8

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Applications Information

Example Calculations

for an Adjustable Power Supply

Using the typical circuit, assuming a typical output volt-

age of 2.0V, a feedback voltage of 0.8V, R1 = 500

Ω,

and R2 = 333

Ω, to adjust or margin the supply 20%

requires a full-scale current equal to [(0.2 x 2.0V) /

500

Ω]. The cur-

rent DAC in this configuration allows the output voltage

to be stepped linearly from 1.6V to 2.4V using 63 set-

tings. This corresponds to a resolution of 12.7mV/step.

Power-Supply Feedback Voltage

The feedback voltage for adjustable power supplies

DS4404 to properly sink/source currents for adjusting

the voltage.

DS4404 address select inputs have an alternate function.

face. This function aborts the current transaction and puts

the SDA driver into a high-impedance state. This hard-

ware reset function should never be required because it

is achievable through software, but it does provide an

To achieve the best results when using the DS4402/

DS4404, 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.

Layout Considerations

Care should be taken to ensure that traces underneath

the DS4402/DS4404 do not short with the exposed pad.

The exposed pad should be connected to the signal

ground, or can be left floating.

SLAVE

ADDRESS*

START

START

a7

a6

a5

a4

a3

a2

a1

R/W

SLAVE

ACK

SLAVE

ACK

SLAVE

ACK

MSB

LSB

MSB

LSB

MSB

LSB

b7

b6

b5

b4

b3

b2

b1

b0

READ/

WRITE

REGISTER/MEMORY ADDRESS

b7

b6

b5

b4

b3

b2

b1

b0

DATA

STOP

SINGLE BYTE WRITE

-WRITE RESISTOR

F9h TO 00h

SINGLE BYTE READ

-READ RESISTOR F8h

START

REPEATED

START

A1h

MASTER

NACK

STOP

1 0100000

11111 000

F8h

10100 001

1 0100000

11111 001

A0h

F9h

STOP

DATA

*THE SLAVE ADDRESS IS DETERMINED BY ADDRESS PINS A0 AND A1 (SEE TABLE 1).

00 000 000

A0h

A)

B)

SLAVE

ACK

SLAVE

ACK

SLAVE

ACK

SLAVE

ACK

SLAVE

ACK

SLAVE

ACK

Chip Information

TRANSISTOR COUNT: 10,992

Package Information

For the latest package outline information and land patterns, go

PACKAGE TYPE

PACKAGE CODE

DOCUMENT NO.

14 TDFN-EP

T1433+1

21-0137