LTC486CS [Linear]
Quad Low Power RS485 Driver; 四通道,低功耗RS485驱动器型号: | LTC486CS |
厂家: | Linear |
描述: | Quad Low Power RS485 Driver |
文件: | 总8页 (文件大小:229K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC486
Quad Low Power
RS485 Driver
U
EATURE
Very Low Power: ICC = 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
S
F
■
■
■
■
DESCRIPTIO
The LTC486 is a low power differential bus/line driver
designedformultipointdatatransmissionstandardRS485
applications with extended common-mode range (12V to
–7V). It also meets RS422 requirements.
TheCMOSdesignofferssignificantpowersavingsoverits
bipolarcounterpartwithoutsacrificingruggednessagainst
overload or ESD damage.
■
■
■
■
■
The driver features three-state outputs, with the driver
outputs maintaining high impedance over the entire
common-moderange.Excessivepowerdissipationcaused
by bus contention or faults is prevented by a thermal
shutdown circuit which forces the driver outputs into a
high impedance state.
28ns Typical Driver Propagation Delays
with 5ns Skew
Pin Compatible with the SN75172, DS96172,
µA96172, and DS96F172
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.
O U
PPLICATI
A
S
■
Low Power RS485/RS422 Drivers
Level Translator
■
U
O
TYPICAL APPLICATI
RS485 Cable Length Specification*
10k
EN
4
EN
1k
4
RECEIVER
1/4 LTC488
2
1
1
120Ω
3
120Ω
DI
DRIVER
12
RO
100
10
4000 FT BELDEN 9841
1/4 LTC486
EN
LTC486 • TA01
10k
100k
1M 2.5M
10M
DATA RATE (bps)
LTC486 • TA09
* APPLIES FOR 24 GAUGE, POLYETHYLENE
DIELECTRIC TWISTED PAIR
1
LTC486
W W W
U
/O
ABSOLUTE AXI U RATI GS
PACKAGE RDER I FOR ATIO
(Note 1)
TOP VIEW
ORDER PART
Supply Voltage (VCC) ............................................... 12V
Control Input Voltages .................... –0.5V to VCC + 0.5V
Driver Input Voltages ...................... –0.5V to VCC + 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
DI1
DO1A
DO1B
EN
1
2
3
4
5
6
7
8
16 V
CC
NUMBER
15 DI4
14 DO4A
13 DO4B
LTC486CN
LTC486CS
LTC486IN
LTC486IS
DO2B
DO2A
DI2
12
EN
11 DO3B
10 DO3A
GND
9
DI3
N PACKAGE
S PACKAGE
16-LEAD PLASTIC DIP 16-LEAD PLASTIC SOL
TJMAX = 125°C, θJA = 70°C/W (N)
JMAX = 150°C, θJA = 95°C/W (S)
T
Consult factory for Military grade parts
DC ELECTRICAL CHARACTERISTICS
VCC = 5V ±5%, 0°C ≤ Temperature ≤ 70°C (Commercial), –40°C ≤ Temperature ≤ 85°C (Industrial) (Note 2, 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
I = 0
5
V
V
V
V
OD1
OD2
O
R = 50Ω; (RS422)
2
R = 27Ω; (RS485) (Figure 1)
1.5
5
V
V
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
R = 27Ω or R = 50Ω
(Figure 1)
0.2
OD
Driver Common-Mode Output Voltage
3
V
V
OC
❘V
❘
Change in Magnitude of Driver Common-Mode
Output Voltage for Complementary Output States
0.2
OC
V
V
Input High Voltage
Input Low Voltage
Input Current
DI, EN, EN
2.0
V
V
IH
0.8
±2
IL
I
I
µA
µA
µA
mA
mA
µA
IN1
CC
Supply Current
No Load
Output Enabled
Output Disabled
110
110
100
100
±10
200
200
250
250
±200
I
I
I
Driver Short-Circuit Current, V
Driver Short-Circuit Current, V
= High
= Low
V = –7V
O
OSD1
OSD2
OZ
OUT
V = 12V
O
OUT
High Impedance State Output Current
V = –7V to 12V
O
U
SWI I
TCH G CHARACTERISTICS
VCC = 5V ±5%, 0°C ≤ Temperature ≤ 70°C (Commercial), –40°C ≤ Temperature ≤ 85°C (Industrial) (Note 2, 3)
SYMBOL
PARAMETER
CONDITIONS
R = 54Ω, C = C = 100pF
DIFF
(Figures 2, 4)
MIN
10
TYP
30
30
5
MAX
50
UNITS
ns
t
t
t
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output High
PLH
L1
L2
10
50
ns
PHL
15
ns
SKEW
t t
r, f
5
15
35
25
ns
t
C = 100pF (Figures 3, 5) S2 Closed
L
70
ns
ZH
2
LTC486
U
SWI I
TCH G CHARACTERISTICS
VCC = 5V ±5%, 0°C ≤ Temperature ≤ 70°C (Commercial), –40°C ≤ Temperature ≤ 85°C (Industrial) (Note 2, 3)
SYMBOL
PARAMETER
CONDITIONS
C = 100pF (Figures 3, 5) S1 Closed
MIN
TYP
35
MAX
UNITS
ns
t
t
t
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
70
70
70
ZL
LZ
HZ
L
C = 15pF (Figures 3, 5) S1 Closed
L
35
ns
C = 15pF (Figures 3, 5) S2 Closed
L
35
ns
Note 1: Absolute maximum ratings are those beyond which the safety of
the device cannot be guaranteed.
