RS485/RS422 transceivers operating on 3.3V supplies.
The receiver includes a logic-selectable 120Ω termina-
tion, one-eighth unit load supporting up to 256 nodes per
bus (C, I-Grade), and a failsafe feature that guarantees a
high output state under conditions of floating or shorted
inputs.
The driver maintains a high output impedance over the
entire common mode range when disabled or when the
supply is removed. Excessive power dissipation caused by
bus contention or a fault is prevented by current limiting
all outputs and by a thermal shutdown.
Enhanced ESD protection allows the LTC2854 to withstand
±25kV (human body model) and the LTC2855 to withstand
±15kV on the transceiver interface pins without latchup
or damage.
■
■
■
■
■
■
■
■
Integrated, Logic-Selectable 120Ω Termination
Resistor
3.3V Supply Voltage
20Mbps Maximum Data Rate
No Damage or Latchup Up to ±25kV HBM
High Input Impedance Supports 256 Nodes
(C, I-Grade)
Operation Up to 125°C (H-Grade)
Guaranteed Failsafe Receiver Operation Over the
Entire Common Mode Range
Current Limited Drivers and Thermal Shutdown
Delayed Micropower Shutdown: 5μA Maximum
(C, I-Grade)
Power Up/Down Glitch-Free Driver Outputs
Low Operating Current: 370μA Typical in
Receive Mode
Compatible with TIA/EIA-485-A Specifications
Available in 10-Pin 3mm
×
3mm DFN, 12-Pin
4mm
×
3mm DFN and 16-Pin SSOP Packages
PRODUCT SELECTION GUIDE
PART NUMBER
LTC2854
LTC2855
DUPLEX
HALF
FULL
PACKAGE
DFN-10
SSOP-16, DFN-12
APPLICATIONS
■
■
■
Low Power RS485/RS422 Transceiver
Level Translator
Backplane Transceiver
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
LTC2854
RO
RE
TE
DE
DI
D
R
LTC2854
R
RO
RE
TE
DE
D
DI
LTC2854 at 20Mbps into 54
Ω
DI
120Ω
120Ω
A
B
2V/DIV
A-B
LTC2854
120Ω
285455 TA01
R
D
20ns/DIV
285455 TA01b
RO RE TE DE
DI
285455fa
1
LTC2854/LTC2855
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (V
CC
) ................................... –0.3V to 7V
⎯ ⎯
Logic Input Voltages (RE, DE, DI, TE)............ –0.3V to 7V
Interface I/O:
A, B, Y, Z ...................................... (V
CC
–15V) to +15V
(A-B) or (B-A) with Terminator Enabled ..................6V
Receiver Output Voltage (RO) ........ –0.3V to (V
CC
+0.3V)
Operating Temperature (Note 4)
LTC2854C, LTC2855C .............................. 0°C to 70°C
LTC2854I, LTC2855I ............................ –40°C to 85°C
LTC2854H, LTC2855H........................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
GN Package ...................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
RO
RO
RE
DE
DI
TE
1
2
3
4
5
11
10 V
CC
9 B
8 A
7 NC
6 GND
RE
DE
DI
TE
GND
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
1
2
3
4
5
6
13
12 V
CC
11 A
10 B
9
8
7
Z
Y
NC
RO
RE
DE
DI
TE
GND
NC
NC
1
2
3
4
5
6
7
8
TOP VIEW
16 V
CC
15 A
14 B
13 Z
12 Y
11 NC
10 NC
9
NC
EXPOSED PAD (PIN 11) PCB GND CONNECTION
T
JMAX
= 125°C,
θ
JA
= 43°C/W
θ
JC
= 2.96°C/W
DE PACKAGE
12-LEAD (4mm
×
3mm) PLASTIC DFN
