11

®

DAC7612

noise, and a set gain of 1.682V/V (4.095/2.435). See Figure

2 for an equivalent circuit schematic of the analog portion of

the DAC7612.

The output amplifier has a 7

µs typical settling time to ±1

LSB of the final value. Note that there are differences in the

settling time for negative-going signals versus positive-

going signals.

The rail-to-rail output stage of the amplifier provides the full-

scale range of 0V to 4.095V while operating on a supply voltage

as low as 4.75V. In addition to its ability to drive resistive loads,

the amplifier will remain stable while driving capacitive loads

of up to 500pF. See Figure 3 for an equivalent circuit schematic

of the amplifier’s output driver and the Typical Performance

Curves section for more information regarding settling time,

load driving capability, and output noise.

POWER SUPPLY

A BiCMOS process and careful design of the bipolar and

CMOS sections of the DAC7612 result in a very low power

device. Bipolar transistors are used where tight matching

and low noise are needed to achieve analog accuracy, and

CMOS transistors are used for logic, switching functions

and for other low power stages.

If power consumption is critical, it is important to keep the

logic levels on the digital inputs (SDI, CLK, CS,

LOADDACS) as close as possible to either VDD or ground.

This will keep the CMOS inputs (see “Supply Current vs

Logic Input Voltages” in the Typical Performance Curves)

from shunting current between VDD and ground.

The DAC7612 power supply should be bypassed as shown

in Figure 1. The bypass capacitors should be placed as close

to the device as possible, with the 0.1

µF capacitor taking

priority in this regard. The “Power Supply Rejection vs

Frequency” graph in the Typical Performance Curves sec-

tion shows the PSRR performance of the DAC7612. This

should be taken into account when using switching power

supplies or DC/DC converters.

In addition to offering guaranteed performance with VDD in

the 4.75V to 5.25V range, the DAC7612 will operate with

reduced performance down to 4.5V. Operation between

4.5V and 4.75V will result in longer settling time, reduced

performance, and current sourcing capability. Consult the

“VDD vs Load Current” graph in the Typical Performance

Curves section for more information.

FIGURE 2. Simplified Schematic of Analog Portion.

FIGURE 3. Simplified Driver Section of Output Amplifier.

N-Channel

P-Channel

V

DD

V

OUT

GND

2R

2R

2R

R

2R

2R

R

R

1

R

R

2

Output Amplifier

R-2R DAC

Bandgap

Reference

2.435V

Typical of DAC A or DAC B

Buffer