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ADP3000AN Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP3000AN
Beschreibung Micropower Step-Up/Step-Down Fixed 3.3 V/ 5 V/ 12 V and Adjustable High Frequency Switching Regulator
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 12 Seiten
ADP3000AN Datasheet, Funktion
a
Micropower Step-Up/Step-Down
Fixed 3.3 V, 5 V, 12 V and Adjustable
High Frequency Switching Regulator
ADP3000
FEATURES
Operates at Supply Voltages from 2 V to 30 V
Works in Step-Up or Step-Down Mode
Very Few External Components Required
High Frequency Operation Up to 400 kHz
Low Battery Detector on Chip
User Adjustable Current Limit
Fixed and Adjustable Output Voltage
8-Pin DIP and SO-8 Package
Small Inductors and Capacitors
APPLICATIONS
Notebook, Palmtop Computers
Cellular Telephones
Hard Disk Drives
Portable Instruments
Pagers
GENERAL DESCRIPTION
The ADP3000 is a versatile step-up/step-down switching
regulator that operates from an input supply voltage of 2 V to
12 V in step-up mode and up to 30 V in step-down mode.
The ADP3000 operates in Pulse Frequency Mode (PFM) and
consumes only 500 µA, making it highly suitable for applica-
tions that require low quiescent current.
The ADP3000 can deliver an output current of 100 mA at
3 V from a 5 V input in step-down configuration and 180 mA at
3.3 V from a 2 V input in step-up configuration.
The auxiliary gain amplifier can be used as a low battery detector,
linear regulator undervoltage lockout or error amplifier.
The ADP3000 operates at 400 kHz switching frequency. This
allows the use of small external components (inductors and
capacitors), making the device very suitable for space constrained
designs.
FUNCTIONAL BLOCK DIAGRAM
SET
A1
VIN
GAIN BLOCK/
ERROR AMP
1.245V
REFERENCE
400kHz
OSCILLATOR
COMPARATOR
DRIVER
R1 R2
ADP3000
GND
SENSE
A0
ILIM
SW1
SW2
VIN
2V–3.2V
100µF
10V
120
6.8µH IN5817
3.3V @
180mA
12
ILIM
VIN
SW1 3
ADP3000-3.3V
FB
(SENSE)
8
GND SW2
54
+ C1
100µF
10V
C1, C2: AVX TPS D107 M010R0100
L1: SUMIDA CD43-6R8
Figure 1. Typical Application
VIN
5V–6V
C1
100µF
10V
RLIM
120
1 23
ILIM VIN SW1
FB 8
ADP3000
GND
5
SW2 4
D1
1N5818
C1, C2: AVX TPS D107 M010R0100
L1: SUMIDA CD43-100
L1
10µH
CL +
100µF
10V
R2
150k
1%
VOUT
3V
100mA
R1
110k
1%
Figure 2. Step-Down Mode Operation
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
which 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: 617/329-4700 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1997






ADP3000AN Datasheet, Funktion
ADP3000
THEORY OF OPERATION
The ADP3000 is a versatile, high frequency, switch mode
power supply (SMPS) controller. The regulated output
voltage can be greater than the input voltage (boost or step-up
mode) or less than the input (buck or step-down mode). This
device uses a gated oscillator technique to provide high perfor-
mance with low quiescent current.
A functional block diagram of the ADP3000 is shown in
Figure 3a. The internal 1.245 V reference is connected to one
input of the comparator, while the other input is externally
connected (via the FB pin) to a resistor divider connected to
the regulated output. When the voltage at the FB pin falls below
1.245 V, the 400 kHz oscillator turns on. A driver amplifier
provides base drive to the internal power switch and the switching
action raises the output voltage. When the voltage at the FB
pin exceeds 1.245 V, the oscillator is shut off. While the
oscillator is off, the ADP3000 quiescent current is only 500 µA.
The comparator’s hysteresis ensures loop stability without
requiring external components for frequency compensation.