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 2: All currents into device pins are positive; all currents out of device
Note 3: All typicals are given for V = 5V and temperature = 25°C.
CC
U
W
W
SWITCHI G TI E WAVEFOR S
3V
f = 1MHz : t 10ns : t 10ns
DI
<
<
f
1.5V
1.5V
r
0V
B
t
t
PHL
PLH
V
O
A
t
t
SKEW
1/2 V
1/2 V
SKEW
O
O
V
O
90%
20%
80%
V
= V(A) – V(B)
DIFF
–V
10%
O
t
t
f
r
Figure 4. Driver Propagation Delays
LTC486 • TA05
3V
0V
5V
f = 1MHz : t 10ns : t 10ns
≤
≤
f
EN
r
1.5V
1.5V
LZ
t
t
ZL
A, B
V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
2.3V
2.3V
0.5V
OL
V
OH
0.5V
A, B
0V
t
t
HZ
ZH
LTC486 • TA06
Figure 5. Driver Enable and Disable Times
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output High Voltage
vs Output Current TA = 25°C
Driver Differential Output Voltage
vs Output Current TA = 25°C
Driver Output Low Voltage
vs Output Current TA = 25°C
–96
–72
64
48
80
60
– 4 8
–24
0
32
16
0
40
20
0
0
0
1
2
3
4
1
2
3
4
0
1
2
3
4
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
LTC486• TPC02
LTC486 • TPC01
OUTPUT VOLTAGE (V)
LTC486 • TPC03
3
LTC486
U W
TYPICAL PERFOR A CE CHARACTERISTICS
TTL Input Threshold vs Temperature
Driver Skew vs Temperature
1.63
5
4
3
2
1
1.61
1.59
1.57
1.55
–50
0
50
100
–50
0
50
100
TEMPERATURE (°C )
LTC486 • TPC04
TEMPERATURE (°C )
LTC486 • TPC05
Driver Differential Output Voltage
vs Temperature RO = 54Ω
Supply Current vs Temperature
130
120
110
100
90
2.3
2.1
1.9
1.7
1.5
–50
0
50
100
–50
0
50
100
TEMPERATURE (°C )
LTC486 • TPC06
TEMPERATURE (°C )
LTC486 • TPC07
O
U
U
FU CTI
TABLE
INPUT
ENABLES
OUTPUTS
OUTB
DI
EN
EN
OUTA
H
L
H
L
H
H
X
X
L
X
X
L
L
H
H
L
H
L
Z
L
H
L
H
Z
H: High Level
L: Low Level
X: Irrelevant
X
Z: High Impedance (Off)
4
LTC486
U
O
U
U
PI
FU CTI
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.
DI1(Pin1):Driver1Input.IfDriver1isenabled,thenalow
onDI1forcesthedriveroutputsDO1AlowandDO1Bhigh.
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 12): Driver Outputs Disabled. See Function Table
for details.
EN(Pin4): DriverOutputsEnabled. SeeFunctionTablefor
details.
DO4B (Pin 13): Driver 4 Output.
DO4A (Pin 14): Driver 4 Output.
DI4 (Pin 15): Driver 4 Input. Refer to DI1.
DO2B (Pin 5): Driver 2 Output.
DO2A (Pin 6): Driver 2 Output.
V
CC (Pin 16): Positive Supply; 4.75V < VCC < 5.25V .
DI2 (Pin 7): Driver 2 Input. Refer to DI1.
