±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,

Up to 1Mbps, True RS-232 Transceivers

______________________________________________________________________________________

13

Applications Information

Capacitor Selection

The capacitor type used for C1–C4 is not critical for

proper operation; polarized or nonpolarized capacitors

can be used. The charge pump requires 0.1µF capaci-

tors for 3.3V operation. For other supply voltages, see

Table 2 for required capacitor values. Do not use val-

ues smaller than those listed in Table 2. Increasing the

capacitor values (e.g., by a factor of 2) reduces ripple

on the transmitter outputs and slightly reduces power

consumption. C2, C3, and C4 can be increased without

changing C1’s value. However, do not increase C1

without also increasing the values of C2, C3, C4,

the other capacitors).

When using the minimum required capacitor values,

make sure the capacitor value does not degrade

excessively with temperature. If in doubt, use capaci-

tors with a larger nominal value. The capacitor’s equiv-

alent series resistance (ESR), which usually rises at low

temperatures, influences the amount of ripple on V+

and V-.

Power-Supply Decoupling

is adequate. In applications sensitive to power-supply

noise, use a capacitor of the same value as charge-

pump capacitor C1. Connect bypass capacitors as

close to the IC as possible.

Operation Down to 2.7V

Transmitter outputs meet EIA/TIA-562 levels of ±3.7V

with supply voltages as low as 2.7V.

MAX3241E

EN

23

R5OUT

15

R4OUT

16

R3OUT

17

R2OUT

18

R1OUT

19

R2OUTB

20

R1OUTB

21

5k

Ω

5k

Ω

5k

Ω

5k

Ω

5k

Ω

R5IN

8

R4IN

7

6

R2IN

5

R1IN

4

SHDN

22

GND

25

T3IN

12

T2IN

13

T1IN

14

C2-

2

C2+

1

C1-

24

C1+

28

T3OUT

11

+V

COMPUTER SERIAL PORT

+V

-V

GND

Tx

T2OUT

10

T1OUT

9

V-

3

V+

27

C4

C3

C1

C2

26

R3IN

MOUSE

Figure 6b. Mouse Driver Test Circuit