DS275N+

DS275N+ FEATURES

(cid:1) Low-power serial transmitter/receiver forbattery-backed systems(cid:1) Transmitter steals power from receive signalline to save power(cid:1) Ultra-low static current, even when connectedto RS-232-E port(cid:1) Variable transmitter level from +5 to +12volts(cid:1) Compatible with RS-232-E signals(cid:1) Available in 8-pin, 150 mil wide SOICpackage (DS275S)(cid:1) Low-power CMOS

DS275N+ PIN DESCRIPTION

RXOUTVDRVTXINGNDTXOUTNCRXINVCC- RS-232 Receiver Output- Transmit driver +V- RS-232 Driver Input- System Ground (0V)- RS-232 Driver Output- No Connection- RS-232 Receive Input-System Logic Supply (+5V)

DS275N+ APPLICATIONS INFORMATION

The DS275 is designed as a low-cost, RS-232-E interface expressly tailored for the unique requirementsof battery-operated handheld products. As shown in the electrical specifications, the DS275 drawsexceptionally low operating and static current. During normal operation when data from the handheldsystem is sent from the TXOUT output, the DS275 only draws significant VDRV current when TXOUTtransitions positively (spacing). This current flows primarily into the RS-232 receiver’s 3-7 kΩΩΩΩ====load at theother end of the attaching cable. When TXOUT is marking (a negative data signal), the VDRV current fallsdramatically 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 usecharge-pump circuits to establish both positive and negative levels at the transmit driver output.To obtain the lowest power consumption from the DS275, observe the following guidelines. First, tominimize VDRV current when connected to an RS-232 port, always maintain TXIN at a logic 1 when data isnot being transmitted (idle state). This will force TXOUT into the marking state, minimizing VDRV current.Second, VDRV current will drop to less than 100 nA when VCC is grounded. Therefore, if VDRV is tieddirectly to the system battery, the logic +5 volts can be turned off to achieve the lowest possible powerstate.