EXPOSED PAD (PIN 13) PCB GND CONNECTION
T
JMAX
= 125°C,
θ
JA
= 44°C/W
θ
JC
= 4.3°C/W
GN PACKAGE
16-LEAD (NARROW 0.150) PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
θ
JC
= 40°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2854CDD#PBF
LTC2854CDD#TRPBF
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
0°C to 70°C
LTC2854IDD#PBF
LTC2854IDD#TRPBF
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
–40°C to 85°C
LTC2854HDD#PBF
LTC2854HDD#TRPBF
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
–40°C to 125°C
LTC2855CDE#PBF
LTC2855CDE#TRPBF
2855
12-Lead (4mm
×
3mm) Plastic DFN
0°C to 70°C
LTC2855IDE#PBF
LTC2855IDE#TRPBF
2855
12-Lead (4mm
×
3mm) Plastic DFN
–40°C to 85°C
LTC2855HDE#PBF
LTC2855HDE#TRPBF
2855
12-Lead (4mm
×
3mm) Plastic DFN
–40°C to 125°C
16-Lead (Narrow 0.150) Plastic SSOP
0°C to 70°C
LTC2855CGN#PBF
LTC2855CGN#TRPBF
2855
LTC2855IGN#PBF
LTC2855IGN#TRPBF
2855I
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 85°C
LTC2855HGN#PBF
LTC2855HGN#TRPBF
2855H
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2854CDD
LTC2854CDD#TR
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
0°C to 70°C
LTC2854IDD
LTC2854IDD#TR
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
–40°C to 85°C
LTC2854HDD
LTC2854HDD#TR
LCQG
10-Lead (3mm
×
3mm) Plastic DFN
–40°C to 125°C
LTC2855CDE
LTC2855CDE#TR
2855
12-Lead (4mm
×
3mm) Plastic DFN
0°C to 70°C
LTC2855IDE
LTC2855IDE#TR
2855
12-Lead (4mm
×
3mm) Plastic DFN
–40°C to 85°C
LTC2855HDE
LTC2855HDE#TR
2855
12-Lead (4mm
×
3mm) Plastic DFN
–40°C to 125°C
LTC2855CGN
LTC2855CGN#TR
2855
16-Lead (Narrow 0.150) Plastic SSOP
0°C to 70°C
LTC2855IGN
LTC2855IGN#TR
2855I
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 85°C
LTC2855HGN
LTC2855HGN#TR
2855H
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
285455fa
2
LTC2854/LTC2855
ELECTRICAL CHARACTERISTICS
SYMBOL
Driver
|V
OD
|
Differential Driver Output Voltage
R =
∞,
V
CC
= 3V (Figure 1)
R = 27Ω, V
CC
= 3V (Figure 1)
R = 50Ω, V
CC
= 3.13V (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
●
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
CC
= 3.3V unless otherwise noted (Note 2).
PARAMETER
CONDITIONS
MIN
TYP
MAX
V
CC
V
CC
V
CC
0.2
UNITS
V
V
V
V
1.5
2
Δ|V
OD
|
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
Driver Three-State (High Impedance)
Output Current on Y and Z
Maximum Driver Short-Circuit Current
V
OC
Δ|V
OC
|
R = 27Ω or R = 50Ω (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
●
●
3
0.2
V
V
I
OZD
I
OSD
Receiver
I
IN
DE = OV, (Y or Z) = –7V, 12V (LTC2855)
–7V ≤ (Y or Z) ≤ 12V (Figure 2)
●
±10
180
±250
300
125
–100
250
–145
96
125
μA
mA
mA
μA
μA
μA
μA
kΩ
●
–250
Receiver Input Current (A, B)
DE = TE = 0V, V
CC
= 0V or 3.3V, V
IN
= 12V
(Figure 3) (C, I-Grade)
DE = TE = 0V, V
CC
= 0V or 3.3V, V
IN
= –7V,
(Figure 3) (C, I-Grade)
DE = TE = 0V, V
CC
= 0V or 3.3V, V
IN
= 12V
(Figure 3) (H-Grade)
DE = TE = 0V, V
CC
= 0V or 3.3V, V
IN
= –7V,
