DS276S Maxim Integrated Products, DS276S Datasheet - Page 2

• Manufacturer Part Number: DS276S
• Description: IC TXRX LOW POWER RS-232 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Transceiverr

Specifications of DS276S

• Number Of Drivers/receivers: 1/1
• Protocol: RS232
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

OPERATION
Designed for the unique requirements of battery-backed systems, the DS276 provides a low-power full-or
half-duplex interface to an RS-232 serial port. Typically, a designer must use an RS-232 device which
uses system power during both negative and positive transitions of the transmit signal to the RS-232 port.
If the connector to the RS-232 port is left connected for an appreciable time after the communication
session has ended, power will statically flow into that port, draining the battery capacity. The DS276
eliminates this static current drain by stealing current from the receive line (RX
when that line is at a negative level (marking). Since most asynchronous communication over an RS-232
connection typically remains in a marking state when data is not being sent, the DS276 will not consume
system power in this condition. Sys-tem power would only be used when positive-going transitions are
needed on the transmit RS-232 output (TX
communication sessions typically exhibit a very low duty-cycle, overall system power consumption
remains low.
RECEIVER SECTION
The RX
negative data signal is called a mark while a positive data signal is called a space. These signals are
inverted and then level-shifted to normal +3 or +5 volt CMOS/TTL logic levels. The logic output
associated with RX
logic 1 at RX
The input threshold of RX
noise rejection. Therefore, an input positive-going signal must exceed 1.8 volts to cause RX
states. A negative-going signal must now be lower than 1.3 volts (typically) to cause RX
again. An open on RX
TRANSMITTER SECTION
TX
mark (negative data signal) at TX
mentioned earlier, the transmitter section employs a unique driver design that can use the RX
swinging to negative levels. RX
to supply this voltage during marking (or idle) states. When TX
it uses the V
many situations it can be tied directly to the V
than or equal to V
The voltage range on V
when TX
happen in a battery-backed condition), only a small leakage current (about 50-100 nA) will be drawn. If
TX
During normal operation (V
course, when TX
upon its voltage and the impedance that TX
volts/us in accordance with RS-232 specifications. In the event TX
ground, internal current-limiting circuitry prevents damage, even if continuously shorted.
RS-232 COMPATIBILITY
The intent of the DS276 is not so much to meet all the requirements of the RS-232 specification as to
offer a low-power solution that will work with most RS-232 ports with a connector length of less than 10
IN
OUT
is the CMOS/TTL-compatible input for data from the user system. A logic 1 at TX
is loaded during such a condition, V
IN
OUT
pin is the receive input for an RS-232 signal whose levels can range from 3 to 15 volts. A
DRV+
OUT
is in a space state. When V
; a space produces a logic 0.
OUT
CC
power pin for this level. V
IN
at all times.
is RX
is spacing, V
IN
is interpreted as a mark, producing a logic 1 at RX
DRV+
IN
OUT
CC
permits the use of a 9V battery in order to provide a higher voltage level
is typically around 1.8 volts with 500 millivolts of hysteresis to improve
= 3 or 5 volts), V
which swings from V
IN
can be connected via external circuitry to V
DRV+
OUT
CC
will draw substantially more current about 3 mA, depending
while a logic 0 produces a space (positive data signal). As
OUT
is shut off to the DS276 and V
DRV+
DRV+
CC
sees. The TX
OUT
DRV+
supply. It is important to note that V
will draw current only if RX
2 of 11
can be a voltage supply between 3 to 12 volts, and in
) when data is sent. However, since synchronous
will draw less than 2 uA when TX
CC
to ground. Therefore, a mark on RX
OUT
OUT
output is slew rate-limited to less than 30
OUT
needs to transition to a positive level,
should be inadvertently shorted to
OUT
DRV+
IN
.
DRV-
is still powered (as might
is not in a negative state.
IN
to allow stored charge
) of the RS-232 port
DRV+
OUT
must be greater
is marking. Of
OUT
IN
IN
OUT
produces a
produces a
IN
to switch
to switch
line for
DS276