Current DAC

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9

Applications Information

Example Calculations

for an Adjustable Power Supply

In this example, the

Typical Operating Circuit is used

as a base to create Figure 3, a DC-DC output voltage

of 2.0V with ±20% margin. The adjustable power sup-

start with the equation:

current for the DS4422/DS4424). Summing the currents

into the feedback node produces the following:

Where:

And:

To create a 20% margin in the supply voltage, the value

is calculated to be 2.67k

4.00k

Ω. The current DAC in this configuration allows

the output voltage to be moved linearly from 1.6V to

2.4V using 127 settings. This corresponds to a resolu-

tion of 6.3mV/step.

To achieve the best results when using the DS4422/

DS4424, decouple the power supply with a 0.01µF or

0.1µF capacitor. Use a high-quality ceramic surface-

mount capacitor if possible. Surface-mount compo-

nents minimize lead inductance, which improves

performance, and ceramic capacitors tend to have

adequate high-frequency response for decoupling

applications.

Power Rail Considerations

Given that the absolute maximum rating for the OUT

power rail be brought up before or at the same time as

the power rail of the source it is controlling.

I

VV

R

R0A

OUT

FB

0A

=

−

I

V

R

R0B

FB

0B

=

V

R

RR

FB

0B

0A +

0B

OUT

=× V

DC-DC

CONVERTER

FB

OUT

SDA

SCL

A0

A1

OUT0

GND

Ω

4.7k

Ω

4.7k

Ω

FS0

Ω

Ω

DS4422/

DS4424

Figure 3. Example Application Circuit