REV. PrD

–10–

PRELIMINARY TECHNICAL DATA

Over-Voltage Protection (OVP) & Reverse-Voltage

Protection (RVP)

The ADP3203 features a comprehensive redundantly moni-

tored OVP and RVP implementation to protect the CPU core

against an excessive or reverse voltage, e.g., as might be

induced by a component or connection failure in the control or

power stage. Two pins are associated with the OVP/RVP

circuitry – a pin for output voltage feedback, COREFB, which

is used also for power good monitoring but not for voltage

regulation, and an output pin, CLAMP.

The CLAMP pin defaults to a low state at startup of the

ADP3203 and remains low until an OV or RV condition is

detected. If either condition is detected, the CLAMP pin is

switched and latched to the VCC pin. The high state of the

CLAMP pin is reset only after several milliseconds as the

softstart pin discharges.

For maximum and fastest protection, the CLAMP pin

should be used to drive the gate of a power MOSFET

whose drain-source is connected across the CPU core

voltage. Detection of OV or RV will clamp the core voltage

to essentially zero, thus quickly removing the fault condition

and preventing further energy from being applied to the

CPU core.

For a less comprehensively protective but also less costly

solution, the CLAMP pin may be used to latch the discon-

nection of input power. The latch should be powered

whenever any input power source is present. Typically,

such a latching circuit is already present in a system design,

so it becomes only a matter of allowing the CLAMP pin to

also trigger the latch. In this configuration, the latched off

state of the system would be indicative of a system failure.

The OV/RV protective means is via not allowing the

continued application of energy to the CPU core. The

design objective should be to ensure that the CPU core

could safely absorb the remaining energy in the power

converter, however, since this energy is not clamped as in

the preferred configuration.

LAYOUT CONSIDERATIONS

Advantages in PCB Layout

Analog Devices Inc., provides ADP3203/3415 as a dedicated

2-phase power management solution for IMVP-3 Intel P4

mobile core supply.

This 2-phase solution separates the controller (ADP3203)

and MOSFET driver (ADP3415). Today, most

motherboards only leave small pieces of PCB area for power

management circuit. Therefore, the separation of the

controller and the MOSFET drivers gives much greater

freedom in layout than any single chip solution can do.

Meanwhile, the separation also provides the freedom to

place the analog controller in a relatively quiet area in the

motherboard. This can minimize the susceptibility of the

controller to injected noise. Any single chip solution with a

high speed loop design will suffer larger susceptibility to

jitter that appears as modulation of the output voltage.

The ADP3203 maximizes the integration of IMVP-3

features. Therefore, no additional externally implemented

functions are required to comply with IMVP-3 specifica-

tions. This saves PCB area for component placement on the

motherboard.

PCB Layout Consideration for ADP3203/3415

The following guidelines are recommended for optimal

performance of the ADP3203 and ADP3415 in a power

converter. The circuitry is considered in three parts: the power

switching circuitry, the output filter, and the control circuitry.

Placement Overview

1. For ideal component placement, the output filter

capacitors will divide the power switching circuitry from

the control section. As an approximate guideline,

considered on a single-sided PCB, the best layout would

have components aligned in the following order:

ADP3415, MOSFETs and input capacitor, output

inductor, current sense resistor, output capacitors,

control components and ADP3203. Note that the

ADP3203 and ADP3415 are completely separated for

an ideal layout, which is impossible with a single-chip

solution. This keeps the noisy switched power section

isolated from the precision control section and gives

more freedom in the layout of the power switching

circuitry.

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

MOSFET) is soldered to a PCB, the liberal use of vias,

both directly on the mounting pad if possible and

immediately surrounding it, is recommended. Two

important reasons for this are: improvement of the

current rating through the vias (if it is a current path),

and improved thermal performance- especially if there is

opportunity to spread the heat with a plane on the

opposite side of the PCB.

Power Switching Circuitry

ADP3415, MOSFETs, and Input Capacitors

3. Locate the ADP3415 near the MOSFETs so the loop

inductance in the path of the top gate drive returned to the

SW pin is small, and similarly for the bottom gate drive

whose return path is the ground plane. The GND pin

should have at least one very close via into the ground

plane.

4. Locate the input bypass MLC capacitors close to the

MOSFETs so that the physical area of the loop enclosed

in the electrical path through the bypass capacitor and

around through the top and bottom MOSFETs (drain-

source) is small and wide. This is the switching power

path loop.

5. Make provisions for thermal management of all the

MOSFETs. Heavy copper and wide traces to ground

and power planes will help to pull the heat out.

Heatsinking by a metal tap soldered in the power plane

ADP3203