent rights.
11
LTC1387
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
G Package
20-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1640)
6.90 – 7.50*
(.272 – .295 )
5.00 – 5.60**
(.197 – .221)
2.0
(.079)
20 19 18 17 16 15 14 13 12 11
1.25 ±0.12
0° – 8°
0.65
(.0256)
BSC
0.55 – 0.95
(.022 – .037)
0.09 – 0.25
(.0035 – .010)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
MILLIMETERS
2. DIMENSIONS ARE IN
(INCHES)
7.40 – 8.20 7.8 – 8.2
(.291 – .323)
5.3 – 5.7
0.05
(.002)
0.22 – 0.38
(.009 – .015)
G20 SSOP 0802
0.42 ±0.03
1 2 3 4 5 6 7 8 9 10
3. DRAWING NOT TO SCALE
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
**DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
SW Package
20-Lead Plastic Small Outline (Wide 0.300)
(LTC DWG # 05-08-1620)
0.496 – 0.512*
(12.598 – 13.005)
0.291 – 0.299**
(7.391 – 7.595)
20
0.093 – 0.104
(2.362 – 2.642)
0.010 – 0.029 × 45°
(0.254 – 0.737)
0° – 8° TYP
18
17
16
15
14
13
12
11
NOTE 1
0.050
0.004 – 0.012
(1.270)
(0.102 – 0.305)
TYP 0.014 – 0.019
(0.356 – 0.482)
NOTE:
TYP
1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS
0.009 – 0.013
(0.229 – 0.330)
19
0.037 – 0.045
(0.940 – 1.143)
0.394 – 0.419
(10.007 – 10.643)
NOTE 1
0.016 – 0.050
(0.406 – 1.270)
1
2
3
4
5
6
7
8
9
10
S20 (WIDE) 0396
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
Low Power RS485 Interface Transceiver
Single 5V Supply, Wide Common Mode Range
LT ® 1137A
Low Power RS232 Transceiver
±15kV IEC-1000-4-2 ESD Protection, Three Drivers, Five Receivers
LTC1320
AppleTalk ® Transceiver
AppleTalk /LocalTalk ® Compliant
LTC1321/LTC1322/LTC1335
RS232/EIA562/RS485 Transceivers
Configurable
LTC1323
Single 5V AppleTalk Transceiver
AppleTalk /LocalTalk Compliant 10kV ESD
LTC1334
Single Supply RS232/RS485 Transceiver
Single 5V Supply, Configurable
LTC1347
5V Low Power RS232 Transceiver
Three Drivers/Five Receivers, Five Receivers Alive in Shutdown
AppleTalk and LocalTalk are registered trademarks of Apple Computer Corp.
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
sn1387 1387fs LT/GP 0197 7K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1997
工商网监
湘ICP备2023018690号
