These devices are BiCMOS interface ICs that are user
configured as either a single RS-422/RS-485 differential
transceiver, or as a dual (2 Tx, 2 Rx) RS-232 transceiver.
In RS-232 mode, the on-board charge pump generates
RS-232 compliant ±5V Tx output levels, from a supply as low
as 3.15V. Four small 0.1µF capacitors are required for the
charge pump. The transceivers are RS-232 compliant, with
the Rx inputs handling up to ±25V.
In RS-485 mode, the transceivers support both the RS-485
and RS-422 differential communication standards. The
RS-485 receiver features "full failsafe" operation, so the Rx
output remains in a high state if the inputs are open or
shorted together. The RS-485 transmitter supports up to
three data rates, two of which are slew rate limited for
problem free communications. The charge pump disables in
RS-485 mode, thereby saving power, minimizing noise, and
eliminating the charge pump capacitors.
Both RS-232/RS-485 modes feature loopback and shutdown
functions. The loopback mode internally connects the Tx
outputs to the corresponding Rx input, which facilitates the
implementation of board level self test functions. The outputs
remain connected to the loads during loopback, where
connection problems (e.g., shorted connectors or cables)
can be detected. The shutdown mode disables the Tx and
Rx outputs, disables the charge pump if in RS-232 mode,
and places the IC in a low current (30µA) mode.
The ISL3331 is a QFN packaged device that offers
additional functionality, including a lower speed and edge
rate option (115kbps) for EMI sensitive designs, or to allow
longer bus lengths. It also features a logic supply voltage pin
(VL) that sets the VOH level of logic outputs, and the
switching points of logic inputs, to be compatible with
another supply voltage in mixed voltage systems. The QFN's
choice of active high or low Rx enable pins increases design
flexibility, allowing Tx/Rx direction control via a single signal
by connecting DEN and RXEN together.
For a dual port version of these devices, please see the
ISL3332/ISL3333 data sheet.

Features
• User Selectable RS-232 or RS-485/RS-422 Interface Port
(Two RS-232 Transceivers or One RS-485/RS-422
Transceiver)
• Operates From a Single 3.3V Supply
• ±15kV (HBM) ESD Protected Bus Pins (RS-232 or
RS-485)
• 5V Tolerant Logic Inputs
• True Flow-Through Pinouts Simplify Board Layouts
• Pb-Free (RoHS Compliant)
• Full Failsafe (Open/Short) Rx in RS-485/RS-422 Mode
• Loopback Mode Facilitates Board Self Test Functions
• User Selectable RS-485 Data Rates . . . . . . . . . . 20Mbps
- Slew Rate Limited. . . . . . . . . . . . . . . . . . . . . . . 460kbps
- Slew Rate Limited (ISL3331 Only) . . . . . . . . . . 115kbps
• Fast RS-232 Data Rate . . . . . . . . . . . . . . . Up to 400kbps
• Low Current Shutdown Mode. . . . . . . . . . . . . . . . . . 30µA
• QFN Package Saves Board Space (ISL3331 Only)
• Logic Supply Pin (VL) Eases Operation in Mixed Supply
Systems (ISL3331 Only)

Applications
• Gaming Applications (e.g., Slot machines)
• Single Board Computers
• Factory Automation
• Security Networks
• Industrial/Process Control Networks
• Level Translators (e.g., RS-232 to RS-422)
• Point of Sale Equipment