MAX220–MAX249
+5V-Powered, Multichannel RS-232
Drivers/Receivers
mode, in three-state mode, or when device power is
_______________Detailed Description
removed. Outputs can be driven to ±±5V. The power-
supply current typically drops to 8µA in shutdown mode.
The MAX220 does not have pullup resistors to force the
outputs of the unused drivers low. Connect unused
The MAX220–MAX249 contain four sections: dual
charge-pump DC-DC voltage converters, RS-232 dri-
vers, RS-232 receivers, and receiver and transmitter
enable control inputs.
inputs to GND or V
.
CC
Dual Charge-Pump Voltage Converter
The MAX220–MAX249 have two internal charge-pumps
that convert +5V to ±±0V (unloaded) for RS-232 driver
operation. The first converter uses capacitor C± to dou-
ble the +5V input to +±0V on C3 at the V+ output. The
second converter uses capacitor C2 to invert +±0V to
-±0V on C4 at the V- output.
The MAX239 has a receiver three-state control line, and
the MAX223, MAX225, MAX235, MAX236, MAX240,
and MAX24± have both a receiver three-state control
line and a low-power shutdown control. Table 2 shows
the effects of the shutdown control and receiver three-
state control on the receiver outputs.
The receiver TTL/CMOS outputs are in a high-imped-
ance, three-state mode whenever the three-state enable
line is high (for the MAX225/MAX235/MAX236/MAX239–
MAX24±), and are also high-impedance whenever the
shutdown control line is high.
A small amount of power may be drawn from the +±0V
(V+) and -±0V (V-) outputs to power external circuitry
(see the Typical Operating Characteristics section),
except on the MAX225 and MAX245–MAX247, where
these pins are not available. V+ and V- are not regulated,
so the output voltage drops with increasing load current.
Do not load V+ and V- to a point that violates the mini-
mum ±5V EIA/TIA-232E driver output voltage when
sourcing current from V+ and V- to external circuitry.
When in low-power shutdown mode, the driver outputs
are turned off and their leakage current is less than ±µA
with the driver output pulled to ground. The driver output
leakage remains less than ±µA, even if the transmitter
output is backdriven between 0V and (V
+ 6V). Below
CC
When using the shutdown feature in the MAX222,
MAX225, MAX230, MAX235, MAX236, MAX240,
MAX24±, and MAX245–MAX249, avoid using V+ and V-
to power external circuitry. When these parts are shut
down, V- falls to 0V, and V+ falls to +5V. ꢁor applica-
tions where a +±0V external supply is applied to the V+
pin (instead of using the internal charge pump to gen-
erate +±0V), the C± capacitor must not be installed and
-0.5V, the transmitter is diode clamped to ground with
±kΩ series impedance. The transmitter is also zener
clamped to approximately V
impedance of ±kΩ.
+ 6V, with a series
CC
The driver output slew rate is limited to less than 30V/µs
as required by the EIA/TIA-232E and V.28 specifica-
tions. Typical slew rates are 24V/µs unloaded and
±0V/µs loaded with 3Ω and 2500pꢁ.
the SHDN pin must be connected to V . This is
CC
because V+ is internally connected to V
mode.
in shutdown
CC
RS-232 Receivers
EIA/TIA-232E and V.28 specifications define a voltage
level greater than 3V as a logic 0, so all receivers invert.
Input thresholds are set at 0.8V and 2.4V, so receivers
respond to TTL level inputs as well as EIA/TIA-232E and
V.28 levels.
RS-232 Drivers
The typical driver output voltage swing is ±8V when
loaded with a nominal 5kΩ RS-232 receiver and V
=
CC
+5V. Output swing is guaranteed to meet the EIA/TIA-
232E and V.28 specification, which calls for ±5V mini-
mum driver output levels under worst-case conditions.
The receiver inputs withstand an input overvoltage up
to ±25V and provide input terminating resistors with
These include a minimum 3kΩ load, V
= +4.5V, and
CC
maximum operating temperature. Unloaded driver out-
Table 2. Three-State Control of Receivers
put voltage ranges from (V+ -±.3V) to (V- +0.5V).
PART
SHDN
EN
EN(R)
RECEIVERS
SHDN
Input thresholds are both TTL and CMOS compatible.
The inputs of unused drivers can be left unconnected
Low
High Low
High High
X
High Impedance
Active
High Impedance
MAX223
__
__
since 400kΩ input pullup resistors to V
are built in
CC
(except for the MAX220). The pullup resistors force the
outputs of unused drivers low because all drivers invert.
The internal input pullup resistors typically source ±2µA,
except in shutdown mode where the pullups are dis-
abled. Driver outputs turn off and enter a high-imped-
ance state—where leakage current is typically
microamperes (maximum 25µA)—when in shutdown
Low
High
High Impedance
Active
MAX225
__
__
__
__
__
MAX235 Low
MAX236 Low
MAX240 High
Low
High
X
High Impedance
Active
High Impedance
14
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