(Figure 3) (H-Grade)
⎯ ⎯
RE = V
CC
or 0V, DE = TE = 0V,
V
IN
= –7V, –3V, 3V, 7V, 12V (Figure 3)
(C, I-Grade)
⎯ ⎯
RE = V
CC
or 0V, DE = TE = 0V,
V
IN
= –7V, –3V, 3V, 7V, 12V (Figure 3)
(H-Grade)
–7V ≤ B ≤ 12V
B = 0V
I(RO) = –4mA, A-B = 200mV, V
CC
= 3V
I(RO) = 4mA, A-B = –200mV, V
CC
= 3V
⎯
R
⎯
E = V
CC
, 0V ≤ RO ≤ V
CC
0V ≤ RO ≤ V
CC
TE = V
CC
, V
AB
= 2V, V
B
= –7V, 0V, 10V
(Figure 8)
V
CC
= 3.6V
V
CC
= 3V
●
●
●
●
●
R
IN
Receiver Input Resistance
●
48
125
kΩ
V
TH
ΔV
TH
V
OH
V
OL
I
OZR
I
OSR
R
TERM
Logic
V
IH
V
IL
I
INL
Supplies
I
CCS
Receiver Differential Input Threshold
Voltage
Receiver Input Hysteresis
Receiver Output HIGH Voltage
Receiver Output LOW Voltage
Receiver Three-State (High Impedance)
Output Current on RO
Receiver Short-Circuit Current
Receiver Input Terminating Resistor
●
±0.2
25
V
mV
V
●
●
●
●
●
2.4
0.4
±1
±85
108
120
156
V
μA
mA
Ω
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
Supply Current in Shutdown Mode
●
●
●
2
0.8
0
±10
V
V
μA
I
CCR
Supply Current in Receive Mode
DE = 0V,
⎯
R
⎯
E = V
CC
, TE = 0V
(LTC2854C/LTC2854I, LTC2855C/LTC2855I)
(LTC2854H, LTC2855H)
⎯ ⎯
DE = 0V, RE = 0V, TE = 0V
●
●
●
0
0
370
5
15
900
μA
μA
μA
285455fa
3
LTC2854/LTC2855
ELECTRICAL CHARACTERISTICS
SYMBOL
I
CCT
I
CCTR
I
CCTERM
I
CCTERMR
I
CCTERMT
I
CCTERMTR
ESD Protection
ESD Protection for RS485/RS422 Pins
A, B on LTC2854, Human Body Model
Y, Z, A, B on LTC2855, Human Body Model
±25
±15
kV
kV
PARAMETER
Supply Current in Transmit Mode
Supply Current with Both Driver and
Receiver Enabled
Supply Current in Termination Mode
Supply Current in Receive and
Termination Mode
Supply Current in Transmit and
Termination Mode
Supply Current with Driver, Receiver
and Termination Enabled
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
CC
= 3.3V, T
E
= 0V unless otherwise noted (Note 2).
CONDITIONS
No Load, DE = V
CC
,
⎯
R
⎯
E = V
CC
, TE = 0V
⎯ ⎯
No Load, DE = V
CC
, RE = 0V, TE = 0V
DE = 0V,
⎯
R
⎯
E = V
CC
, TE = V
CC
⎯ ⎯
DE = 0V, RE = 0V, TE = V
CC
DE = V
CC
,
⎯
R
⎯
E = V
CC
, TE = V
CC
DE = V
CC
,
⎯
R
⎯
E = 0V, TE = V
CC
●
●
●
●
●
●
MIN
TYP
450
450
110
450
470
470
MAX
1000
1000
180
950
1000
1000
UNITS
μA
μA
μA
μA
μA
μA
SWITCHING CHARACTERISTICS
SYMBOL
Driver
f
MAX
t
PLHD
, t
PHLD
Δt
PD
t
SKEWD
t
RD
, t
FD
t
ZLD
, t
ZHD
, t
LZD
,
t
HZD
t
ZHSD
, t
ZLSD
t
SHDN
Receiver
t
PLHR
, t
PHLR
t
SKEWR
t
RR
, t
FR
t
ZLR
, t
ZHR
, t
LZR
,
t
HZR
t
ZHSR
, t
ZLSR
t
RTEN
, t
RTZ
Receiver Input to Output
Differential Receiver Skew
|t
PLHR
-t
PHLR
|
Receiver Output Rise or Fall Time
Receiver Enable/Disable
Receiver Enable from Shutdown
Termination Enable or Disable Time
Maximum Data Rate
Driver Input to Output
Driver Input to Output Difference
|t
PLHD
-t
PHLD
|
Driver Output Y to Output Z
Driver Rise or Fall Time
Driver Enable or Disable Time
Driver Enable from Shutdown
Time to Shutdown
PARAMETER
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
CC
= 3.3V, T
E
= 0V unless otherwise noted (Note 2).
