MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
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Detailed Description
Dual Charge-Pump
Voltage Converter
The MAX3388E/MAX3389E’s internal power supply
consists of a regulated dual charge pump that provides
output voltages of +4.2V (doubling charge pump) and -
4.2V (inverting charge pump), regardless of the input
voltage (V
CC
) over a +2.5V to +3.0V range. The charge
pumps operate in a discontinuous mode: if the output
voltages are less than 4.2V, the charge pumps are
enabled; if the output voltages exceed 4.2V, the charge
pumps are disabled. Each charge pump requires flying
capacitors (C1, C2) and reservoir capacitors (C3, C4)
to generate the V+ and V- supplies.
RS-232 Transmitters
The transmitters are inverting level translators that convert
CMOS-logic levels to ±3.7V EIA/TIA-232-compatible
levels.
The MAX3388E/MAX3389E’s transmitters guarantee a
250kbps data rate with loads of 3kΩ in parallel with
1000pF and 460kbps data rate with loads of 3kΩ in paral-
lel with 150pF. Figure 1 shows a complete system con-
nection.
These RS-232 output stages are turned off (high
impedance) when the devices are in shutdown mode.
When the power is off, the MAX3388E/MAX3389E permit
the outputs to be driven up to ±12V.
The transmitter inputs do not have pullup resistors.
Connect unused inputs to GND or V
L
.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3388E/MAX3389E’s receivers
have inverting outputs. The outputs are high imped-
ance in shutdown.
Shutdown Mode
Supply current falls to less than 1µA when the
MAX3388E/MAX3389E are placed in shutdown mode
(SHDN logic low). When shut down, the device’s charge
pumps are turned off, V+ decays to V
CC
, V- is pulled to
ground, the switch is opened, and the transmitter outputs
are disabled (high impedance). The time required to exit
