1µA Supply Current, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
Pin Description
PIN
MAX3224
MAX3225
1
2
3
4
5
6
7
8, 17
9, 16
10, 15
11
12, 13
14
18
19
20
—
MAX3226
MAX3227
1
2
3
4
5
6
7
13
8
9
10
11
12
14
15
16
—
MAX3244
MAX3245
—
28
27
24
1
2
3
9–11
4–8
15–19
21
12–14
23
25
26
22
20
NAME
FUNCTION
MAX3224–MAX3227/MAX3244/MAX3245
READY
C1+
V+
C1-
C2+
C2-
V-
T_OUT
R_IN
R_OUT
INVALID
T_IN
FORCEON
GND
V
CC
FORCEOFF
R2OUTB
Ready to Transmit Output, active high. READY is enabled high when
V- goes below -4V and the device is ready to transmit.
Positive Terminal of Voltage-Doubler Charge-Pump Capacitor
+5.5V generated by the charge pump
Negative Terminal of Voltage-Doubler Charge-Pump Capacitor
Positive Terminal of Inverting Charge-Pump Capacitor
Negative Terminal of Inverting Charge-Pump Capacitor
-5.5V generated by the charge pump
RS-232 Transmitter Outputs
RS-232 Receiver Inputs
TTL/CMOS Receiver Outputs
Valid Signal Detector Output, active low. A logic high indicates that a valid
RS-232 level is present on a receiver input.
TTL/CMOS Transmitter Inputs
Force-On Input, active high. Drive high to override AutoShutdown Plus,
keeping transmitters and receivers on (FORCEOFF must be high) (Table 1).
Ground
+3.0V to +5.5V Single Supply Voltage
Force-Off Input, active low. Drive low to shut down transmitters, receivers
(except R2OUTB), and charge pump. This overrides AutoShutdown Plus
and FORCEON (Table 1).
TTL/CMOS Noninverting Complementary Receiver Outputs. Always active.
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3224–MAX3227/MAX3244/MAX3245’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), over
the +3.0V to +5.5V range. The charge pump operates
in discontinuous mode: if the output voltages are less
than 5.5V, the charge pump is enabled; if the output
voltages exceed 5.5V, the charge-pump is disabled.
Each charge pump requires a flying capacitor (C1, C2)
and a reservoir capacitor (C3, C4) to generate the V+
and V- supplies.
The READY output (MAX3224–MAX3227) is low when
the charge pumps are disabled in shutdown mode. The
READY signal asserts high when V- goes below -4V.
RS-232 Transmitters
The transmitters are inverting level translators that
convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3224/MAX3226/MAX3244 guarantee a
250kbps data rate (1Mbps for the MAX3225/MAX3227/
MAX3245) with worst-case loads of 3kΩ in parallel with
1000pF, providing compatibility with PC-to-PC com-
munication software (such as LapLink™). Transmitters
can be paralleled to drive multiple receivers. Figure 1
shows a complete system connection.
LapLink is a trademark of Traveling Software.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
