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부품번호 ADP3178 기능
기능 (ADP3158 / ADP3178) 4-Bit Programmable Synchronous Buck Controllers
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ADP3178 데이터시트, 핀배열, 회로
www.DataSheet4U.com
a
FEATURES
Optimally Compensated Active Voltage Positioning
with Gain and Offset Adjustment (ADOPT™) for
Superior Load Transient Response
Complies with VRM Specifications with Lowest
System Cost
4-Bit Digitally Programmable 1.3 V to 2.05 V Output
N-Channel Synchronous Buck Driver
Total Accuracy ؎0.8% Over Temperature
Two On-Board Linear Regulator Controllers Designed
to Meet System Power Sequencing Requirements
High Efficiency Current-Mode Operation
Short Circuit Protection for Switching Regulator
Overvoltage Protection Crowbar Protects Micro-
processors with No Additional External Components
APPLICATIONS
Core Supply Voltage Generation for:
Intel Pentium® III
Intel Celeron™
4-Bit Programmable
Synchronous Buck Controllers
ADP3158/ADP3178
FUNCTIONAL BLOCK DIAGRAM
VCC
UVLO
& BIAS
CT
ADP3158/ ADP3178
OSCILLATOR
PWM
DRIVE
REFERENCE REF
DRVH
DRVL
GND
LRFB1
VLR1
LRDRV1
LRFB2
VLR2
LRDRV2
COMP
REF
DAC+20%
CMP
–+
CS–
CS+
gm
VID DAC
VID3 VID2 VID1 VID0
GENERAL DESCRIPTION
The ADP3158 and ADP3178 are highly efficient synchronous
buck switching regulator controllers optimized for converting a
5 V main supply into the core supply voltage required by high-
performance processors. These devices use an internal 4-bit DAC
to read a voltage identification (VID) code directly from the
processor, which is used to set the output voltage between 1.3 V
and 2.05 V. They use a current mode, constant off-time archi-
tecture to drive two N-channel MOSFETs at a programmable
switching frequency that can be optimized for regulator size and
efficiency.
The ADP3158 and ADP3178 also use a unique supplemental
regulation technique called Analog Devices Optimal Positioning
Technology (ADOPT) to enhance load transient performance.
Active voltage positioning results in a dc/dc converter that
meets the stringent output voltage specifications for high-
performance processors, with the minimum number of output
capacitors and smallest footprint. Unlike voltage-mode and
standard current-mode architectures, active voltage positioning
adjusts the output voltage as a function of the load current so it
is always optimally positioned for a system transient. They also
provide accurate and reliable short circuit protection and
adjustable current limiting. The devices include an integrated
overvoltage crowbar function to protect the microprocessor
from destruction in case the core supply exceeds the nominal
programmed voltage by more than 20%.
The ADP3158 and ADP3178 contain two linear regulator
controllers that are designed to drive external N-channel
MOSFETs. The outputs are internally fixed at 2.5 V and 1.8 V
in the ADP3158, while the ADP3178 provides adjustable out-
puts that are set using an external resistor divider. These
linear regulators are used to generate the auxiliary voltages
(AGP, GTL, etc.) required in most motherboard designs,
and have been designed to provide a high bandwidth load-
transient response.
The ADP3158 and ADP3178 are specified over the commercial
temperature range of 0°C to 70°C and are available in a 16-lead
SOIC package.
ADOPT is a trademark of Analog Devices, Inc.
Pentium is a registered trademark of Intel Corporation.
Celeron is a trademark of Intel Corporation.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001




ADP3178 pdf, 반도체, 판매, 대치품
ADP3158/ADP3178Typical Performance Characteristics
60
50
40
30
20
10
0
0 100 200 300 400 500 600 700 800
OSCILLATOR FREQUENCY kHz
TPC 1. Supply Current vs. Operating Frequency Using
MOSFETs of Figure 3
TEK RUN
TRIG'D
VCC
1
VCORE
2
CH1 5.00V BW CH2 500mV BW M 10.0ms A CH1
0.00000 s
5.90V
TPC 4. Power-On Start-Up Waveform
TEK RUN
DRVH
TRIG'D
1
DRVL
CH1 5.00V BW CH2 5.00V BW M 1.00s A CH1
2.6500s
5.90V
TPC 2. Gate Switching Waveforms Using MOSFETs of
Figure 3
25
TA = 25؇C
VOUT = 1.65V
20
15
10
5
0
0.5 0
0.5
OUTPUT ACCURACY % of Nominal
TPC 5. Output Accuracy Distribution
TEK RUN
TRIG'D
DRVH
DRVL
CH1 2.00V BW CH2 2.00V BW M 1.00ns A CH1
150.000s
5.88V
TPC 3. Driver Transition Waveforms Using MOSFETs of
Figure 3
–4–
REV. A

