±15kV ESD-Protected, 2.5V, 1µA, 460kbps,

RS-232 Compatible Transceivers

8

_______________________________________________________________________________________

down is typically 30µs, as shown in Figure 2. Connect

has no effect on R_OUT.

MAX3318E/MAX3319E

AutoShutdown Plus Mode

Maxim’s AutoShutdown Plus feature on the MAX3318E/

MAX3319E allows the supply current to fall to 1µA.

These devices will enter the AutoShutdown Plus mode if

FORCEOFF is high, FORCEON is low, and they do not

sense a valid signal transition on any receiver or trans-

mitter input for 30 seconds. This may occur if the RS-232

cable is disconnected or if the peripheral transmitters

are turned off, and the UART driving the transmitter

inputs is inactive. The system turns on again when a

valid transition is applied to any RS-232 receiver or

transmitter input. As a result, the system saves power

without changes to the existing BIOS or operating system.

Figure 4a depicts valid and invalid RS-232 receiver volt-

age levels. INVALID indicates the receiver input’s condi-

tion and is independent of FORCEON and FORCEOFF

states. Figure 3 and Table 1 summarize the operating

modes of the MAX3318E/MAX3319E. FORCEON and

FORCEOFF override AutoShutdown Plus circuitry. When

neither control is asserted, the IC selects between these

states automatically based on the last receiver or trans-

mitter edge received.

When shut down, the device’s charge pumps turn off,

outputs are high impedance, and READY is driven low.

The time required to exit shutdown is typically 30µs

(Figure 2).

X

X

X

X

VALID RECEIVER

LEVEL

Active

Active

Active

Active

R_OUT

No

Yes

X

X

RECEIVER OR

TRANSMITTER

EDGE WITHIN

30s

High-Z

Active

Active

High-Z

T_OUT

Shutdown

(AutoShutdown Plus)

0

1

Normal Operation

(AutoShutdown Plus)

0

1

Normal Operation

(Forced On)

1

1

Shutdown (Forced

Off)

X

0

OPERATION

STATUS

FORCEON

FORCEOFF

No

Yes

No

X

Yes

Active

Active

Active

Active

Active

X

X

No

Yes

X

High-Z

Active

High-Z

Active

Active

Shutdown

(AutoShutdown)

INVALID**

INVALID**

Normal Operation

(AutoShutdown)

INVALID**

INVALID**

Shutdown

INVALID*

1

Normal Operation

INVALID*

1

Normal Operation

INVALID*

1

Table 1. Output Control Truth Table (MAX3318E/MAX3319E)

Table 2. Shutdown and Enable Control

Truth Table (MAX3317E)

X = Don’t care

*INVALID connected to FORCEON

**INVALID connected to FORCEON and FORCEOFF

SHDN

EN

T_OUT

R_OUT

0

0

High-Z

Active

0

1

High-Z

High-Z

1

0

Active

Active

1

1

Active

High-Z