ADP3026 データシートの表示（PDF） - Analog Devices

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ADP3026

High Efficiency Dual Power Supply Controller

Analog Devices 

Power Circuitry

10. Route the switching power path on the PCB to encompass

the smallest possible area in order to minimize radiated

switching noise energy (i.e., EMI). Failure to take proper

precautions often results in EMI problems for the entire PC

system as well as noise related operational problems in the

power converter control circuitry. The switching power

path is the loop formed by the current path through the

input capacitors, the two FETs, and the power Schottky

diode, if used, including all interconnecting PCB traces and

planes. The use of short and wide interconnection traces is

especially critical in this path for two reasons: it minimizes

the inductance in the switching loop, which causes high

energy ringing, and it accommodates the high current

demand with minimal voltage loss.

11. A power Schottky diode (1 A ~ 2 A dc rating) placed from

the lower FET’s source (anode) to drain (cathode) helps to

minimize switching power dissipation in the upper FET. In

the absence of an effective Schottky diode, this dissipation

occurs through the following sequence of switching events.

The lower FET turns off in advance of the upper FET

turning on (necessary to prevent cross-conduction). The

circulating current in the power converter, no longer

finding a path for current through the channel of the lower

FET, draws current through the inherent body-drain diode

of the FET. The upper FET turns on, and the reverse

recovery characteristic of the lower FET’s body-drain

diode prevents the drain voltage from being pulled high

quickly.

The upper FET then conducts very large current while it

momentarily has a high voltage forced across it, which

translates into added power dissipation in the upper FET.

The Schottky diode minimizes this problem by carrying a

majority of the circulating current when the lower FET is

turned off, and by virtue of its essentially nonexistent

reverse recovery time.

ADP3026

12. Whenever a power-dissipating component (e.g., a power

MOSFET) is soldered to a PCB, liberally use vias, both

directly on the mounting pad and immediately

surrounding it. Two important reasons for this are

improved current rating through the vias (if it is a current

path) and improved thermal performance, especially if the

vias are extended to the opposite side of the PCB where a

plane can more readily transfer the heat to the air.

13. Route the output power path, though not as critical as the

switching power path, to encompass a small area. The

output power path is formed by the current path through

the inductor, the output capacitors, and back to the input

capacitors.

14. Extend the power ground plane fully under all the power

components except the output capacitors for best EMI

containment. These are the input capacitors, the power

MOSFETs and Schottky diode, the inductor, and any

snubbing elements that might be added to dampen ringing.

Avoid extending the power ground under any other

circuitry or signal lines, including the voltage and current

sense lines.

Signal Circuitry

15. Kelvin connect the CS and SW traces to the upper

MOSFET drain and source so that the additional voltage

drop due to current flow on the PCB at the current sense

comparator connections does not affect the sensed voltage.

It is desirable to have the ADP3026 close to the output

capacitor bank and not in the output power path, so that

any voltage drop between the output capacitors and the

AGND pin is minimized, and voltage regulation is not

compromised.

Rev. 0 | Page 17 of 20

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