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MAX222 Datasheet

  • MAX222

  • "+5V-Powered, Multichannel RS-232 Drivers/ Receivers"

  • 454.20KB

  • Maxim

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+5V-Powered, Multichannel RS-232
Drivers/Receivers
MAX220鈥揗AX249
_______________Detailed Description
The MAX220鈥揗AX249 contain four sections: dual
charge-pump DC-DC voltage converters, RS-232 dri-
vers, RS-232 receivers, and receiver and transmitter
enable control inputs.
mode, in three-state mode, or when device power is
removed. Outputs can be driven to 卤15V. The power-
supply current typically drops to 8碌A in shutdown mode.
The MAX220 does not have pull-up resistors to force the
ouputs of the unused drivers low. Connect unused inputs
to GND or V
CC
.
The MAX239 has a receiver three-state control line, and
the MAX223, MAX225, MAX235, MAX236, MAX240,
and MAX241 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鈥?/div>
MAX241), and are also high-impedance whenever the
shutdown control line is high.
When in low-power shutdown mode, the driver outputs
are turned off and their leakage current is less than 1碌A
with the driver output pulled to ground. The driver output
leakage remains less than 1碌A, even if the transmitter
output is backdriven between 0V and (V
CC
+ 6V). Below
-0.5V, the transmitter is diode clamped to ground with
1k鈩?series impedance. The transmitter is also zener
clamped to approximately V
CC
+ 6V, with a series
impedance of 1k鈩?
The driver output slew rate is limited to less than 30V/碌s
as required by the EIA/TIA-232E and V.28 specifica-
tions. Typical slew rates are 24V/碌s unloaded and
10V/碌s loaded with 3鈩?and 2500pF.
Dual Charge-Pump Voltage Converter
The MAX220鈥揗AX249 have two internal charge-pumps
that convert +5V to 卤10V (unloaded) for RS-232 driver
operation. The first converter uses capacitor C1 to dou-
ble the +5V input to +10V on C3 at the V+ output. The
second converter uses capacitor C2 to invert +10V to
-10V on C4 at the V- output.
A small amount of power may be drawn from the +10V
(V+) and -10V (V-) outputs to power external circuitry
(see the
Typical Operating Characteristics
section),
except on the MAX225 and MAX245鈥揗AX247, 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 卤5V EIA/TIA-232E driver output voltage when
sourcing current from V+ and V- to external circuitry.
When using the shutdown feature in the MAX222,
MAX225, MAX230, MAX235, MAX236, MAX240,
MAX241, and MAX245鈥揗AX249, avoid using V+ and V-
to power external circuitry. When these parts are shut
down, V- falls to 0V, and V+ falls to +5V. For applica-
tions where a +10V external supply is applied to the V+
pin (instead of using the internal charge pump to gen-
erate +10V), the C1 capacitor must not be installed and
the
SHDN
pin must be tied to V
CC
. This is because V+
is internally connected to V
CC
in shutdown mode.
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.
The receiver inputs withstand an input overvoltage up
to 卤25V and provide input terminating resistors with
RS-232 Drivers
The typical driver output voltage swing is 卤8V when
loaded with a nominal 5k鈩?RS-232 receiver and V
CC
=
+5V. Output swing is guaranteed to meet the EIA/TIA-
232E and V.28 specification, which calls for 卤5V mini-
mum driver output levels under worst-case conditions.
These include a minimum 3k鈩?load, V
CC
= +4.5V, and
maximum operating temperature. Unloaded driver out-
put voltage ranges from (V+ -1.3V) to (V- +0.5V).
Input thresholds are both TTL and CMOS compatible.
The inputs of unused drivers can be left unconnected
since 400k鈩?input pull-up resistors to V
CC
are built in
(except for the MAX220). The pull-up resistors force the
outputs of unused drivers low because all drivers invert.
The internal input pull-up resistors typically source 12碌A,
except in shutdown mode where the pull-ups are dis-
abled. Driver outputs turn off and enter a high-imped-
ance state鈥攚here leakage current is typically
microamperes (maximum 25碌A)鈥攚hen in shutdown
14
Table 2. Three-State Control of Receivers
PART
MAX223
SHDN
SHDN
__
Low
High
High
__
EN
X
Low
High
__
EN(R)
__
Low
High
Low
High
X
RECEIVERS
High Impedance
Active
High Impedance
High Impedance
Active
High Impedance
Active
High Impedance
MAX225
MAX235
MAX236
MAX240
__
Low
Low
High
__
__
______________________________________________________________________________________

MAX222 PDF文件相关型号

MAX223,MAX225,MAX230,MAX231,MAX232A,MAX233,MAX233A,MAX234,MAX235,MAX236,MAX237,MAX238,MAX239,MAX240,MAX242,MAX243,MAX244,MAX245,MAX246,MAX247,MAX248,MAX249

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