UT3221EL-R16-T datasheet(6/10 Pages) UTC

6 / 10 page

UT3221/E

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 10

www.unisonic.com.tw

QW-R103-128.C



DETAILED DESCRIPTION

Charge-Pump Voltage Converter

The UTC UT3221/E 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 Transmitter

UTC UT3221/E’s transmitter is 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.

Transmitter can be paralleled to drive multiple receiver or mouse. When FORCEOFF is driven to ground, or

shutdown circuitry senses invalid voltage levels at the receiver input, the transmitter is disabled and the output is

forced into a high-impedance state.

RS-232 Receiver

The UTC UT3221/E’s receiver convert RS-232 signals to CMOS-logic output levels. The receiver has one

inverting three-state output. In shutdown or in autoshutdown, the UT3221/E’s receiver is active. Drive EN high to

place the receiver in a high-impedance state.

Table 1. EN Control Truth Table

R_OUT

Active

High-Z

Shutdown Function(UT3221E)

Supply current falls to less than 1μA in shutdown mode ( FORCEOFF = GND). When shutdown, the device’s

charge pumps are shut off, V+ is pulled down to VCC, V- is pulled to ground, and the transmitter outputs are

disabled (high impedance). Connect FORCEOFF to VCC if shutdown mode is not used. FORCEOFF has no effect

on R_OUT.

Shutdown Function(UT3221)

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

FORCEOFF is high. When the UTC UT3221 senses no valid signal levels on the receiver input for 30µs, the

on-board power supply and driver is shut off, reducing supply current to 1µA. This occurs if the RS-232 cable is

disconnected or the connected peripheral transmitter is turned off. The system turns on again when a valid level is

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

operating system. INVALID indicates the receiver input’ 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

OPERATION STATUS

FORCEOFF

INPUT

FORCEON

INPUT

INVALID

OUTPUT

T_OUT

Normal Operation (Forced On)

Active

Normal Operation (AutoShutdown)

Active

Normal Operation (AutoShutdown)

High-Z

Shutdown (Forced Off)

High-Z

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