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PDF LT1537CSW Data sheet ( Hoja de datos )
| Número de pieza | LT1537CSW | |
| Descripción | Advanced Low Power 5V RS232 Transceiver with Small Capacitors | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1537
Advanced Low Power
5V RS232 Transceiver with
Small Capacitors
FEATURES
s Low Cost
s Uses Small Capacitors: 0.1µF, 0.2µF
s 1µA Supply Current in Shutdown
s 120kBaud Operation for RL = 3k, CL = 2500pF
s 250kBaud Operation for RL = 3k, CL = 1000pF
s CMOS Comparable Low Power: 40mW
s Operates from a Single 5V Supply
s Easy PC Layout: Flow-through Architecture
s Rugged Bipolar Design
s Outputs Assume a High Impedance State When Off
or Powered Down
s Improved Protection: RS232 I/O Lines Can Be Forced
to ±25V Without Damage
s Output Overvoltage Does Not Force Current Back
into Supplies
s Absolutely No Latch-Up
s Available in SO Package
APPLICATI S
s Notebook Computers
s Palmtop Computers
DESCRIPTIO
The LT ®1537 is a three-driver, five-receiver RS232 trans-
ceiver, pin compatible with the LT1137A, offering perfor-
mance improvements and two shutdown modes. The
LT1537’s charge pump is designed for extended compli-
ance and can deliver over 35mA of load current. Supply
current is typically 8mA, competitive with similar CMOS
devices. An advanced driver output stage operates up to
250kbaud while driving heavy capacitive loads.
The LT1537 is fully compliant with all RS232 specifica-
tions. Special bipolar construction techniques protect the
drivers and receivers beyond the fault conditions stipu-
lated for RS232. Driver outputs and receiver inputs can be
shorted to ±25V without damaging the device or the
power supply generator. In addition, the RS232 I/O pins
are resilient to multiple ±5kV ESD strikes.
The transceiver has two shutdown modes. One mode
disables the drivers and the charge pump, the other shuts
down all circuitry. While shut down, the drivers and
receivers assume high impedance output states.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
+
0.1µF
+
2 × 0.1µF
V+
5V VCC
1
2
3
4
DRIVER OUT 5
RX IN 6
DRIVER OUT 7
TO
LINE
RX IN
RX IN
8
9
RX IN 10
DRIVER OUT 11
RX IN 12
13
ON/OFF = 5V
14
LT1537
28 V–
27 0.1µF
26 2 × 0.1µF
25
DRIVER IN
24
RX OUT
23 DRIVER IN
22
RX OUT
21
RX OUT
20 RX OUT
19
DRIVER IN
18 RX OUT
17 GND
TO LOGIC
16 DRIVER
15 DISABLE
LT1537 • TA01
RECEIVER
OUTPUT
CL = 50pF
R DRIVER
OUTPUT
RL = 3k
CL = 2500pF
INPUT
Output Waveforms
LT1537 • TA02
1
1 page  
LT1537
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown to Driver Output
Driver Output Waveforms
DRIVER
OUTPUT HIGH
RL = 3k
10
5
0
DRIVER – 5
OUTPUT LOW
RL = 3k – 10
ON/OFF PIN
DRIVER OUTPUT
RL = 3k
DRIVER OUTPUT
RL = 3k
CL = 2500pF
INPUT
LT1537 • TPC12
LT1537 • TPC13
PI FU CTIO S
VCC: 5V Input Supply Pin. Supply current drops to zero in
the shutdown mode. This pin should be decoupled with a
0.1µF ceramic capacitor close to the package pin. Insuffi-
cient supply bypassing can result in low output drive levels
and erratic charge pump operation.
GND: Ground Pin.
ON/OFF: TTL/CMOS Compatible Operating Mode Control.
A logic LOW puts the device in the shutdown mode which
reduces input supply current to zero and places all of the
drivers and receivers in high impedance state. A logic
HIGH fully enables the transceiver.
DRIVER DISABLE: This pin provides an alternate control
for the charge pump and RS232 drivers. A logic HIGH on
this pin shuts down the charge pump and places all drivers
in a high impedance state. Receivers remain active under
these conditions. Floating the driver disable pin or driving
it to a logic LOW level fully enables the transceiver. A logic
LOW on the On/Off pin supersedes the state of the Driver
Disable pin. Supply current drops to 1.5mA when in
DRIVER DISABLE mode.
V+: Positive Supply Output (RS232 Drivers). V+ ≈ 2VCC –
1.5V. This pin requires an external charge storage capaci-
tor C ≥ 0.1µF, tied to ground or VCC. Larger value capaci-
tors may be used to reduce supply ripple. With multiple
transceivers, the V + and V – pins may be paralleled into
common capacitors. For large numbers of transceivers,
increasing the size of the shared common storage capaci-
tors is recommended to reduce ripple.
V–: Negative Supply Output (RS232 Drivers). V – ≈
–(2VCC – 2.5V). This pin requires an external charge
storage capacitor C ≥ 0.1µF. V – is short-circuit proof for
30 seconds.
C1+, C1–, C2+, C2–: Commutating Capacitor Inputs. These
pins require two external capacitors C ≥ 0.2µF: one from
C1+ to C1– and another from C2+ to C2–. To maintain
charge pump efficiency, the capacitor’s effective series
resistance should be less than 2Ω. Low ESR ceramic
capacitors work well in this application.
DRIVER IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs to VCC.
DRIVER OUT: Driver Outputs at RS232 Voltage Levels.
Driver output swing meets RS232 levels for loads up to 3k.
Slew rates are controlled for lightly loaded lines. Output
current capability is sufficient for load conditions up to
2500pF. Outputs are in a high impedance state when in
shutdown mode, VCC = 0V or when the driver disable pin
is active. Outputs are fully short-circuit protected from V –
+ 25V to V+ – 25V. Applying higher voltages will not
damage the device if the overdrive is moderately current
limited. Short circuits on one output can load the power
supply generator and may disrupt the signal levels of the
other outputs. The driver outputs are protected against
ESD to ±5kV for human body model discharges.
5
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1537CSW.PDF ] | |
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