DS276S Maxim Integrated Products, DS276S Datasheet - Page 3

• 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

DS276
feet. As a prime example, the DS276 will not meet the RS-232 requirement that the signal levels be at
least 5 volts minimum when terminated by a 3 k =load and V
= +3-5 volts. Typically 2.5 to 4 volts
DRV+
will be present at TX
when spacing under this condition, depending on the supply voltage. However,
OUT
since most RS-232 receivers will correctly interpret any voltage over 2 volts as a space, there will be no
problem transmitting data.
DS276 BLOCK DIAGRAM Figure 1
APPLICATIONS INFORMATION
The DS276 is designed as a low-cost, RS-232-E interface expressly tailored for the unique requirements
of battery-operated handheld products. As shown in the electrical specifications, the DS276 draws
exceptionally low operating and static current. During normal operation when data from the handheld
system is sent from the TX
output, the DS276 only draws significant V
current when TX
OUT
DRV+
OUT
transitions positively (spacing). This current flows primarily into the RS-232 receiver’s 3-7 k =load at
the other end of the attaching cable. When TX
is marking (a negative data signal), the V
current
OUT
DRV+
falls dramatically since the negative voltage is provided by the transmit signal from the other end of the
cable. This represents a large reduction in overall operating current, since typical RS-232 interface chips
use charge-pump circuits to establish both positive and negative levels at the transmit driver output. To
obtain the lowest power consumption from the DS276, observe the following guidelines: First, to
minimize V
current when connected to an RS-232 port, always maintain TX
at a logic 1 when data
DRV+
IN
is not being transmitted (idle state). This will force TX
into the marking state, minimizing V
OUT
DRV+
current. Second, V
current will drop significantly when V
is grounded. Therefore, if V
is
DRV+
CC
DRV+
derived independently from V
(for example connected to a 9V battery), the logic supply voltage can be
CC
turned off to achieve the lowest possible power state.
FULL-DUPLEX OPERATION
The DS276 is intended for full-duplex operation using the full-duplex circuit shown in Figure 4 to
generate a negative rail from RX
. The 22 F capacitor forms a negative-charge reservoir; consequently,
IN
when the TXD line RX
is spacing (positive), TX
still has a negative source available for a time
IN
OUT
period determined by the capacitor and the load resistance at the other end (3-7 k ).
SUPPLY VOLTAGE OPTIONS
The DS276 is intended primarily for use in single supply 3- or 5- volts systems. However, several supply
configurations are possible.
3V OPERATION
The simplest configuration is to use a single 3V supply for V
and V
, and connect V
to ground.
CC
drv+
drv-
This will result in the lowest power consumption and will give adequate serial communication between
3 of 11