MAX3320ACAP 데이터 시트보기 (PDF) - Maxim Integrated

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MAX3320ACAP

3V to 5.5V, up to 250kbps True RS-232 Transceiver with 4µA AutoShutdown Plus and Power-On Reset

Maxim Integrated 

3V to 5.5V, up to 250kbps True RS-232 Transceiver

with 4µA AutoShutdown Plus and Power-On Reset

reducing supply current to 4µA. This occurs if the RS-232

cable is disconnected or the connected peripheral trans-

mitters turn off. The system turns on again when a valid

transition occurs at any RS-232 receiver or transmitter

input. As a result, the system saves power without

changes to the existing BIOS or operating system. The

INVALID output is high when the receivers are active.

Since INVALID indicates the receiver inputs’ condition, it

can be used in any mode (Figure 2).

Tables 1 and 2 and Figure 2 summarize the MAX3320’s

operating modes. FORCEON and FORCEOFF override

the automatic circuitry and force the transceiver into its

normal operating state or into its low-power standby

state. When neither control is asserted, the IC enters

AutoShutdown Plus mode and 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,

V+ decays to VCC , V- decays to ground, and the trans-

mitter outputs turn off (high impedance). The time

required to exit shutdown is typically 25µs (Figure 3a).

Software-Controlled Shutdown

If direct software control is desired, use INVALID to indi-

cate DTR or Ring Indicator signal. Connect FORCEOFF

and FORCEON together to bypass the AutoShutdown

Plus feature so the line acts like a SHDN input.

Power-On Reset

In addition to issuing a reset to the microprocessor (µP)

during power-up, power-down, and brownout condi-

tions, the MAX3320 is relatively immune to short-

duration, negative-going VCC transitions (glitches).

Typically, a VCC transient that goes 100mV below the

reset threshold and lasts 20µs or less does not cause a

reset pulse (see Typical Operating Characteristics).

Additional bypass capacitance mounted as close as

possible to the VCC pin provides additional transient

immunity.

Table 2. INVALID Truth Table

RS-232 SIGNAL PRESENT AT

RECEIVER INPUT

INVALID

OUTPUT

Yes

H

No

L

+0.3V

R_IN

90µs

TIMER INVALID

-0.3V

R

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

AT LEAST 90µs.

Figure 2a. INVALID Functional Diagram, INVALID Low

+2.7V

R_IN

90µs

TIMER INVALID

-2.7V

R

INVALID DEASSERTED IF EITHER RECEIVER INPUT HAS BEEN BETWEEN +2.7V

AND -2.7V FOR LESS THAN 90µs.

Figure 2b. INVALID Functional Diagram, INVALID High

T_IN

EDGE

DETECT

R_IN

EDGE

DETECT

FORCEOFF

S

30sec

TIMER

R

AUTOSHDN

FORCEON

Figure 2c. AutoShutdown Plus Logic

FORCEOFF

FORCEON

AUTOSHDN

* POWERDOWN IS ONLY AN INTERNAL SIGNAL.

IT CONTROLS THE OPERATIONAL STATUS OF

THE TRANSMITTERS AND THE POWER SUPPLIES.

Figure 2d. Power-Down Logic

POWERDOWN*

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