ADM3252E

Data Sheet

Rev. 0 | Page 12 of 16

APPLICATIONS INFORMATION

PCB LAYOUT

The ADM3252E requires no external circuitry for its logic

interfaces. Power supply bypassing is required at the input

and output supply pins (see Figure 20). Bypass capacitors are

Figure 20. Recommended Printed Circuit Board Layout

To suppress noise and reduce ripple, a parallel combination of at

least two capacitors is recommended. The recommended capacitor

capacitor must have a low ESR; best practice suggests use of a

ceramic capacitor. Do not exceed 2 mm for the total lead length

between both ends of the low ESR capacitor and the input power

supply pin.

Because it is not possible to apply a heat sink to an isolation

device, the device primarily depends on heat dissipating into

the PCB through the ground pins. If the device is used at high

ambient temperatures, take care to provide a thermal path from

the ground pins to the PCB ground plane. The board layout in

The BGA balls are also grouped together to simplify layout and

routing. To significantly reduce the temperature inside the chip,

implement multiple vias from each of the pads to the ground

plane. The dimensions of the expanded pads are at the discre-

tion of the designer and the available board space.

In applications involving high common-mode transients,

ensure that board coupling across the isolation barrier is

minimized. Furthermore, design the board layout such that

any coupling that does occur equally affects all pins on a given

component side.

The power supply section of the ADM3252E uses a 180 MHz

oscillator frequency to pass power through its chip scale

transformers. Operation at these high frequencies may raise

concerns about radiated emissions and conducted noise. PCB

layout and construction are very important tools for controlling

radiated emissions. Refer to the AN-0971 Application Note,

Recommendations for Control of Radiated Emissions with isoPower

Devices, for extensive guidance on radiation mechanisms and

board layout considerations.

START-UP BEHAVIOR

The ADM3252E does not contain a soft start circuit. Therefore,

the start-up current and voltage behavior must be taken into

account when designing with this device.

to operate and draw current when the UVLO minimum voltage

is reached (approximately 2.7 V). The switching circuit drives

the maximum available power to the output until it reaches the

regulation voltage, which is where PWM control begins. The

amount of current and the time required to reach regulation

the output can turn on; therefore, the peak current is proportional

to the maximum input voltage.

minimum voltage. The current surge is approximately 300 mA

behavior during startup is similar to when the device load is a

short circuit.

When powering up the device, do not limit the current available

may not be able to drive the output to the regulation point if a

As a result, the ADM3252E device can draw large amounts of

current at low voltage for extended periods of time.

overshoot to approximately 4 V during startup (see Figure 13

and Figure 14). If this overshoot could potentially damage compo-

diode, can be used to clamp the voltage.

A

B

C

D

E

F

G

9

10

8

11

7

5

6

4

2

3

1

H

J

K

L

C3

C1

C2

C4

A1 BALL

CORNER

0.1µF

0.1µF