11

A multi-layer printed circuit board is recommended. Figure 9

shows the connections of most of the components in the

converter. Note that the individual capacitors shown each

could represent numerous physical capacitors. Dedicate one

solid layer for a ground plane and make all critical

component ground connections through vias placed as close

to the component terminal as possible. Dedicate another

solid layer as a power plane and break this plane into

smaller islands of common voltage levels. Ideally, the power

plane should support both the input power and output power

nodes. Use copper filled polygons on the top and bottom

circuit layers to create power islands connecting the filtering

components (output capacitors) and the loads. Use the

remaining printed circuit layers for small signal wiring.

Component Selection Guidelines

Output Capacitors Selection

The output capacitors for all outputs should be selected to

allow the output voltage to meet the dynamic regulation

requirements of active state operation (S0, S1). The load

transient for the various microprocessor system’s

components may require high quality capacitors to supply

the high slew rate (di/dt) current demands. Thus, it is

recommended that the output capacitors be selected for

transient load regulation, paying attention to their parasitic

components (ESR, ESL).

Also, during the transition between active and sleep states,

there is a short interval of time during which none of the

power pass elements are conducting - during this time the

output capacitors have to supply all the output current. The

output voltage drop during this brief period of time can be

easily approximated with the following formula:

, where

The output voltage drop is heavily dependent on the ESR

(equivalent series resistance) of the output capacitor bank,

the choice of capacitors should be such as to maintain the

output voltage above the lowest allowable regulation level.

loop stability. Figure 10 outlines a capacitance vs. equivalent

series resistance envelope. For stable operation and

combination of capacitors with characteristics within the

shown envelope.

Input Capacitors Selection

The input capacitors for an HIP6502 application have to

have a sufficiently low ESR as to not allow the input voltage

to dip excessively when energy is transferred to the output

capacitors. If the ATX supply does not meet the

specifications, certain imbalances between the ATX’s

outputs and the HIP6502’s regulation levels could have as a

FIGURE 9. PRINTED CIRCUIT BOARD ISLANDS

Q1

Q2

Q3

Q4

VIA CONNECTION TO GROUND PLANE

ISLAND ON POWER PLANE LAYER

ISLAND ON CIRCUIT/POWER PLANE LAYER

HIP6502

SS

GND

VSEN2

5VDLSB

DRV2

3V3DLSB

KEY

12V

5VSB

DLA

Q5

5VDL

3V3DL

5V

3V3

VSEN1

VCLK

Q6

V

OUT

∆

I

OUT

ESR

OUT

t

t

C

OUT

----------------

+







×

=

1

0.1

10

0.01

CAPACITANCE (

µF)

10

100

1000

HIP6502