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

RS-232 Transceivers with AutoShutdown Plus

peripheral transmitters are turned off, and the UART dri-

ving 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 sys-

tem saves power without changes to the existing BIOS

or operating system.

Figures 3a and 3b depict valid and invalid RS-232

receiver voltage levels. INVALID indicates the receiver

input’s condition, and is independent of FORCEON and

FORCEOFF states. Figure 3 and Tables 1 and 2 sum-

marize the operating modes of the MAX3224E–

MAX3227E/MAX3244E/MAX3245E. 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 transmitter input edge received.

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

ter outputs are high impedance, and READY

(MAX3224E–MAX3227E) is driven low. The time

required to exit shutdown is typically 100µs (Figure 8).

By connecting FORCEON to INVALID, the MAX3224E–

MAX3227E/MAX3244E/MAX3245E shut down when no

valid receiver level and no receiver or transmitter edge is

detected for 30s, and wake up when a valid receiver

level or receiver or transmitter edge is detected.

+0.3V

-0.3V

INVALID

R_IN

INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR

AT LEAST 30

μs.

30

μs

TIMER

R

+2.7V

-2.7V

INVALID

R_IN

INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V

FOR LESS THAN 30

μs.

30

μs

TIMER

R

AUTOSHDN

R_IN

T_IN

R

S

30s

TIMER

EDGE

DETECT

EDGE

DETECT

FORCEOFF

FORCEON

Figure 3a. INVALID Functional Diagram, INVALID Low

Figure 3b. INVALID Functional Diagram, INVALID High

Figure 3c. AutoShutdown Plus Logic

POWERDOWN*

AUTOSHDN

FORCEOFF

FORCEON

* POWERDOWN IS ONLY AN INTERNAL SIGNAL.

IT CONTROLS THE OPERATIONAL STATUS OF

THE TRANSMITTERS AND THE POWER SUPPLIES.

Figure 3d. Power-Down Logic

-2.7V

-0.3V

+2.7V

+0.3V

0

INDETERMINATE

INVALID HIGH

INVALID LOW

INVALID HIGH

INDETERMINATE

Figure 4a. Receiver Positive/Negative Thresholds for INVALID

RS-232 SIGNAL

PRESENT AT ANY

RECEIVER INPUT

INVALID OUTPUT

Yes

High

No

Low

Table 2. INVALID Truth Table

Maxim Integrated

11

MAX3224E/MAX3225E/

MAX3226E/MAX3227E/MAX3244E/MAX3245E