ADP3203 데이터 시트보기 (PDF) - Analog Devices

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ADP3203

2-Phase IMVP-II and IMVP-III Core Controller for Mobile CPUs

Analog Devices 

ADP3203

Two pins are associated with the OVP/RVP circuitry—a pin for

output voltage feedback, COREFB, which is also used 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 overvoltage or reverse voltage 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 soft

start 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

overvoltage or reverse voltage 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 disconnec-

tion 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 overvoltage/reverse voltage

protective means is via not allowing the continued application of

energy to the CPU core. The design objective should be,

however, to ensure that the CPU core could safely absorb the

remaining energy in the power converter, since this energy is not

clamped as in the preferred configuration.

LAYOUT CONSIDERATIONS

Advantages in PCB Layout

This 2-phase solution separates the controller (ADP3203) and

the MOSFET drivers (ADP3415). Today, most motherboards

only leave small pieces of PCB area for the power management

circuit. Therefore, the separation of the controller and the

MOSFET drivers gives much greater freedom in layout than

any single chip solution.

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-III features.

Therefore, no additional externally implemented functions are

required to comply with IMVP-III specifications. This saves

PCB area for component placement on the motherboard.

PCB Layout Consideration for ADP3203/ADP3415

The following guidelines are recommended for optimal perfor-

mance 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 that 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 near the MOSFETs will help. Even just a small

airflow can help tremendously. Paralleled MOSFETs to achieve

a given resistance will help spread the heat.

6. An external Schottky diode (across the bottom MOSFET)

may increase efficiency by a small amount (< ~1%), depend-

ing on its forward voltage drop compared to the MOSFET’s

body diode at a given current; a MOSFET with a built-in

Schottky is more effective. For an external Schottky, it should

be placed next to the bottom MOSFET or it may not be

effective at all.

7. The VCC bypass capacitor should be close to the VCC pin

and connected on either a very short trace to the GND pin

or to the GND plane.

Output Filter

Output Inductor and Capacitors, Current Sense Resistor

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

voltage plane.

9. The load-side heads of sense resistors should join as closely as

possible for accurate current signal measurement of each phase.

10. PCB trace resistances from the current sense resistors to

the regulation point should be minimized, known (calcu-

lated or measured), and compensated for as part of the

design if it is significant. (Remote sensing is not sufficient

–12–

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