Complete 230kbps, 2.7V to 5.25V

Serial Interface for Notebook Computers

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7

the MAX562 transmitter outputs when

SHDN rises. Two

transmitter outputs are shown going to opposite EIA/TIA-

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

Each transmitter is loaded with 3k

Ω in parallel with

2500pF. The transmitter outputs are well behaved, with

no ringing or undesirable transients as they come out of

shutdown.

Driving Multiple Receivers

Each transmitter is designed to drive a single receiver.

Transmitters can be paralleled to drive multiple

receivers.

EIA/TIA-562 Receivers

All 5 receivers are identical and accept EIA/TIA-562 or

EIA/TIA-232 signals. The CMOS receiver outputs swing

compatibility with the driver outputs.

The guaranteed 0.8V and 2.4V receiver input thresh-

olds are significantly tighter than the ±3.0V thresholds

required by the EIA/TIA-562 specification. This allows

the receiver inputs to respond to TTL/CMOS logic lev-

els as well as EIA/TIA-562/232 levels. Also, the

MAX562's guaranteed 0.8V lower threshold ensures

that receivers shorted to ground will have a logic 1 out-

put. The 5k

Ω input resistance to ground ensures that a

receiver with its input left open will also have a logic 1

output.

The receiver inputs have approximately 0.3V hysteresis

when

SHDN is high. This provides clean output transi-

tions, even with slowly moving input signals with mod-

erate noise and ringing.

The receivers are active when EN is high. When EN is

low, the receiver outputs are high impedance. This

allows wire-OR connection of two EIA/TIA-562 ports (or

ports of different types) at the UART.

The receivers are always active,when EN is high, irre-

spective of

SHDN's state. When SHDN is high, the

receivers have hysteresis and experience the shortest

propagation delays (typically 100ns falling, 250ns ris-

ing). When

SHDN is low, the receivers have longer

propagation delays (typically 3µs falling, 2µs rising)

and have no hysteresis. The receiver outputs are not

valid for 50µs after

SHDN goes low.

Shutdown and Enable Control

SHDN and EN determine the operation of the MAX562

as shown in Table 1.

__________Applications Information

Capacitor Selection

The capacitor type is not critical for proper MAX562

operation. Any low cost ceramic capacitor (e.g., Z5U,

Y5V) is acceptable for operating at room temperature,

0

200

300

100

SHDN

5

0

6

4

2

0

-2

-4

TIME (

µs)

Figure 5. Time for Transmitters to Exit Shutdown

Table 1. MAX562 Control Pin Configurations

SHDN

EN

CHARGE-PUMP

OPERATION

STATUS

TRANSMITTERS

T1-T3

RECEIVERS

R1-R5

SUPPLY

CURRENT

TYP (A)

0

0

Shutdown

High-Z

High-Z

1µ

0

1

Shutdown

High-Z

Active*

45µ

1

0

Normal Operation

Active

High-Z

24m

1

1

Normal Operation

Active

Active

24m

* Active, but with reduced performance (see

EIA/TIA-562 Receivers section). This is “keep-awake” mode.