AN1488.0 INTERSIL [Intersil Corporation], AN1488.0 Datasheet - Page 2

• Manufacturer Part Number: AN1488.0
• Description: Fixed DC/DC Regulator Output Margining Using Digitally Controlled Potentiometer
• Manufacturer: INTERSIL [Intersil Corporation]

Thus, the ideal DCP for this example should have an Rtotal
resistance of 10kΩ and minimum wiper resistance.
There are some other features that should be taken into
account when choosing the appropriate DCP, such as digital
interface, non-volatile programmability, Rtotal tolerance and
Temperature Coefficient (TCr). Most of the available DCPs
on the market have a ±20% Rtotal tolerance from part to
part. That means each DC/DC regulator requires calibration
and that the calibrated value of the wiper position can be
stored in the non-volatile memory.
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
2
Application Note 1488
The perfect solution for DC/DC margining uses a 1%
precision DCP, like the ISL22317, which eliminates the
necessity of individual calibration and provides 0Ω of wiper
resistance and low TCr. The Vout curve versus ISL22317W
tap position is shown in Figure 3. Since Equation 2 is a
hyperbola, the Vout resolution per step changes with the tap
position, from 50mV per tap at the low end to 2mV per tap at
the high end of the DCP settings in our example.
FIGURE 3. THE ISL85001 VOUT vs THE ISL22317W TAP
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
POSITION
20
TAP POSITION (DECIMAL)
40
60
80
100
August 17, 2009
120
AN1488.0