UT3238

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 10

www.unisonic.com.tw



DETAILED DESCRIPTION

Charge-Pump Voltage Converter

The UTC UT3238 consists of a regulated dual charge pumps that provide output voltages of +5.5V and -5.5V,

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.

Each charge pump requires a flying capacitor (C1, C2) and a reservoir capacitor (C3, C4) to generate the V+ and

V- supplies, refer to application circuit.

RS-232 Transmitter

UTC UT3238’s transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232

levels. They guarantee a 250kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF, providing

compatibility with PC-to-PC communication software. Typically, the UTC UT3238 can operate at data rates of

235kbps.

shutdown circuitry senses invalid voltage levels at all receiver inputs, the transmitters are disabled and the outputs

are forced into a high-impedance state.

RS-232 Receiver

The UTC UT3238’s receivers convert RS-232 signals to CMOS-logic output levels. All receivers have one

inverting three-state output. If the receivers is in shutdown, the outputs of receivers are high impedance.

receiver activity while the other receivers are high impedance. This allows Ring Indicator to be monitored without

shutdown to accommodate peripherals.

RS-232 SIGNAL PRESENT AT RECEIVER INPUT

INVALID

OUTPUT

YES

High

NO

Low

Shutdown Function

A 1µA supply current is achieved with shutdown feature, which operates when FORCEON is low and

input for 30sec, the on-board charge pumps are shutdown, reducing supply current to 1µA. This occurs if the RS-232

cable is disconnected or the connected peripheral transmitters are turned off. The system turns on again when a

valid transition is applied to any RS-232 receiver or transmitter input (Table 2). As a result, the system saves power

Table 2. Shutdown Logic Control Truth Table

FORCEON

FORCEOFF

Auto shutdown

Operation Status

T_OUT

R_OUT

R1OUTB

X

0

X

Shutdown(Forced off)

High-Z

High-Z

Active

1

1

X

Normal Operation(Forced on)

Active

Active

Active

0

1

<30sec*

Normal Operation(Auto shutdown)

Active

Active

Active

0

1

>30sec*

Shutdown(Auto shutdown)

High-Z

Active

Active

X=Do not care

* Time since last receiver or transmitter input transition.