MAX3224ECTP datasheet(10/21 Pages) MAXIM

10 / 21 page

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

RS-232 Transceivers with AutoShutdown Plus

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic

output levels. The MAX3224E–MAX3227E feature

inverting outputs that always remain active (Table 1).

The MAX3244E/MAX3245E have inverting three-state

outputs that are high impedance when shut down

(FORCEOFF = GND) (Table 1).

The MAX3244E/MAX3245E feature an extra, always

active, noninverting output, R2OUTB. R2OUTB output

monitors receiver activity while the other receivers are

high impedance, allowing ring indicator applications to

be monitored without forward biasing other devices

connected to the receiver outputs. This is ideal for sys-

tems where VCC is set to ground in shutdown to

accommodate peripherals such as UARTs (Figure 2).

The MAX3224E–MAX3227E/MAX3244E/MAX3245E fea-

ture an INVALID output that is enabled low when no

valid RS-232 voltage levels have been detected on all

receiver inputs. Because INVALID indicates the receiv-

er input’s condition, it is independent of FORCEON and

FORCEOFF states (Figures 3 and 4).

AutoShutdown Plus Mode

The MAX3224E–MAX3227E/MAX3244E/MAX3245E

achieve a 1µA supply current with Maxim’s AutoShutdown

Plus feature, which operates when FORCEOFF is high

and a FORCEON is low. When these devices do not

sense a valid signal transition on any receiver and trans-

mitter input for 30s, the on-board charge pumps are

shut down, reducing supply current to 1µA. This occurs

if the RS-232 cable is disconnected or if the connected

Table 1. Output Control Truth Table

OPERATION

STATUS

FORCEON

FORCEOFF

VALID

RECEIVER

LEVEL

RECEIVER OR

TRANSMITTER

EDGE WITHIN

30s

T_OUT

R_OUT

(MAX3224E/

MAX3225E/

MAX3226E/

MAX3227E)

R_OUT

(MAX3244E/

MAX3245E)

R2OUTB

(MAX3244E/

MAX3245E)

Shutdown

(Forced Off)

High-Z

Active

High-Z

Active

Normal

Operation

(Forced On)

Active

Normal

Operation

(AutoShutdown

Plus)

Yes

Active

Shutdown (Auto-

Shutdown Plus)

High-Z

Active

Normal

Operation

INVALID*

Yes

Active

Normal

Operation

INVALID*

Yes

Active

Shutdown

INVALID*

High-Z

Active

Normal

Operation

(AutoShutdown)

INVALID*

INVALID**

Yes

Active

Shutdown

(AutoShutdown)

INVALID*

INVALID**

High-Z

Active

High-Z

Active

X = Don’t care

* INVALID

connected to FORCEON

** INVALID

connected to FORCEON and FORCEOFF

Maxim Integrated

MAX3224E/MAX3225E/

MAX3226E/MAX3227E/MAX3244E/MAX3245E

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