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ADP3171 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP3171
Beschreibung Synchronous Buck Controller with Dual Linear Regulator Controllers
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 12 Seiten
ADP3171 Datasheet, Funktion
a
Synchronous Buck Controller
with Dual Linear Regulator Controllers
ADP3171
FEATURES
Fixed 1.2 V N-Channel Synchronous Buck Driver
Two On-Board Linear Regulator Controllers
Total Accuracy ±1% over Temperature
High Efficiency Current-Mode Operation
Short Circuit Protection
Power Good Output
Overvoltage Protection Crowbar Protects Switching
Output with No Additional External Components
APPLICATIONS
Auxiliary System Supplies for Desktop
Computer Systems
General-Purpose Low Voltage Supplies
FUNCTIONAL BLOCK DIAGRAM
VCC
UVLO
AND BIAS
REFERENCE
CT
8
OSCILLATOR
SET
RESET
CROWBAR
REF
PWM
LOGIC
DRVH
DRVL
GND 1
1.5V
LRFB1 3
DAC +20%
PWRGD
LRDRV1 4
LRFB2
LRDRV2
1.8V
COMP
ADP3171
CMP
DAC –20%
CS–
7 CS+
5 FB
gm
1.2V
GENERAL DESCRIPTION
The ADP3171 is a highly efficient output synchronous buck
switching regulator controller optimized for converting a 5 V
main supply into the auxiliary supply voltages required by
processors and chipsets. The ADP3171 provides a fixed
output voltage of 1.2 V at up to 15 A, depending on the
power ratings of the external MOSFETs and inductor. The
ADP3171 uses a current-mode, constant off time architecture to
drive two N-channel MOSFETs at a programmable switching
frequency that can be optimized for regulator size and efficiency.
The ADP3171 provides accurate and reliable short circuit
protection and adjustable current limiting. It also includes an
integrated overvoltage crowbar function to protect the load in
case the output voltage exceeds the nominal programmed
voltage by more than 20%.
The ADP3171 contains two fixed output voltage linear regulator
controllers that are designed to drive external N-channel
MOSFETs. These linear regulators are used to generate the
auxiliary voltages required in most motherboard designs and have
been designed to provide a high bandwidth load-transient response.
The ADP3171 is specified over the commercial temperature
range of 0°C to 70°C and is available in a 14-lead SOIC package.
REV. 0
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., 2002






ADP3171 Datasheet, Funktion
ADP3171
5V
5VSB
D1
MBR052LT1
12V
D2
MBR052LT1
5VSB
Q1
2N7000
C1
1F
C2
10F
C3
100pF
+ C5
1000F
+ C6
4.7F
C7
100nF
C8
22F
L1
1.7H
1 GND
DRVH 14
2 PWRGD DRVL 13
3 LRFB1
VCC 12
4 LRDRV1 LRFB2 11
5 FB
LRDRV2 10
6 CS–
COMP 9
7 CS+
CT 8
C9
150pF
R1
220
C3
1nF
R2
220
R3 R4
1k249
Q2
FDS6982
C10
100pF
R8
10k
R9
8.25k
5VSB
Q3
IRFU014
C12
1F
+ C13
220F
R6 820F ؋ 4
7.5m7.5mESR (EACH)
C14 C15 C16 C17
1.5V, 5A
3.3VSB, 1.5A
1.5VSB, 35mA
Figure 3. Pentium® III Auxiliary Supply Generating 1.5 V, 1.5 V Standby, and 3.3 V Standby
be disabled in standby mode, but the linear regulators will
begin conducting once VCC rises above about 1 V. During
startup, the linear outputs will track the 3.3 V supply up until
they reach their respective regulation points, regardless of the
state of the 12 V supply. Once the 12 V supply has exceeded
the 5 VSB supply, the controller IC will track the 12 V supply.
Once the 12 V supply has risen above the UVLO value, the
switching regulator will begin its start-up sequence.
tOFF
=
1 –
VOUT
VIN

×
1
fNOM
tOFF
=
1
1.5 V
5V

×
1
200 kHz
= 3.5 µs
(1)
The timing capacitor can be calculated from the equation:
APPLICATION INFORMATION
Specifications for a Design Example
The design parameters for a typical auxiliary supply for a Pen-
tium III application (shown in Figure 3) are as follows:
Input Voltage: (VIN) = 5 V
Auxiliary Input: (VCC) = 12 V
Main Output: (VOUT) = 1.5 V @ 5 A
LDO 1 Output: (1.5 VSB) = 1.5 V @ 35 mA
LDO 2 Output: (3.3 VSB) = 3.3 V @ 1.5 A
CT Selection for Operating Frequency
The ADP3171 uses 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 voltage across
CT is reset to approximately 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 voltage of 1.5 V, the corresponding off time is:
CT
= tOFF × ICT
VT(TH)
=
3.5
µs
× 150
3V
µA
= 175
pF
(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 )
fMIN
=1×
3.5 µs
5V – 5 A × (15 mΩ + 7.5 mΩ + 3 m) – 1.5V = 192 kHz
5V – 5 A × (15 mΩ + 7.5 mΩ + 3 m– 28 m)
The nearest standard value is 150 pF. The converter operates at
the nominal operating frequency only 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 = 1.5 V is calculated to be 192 kHz (see Equation 3),
where:
RDS(ON)HSF is the resistance of the high side MOSFET
(estimated value: 15 m)
RDS(ON)LSF is the resistance of the low side MOSFET
(estimated value: 28 m)
RSENSE is the resistance of the sense resistor
(estimated value: 7.5 m)
RL is the resistance of the inductor (estimated value: 3 m)
Pentium is a registered trademark of Intel Corporation.
–6– REV. 0

6 Page









ADP3171 pdf, datenblatt
ADP3171
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm)
14-Lead Narrow SOIC
(R-14)
0.3444 (8.75)
0.3367 (8.55)
0.1574 (4.00) 14
0.1497 (3.80)
1
8 0.2440 (6.20)
0.2284 (5.80)
7
PIN 1 0.050 (1.27) 0.0688 (1.75)
BSC
0.0532 (1.35)
0.0196 (0.50)
0.0099 (0.25)؋ 45؇
0.0098 (0.25)
0.0040 (0.10)
8؇
0.0192 (0.49)
0.0138 (0.35)
SEATING
PLANE
0.0099 (0.25) 0؇
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
–12–

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