UT3243L-R28-T datasheet(6/9 Pages) UTC

6 / 9 page

UT3243

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R502-573.F



DETAILED DESCRIPTION

Charge-Pump Voltage Converter

The UTC UT3243 consists of a regulated dual charge pumps that provide output voltages of +5.5V and -5.5V,

regardless of the input voltage (VCC) changing from +3.0V to +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 Transmitters

UTC UT3243’s transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232

levels. They guarantee a 120kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF, providing

compatibility with PC-to-PC communication software. Typically, the UTC UT3243 can operate at data rates of

235kbps.

Transmitters can be paralleled to drive multiple receivers or mouse. When FORCEOFF is driven to ground, or

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 Receivers

The UTC UT3243’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.

The UTC UT3243 has an always-active complementary output (R2OUTB). R2OUTB is an extra output that monitors

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

forward biasing other devices connected to the receiver outputs. This is ideal for systems where VCC is set to 0V in

shutdown to accommodate peripherals.

Table 1. FORCEOFF Control Truth Table

FORCEOFF

T_OUT

R_OUT

R2OUTB

High-Z

Active

Active (Note 3)

Active

Note: 3. If the part is in shutdown mode ( FORCEOFF = VCC, FORCEON = GND), it is shutdown if no valid RS-232

levels are present on all receiver inputs.

Shutdown Function

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

is high. When the UTC UT3243 senses no valid signal levels on all receiver inputs for 30µs, the on-board power

supply and drivers are shut off, 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 level is applied to any

RS-232 receiver input. As a result, the system saves power without changes to the existing BIOS or operating

system. INVALID indicates the receiver inputs’ condition, when using shutdown function, the INVALID output is high

when the device is on and low when the device is shut down.

Table 2. Shutdown Logic Control Truth Table

RS-232 SIGNAL AT

RECEIVER INPUT

FORCEOFF

INPUT

FORCEON

INPUT

INVALID

OUTPUT

TRANSCEIVER STATUS

Yes

Normal Operation

Normal Operation (Forced On)

Shutdown

Yes

Shutdown (Forced Off)

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