TEST CIRCUITS
EN
S1
A
V
CC
CI1
500Ω
R
OUTPUT
UNDER TEST
A
V
OD
DI
DRIVER
R
DIFF
C
L
R
S2
V
OC
B
B
CI2
LTC486 • TA04
LTC486 • TA03
EN
LTC486 • TA02
Figure 1. Driver DC Test Load
Figure 2. Driver Timing Test Circuit
Figure 3. Driver Timing Test Load #2
W
U
O U
I FOR ATIO
S
PPLICATI
A
Typical Application
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°Candturnsthembackonwhenthetemperaturecools
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.
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.
Cable and Data Rate
The transmission line of choice for RS485 applications is
atwistedpair.Therearecoaxialcables(twinaxial)madefor
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.
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
5
LTC486
W
I FOR ATIO
S
EN
U
O U
PPLICATI
A
EN
SHIELD
SHIELD
4
3
4
2
3
1
120Ω
120Ω
DX
RX
DX
RX
2
1
12
12
EN
EN
EN
1/4 LTC486
EN
1/4 LTC488
4
4
3
1
3
1
DX
DX
RX
RX
2
2
12
EN
1/4 LTC486
12
EN
1/4 LTC488
LTC486 • TA07
Figure 6. Typical Connection
10k
Losses in a transmission line are a complex combination
of DC conductor loss, AC losses (skin effect), leakage, and
AC losses in the dielectric. In good polyethylene cables
such as the Belden 9841, the conductor losses and dielec-
tric losses are of the same order of magnitude, with
relatively low overall loss (Figure 7).
1k
100
10
10
10k
100k
1M 2.5M
10M
DATA RATE (bps)
1
LTC486 • TA09
Figure 8. Cable Length vs Data Rate
distorted waveforms will result. In severe cases, distorted
(false) data and nulls will occur. A quick look at the output
of the driver will tell how well the cable is terminated. It is
best to look at a driver connected to the end of the cable,
since this eliminates the possibility of getting reflections
from two directions. Simply look at the driver output while
transmitting square wave data. If the cable is terminated
properly, the waveform will look like a square wave
(Figure 9).
0.1
0.1
1
10
100
FREQUENCY (MHz)
LTC486 • TA08
Figure 7. Attenuation vs Frequency for Belden 9841
When using low loss cables, Figure 8 can be used as a
guidelineforchoosingthemaximumlinelengthforagiven
data rate. With lower quality PVC cables, the dielectric loss
factor can be 1000 times worse. PVC twisted pairs have
terrible losses at high data rates (>100kbs) and greatly
reduce the maximum cable length. At low data rates
however, they are acceptable and much more economical.
If the cable is loaded excessively (e.g., 47Ω), the signal
initially sees the surge impedance of the cable and jumps
to an initial amplitude. The signal travels down the cable
and is reflected back out of phase because of the
mistermination. When the reflected signal returns to the
driver, the amplitude will be lowered. The width of the
pedestal is equal to twice the electrical length of the cable
(about1.5ns/ft). If the cable is lightly loaded (e.g., 470Ω),
Cable Termination
Theproperterminationofthecableisveryimportant.Ifthe
cable is not terminated with its characteristic impedance,
6
LTC486
W
U
O U
S
I FOR ATIO
PPLICATI
A
PROBE HERE
represents an electrical one-tenth wavelength. The value
of the coupling capacitor should therefore be set at 16.3pF
perfootofcablelengthfor120Ω cables. Withthecoupling
capacitors in place, power is consumed only on the signal
edges, not when the driver output is idling at a 1 or 0 state.
A 100nF capacitor is adequate for lines up to 4000 feet in
length. Be aware that the power savings start to decrease
once the data rate surpasses 1/(120Ω × C).
Rt
DX
DRIVER
RECEIVER
RX
Rt = 120Ω
Rt = 47Ω
Receiver Open-Circuit Fail-Safe
Some data encoding schemes require that the output of
the receiver maintains a known state (usually a logic 1)
when the data is finished transmitting and all drivers on
the line are forced into three-state. All LTC RS485
receivers have a fail-safe feature which guarantees the
output to be in a logic 1 state when the receiver inputs
areleftfloating(open-circuit). However, whenthecable
is terminated with 120Ω, the differential inputs to the
receiver are shorted together, not left floating.
Rt = 470Ω
LTC486 • TA10
Figure 9. Termination Effects
the signal reflects in phase and increases the amplitude at
the driver output. An input frequency of 30kHz is adequate
for tests out to 4000 ft. of cable.
