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PDF LTC2846 Data sheet ( Hoja de datos )
| Número de pieza | LTC2846 | |
| Descripción | 3.3V Software-Selectable Multiprotocol Transceiver with Termination | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC2846
3.3V Software-Selectable
Multiprotocol Transceiver
with Termination
FEATURES
s Software-Selectable Transceiver Supports:
RS232, RS449, EIA530, EIA530-A, V.35, V.36, X.21
s Operates from Single 3.3V Supply
s TUV Rheinland of North America Inc. Certified NET1,
NET2 and TBR2 Compliant, Report No.:
TBR2/050101/02, TBR2/051501/02
s 1.2MHz Boost Switching Regulator for 3.3V to 5V
Conversion
s On-Chip Cable Termination
s Complete DTE or DCE Port with LTC2844 or LTC2845
s Small Footprint
s Available in 36-Lead SSOP (0.209 Wide) Package
U
APPLICATIO S
s Data Networking
s CSU and DSU
s Data Routers
DESCRIPTIO
The LTC®2846 is a 3-driver/3-receiver multiprotocol trans-
ceiver with on-chip cable termination. When combined with
the LTC2844 or LTC2845, this chip set forms a complete
software-selectable DTE or DCE interface port that supports
the RS232, RS449, EIA530, EIA530-A, V.35, V.36 and X.21
protocols. All necessary cable termination is provided inside
the LTC2846. The LTC2846 has a boost regulator that takes
in a 3.3V input and switches at 1.2MHz, allowing the use of
tiny, low cost capacitors and inductors 2mm or less in height.
The 5V output drives an internal charge pump that requires
only five space-saving surface mounted capacitors. The
LTC2846 is available in a 36-lead SSOP surface mount
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Complete DTE or DCE Multiprotocol Serial Interface with DB-25 Connector
LL CTS DSR
DCD DTR RTS
RXD RXC
TXC SCTE TXD
LTC2844
D4
R4 R3 R2 R1
D3 D2 D1
LTC2846
D3 D2 D1
R3 R2 R1
TT
TTT
18 13 5 22 6
10 8 23 20 19 4 1 7 16 3 9 17
12 15 11 24 14 2
DataSheet4 U .com
DB-25 CONNECTOR
2846 TA01
sn2846 2846fs
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LTC2846
ELECTRICAL CHARACTERISTICS The q denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VIN = 3.3V, VSHDN = VIN, unless otherwise noted. (Notes 2, 3)
SYMBOL PARAMETER
V.28 Receiver
VTHL Input Low Threshold Voltage
VTLH Input High Threshold Voltage
∆VTH
Receiver Input Hysteresis
RIN Receiver Input Impedance
tr, tf Rise or Fall Time
tPLH Input to Output
tPHL Input to Output
Boost Switching Regulator (Note 4)
VIN Operating Voltage
VFB Feedback Voltage
IFB FB Pin Bias Current
IQ Quiescent Current
Quiescent Current in Shutdown
∆VFB(LR)
f
Reference Line Regulation
Switching Frequency
DCMAX
ILIM
VSAT
ILEAK
Maximum Duty Cycle
Switch Current Limit
Switch VCESAT
Switch Leakage Current
CONDITIONS
(Figure 12)
(Figure 12)
(Figure 12)
– 15V ≤ VA ≤ 15V
CL = 50pF (Figures 12, 16)
CL = 50pF (Figures 12, 16)
CL = 50pF (Figures 12, 16)
VFB = 1.255V
VSHDN = 2.4V, Not Switching
VSHDN = 0V, VIN = 3V
3V ≤ VIN ≤ 3.6V
(Note 5)
ISW = 900mA
VSW = 5V
MIN TYP MAX
q
q2
q0
q3
q
q
0.8
0.05 0.3
57
15
60 300
160 300
3
q 1.230
q
q 0.85
q 82
1
3.3
1.255
120
4.2
0.01
0.01
1.2
90
1.2
350
0.01
3.6
1.280
360
6
1
0.05
1.6
2
1
UNITS
V
V
V
kΩ
ns
ns
ns
V
V
nA
mA
µA
%/V
MHz
%
A
mV
µA
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
are negative. All voltages are referenced to device ground unless otherwise
specified.
Note 3: All typicals are given for VCC = 5V, VIN = 3.3V, CVCC = CVIN = 10µF,
CVDD = 1µF, CVEE = 3.3µF and TA = 25°C.
Note 4: The Boost Regulator is specified for VIN = 3V unless otherwise
noted.
Note 5: Current limit guaranteed by design and/or correlation to static test.
TYPICAL PERFOR A CE CHARACTERISTICS
V.11 Mode ICC vs Data Rate
170
TA = 25°C
160
150
140
130
120
110
100
90
10
100 1000
DATA RATE (kBd)
10000
2846 G04
V.35 Mode ICC vs Data Rate
150
TA = 25°C
145
140
135
130
125
120
10
100 1000
DATA RATE (kBd)
10000
2846 G05
DataSheet4 U .com
V.28 Mode ICC vs Data Rate
60
TA = 25°C
55
50
45
40
35
30
10
20 40 60 80 100
DATA RATE (kBd)
2846 G06
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UW
W
SWITCHI G TI E WAVEFOR S
3V
D
0V
VO
A
–VO
1.5V
tPHL
3V
0V SR = 6V
–3V tf
tf
Figure 15. V.28 Driver Propagation Delays
LTC2846
1.5V
tPLH
0V
–3V
tr
3V
SR = 6V
tr
2846 F15
VIH
A
VIL
VOH
R
VOL
1.5V
tPHL
1.65V
1.5V
tPLH
1.65V
2846 F16
Figure 16. V.28 Receiver Propagation Delays
APPLICATIO S I FOR ATIO
Overview
The LTC2846 consists of a boost switching regulator, a
charge pump and a 3-driver/3-receiver transceiver. The
boost switching regulator generates a 5V VCC from the
3.3V input at VIN to power the charge pump and trans-
ceiver. The charge pump generates the VDD and VEE
supplies. The LTC2846’s VCC, VDD and VEE supplies can
be used to power a companion chip like the LTC2844 or
LTC2845. The receiver outputs are driven between 0V and
VIN to interface with 3.3V logic.
The LTC2846 and LTC2844 form a complete software-
selectable DTE or DCE interface port that supports the
RS232, RS449, EIA530, EIA530-A, V.35, V.36 and X.21
protocols. Cable termination is provided on-chip, elimi-
nating the need for discrete termination designs.
A complete DCE-to-DTE interface operating in EIA530
mode is shown in Figure 17. The LTC2846 half of each port
is used to generate and appropriately terminate the clock
and data signals. The LTC2844 is used to generate the
control signals along with LL (Local Loopback).
Mode Selection
The interface protocol is selected using the mode select
pins M0, M1 and M2 (see Table 1).
For example, if the port is configured as a V.35 interface,
the mode selection pins should be M2 = 1, M1 = 0, M0 =␣ 0.
For the control signals, the drivers and receivers will
operate in V.28 (RS232) electrical mode. For the clock and
data signals, the drivers and receivers will operate in V.35
electrical mode. The DCE/DTE pin will configure the port
for DCE mode when high, and DTE when low.
The interface protocol may be selected simply by plugging
the appropriate interface cable into the connector. The
mode pins are routed to the connector and are left uncon-
nected (1) or wired to ground (0) in the cable as shown in
Figure 18. The internal pull-up current sources will ensure
a binary 1 when a pin is left unconnected.
The mode selection may also be accomplished by using
jumpers to connect the mode pins to ground or VIN.
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| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC2846.PDF ] | |
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