ADP3204 Analog Devices, ADP3204 Datasheet - Page 13

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

Power Switching Circuitry
ADP3415, MOSFETs, and Input Capacitors
3.
4.
5.
6.
Output Filter
Output Inductor and Capacitors, Current Sense Resistor
8.
9.
10. PCB trace resistances from the current sense resistors to
11. Whenever high currents must be routed between PCB
REV. 0
7.
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.
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.
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. Heat sinking 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.
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.
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.
Locate the current sense resistors very near to the output
voltage plane.
The load-side heads of sense resistors should join as closely
as possible for accurate current signal measurement of
each phase.
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
for relieving this requirement.) A square section of 1-ounce
copper trace has a resistance of ~0.5 mΩ, which adds to
the specified DC output resistance of the power converter.
The output capacitors should similarly be close to the
regulation point and well tied into power planes as imped-
ance here will add to the “AC output resistance” (i.e., the
ESR) that is implicitly specified as well.
layers, vias should be used liberally to create parallel current
paths so that the resistance and inductance are minimized
and the via current rating is not exceeded.
–13–
Control Circuitry
ADP3204, Control Components
12. If the ADP3204 cannot be placed as previously recom-
13. Noise immunity can be improved by the use of a devoted
14. If critical signal lines (i.e., signals from the current sense
15. Absolutely avoid crossing any signal lines over the switching
16. Accurate voltage positioning depends on accurate current
17. The RC filter used for the current sense signal should be
APPLICATION INFORMATION
Theoretical Background
This application section presents the theoretical background for
multiphase dc-to-dc converters using the ADP320x family of
controllers for mobile CPUs. Members of that family control
multiphase ripple regulators (also called hysteretic regulators) in
a configuration that allows employing ADOPT, Analog Devices’
optimal voltage positioning technique to implement the desired
output voltage and load line, both statically and dynamically, as
required by Intel’s IMVP-II and IMVP-III specifications.
Single-Phase Hysteretic Regulator with ADOPT
Figure 2 shows the conventional single-phase hysteretic
regulator and the characteristic waveforms. The operation is as
follows. During the time the upper transistor, Q1, is turned on,
the inductor current, I
increase. When V
hysteretic comparator, Q1 is turned off, Q2 is turned on, and
the inductor current and the output voltage decrease. The cycle
repeats after V
comparator.
mended, care should be taken to keep the device and
surrounding components away from radiation sources
(e.g., from power inductors) and capacitive coupling from
noisy power nodes.
signal ground plane for the power controller and its
surrounding components. Space for a ground plane might
readily be available on a signal plane of the PCB since it is
often unused in the vicinity of the power controller.
resistor leading back to the ADP3204) must cross through
power circuitry, it is best if a signal ground plane can be
interposed between those signal lines and the traces of the
power circuitry. This serves as a shield to minimize noise
injection into the signals.
power path loop, described previously.
sensing, so the control signals that monitor the voltage
differentially across the current sense resistor should be
Kelvin-connected. Please refer to ADI Evaluation Board of
the ADP3204 and its documentation for control signal
connection with sense resistors.
located near the control components as this serves the
dual purpose of filtering out the effect of the current sense
resistors’ parasitic inductance and the noise picked up along
the routing of the signal. The former purpose is achieved by
having the time constant of the RC filters approximately
matched to that of the sense resistors, and is important
for maintaining the accuracy of the current signal.
OUT
OUT
reaches the lower threshold of the hysteretic
reaches the upper threshold of the
L
, and also the output voltage, V
ADP3204
OUT
,