AC Cable Termination
If the receiver output must be forced to a known state,
the circuits of Figure 11 can be used.
Cable termination resistors are necessary to prevent un-
wanted reflections, but they consume power. The typical
differentialoutputvoltageofthedriveris2Vwhenthecable
is terminated with two 120Ω resistors. When no data is
being sent 33mA of DC current flows in the cable . This DC
current is about 220 times greater than the supply current
of the LTC486. One way to eliminate the unwanted current
is by AC coupling the termination resistors as shown in
Figure 10.
The termination resistors are used to generate a DC bias
which forces the receiver output to a known state, in this
case a logic 0. The first method consumes about
208mW and the second about 8mW. The lowest power
5V
110Ω
110Ω
130Ω
130Ω
RECEIVER
RECEIVER
RX
RX
5V
120Ω
1.5k
RECEIVER
RX
C
140Ω
1.5k
C = LINE LENGTH (FT) × 16.3pF
LTC486 • TA11
C
100k
Figure 10. AC Coupled Termination
5V
120Ω
The coupling capacitor allows high frequency energy to
flow to the termination, but blocks DC and low frequen-
cies. The dividing line between high and low frequency
depends on the length of the cable. The coupling capacitor
must pass frequencies above the point where the line
RECEIVER
RX
LTC486 • TA12
Figure 11. Forcing “0” When All Dirvers Are Off
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
7
LTC486
PPLICATI
solution is to use an AC termination with a pull-up resistor.
Simply swap the receiver inputs for data protocols ending
in logic 1.
W
U
O U
I FOR ATIO
S
A
breakdown voltages and prices. Be sure to pick a break-
down voltage higher than the common-mode voltage
required for your application (typically 12V). Also, don’t
forget to check how much the added parasitic capacitance
will load down the bus.
Fault Protection
All of LTC’s RS485 products are protected against ESD
transients up to ±2kV using the human body model
(100pF,1.5kΩ).However,someapplicationsneedgreater
protection. The best protection method is to connect a
bidirectionalTransZorb® fromeachlinesidepintoground
(Figure 12).
A TransZorb® is a silicon transient voltage suppressor that
has exceptional surge handling capabilities, fast response
time, and low series resistance. They are available from
GeneralSemiconductorIndustriesandcomeinavarietyof
Y
120Ω
DRIVER
Z
LTC486 • TA13
Figure 12. ESD Protection
TransZorb® is a registrated trademark of General Instruments, GSI
U
O
TYPICAL APPLICATI
RS232 to RS485 Level Translator with Hysteresis
R = 220k
Y
10k
120Ω
RS232 IN
5.6k
DRIVER
VY - VZ
R
19k
Z
1/4 LTC486
———— ——
HYSTERESIS = 10k ×
≈
R
LTC486 • TA14
U
PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.
0.770
(19.558)
MAX
0.300 – 0.325
0.130 ± 0.005
0.045 – 0.065
(7.620 – 8.255)
(3.302 ± 0.127)
(1.143 – 1.651)
14
12
10
9
8
15
13
11
16
0.015
(0.381)
MIN
0.260 ± 0.010
(6.604 ± 0.254)
N Package
16-Lead Plastic DIP
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
+0.025
–0.015
2
1
3
4
6
5
7
0.325
0.125
(3.175)
MIN
0.045 ± 0.015
(1.143 ± 0.381)
0.018 ± 0.003
(0.457 ± 0.076)
+0.635
8.255
(
)
–0.381
0.100 ± 0.010
(2.540 ± 0.254)
0.398 – 0.413
(10.109 – 10.490)
(NOTE 2)
0.291 – 0.299
(7.391 – 7.595)
(NOTE 2)
0.037 – 0.045
(0.940 – 1.143)
0.093 – 0.104
(2.362 – 2.642)
15 14
12
10
9
16
13
11
0.005
(0.127)
RAD MIN
0.010 – 0.029
× 45°
(0.254 – 0.737)
S Package
16-Lead Plastic SOL
0° – 8° TYP
0.050
(1.270)
TYP
0.394 – 0.419
(10.007 – 10.643)
NOTE 1
0.004 – 0.012
(0.102 – 0.305)
0.009 – 0.013
(0.229 – 0.330)
NOTE 1
0.014 – 0.019
0.016 – 0.050
(0.356 – 0.482)
TYP
(0.406 – 1.270)
NOTE:
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.
2. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
2
3
5
7
8
1
4
6
LT/GP 0294 5K REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1994
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
8
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
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