DAC7741YCSLASH2K datasheet(14/23 Pages) TI2

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DAC7741

SBAS248B

www.ti.com

ANALOG OUTPUTS

The output amplifier can swing to within 1.4V of the supply

rails, specified over the –40

°C to +85°C temperature range.

This allows for a

±10V DAC voltage output operation from

±12V supplies with a typical 5% tolerance.

When the DAC7741 is configured for a unipolar, 0V to 10V

output, a negative voltage supply is required. This is due to

internal biasing of the output stage. Please refer to the

“Electrical Characteristics” table for more information.

The minimum and maximum voltage output values are de-

pendent upon the output configuration implemented and

reference voltage applied to the DAC7741. Please note that

VSS (the negative power supply) must be in the range of

–4.75V to –15.75V for unipolar operation. The voltage on VSS

sets several bias points within the converter and is required

in all modes of operation. If VSS is not in one of these two

configurations, the bias values may be in error and proper

operation of the device is not ensured.

Supply sequence is important in establishing the correct

startup of the DAC. The digital supply (VDD) needs to estab-

lish correct bias conditions before the analog supplies (VCC,

VSS) are brought up. If the digital supply cannot be brought

up first, it must come up before either analog supply (VCC or

VSS), with the preferred sequence of: VSS (device substrate),

VDD then VCC.

REFERENCE INPUTS

The DAC7741 provides a built-in +10V voltage reference and

on-chip buffer to allow external component reference drive. To

use the internal reference, REFEN must be LOW, enabling the

reference circuitry of the DAC7741 (see Table I) and the

REFOUT pin must be connected to REFIN. This is the input to

the on-chip reference buffer. The buffers output is provided at

REFEN

ACTION

Internal Reference disabled;

REFOUT = HIGH Impedance

Internal Reference enabled;

REFOUT = +10V

TABLE I. REFEN Action.

TABLE II. DAC7741 Logic Truth Table.

the VREF pin. In this configuration, VREF is used to setup the

DAC7741 output amplifier into one of three voltage output

modes as discussed earlier. VREF can also be used to drive

other system components requiring an external reference.

The internal reference of the DAC7741 can be disabled when

use of an external reference is desired. When using an

external reference, the reference input, REFIN , can be any

voltage between 4.75V (or VSS + 14V, whichever is greater)

and VCC – 1.4V.

DIGITAL INTERFACE

Table III shows the data format for the DAC7741 and

Table II illustrates the basic control logic of the device. The

interface consists of a chip select input (CS), read/write

control input (R/W), data inputs (DB0-DB15) and a load DAC

input (LDAC). An asynchronous reset input (RST) which is

active low, is provided to simplify start-up conditions, periodic

resets, or emergency resets to a known state, depending on

the status of the reset select (RSTSEL) signal. The DAC

code is provided via a 16-bit parallel interface, as shown in

Table II. The input word makes up the DAC code to be

loaded into the data input register of the device. The data is

latched into the input register on rising CS and is loaded into

the DAC register upon reception of a rising edge on the

LDAC input. This action updates the analog output, VOUT, to

the desired value. LDAC inputs of multiple DAC7741 devices

can be connected when a synchronized update of numerous

DAC outputs is desired. Please refer to the timing section for

more detailed data I/O information.

CONTROL STATUS

COMMAND

R/W

RST

RSTSEL

LDAC

Input Register

DAC Register

Mode

H, L,

↓

Write

Hold

Write Data to Input Register

↑

Hold

Write

Update DAC register with data from input

↑

Transparent

Write

Write DAC register directly from data bus

H, L,

↓

Read

Hold

Read data in input register.

H, L,

↓

Hold

No Change

Reset to Min-Scale Reset to Min-Scale Reset to Input and DAC Register (0000

Min-Scale

Reset to Mid-Scale Reset to Mid-Scale Reset to Input and DAC Register (8000

Mid-Scale

ANALOG OUTPUT

TABLE III. DAC7741 Data Format.

DIGITAL INPUT

Unipolar Configuration

Bipolar Configuration

Unipolar Straight Binary

Bipolar Offset Binary

0x0000

Zero (0V)

–Full-Scale (–VREF or –VREF/2)

0x0001

Zero + 1LSB

–Full-Scale + 1LSB

0x8000

1/2 Full-Scale

Bipolar Zero

0x8001

1/2 Full-Scale + 1LSB

Bipolar Zero + 1LSB

0xFFFF

Full-Scale (VREF – 1LSB)

+Full-Scale (+VREF – 1LSB

or +VREF/2 – 1LSB)

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