_______________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 3k

Ω 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.

1µA Supply Current, 1Mbps, 3.0V to 5.5V,

RS-232 Transceivers with AutoShutdown Plus

_______________________________________________________________________________________

7

PIN

NAME

MAX3224

MAX3225

MAX3226

MAX3227

MAX3244

MAX3245

1

1

—

READY

2

2

28

C1+

Positive Terminal of Voltage-Doubler Charge-Pump Capacitor

3

3

27

V+

+5.5V generated by the charge pump

4

4

24

C1-

Negative Terminal of Voltage-Doubler Charge-Pump Capacitor

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, 17

13

9–11

T_OUT

RS-232 Transmitter Outputs

9, 16

8

4–8

R_IN

RS-232 Receiver Inputs

10, 15

9

15–19

R_OUT

TTL/CMOS Receiver Outputs

11

10

21

INVALID

Valid Signal Detector Output, active low. A logic high indicates that a valid

RS-232 level is present on a receiver input.

12, 13

11

12–14

T_IN

TTL/CMOS Transmitter Inputs

14

12

23

FORCEON

Force-On Input, active high. Drive high to override AutoShutdown Plus,

keeping transmitters and receivers on (FORCEOFF must be high) (Table 1).

18

14

25

GND

Ground

19

15

26

+3.0V to +5.5V Single Supply Voltage

20

16

22

FORCEOFF

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).

—

—

20

R2OUTB

TTL/CMOS Noninverting Complementary Receiver Outputs. Always active.

Ready to Transmit Output, active high. READY is enabled high when

V- goes below -4V and the device is ready to transmit.

FUNCTION

Pin Description

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