ADP3160/ADP3167
THEORY OF OPERATION
Active Voltage Positioning
The ADP3160 and ADP3167 combine a current-mode, fixed
frequency PWM controller with antiphase logic outputs in a
controller for a 2-phase synchronous buck power converter.
Two-phase operation is important for switching the high currents
required by high-performance microprocessors. Handling the
high current in a single-phase converter would place difficult
requirements on the power components such as inductor wire
size, MOSFET ON resistance, and thermal dissipation. Their
high-side current sensing topology ensures that the load currents
are balanced in each phase, such that neither phase has to carry
more than half of the power. An additional benefit of high-side
current sensing over output current sensing is that the average
current through the sense resistor is reduced by the duty cycle
of the converter, allowing the use of a lower power, lower cost
resistor. The outputs of the ADP3160/ADP3167 are logic
drivers only and are not intended to drive external power
MOSFETs directly. Instead, the ADP3160/ADP3167 should
The ADP3160 and ADP3167 use Analog Devices Optimal
Positioning Technology (ADOPT), a unique supplemental
regulation technique that uses active voltage positioning and
provides optimal compensation for load transients. When imple-
mented, ADOPT adjusts the output voltage as a function of the
load current, so that it is always optimally positioned for a load
transient. Standard (passive) voltage positioning has poor dynamic
performance, rendering it ineffective under the stringent repetitive
transient conditions required by high-performance processors.
ADOPT, however, provides optimal bandwidth for transient
response that yields optimal load transient response with the
minimum number of output capacitors.
Reference Output
A 3.0 V reference is available and is commonly used to set the
voltage positioning accurately using a resistor divider to the
COMP pin. In addition, the reference can be used for other
functions such as generating a regulated voltage with an external
amplifier. The reference is bypassed with a 1 nF capacitor to
ground. It is not intended to supply current to large capacitive
loads, and it should not be used to provide more than 1 mA of
output current.
be paired with drivers such as the ADP3414 or ADP3417.
A
system level block diagram of a 2-phase power supply for high
current CPUs is shown in Figure 5.
The frequency of the device is set by an external capacitor
connected to the CT pin. Each output phase operates at half of
the frequency set by the CT pin. The error amplifier and
current sense comparator control the duty cycle of the PWM
outputs to maintain regulation. The maximum duty cycle per
phase is inherently limited to 50% because the PWM outputs
toggle in 2-phase operation. While one phase is on, the other
phase is off. In no case can both outputs be high at the same time.
Cycle-by-Cycle Operation
During normal operation (when the output voltage is regulated), the
voltage-error amplifier and the current comparator are the main
control elements. The voltage at the CT pin of the oscillator ramps
between 0 V and 3 V. When that voltage reaches 3 V, the oscillator
sets the driver logic, which sets PWM1 high. During the ON time
of Phase 1, the driver IC turns on the high-side MOSFET. The CS+
and CS– pins monitor the current through the sense resistor that
feeds both high-side MOSFETs. When the voltage between the
two pins exceeds the threshold level set by the voltage error ampli-
fier (gm), the driver logic is reset and the PWM output goes low.
This signals the driver IC to turn off the high-side MOSFET and
turn on the low-side MOSFET. On the next cycle of the oscillator,
the driver logic toggles and sets PWM2 high. On each following
cycle of the oscillator, the outputs toggle between PWM1 and
PWM2. In each case, the current comparator resets the PWM
output low when the current comparator threshold is reached. As
the load current increases, the output voltage starts to decrease.
This causes an increase in the output of the gm amplifier, which in
turn leads to an increase in the current comparator threshold,
thus programming more current to be delivered to the output so
that voltage regulation is maintained.
Output Voltage Sensing
The output voltage is sensed at the FB pin allowing for remote
sensing. To maintain the accuracy of the remote sensing, the
GND pin should also be connected close to the load. A voltage
error amplifier (gm) amplifies the difference between the output
voltage and a programmable reference voltage. The reference volt-
age is programmed between 1.1 V and 1.85 V by an internal 5-bit
DAC that reads the code at the voltage identification (VID) pins.
Refer to Table I for the output voltage versus VID pin code
information.
5V
5V
OR
12V
I
L1
I
ADP3412
OUT
PWM1
SYNCHRONOUS
DRIVER
I
L2
ADP3160/
ADP3167
I
L1
2-PHASE
SYNCHRONOUS
BUCK
OUT
5V OR 12V
+
5V
CONTROLLER
PWM2
PWM1
I
L2
ADP3412
PWM2
SYNCHRONOUS
DRIVER
Figure 5. 2-Phase CPU Supply System Level Block Diagram
–6–
REV. B
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