AD5313 datasheet(16/20 Pages) AD

16 / 20 page

REV. F

–16–

AD5305/AD5315/AD5325

If an output range of 0 V to VDD is required, the simplest solution

is to connect the reference input to VDD. As this supply may not be

very accurate and may be noisy, the AD5305/AD5315/AD5325

may be powered from the reference voltage; for example, using

a 5 V reference such as the REF195. The REF195 will output

a steady supply voltage for the AD5305/AD5315/AD5325. The

typical current required from the REF195 is 600

µA supply cur-

rent and approximately 112

µA into the reference input. This is

with no load on the DAC outputs. When the DAC outputs are

loaded, the REF195 also needs to supply the current to the loads.

The total current required (with a 10 k

Ω load on each output) is

712

4 5

2 70

µAV

() =

Ω

The load regulation of the REF195 is typically 2 ppm/mA, which

results in an error of 5.4 ppm (27

µV) for the 2.7 mA current

drawn from it. This corresponds to a 0.0014 LSB error at eight

bits and 0.022 LSB error at 12 bits.

Bipolar Operation Using the AD5305/AD5315/AD5325

The AD5305/AD5315/AD5325 have been designed for single-

supply operation, but a bipolar output range is also possible using

the circuit in Figure 12. This circuit will give an output voltage

range of

±5 V. Rail-to-rail operation at the ampliﬁer output is

achievable using an AD820 or an OP295 as the output ampliﬁer.

+5V

–5V

AD820/

OP295

10 F

6V TO 12V

AD5305

0.1 F

VDD

VOUTA

R1 = 10k

R2 = 10k

REFIN

GND

VOUT

VIN

AD1585

1 F

+5V

2-WIRE

SERIAL

INTERFACE

SCL SDA

VOUTC

VOUTD

VOUTB

GND

Figure 12. Bipolar Operation with the AD5305

The output voltage for any input code can be calculated as

follows:

REFIN

D 2

REFIN

R2 R1

OUT

()×

()













()













–/

where

D is the decimal equivalent of the code loaded to the DAC.

N is the DAC resolution.

REFIN is the reference voltage input.

with

REFIN= 5 V, R1 = R2 = 10 k

Ω:

VD 2

OUT

=×

()

/–

Multiple Devices on One Bus

Figure 13 shows two AD5305 devices on the same serial bus.

Each has a different slave address since the state of the A0 pin is

different. This allows each of eight DACs to be written to or

read from independently.

PULL-UP

RESISTORS

MICRO-

CONTROLLER

SCL

SDA

AD5305

SCL

SDA

VDD

Figure 13. Multiple AD5305 Devices on One Bus

AD5305/AD5315/AD5325 as a Digitally Programmable Window

Detector

A digitally programmable upper/lower limit detector using two

of the DACs in the AD5305/AD5315/AD5325 is shown in

Figure 14. The upper and lower limits for the test are loaded to

DACs A and B, which, in turn, set the limits on the CMP04. If

the signal at the VIN input is not within the programmed window,

an LED will indicate the fail condition. Similarly, DACs C and

D can be used for window detection on a second VIN signal.

1/2

AD5305/

AD5315/

AD5325*

VDD

VOUTA

GND

REFIN

VIN

PASS/

FAIL

1/2

CMP04

1/6 74HC05

FAIL

PASS

0.1 F10 F

SCL

SDA

SCL

DIN

VOUTB

VREF

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 14. Window Detection

Coarse and Fine Adjustment Using the AD5305/AD5315/

AD5325

Two of the DACs in the AD5305/AD5315/AD5325 can be

paired together to form a coarse and ﬁne adjustment function,

as shown in Figure 15. DAC A is used to provide the coarse

adjustment while DAC B provides the ﬁne adjustment. Varying

the ratio of R1 and R2 will change the relative effect of the

coarse and ﬁne adjustments. With the resistor values and exter-

nal reference shown, the output ampliﬁer has unity gain for the

DAC A output, so the output range is 0 V to 2.5 V – 1 LSB. For

DAC B, the ampliﬁer has a gain of 7.6

× 10–3, giving DAC B

a range equal to 19 mV. Similarly, DACs C and D can be paired

together for coarse and ﬁne adjustment.

The circuit is shown with a 2.5 V reference, but reference volt-

ages up to VDD may be used. The op amps indicated will allow

a rail-to-rail output swing.

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