Figure 3. Transition Slew-Rate Circuit
_______________Detailed Description
The MAX202E–MAX213E, MAX232E/MAX241E consist of
three sections: charge-pump voltage converters,
drivers (transmitters), and receivers. These E versions
provide extra protection against ESD. They survive
±15kV discharges to the RS-232 inputs and outputs,
tested using the Human Body Model. When tested
according to IEC1000-4-2, they survive ±8kV contact-
discharges and ±15kV air-gap discharges. The rugged
E versions are intended for use in harsh environments
or applications where the RS-232 connection is
frequently changed (such as notebook computers). The
standard (non-“E”) MAX202, MAX203, MAX205–
MAX208, MAX211, MAX213, MAX232, and MAX241 are
recommended for applications where cost is critical.
+5V to ±10V Dual Charge-Pump
Voltage Converter
The +5V to ±10V conversion is performed by dual
charge-pump voltage converters (Figure 4). The first
charge-pump converter uses capacitor C1 to double
the +5V into +10V, storing the +10V on the output filter
capacitor, C3. The second uses C2 to invert the +10V
into -10V, storing the -10V on the V- output filter
capacitor, C4.
In shutdown mode, V+ is internally connected to V
CC
by
a 1kΩ pull-down resistor, and V- is internally connected
to ground by a 1kΩ pull up resistor.
RS-232 Drivers
With V
CC
= 5V, the typical driver output voltage swing
is ±8V when loaded with a nominal 5kΩ RS-232
receiver. The output swing is guaranteed to meet
EIA/TIA-232E and V.28 specifications that call for ±5V
minimum output levels under worst-case conditions.
These include a 3kΩ load, minimum V
CC
, and
maximum operating temperature. The open-circuit
output voltage swings from (V+ - 0.6V) to V-.
Input thresholds are CMOS/TTL compatible. The
unused drivers’ inputs on the MAX205E–MAX208E,
MAX211E, MAX213E, and MAX241E can be left
unconnected because 400kΩ pull up resistors to V
CC
are included on-chip. Since all drivers invert, the pull up
resistors force the unused drivers’ outputs low. The
MAX202E, MAX203E, and MAX232E do not have pull
up resistors on the transmitter inputs.
