ADP3204 Analog Devices, ADP3204 Datasheet - Page 12

• Manufacturer Part Number: ADP3204
• Description: 3-Phase IMVP-II and IMVP-III Core Controller for Mobile CPUs
• Manufacturer: Analog Devices

ADP3204
SoftStart and Hiccup
A capacitor from the SS pin to ground determines both the soft
start time and the frequency at which hiccup will occur under a
continuous short circuit or overload.
System Signal Interface
Several pins of the ADP3204 are meant to connect directly to
system signals. The VID pins connect to the system VID
control signals. The DPRSLP pin connects to the system’s
DPRSLPVR signal. The DPSLP pin connects to the system’s
DPSLP or STPCPU signal. The BOM signal connects to the
system’s GMUXSEL signal. In an IMVP-II system, the
GMUXSEL signal precedes any VID code change with a few
nanoseconds, while in an IMVP-III system, it follows it with a
maximum 12 µs delay. To comply with both specifications, the
ADP3204 has a VID register in front of the DAC inputs that is
written by a short pulse generated at the rising or falling edge of
the GMUXSEL signal. In an IMVP-II configuration, if the
external VID multiplex settling time is longer than the internal
VID register’s write pulsewidth, then the insertion of an external
RC delay network in the GMUXSEL signal path (in front of the
BOM pin) is recommended. The Intel specification calls for
maximum 200 ns VID code setup time. This specification can
be met with a simple RC network that consists of only a 220 kΩ
resistor and no external capacitor, just the BOM pin’s capacitance.
Undervoltage Lockout
The ADP3204’s supply pin, VCC, has undervoltage lockout
(UVLO) functionality to ensure that if the supply voltage is too
low to maintain proper operation, the IC will remain off and in
a low current state.
Overvoltage Protection (OVP) and Reverse Voltage
Protection (RVP)
The ADP3204 features a comprehensive redundantly monitored
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 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
ADP3204 and remains low until an overvoltage or reverse
voltage condition is detected. If either condition is detected, the
CLAMP signal is asserted and latched high.
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 and less costly solution,
the CLAMP pin may be used to latch the disconnection 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
–12–
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
Analog Devices provides ADP3204/3415 as a dedicated three-
phase power management solution for IMVP-III Intel P4
mobile core supply.
This three-phase solution separates the controller (ADP3204)
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 ADP3204 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 ADP3204/3415
The following guidelines are recommended for optimal perfor-
mance of the ADP3204 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
2. Whenever a power dissipating component (e.g., a power
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 ADP3204. Note that
the ADP3204 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.
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.
REV. 0