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ADP3178 전자부품, 판매, 대치품
ADP3158/ADP3178
CT Selection for Operating Frequency
The ADP3158 and ADP3178 use a constant off-time architecture
with tOFF determined by an external timing capacitor CT. Each
time the high-side N-channel MOSFET switch turns on, the volt-
age across CT is reset to 0 V. During the off-time, CT is charged
by a constant current of 150 µA. Once CT reaches 3.0 V, a new
on-time cycle is initiated. The value of the off-time is calculated
using the continuous-mode operating frequency. Assuming a
nominal operating frequency (fNOM) of 200 kHz at an output volt-
age of 1.7 V, the corresponding off-time is:
tOFF
=
1
VOUT
VIN

×
1
fNOM
tOFF
=
1
1.7 V
5V

×
1
200 kHz
=
3.3 µs
(1)
The timing capacitor can be calculated from the equation:
CT
= tOFF × ICT
VT (TH )
= 3.3 µs × 150 µA 150 pF
3V
(2)
(3)
fMIN
=1
tOFF
× VIN IO( MAX ) × (RDS(ON )HSF + RSENSE + RL ) VOUT
VIN IO( MAX ) × (RDS(ON )HSF + RSENSE + RL RDS(ON )LSF ) )
The converter only operates at the nominal operating frequency
at the above-specified VOUT and at light load. At higher values
of VOUT, or under heavy load, the operating frequency decreases
due to the parasitic voltage drops across the power devices. The
actual minimum frequency at VOUT = 1.7 V is calculated to be
195 kHz (see Equation 3), where:
RDS(ON)HSF is the resistance of the high-side MOSFET
(estimated value: 14 m)
RDS(ON)LSF is the resistance of the low-side MOSFET
(estimated value: 6 m)
RSENSE is the resistance of the sense resistor
(estimated value: 4 m)
RL is the resistance of the inductor
(estimated value: 3 m)
Inductance Selection
The choice of inductance determines the ripple current in the
inductor. Less inductance leads to more ripple current, which
increases the output ripple voltage and the conduction losses in
the MOSFETs, but allows using smaller-size inductors and, for
a specified peak-to-peak transient deviation, output capacitors
with less total capacitance. Conversely, a higher inductance means
lower ripple current and reduced conduction losses, but requires
larger-size inductors and more output capacitance for the same
peak-to-peak transient deviation. The following equation shows
the relationship between the inductance, oscillator frequency,
peak-to-peak ripple current in an inductor and input and
output voltages.
L = VOUT × tOFF
IL(RIPPLE )
(4)
For 4 A peak-to-peak ripple current, which corresponds to
approximately 25% of the 15 A full-load dc current in an inductor,
Equation 4 yields an inductance of
L = 1.7V × 3.3 µs = 1.4 µH
4A
A 1.5 µH inductor can be used, which gives a calculated ripple
current of 3.8 A at no load. The inductor should not saturate at
the peak current of 17 A and should be able to handle the sum
of the power dissipation caused by the average current of 15 A
in the winding and the core loss.
Designing an Inductor
Once the inductance is known, the next step is either to design an
inductor or find a standard inductor that comes as close as
possible to meeting the overall design goals. The first decision
in designing the inductor is to choose the core material. There
are several possibilities for providing low core loss at high frequen-
cies. Two examples are the powder cores (e.g., Kool-Mµ® from
Magnetics, Inc.) and the gapped soft ferrite cores (e.g., 3F3 or 3F4
from Philips). Low frequency powdered iron cores should be
avoided due to their high core loss, especially when the inductor
value is relatively low and the ripple current is high.
Two main core types can be used in this application. Open
magnetic loop types, such as beads, beads on leads, and rods
and slugs, provide lower cost but do not have a focused mag-
netic field in the core. The radiated EMI from the distributed
magnetic field may create problems with noise interference in
the circuitry surrounding the inductor. Closed-loop types, such
as pot cores, PQ, U, and E cores, or toroids, cost more, but
have much better EMI/RFI performance. A good compromise
between price and performance are cores with a toroidal shape.
REV. A
–7–

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