MAX3230E_08 datasheet(6/16 Pages) MAXIM | ±15kV ESD-Protected +2.5V to +5.5V RS-232 Transceivers in UCSP and WLP

6 page

±15kV ESD-Protected +2.5V to +5.5V

RS-232 Transceivers in UCSP and WLP

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Detailed Description

Dual Mode™ Regulated Charge-Pump

Voltage Converter

The MAX3230E/AE and MAX3231E/AE internal power

supply consists of a dual-mode regulated charge

pump. For supply voltages above +3.7V, the charge

pump generates +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

generates +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 MAX3230E/AE and MAX3231E/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

VCC = +3.6V, and the charge pump generates an out-

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

MAX3230E/AE and MAX3231E/AE maintain the outputs

in regulation until the battery voltage drops below +3.1V.

The output regulation points then change to ±4.0V.

When VCC is rising, the charge pump generates an out-

put voltage of ±4.0V, while VCC is between +2.5V and

+3.5V. When VCC rises above the switchover voltage of

+3.5V, the charge pump switches modes to generate

an output of ±5.5V.

Table 1 shows different supply schemes and their oper-

ating voltage ranges.

RS-232 Transmitters

The transmitters are inverting level translators that

convert CMOS logic levels to RS-232 levels. The

MAX3230E/AE and MAX3231E/AE automatically reduce

the RS-232-compliant levels (±5.5V) to RS-232-compat-

ible levels (±4.0V) when VCC falls below approximately

+3.1V. The reduced levels also reduce supply-current

requirements, extending battery life. Built-in hysteresis

of approximately 400mV for VCC ensures that the RS-

Figure 1. V+ Switchover for Changing VCC

20ms/div

VCC

V+

Dual Mode is a trademark of Maxim Integrated Products, Inc.

BUMP

MAX3230E/

MAX3230AE

MAX3231E/

MAX3231AE

NAME

FUNCTION

C6, D6

R_OUT

Receiver Output(s)

C1-

Positive Regulated Charge-Pump Capacitor Negative Terminal

GND

Ground

INVALID

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

present on any receiver input.

E3, E4

T_OUT

RS-232 Transmitter Output(s)

E5, E6

R_IN

RS-232 Receiver Input(s)

—

B6, D6, E4,

N.C.

No Connection. These locations are populated with solder bumps, but are electrically

isolated.

Pin Description (continued)

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