The maximum current in the internal power switch can be set
by connecting a resistor between VIN and the ILIM pin. When
the maximum current is exceeded, the switch is turned OFF.
The current limit circuitry has a time delay of about 0.3 µs. If
an external resistor is not used, connect ILIM to VIN. This
yields the maximum feasible current limit. Further information
on ILIM is included in the “Applications” section of this data
sheet. The ADP3000 internal oscillator provides typically 1.7
µs ON and 0.8 µs OFF times.
An uncommitted gain block on the ADP3000 can be con-
nected as a low battery detector. The inverting input of the
gain block is internally connected to the 1.245 V reference.
The noninverting input is available at the SET pin. A resistor
divider, connected between VIN and GND with the junction
connected to the SET pin, causes the AO output to go LOW
when the low battery set point is exceeded. The AO output is
an open collector NPN transistor that can sink in excess of
300 µA.
The ADP3000 provides external connections for both the
collector and emitter of its internal power switch, which permits
both step-up and step-down modes of operation. For the step-
up mode, the emitter (Pin SW2) is connected to GND and the
collector (Pin SW1) drives the inductor. For step-down mode,
the emitter drives the inductor while the collector is connected
to VIN.
The output voltage of the ADP3000 is set with two external
resistors. Three fixed voltage models are also available:
ADP3000–3.3 (+3.3 V), ADP3000–5 (+5 V) and ADP3000–12
(+12 V). The fixed voltage models include laser-trimmed
voltage-setting resistors on the chip. On the fixed voltage models
of the ADP3000, simply connect the feedback pin (Pin 8)
directly to the output voltage.
APPLICATIONS INFORMATION
COMPONENT SELECTION
Inductor Selection
For most applications the inductor used with the ADP3000 will
fall in the range between 4.7 µH to 33 µH. Table I shows
recommended inductors and their vendors.
When selecting an inductor, it is very important to make sure
that the inductor used with the ADP3000 is able to handle a
current that is higher than the ADP3000’s current limit without
saturation.
As a rule of thumb, powdered iron cores saturate softly, whereas
Ferrite cores saturate abruptly. Rod or “open” drum core
geometry inductors saturate gradually. Inductors that saturate
gradually are easier to use. Even though rod or drum core
inductors are attractive in both price and physical size, these
types of inductors must be handled with care because they have
high magnetic radiation. Toroid or “closed” core geometry
should be used when minimizing EMI is critical.
In addition, inductor dc resistance causes power loss. It is best
to use low dc resistance inductors so that power loss in the
inductor is kept to the minimum. Typically, it is best to use an
inductor with a dc resistance lower than 0.2 .
Table I. Recommended Inductors
Vendor Series
Core Type Phone Numbers
Coiltronics
Coiltronics
Sumida
Sumida
OCTAPAC
UNIPAC
Toroid
Open
CD43, CD54
Open
CDRH62, CDRH73, Semi-Closed
CDRH64
Geometry
(407) 241-7876
(407) 241-7876
(847) 956-0666
(847) 956-0666
Capacitor Selection
For most applications, the capacitor used with the ADP3000
will fall in the range between 33 µF to 220 µF. Table II shows
recommended capacitors and their vendors.
For input and output capacitors, use low ESR type capacitors
for best efficiency and lowest ripple. Recommended capacitors
include AVX TPS series, Sprague 595D series, Panasonic HFQ
series and Sanyo OS-CON series.
When selecting a capacitor, it is important to make sure the
maximum capacitor ripple current rms rating is higher than the
ADP3000’s rms switching current.
It is best to protect the input capacitor from high turn-on cur-
rent charging surges by derating the capacitor voltage by 2:1.
For very low input or output voltage ripple requirements,
Sanyo OS-CON series capacitors can be used since this type of
capacitor has very low ESR. Alternatively, two or more tanta-
lum capacitors can be used in parallel.
–6– REV. 0

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