3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232

Transceivers Using Four 0.1µF External Capacitors

_______________________________________________________________________________________

9

Power-Supply Decoupling

In most circumstances, a 0.1µF bypass capacitor is

adequate. In applications that are sensitive to power-

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 will meet EIA/TIA-562 levels of

±3.7V with supply voltages as low as 2.7V.

Transmitter Outputs when

Exiting Shutdown

Figure 3 shows two transmitter outputs when exiting

shutdown mode. As they become active, the two trans-

mitter outputs are shown going to opposite RS-232 lev-

els (one transmitter input is high, the other is low).

Each transmitter is loaded with 3k

Ω in parallel with

2500pF. The transmitter outputs display no ringing or

undesirable transients as they come out of shutdown.

Note that the transmitters are enabled only when the

magnitude of V- exceeds approximately 3V.

Mouse Driveability

The MAX3241 has been specifically designed to power

serial mice while operating from low-voltage power sup-

plies. It has been tested with leading mouse brands from

manufacturers such as Microsoft and Logitech. The

MAX3241 successfully drove all serial mice tested and

met their respective current and voltage requirements.

Figure 4a shows the transmitter output voltages under

increasing load current at 3.0V. Figure 4b shows a typical

mouse connection using the MAX3241.

Table 1. MAX3222/MAX3237/MAX3241

Shutdown and Enable Control Truth Table

Table 2. Required Minimum Capacitor Values

5V/div

C1–C4 = 0.1

µF

2V/div

T2

50

µs/div

T1

Figure 3. Transmitter Outputs when Exiting Shutdown or

Powering Up

(V)

C1

(µF)

4.5 to 5.5

0.047

3.0 to 5.5

0.1

C2, C3, C4

(µF)

MAX3222/MAX3232/MAX3241

0.33

0.47

1

Active

0

1

Active

1

S

SH

HD

DN

N

High-Z

1

0

High-Z

0

0

T_OUT

E

EN

N

High-Z

Active

High-Z

Active

R_OUT

R_OUTB

(MAX3237/

MAX3241)

Active

Active

Active

Active

3.0 to 3.6

0.22

3.15 to 3.6

0.1

MAX3237

0.22

0.1

4.5 to 5.5

0.047

3.0 to 5.5

0.22

0.33

1.0

3.0 to 3.6

0.1

0.1