REV. B

AD8381

–10–

FUNCTIONAL DESCRIPTION

The AD8381 is a system building block designed to directly

drive the columns of LCD panels of the type popularized for use

in data projectors. It comprises six channels of precision 10-bit

digital-to-analog converters loaded from a single, high speed,

10-bit-wide input. Precision current feedback amplifiers, provid-

ing well-damped pulse response and rapid voltage settling into

large capacitive loads, buffer the six outputs. Laser trimming at

the wafer level ensure low absolute output errors and tight channel-

to-channel matching. In addition, tight part-to-part matching

in high channel count systems is guaranteed by the use of an

external voltage reference.

Input Data Loading (STart SeQuence Control—STSQ)

A valid STSQ control input initiates a new six-clock pulse

loading cycle, during which six input data words are loaded

sequentially into six internal channels. A new loading sequence

begins on the current active CLK edge only when STSQ was

held high at the preceding active CLK edge.

Data Loading—Expanded Systems (Even/Odd Control)

To facilitate expanded, even/odd systems, the active CLK edge, at

which input data is loaded, is set with the E/O control input.

Input data is loaded on rising CLK edges while the E/O input is

held high and loaded on falling CLK edges while the E/O input

is held low.

Data Loading—Inverted Images (Right/Left Control)

To facilitate image mirroring, the order in which input data is

loaded is set with the R/L input.

A new loading sequence begins at Channel 0 and proceeds

to Channel 5 when the R/L input is held high and begins at

Channel 5 and proceeding to Channel 0 when the R/L input

is held low.

Data Transfer to Outputs (XFR Control)

Data transfer to all outputs is initiated by the XFR control input.

When XFR is held high during a rising CLK edge, data is

simultaneously transferred to all outputs on the immediately

following falling CLK edge.

VCOM Reference (VMID Reference Input)

An external analog reference voltage connected to this input

sets the reference level at the outputs. This input is normally

connected to VCOM.

Full-Scale Output (VREFHI, VREFLO Reference Inputs)

The difference between two external analog reference voltages,

connected to these inputs, sets the full-scale output voltage at

the outputs. VREFLO is normally tied to VMID.

Analog Voltage Inversion (INVert Control)

To facilitate systems that use column, row or pixel inversion,

the analog output voltage inversion is controlled by the INV

control input. While INV is high, the analog voltage equivalent

of the input code is subtracted from (VMID + VFS) at each

output. While INV is low, the analog voltage equivalent of the

input code is added to (VMID – VFS) at each output.

Standby Mode (STBY Control)

A high applied to the STBY input debiases the internal

circuitry, dropping the quiescent power dissipation to a few

milliwatts. Since both digital and analog circuits are debiased,

all stored data will be lost. Upon returning STBY to low, nor-

mal operation is restored.