MAX3228E(2001) Просмотр технического описания (PDF) - Maxim Integrated

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MAX3228E
(Rev.:2001)

±15kV ESD-Protected +2.5V to +5.5V RS-232 Transceivers in UCSP

Maxim Integrated 

±15kV ESD-Protected +2.5V to +5.5V

RS-232 Transceivers in UCSP

Pin Description (continued)

PIN

MAX3228E MAX3229E

C5

C5

C6, D6

C6

D1

D1

E1

E1

E2

E2

E3, E4

E3

E5, E6

E5

NAME

FORCEOFF

R_OUT

C1-

GND

INVALID

T_OUT

R_IN

FUNCTION

FORCEOFF Input, Active-Low. Drive FORCEOFF low to shut down transmitters,

receivers, and on-board charge pump. This overrides all automatic circuitry and

FORCEON. Pulls itself high internally if not connected.

Receiver Output(s)

Negative Terminal of Positive Regulated Charge-Pump Capacitor

Ground

Output of Valid Signal Detector. INVALID is enabled low if no valid RS-232 level is

present on any receiver input.

RS-232 Transmitter Output(s)

RS-232 Receiver Input(s)

Table 1. Operating Supply Options

SYSTEM SUPPLY (V)

1 Li+ Cell

3 NiCad/NiMh Cells

Regulated Voltage Only

(VCC falling)

Regulated Voltage Only

(VCC falling)

VCC (V)

+2.4 to +4.2

+2.4 to +3.8

+3.0 to +5.5

+2.5 to +3.0

VL (V)

Regulated System Voltage

Regulated System Voltage

+3.0 to +5.5

+2.5 to +3.0

RS-232 MODE

Compliant/Compatible

Compliant/Compatible

Compliant

Compatible

Detailed Description

Dual-Mode Regulated Charge-Pump

Voltage Converter

The MAX3228E/MAX3229E internal power supply con-

sists of a dual-mode regulated charge pump. For sup-

ply voltages above +3.7V, the charge pump will

generate +5.5V at V+ and -5.5V at V-. The charge

pumps operate in a discontinuous mode. If the output

voltages are less than ±5.5V, the charge pumps are

enabled, if the output voltages exceed ±5.5V, the

charge pumps are disabled.

For supply voltages below +2.85V, the charge pump

will generate +4.0V at V+ and -4.0V at V-. The charge

pumps operate in a discontinuous mode. If the output

voltages are less than ±4.0V, the charge pumps are

enabled, if the output voltages exceed ±4.0V, the

charge pumps are disabled.

Each charge pump requires a flying capacitor (C1, C2)

and a reservoir capacitor (C3, C4) to generate the V+

and V- supply voltages.

Voltage Generation in the

Switchover Region

The MAX3228E/MAX3229E include a switchover circuit

between these two modes that have approximately

400mV of hysteresis around the switchover point. The

hysteresis is shown in Figure 1. This large hysteresis

eliminates mode changes due to power-supply

bounce.

For example, a three-cell NiMh battery system starts at

VCC = +3.6V, and the charge pump will generate an

output voltage of ±5.5V. As the battery discharges, the

VCC

4V

0

V+

6V

0

20ms/div

Figure 1. V+ Switchover for Changing VCC

6 _______________________________________________________________________________________

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