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PDF LT1331 Data sheet ( Hoja de datos )
| Número de pieza | LT1331 | |
| Descripción | 3V RS562 or 5V/3V RS232 Transceiver with One Receiver Active in Shutdown | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1331
3V RS562 or 5V/3V RS232
Transceiver with One Receiver
Active in Shutdown
FEATURES
s RS232 Compatible 3V Operation
s 3V Logic Interface
s ESD Protection Over ±10kV
s 120kbaud Operation for RL = 3k, CL = 2500pF
s 250kbaud Operation for RL = 3k, CL = 1000pF
s One Low Power Receiver Remains Active While
in Shutdown
s 60µA Supply Current in Shutdown
s Low Power Driver Disable Mode
s Uses Small Capacitors: 0.1µF, 0.2µF
s CMOS Comparable Low Power: 60mW
s Easy PC Layout: Flowthrough Architecture
s Rugged Bipolar Design
s Outputs Assume a High Impedance State When
Off or Powered Down
APPLICATI S
s Notebook Computers
s Palmtop Computers
DESCRIPTIO
The LT®1331 is a 3-driver, 5-receiver RS232 transceiver
designed for 3V and mixed 3V/5V systems. Receivers
operate from 3V logic supply VL, while the onboard charge
pump and drivers operate from 5V or 3V supply VCC.
The transceiver has two shutdown modes. One mode
disables the drivers and the charge pump, the other shuts
down all circuitry except for one low power receiver which
can be used for ring detection. The VCC supply may be shut
down while in ring detection mode. While shut down, the
drivers and receivers assume high impedance output
states.
The LT1331 is fully compliant with all EIA-RS232 specifi-
cations when VCC = 5V. If VCC = 3V, output drive levels are
compatible with all known interface circuits. Special bipo-
lar construction techniques protect the drivers and receiv-
ers beyond the fault conditions stipulated for RS232. The
RS232 I/O pins are resilient to multiple ±10kV ESD strikes.
An advanced driver output stage operates up to 120kbaud
while driving heavy capacitive loads.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
3.3V Operation
+
0.1µF
+
2 × 0.1µF
V+
VCC = 3.3V
1
2
3
4
TO LINE
DRIVER 1 OUT
RX1 IN
DRIVER 2 OUT
RX2 IN
RX3 IN
RX4 IN
DRIVER 3 OUT
RX5 IN (LOW-Q)
ON/OFF
3.3V VL
5
6
7
8
9
10
11
12
13
14
LT1331
28 V –
27 0.1µF
26 2 × 0.1µF
25 DRIVER 1 IN
24 RX1 OUT
23 DRIVER 2 IN
22 RX2 OUT
21
RX3 OUT
20 RX4 OUT
19 DRIVER 3 IN
18 RX5 OUT (LOW-Q)
17
GND
16
DRIVER DISABLE
15
NC
TO LOGIC
RING DETECT IN
µCONTROLLER
OR
µPROCESSOR
SHUTDOWN
CONTROL OUT
1331 TA01
RECEIVER
OUTPUT
CL = 50pF
R
DRIVER
OUTPUT
RL = 3k
CL = 2500pF
INPUT
1331 TA02
1
1 page  
LT1331
PI FU CTIO S
V+ (Pin 1): Positive Supply Output. V+ ≅ 2VCC – 1.5V. This
pin requires an external capacitor for charge storage,
chosen to minimize ripple to acceptable levels. A mini-
mum size of 0.1µF is recommended.
VCC (Pin 2): Power Supply for Charge Pump and Drivers.
Proper circuit operation is insured for VCC = 3V to 6V.
VCC = 5V operation gives full RS232 compliant perfor-
mance, 3V operation results in lower driver output ampli-
tude. The VCC pin should be decoupled with a 0.1µF
ceramic capacitor.
C1+, C1–, C2+, C2– (Pins 3, 4, 26, 27): 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 tantalum capacitors work well
in this application, small value ceramic capacitors may
also be used with minimal reduction in charge pump
compliance.
DRIVER OUT (Pins 5, 7, 11): RS232 Driver Outputs.
Outputs are in a high impedance state when in shutdown,
driver disable, or VCC = 0V. Outputs are fully short-circuit
protected from V – + 30V to V + – 30V. Although the
outputs are protected, 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 ±10kV for human body model
discharges. Output levels of – 3.3V to 4V are achieved
when the circuit is operated with VCC = 3.3V.
RX IN (Pins 6, 8, 9, 10): Receiver Inputs with 0.4V of
Hysteresis for Noise Immunity. These pins accept RS232
level signals (±30V) into a protected 5k terminating
resistor. The receiver inputs are protected against ESD to
±10kV for human body model discharges.
LOW-Q RX IN (Pin 12): Low Power Receiver Input. This
receiver remains active in shutdown mode, consuming
only 60µA from supply VL. This receiver has the same
input and protection characteristics as receivers RX1
through RX4.
ON/OFF (Pin 13): A TTL/CMOS Compatible Operating
Mode Control. A logic low puts the device in the shutdown
mode. All drivers and four of the receivers go to a high
impedance state, and the VCC supply may be turned off. A
logic high fully enables the transceiver.
VL (Pin 14): Power Supply for Receivers. This pin should
be powered to the same voltage as the logic circuits
connected to the receiver outputs, either 5V or 3V. The VL
pin should be decoupled with a 0.1µF ceramic capacitor.
DRIVER DISABLE (Pin 16): A logic high shuts down the
charge pump, placing all drivers in a high impedance state.
All receivers remain active. Floating the pin, or driving it
to a logic low, fully enables the transceiver. A low voltage
on the ON/OFF pin supersedes the state of the driver
disable control.
GND (Pin 17): Ground.
LOW-Q RX OUT (Pin 18): Low Power Receiver Output.
This pin produces the same output levels as standard
receivers, with slightly decreased speed and short-circuit
current.
DRIVER IN (Pins 19, 23, 25): RS232 Driver Inputs.
Inputs are TTL/CMOS compatible. Tie unused inputs
to VCC.
RX OUT (Pins 20, 21, 22, 24): Receiver Outputs. RX1
through RX4 outputs are in a high impedance state when
in shutdown mode to allow data line sharing. Outputs,
including LOW-Q RX OUT, are fully short-circuit pro-
tected to ground, VCC, or VL. Output voltage levels are
determined by the choice of power supply VL.
V – (Pin 28): Negative Supply Output. V – ≅ – (2VCC –
2.5V). This pin requires an external charge storage
capacitor, chosen to minimize ripple on V –. A minimum
value of 0.1µF is recommended.
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1331.PDF ] | |
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