CONDITIONS
Note 3
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
⎯ ⎯
R
L
= 500Ω, C
L
= 50pF, RE = 0 (Figure 5)
R
L
= 500Ω, C
L
= 50pF,
⎯
R
⎯
E = V
CC
(Figure 5)
(DE =
↓, ⎯
R
⎯
E = V
CC
) or (DE = 0,
⎯
R
⎯
E
↑)
(Figure 5)
C
L
= 15pF, V
CM
= 1.5V, |V
AB
| = 1.5V, t
R
and
t
F
< 4ns (Figure 6)
C
L
= 15pF (Figure 6)
C
L
= 15pF (Figure 6)
R
L
= 1k, C
L
=15pF, DE = V
CC
(Figure 7)
R
L
= 1k, C
L
= 15pF, DE = 0V (Figure 7)
⎯ ⎯
V
B
= 0V, V
AB
= 2V, RE = V
CC
, DE = 0V
(Figure 8)
●
●
●
●
●
●
●
●
MIN
20
TYP
MAX
UNITS
Mbps
10
1
1
4
50
6
±6
12.5
70
8
100
ns
ns
ns
ns
ns
μs
ns
●
●
●
●
●
●
50
1
3
70
6
12.5
50
8
100
ns
ns
ns
ns
μs
μs
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
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:
Maximum data rate is guaranteed by other measured parameters
and is not tested directly.
Note 4:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions.
Overtemperature protection activates at a junction temperature exceeding
150°C. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
285455fa
4
LTC2854/LTC2855
TEST CIRCUITS
Y
GND
DI
OR
V
CC
DRIVER
Z
+
V
OD
–
R
Y
GND
OR
DI
V
CC
I
OSD
DRIVER
Z
R
+
V
OC
–
+
–
285455 F01-2
–7V to +12V
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
I
IN
A OR B
RECEIVER
B OR A
285455 F03
V
IN
+
–
V
R
IN
=
IN
I
IN
Figure 3. Receiver Input Current and Input Resistance
V
CC
Y
DI
C
L
DRIVER
R
DIFF
C
L
Z
285455 F04a
DI
0V
t
PLHD
t
SKEWD
t
PHLD
Y, Z
V
O
1/2 V
O
90%
Y-Z
10%
0
t
RD
0
90%
10%
t
FD
285455 F04b
Figure 4. Driver Timing Measurement
V
CC
Y
V
CC
OR
GND
DI
C
L
DRIVER
R
L
DE
Z
C
L
V
CC
OR
GND
285455 F05a
R
L
GND
OR
V
CC
DE
0V
V
CC
Y OR Z
V
OL
V
OH
Z OR Y
0V
V
O
1/2 V
CC
t
ZLD,
t
ZLSD
1/2 V
CC
t
LZD
0.5V
0.5V
t
HZD,
t
SHDN
285455 F05b
1/2 V
CC
t
ZHD,
t
ZHSD
Figure 5. Driver Enable and Disable Timing Measurements
C++ 属于面向对象的编程语言，OOP的思想不必多说，特别对于复杂的软件工程来说，利用OOP绝对是事半功倍，相对于传统的C来说； 当然用C来写单片机程序无可厚非，已经延续了一个传统，从大学时学的开始到工作岗位，好多人都是一直用C来做，但是既然Keil支持C++编译， 可以用C++来编写你的代码，可以利用高级语言来结构化，清晰化你的程序，为嘛不用呢！哈哈，个人看法！下面进入正题： C+...[详细]
FPGA/CPLD
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