±15kV ESD-Protected +2.5V to +5.5V

RS-232 Transceivers in UCSP and WLP

6

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Detailed Description

Dual-Mode Regulated Charge-Pump

Voltage Converter

The MAX3228E/AE and MAX3229E/AE internal power

supply consists of a dual-mode regulated charge

pump. For supply 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/AE and MAX3229E/AE 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

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

PIN

MAX3228E/

MAX3228AE

MAX3229E/

MAX3229AE

NAME

FUNCTION

C5

C5

FORCEOFF

Active-Low FORCEOFF Input. 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.

C6, D6

C6

R_OUT

Receiver Output(s)

D1

D1

C1-

Positive Regulated Charge-Pump Capacitor Negative Terminal

E1

E1

GND

Ground

E2

E2

INVALID

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

on any receiver input.

E3, E4

E3

T_OUT

RS-232 Transmitter Output(s)

E5, E6

E5

R_IN

RS-232 Receiver Input(s)

Pin Description (continued)

SYSTEM SUPPLY (V)

RS-232 MODE

1 Li+ Cell

+2.4 to +4.2

Regulated System Voltage

Compliant/Compatible

3 NiCad/NiMh Cells

+2.4 to +3.8

Regulated System Voltage

Compliant/Compatible

Regulated Voltage Only

+3.0 to +5.5

+3.0 to +5.5

Compliant

Regulated Voltage Only

+2.5 to +3.0

+2.5 to +3.0

Compatible

Table 1. Operating Supply Options

0

6V

4V

0

20ms/div

V+