EVAL-AD5532EB【PDF 12/16 页】32-Channel, 14-Bit Voltage-Output DAC

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AD5532

–12–

TRACK

DAC

ACQUISITION

CIRCUIT

OUT

BUSY

OUTPUT

STAGE

CONTROLLER

THRESHOLD

VOLTAGE

DRIVER

DEVICE

UNDER

TEST

ONLY ONE CHANNEL SHOWN FOR SIMPLICITY

AD5532

Figure 18. Typical ATE Circuit Using

TRACK

Input

This is useful in an application where the user wants to ramp up

until V

OUT

reaches a particular level (Figure 18). V

does

not need to be acquired continuously while it is ramping up.

TRACK

can be kept low and only when V

OUT

has reached its

desired voltage is

TRACK

brought high. At this stage, the

acquisition of V

begins.

In the example shown, a desired voltage is required on the out-

put of the pin driver. This voltage is represented by one input to

a comparator. The microcontroller/microprocessor ramps up

the input voltage on V

through a DAC.

TRACK

is kept low

while the voltage on V

ramps up so that V

is not continu-

ally acquired. When the desired voltage is reached on the output

of the pin driver, the comparator output switches. The

then knows what code is required to be input in order to obtain

the desired voltage at the DUT. The

TRACK

input is now

brought high and the part begins to acquire V

. At this stage

BUSY

goes low until V

has been acquired. The output buffer

is then switched from V

to the output of the DAC.

MODES OF OPERATION

The AD5532 can be used in four different modes of opera-

tion. These modes are set by two mode bits, the first two bits in

the serial word.

Table II. Modes of Operation

Mode Bit 1

Mode Bit 2

Operating Mode

SHA Mode

DAC Mode

Acquire and Readback

Readback

1. DAC Mode

In this standard mode a selected DAC register is loaded serially.

This requires a 24-bit write (10 bits to address the relevant DAC

plus an extra 14 bits of DAC data). MSB is written first. The

user must allow 400 ns (min) between successive writes in DAC

mode.

2. SHA Mode

In this mode a channel is addressed and that channel acquires

the voltage on V

. This mode requires a 10-bit write (see Fig-

ure 21) to address the relevant channel (V

OUT

0–V

OUT

31, offset

channel or all channels) MSB is written first.

3. Acquire and Readback Mode

This mode allows the user to acquire V

and read back the data

in a particular DAC register. The relevant channel is addressed

(10-bit write, MSB first) and V

is acquired in 16

s (max).

Following the acquisition, after the next falling edge of

SYNC

the data in the relevant DAC register is clocked out onto the

OUT

line in a 14-bit serial format. The full acquisition time

must elapse before the DAC register data can be clocked out.

4. Readback Mode

Again, this is a readback mode but no acquisition is performed.

The relevant channel is addressed (10-bit write, MSB first) and

on the next falling edge of

SYNC

, the data in the relevant DAC

OUT

line in a 14-bit serial format.

The user must allow 400 ns (min) between the last SCLK fall-

ing edge in the 10-bit write and the falling edge of

SYNC

the 14-bit readback. The serial write and read words can be

seen in Figure 19.

This feature allows the user to read back the DAC register code

of any of the channels. In DAC mode this is useful in verification

of write cycles. In SHA mode readback is useful if the system

has been calibrated and the user wants to know what code in

the DAC corresponds to a desired voltage on V

OUT

. If the user

requires this voltage again, he can input the code directly to the

DAC register without going through the acquisition sequence.

INTERFACES

Serial Interface

The SER/

PAR

pin is tied high to enable the serial interface and

to disable the parallel interface. The serial interface is controlled

by four pins as follows:

SYNC

, D

, SCLK

Standard 3-wire interface pins. The

SYNC

pin is shared

with the

function of the parallel interface.

OUT

Data Out pin for reading back the contents of the DAC

registers. The data is clocked out on the rising edge of SCLK

and is valid on the falling edge of SCLK.

Mode Bits

There are four different modes of operation as described above.

Cal Bit

In DAC mode this is a test bit. When it is high it is used to load

all zeros or all ones to the 32DACs simultaneously. In SHA mode

all 32 channels acquire V

simultaneously when this bit is high.

In SHA mode the acquisition time is then 45

s (typ) and accu-

racy may be reduced. This bit is set low for normal operation.

Offset_Sel Bit

If this is set high, the offset channel is selected and Bits A4–

A0 are ignored.

Test Bit

This must be set low for correct operation of the part.

A4–A0

Used to address any one of the 32 channels (A4 = MSB of

address, A0 = LSB).

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