REV. 0

ADP3422

–14–

6. An external “antiparallel” schottky diode (across the bottom

MOSFET) may help efficiency a small amount (< ~1 %); a

MOSFET with a built in antiparallel schottky is more effec-

tive. For an external schottky, it should be placed next to

the bottom MOSFET or it may not be effective at all. Also,

a higher current rating (bigger device with lower voltage

drop) is more effective.

7. The ground pin of the ADP3415 should be connected into

the power switching circuitry ground plane, and the VCC

bypass capacitor should be close to the VCC pin and con-

nected into the same ground plane.

Output Filter

Output Inductor and Capacitors, Current Sense Resistor

8. Locate the current sense resistor very near to the output

capacitors.

9. PCB trace resistances from the current sense resistor to the

output capacitors, and from the output capacitors to the

load should be minimized, known (calculated or measured),

and compensated for as part of the design if it is significant.

(Remote sensing is not sufficient for relieving this require-

ment!) A square section of 1-ounce copper trace has a

resistance of ~500 mW. Using 2~3 squares of copper can

make a noticeable impact on a 15 A design.

10. Whenever high currents must be routed between PCB layers,

vias should be used liberally to create several parallel current

paths so that the resistance and inductance introduced by

these current paths is minimized and the via current rating is

not exceeded.

11. The ground connection of the output capacitors should be

close to the ground connection of the lower MOSFET and

it should be a ground plane. Current may pulsate in this

path if the power source ground is closer to the output

capacitors than the power switching circuitry, so a close

connection will minimize the voltage drop.

Control Circuitry

ADP3422, Control Components

12. If the placement overview cannot be followed, then in order

to avoid introducing ground noise from the power switching

stage into the control circuitry, the ground pin of the

ADP3422 should be Kelvin-connected into the ground plane

near the output capacitors. All other control components

should be grounded on that same signal ground.

13. If critical signal lines (i.e., signals from the current sense

resistor leading back to the ADP3422) must cross through

power circuitry, it is best if a signal ground plane can be

interposed between those signal lines and the traces of the

power circuitry. This serves as a shield to minimize noise

injection into the signals at the expense of making signal

ground a bit noisier.

14. Absolutely avoid crossing any signal lines over the switching

power path loop, described previously.

15. Accurate voltage positioning depends on accurate current

sensing, so the control signals which monitor the voltage

differentially across the current sense resistor should be

kelvin connected.

16. The RC filter used for the current sense signal should be

located near the control components.

Table I. VID Code

VID4

VID3

VID2

VID1

VID0

0

0

0

0

0

1.750

0

0

0

0

1

1.700

0

0

0

1

0

1.650

0

0

0

1

1

1.600

0

0

1

0

0

1.550

0

0

1

0

1

1.500

0

0

1

1

0

1.450

0

0

1

1

1

1.400

0

1

0

0

0

1.350

0

1

0

0

1

1.300

0

1

0

1

0

1.250

0

1

0

1

1

1.200

0

1

1

0

0

1.150

0

1

1

0

1

1.100

0

1

1

1

0

1.050

0

1

1

1

1

1.000

1

0

0

0

0

0.975

1

0

0

0

1

0.950

1

0

0

1

0

0.925

1

0

0

1

1

0.900

1

0

1

0

0

0.875

1

0

1

0

1

0.850

1

0

1

1

0

0.825

1

0

1

1

1

0.800

1

1

0

0

0

0.775

1

1

0

0

1

0.750

1

1

0

1

0

0.725

1

1

0

1

1

0.700

1

1

1

0

0

0.675

1

1

1

0

1

0.650

1

1

1

1

0

0.625

1

1

1

1

1

0.600