_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3233E/MAX3235E’s internal power supply
consists of a regulated dual charge pump that provides
output voltages of +5.5V (doubling charge pump) and
-5.5V (inverting charge pump), with no external capaci-
tors. The charge pump operates in discontinuous
mode: if the output voltages are less than 5.5V, the
charge pump is enabled; if the output voltages exceed
5.5V, the charge pump is disabled.
RS-232 Transmitters
The transmitters are inverting level translators that
convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The devices guarantee a 250kbps data rate with worst-
case loads of 3kΩ in parallel with 1000pF, providing
compatibility with PC-to-PC communication software
(such as LapLink™). Transmitters can be paralleled to
drive multiple receivers. Figure 1 shows a complete
system connection.
When FORCEOFF is driven to ground or when the Auto-
Shutdown Plus circuitry senses that all receiver and
transmitter inputs are inactive for more than 30sec, the
transmitters are disabled and the outputs go into a high-
impedance state. When powered off or shut down, the
outputs can be driven to ±12V. The transmitter inputs
do not have pull-up resistors. Connect unused inputs to
GND or V
CC
.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. They feature inverting outputs that always
remain active (Table 1).
The MAX3233E/MAX3235E feature an INVALID output
that is enabled low when no valid RS-232 voltage levels
have been detected on all receiver inputs. Because
INVALID indicates the receiver input’s condition, it is
independent of FORCEON and FORCEOFF states
(Figures 2 and 3).
AutoShutdown Plus Mode
The devices achieve a1µA supplycurrent with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFF is high and a FORCEON is low. When these
devices do not sense a valid signal transition on any
receiver or transmitter input for 30sec, the on-board
charge pumps are shut down, reducing supply current
to 1µA. This occurs if the RS-232 cable is disconnected,
or if the connected peripheral transmitters are turned off
and the UART driving the transmitter inputs is inactive.
The system turns on again when a valid transition is
MAX3233E/MAX3235E
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
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