AD5300

–11–

REV.

0.1 F

10k

POWER

10 F

SYNC

SCLK

DATA

AD5300

5V

REGULATOR

10k

10k

DIN

SYNC

SCLK

GND

Figure 32. AD5300 with an Opto-Isolated Interface

Power Supply Bypassing and Grounding

When accuracy is important in a circuit, it is helpful to carefully

consider the power supply and ground return layout on the

board. The printed circuit board containing the AD5300 should

have separate analog and digital sections, each having its own

area of the board. If the AD5300 is in a system where other

devices require an AGND to DGND connection, the connec-

tion should be made at one point only. This ground point should

be as close as possible to the AD5300.

The power supply to the AD5300 should be bypassed with

10

µF and 0.1 µF capacitors. The capacitors should be physi-

cally as close as possible to the device with the 0.1

µF capacitor

ideally right up against the device. The 10

µF capacitors are the

tantalum bead type. It is important that the 0.1

µF capacitor

has low effective series resistance (ESR) and effective series

inductance (ESI), e.g., common ceramic types of capacitors. This

0.1

µF capacitor provides a low impedance path to ground for

high frequencies caused by transient currents due to internal

logic switching.

The power supply line itself should have as large a trace as pos-

sible to provide a low impedance path and reduce glitch effects

on the supply line. Clocks and other fast switching digital signals

should be shielded from other parts of the board by digital

ground. Avoid crossover of digital and analog signals if possible.

When traces cross on opposite sides of the board, ensure that

they run at right angles to each other to reduce feedthrough

effects through the board. The best board layout technique is

the microstrip technique where the component side of the board

is dedicated to the ground plane only and the signal traces are

placed on the solder side. However, this is not always possible

with a 2-layer board.

R2 = 10k

+5V

–5V

AD820/

OP295

3-WIRE

SERIAL

INTERFACE

+5V

AD5300

10 F

0.1 F

R1 = 10k

5V

Figure 30. Bipolar Operation with the AD5300

Two 8-Bit AD5300s Together Make One 15-Bit DAC

By using the configuration in Figure 31, it can be seen that one

15-bit DAC can be made with two 8-bit AD5300s. Because of

the low supply current the AD5300 requires, the output of one

DAC may be directed into the supply pin of the second DAC.

The first DAC has no problem sourcing the required 140

µA

of current for the second DAC.

Since the AD5300 works on any supply voltage between 2.5 V

and 5.5 V, the output of the first DAC can be anywhere above

its output range (2.5 V to 5 V), which gives 7-bit resolution on

the output voltage. This output then becomes the supply and

reference for the second DAC. The second DAC has 8-bit reso-

lution on the output range, which gives an overall resolution for

the system of 15 bits.

A level-shifter is required to ensure that the logic input voltages

do not exceed the supply voltage of the part. The microcontroller

outputs 5 V signals, which need to be level shifted down to 2.5 V

in the case of the second DAC having a supply of only 2.5 V.

5V

MICRO-

CONTROLLER

LEVEL

SHIFTER

15-BIT

RESOLUTION

SYNC

SCLK

DIN

AD5300

AD5300

SYNC

SCLK

DIN

Figure 31. 15-Bit DAC Using Two AD5300s

Using AD5300 with an Opto-Isolated Interface

In process-control applications in industrial environments, it is

often necessary to use an opto-isolated interface to protect and

isolate the controlling circuitry from any hazardous common-

mode voltages that may occur in the area where the DAC is

functioning. Opto-isolators provide isolation in excess of 3 kV.

Because the AD5300 uses a 3-wire serial logic interface, it

requires only three opto-isolators to provide the required isola-

tion (see Figure 32). The power supply to the part also needs to

be isolated. This is done by using a transformer. On the DAC

side of the transformer, a 5 V regulator provides the 5 V supply

required for the AD5300.

D