Datasheet

Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3221/MAX3223/MAX3243’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), regardless of the input
voltage (V
CC
) over the +3.0V to +5.5V range. The charge
pumps operate in a discontinuous mode: if the output
voltages are less than 5.5V, the charge pumps are
enabled; if the output voltages exceed 5.5V, the charge
pumps are disabled. Each charge pump requires a flying
capacitor (C1, C2) and a reservoir capacitor (C3, C4) to
generate the V+ and V- supplies.
RS-232 Transmitters
The transmitters are inverting level translators that
convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
They guarantee a 120kbps data rate with worst-case
loads of 3kΩ in parallel with 1000pF, providing compatibility with
PC-to-PC communication software (such as Laplink™).
Typically, the MAX3221/MAX3223/MAX3243 can operate
at data rates of 235kbps. Transmitters can be paralleled
to drive multiple receivers or mice (MAX3243). Figure 1
shows a complete system connection.
When FORCEOFF is driven to ground, or the auto-shut-
down circuitry senses invalid voltage levels at all receiver
inputs, the transmitters are disabled and the outputs are
forced into a high-impedance state.
LapLink is a trademark of Traveling Software.
PIN
NAME FUNCTION
MAX3221 MAX3223 MAX3243
1 1 — EN
Receiver Enable Control. Drive low for normal operation. Drive high to
force the receiver outputs into a high-Z state.
5 5 1 C2+ Positive terminal of inverting charge-pump capacitor
6 6 2 C2- Negative terminal of inverting charge-pump capacitor
7 7 3 V- -5.5V generated by the charge pump
8 9, 16 4–8 R_IN RS-232 Receiver Inputs
13 8, 17 9, 10, 11 T_OUT RS-232 Transmitter Outputs
11 12, 13 12, 13, 14 T_IN TTL/CMOS Transmitter Inputs
9 10, 15 15–19 R_OUT TTL/CMOS Receiver Outputs
— — 20 R2OUTB Noninverting Receiver Output—active in shutdown
10 11 21 INVALID
Output of the valid signal detector. Indicates if a valid RS-232 level is
present on receiver inputs logic “1”.
16 20 22 FORCEOFF
Drive low to shut down transmitters and on-board power supply.
This overrides all automatic circuitry and FORCEON (Table 1).
12 14 23 FORCEON
Drive high to override automatic circuitry keeping transmitters on
(FORCEOFF must be high) (Table 1).
4 4 24 C1- Negative terminal of the voltage doubler charge-pump capacitor
14 18 25 GND Ground
15 19 26 V
CC
+3.0V to +5.5V Supply Voltage
3 3 27 V+ +5.5V generated by the charge pump
2 2 28 C1+ Positive terminal of the voltage doubler charge-pump capacitor
Pin Description
MAX3221/MAX3223/
MAX3243
+3V to +5.5V RS-232
Transceivers with AutoShutdown
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