High Data Rates

The MAX3221E/MAX3223E/MAX3243E maintain the RS-

232 ±5.0V minimum transmitter output voltage even at

high data rates. Figure 9 shows a transmitter loopback

test circuit. Figure 10 shows a loopback test result at

120kbps, and Figure 11 shows the same test at 250kbps.

For Figure 10, all three transmitters were driven simulta-

neously at 120kbps into RS-232 loads in parallel with

1000pF. For Figure 11, a single transmitter was driven at

250kbps, and all three transmitters were loaded with an

RS-232 receiver in parallel with 1000pF.

Mouse Driveability (MAX3243E)

The MAX3243E has been specifically designed to power

serial mice while operating from low-voltage power sup-

plies. It has been tested with leading mouse brands such

as Logitech and Microsoft. When tested, the MAX3243E

successfully drove all serial mice and met their respective

current and voltage requirements. The MAX3243E’s regu-

lated dual charge pump ensures the transmitters will sup-

ply at least ±5V during worst-case conditions. Figure 12a

shows the transmitter outputs under increasing load cur-

rent. The AutoShutdown feature does not work with a

mouse, so FORCEOFF and FORCEON should be con-

a mouse driver test circuit. To achieve mouse driveability

with 1µA supply current when the port is inactive, use

parts with the AutoShutdown Plus feature (such as the

MAX3244E and MAX3245E).

±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,

RS-232 Transceivers with AutoShutdown

12

______________________________________________________________________________________

Figure 12a. Transmitter Output Voltage vs. Load Current per

Transmitter

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

0

1

2

3

4

5

6

7

8

9

10

LOAD CURRENT PER TRANSMITTER (mA)

Figure 9. Loopback Test Circuit

MAX3221E

MAX3223E

MAX3243E

5k

R_ IN

R_ OUT

EN (MAX3221/3E)

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

µF

FORCEOFF

T_ OUT

T_ IN

GND

0V

1000pF

2

µs/div

T1IN

T1OUT

R1OUT

5V/div

5V/div

5V/div

Figure 11. Loopback Test Result at 250kbps

Figure 10. Loopback Test Result at 120kbps

2

µs/div

T1IN

T1OUT

R1OUT

5V/div

5V/div

5V/div