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ADP1109AAR-33 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP1109AAR-33
Beschreibung Micropower Low Cost Fixed 3.3 V/ 5 V/ 12 V and Adjustable DC-to-DC Converter
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADP1109AAR-33 Datasheet, Funktion
a
Micropower Low Cost
Fixed 3.3 V, 5 V, 12 V and Adjustable
DC-to-DC Converter
FEATURES
Operates at Supply Voltages 2 V to 9 V
Fixed 3.3 V, 5 V, 12 V and Adjustable Output
Minimum External Components Required
Ground Current: 460 A
Oscillator Frequency: 120 kHz
Logic Shutdown
8-Lead DIP and SO-8 Packages
APPLICATIONS
Cellular Telephones
Single-Cell to 5 V Converters
Laptop and Palmtop Computers
Pagers
Cameras
Battery Backup Supplies
Portable Instruments
Laser Diode Drivers
Hand-Held Inventory Computers
GENERAL DESCRIPTION
The ADP1109A is a versatile step-up switching regulator. The
device requires only minimal external components to operate as
a complete switching regulator.
The ADP1109A-5 can deliver 100 mA at 5 V from a 3 V input
and the ADP1109A-12 can deliver 60 mA at 12 V from a 5 V
input. The device also features a logic controlled shutdown
capability that, when a logic low is applied, will shut down the
oscillator. The 120 kHz operating frequency allows for the use
of small surface mount components.
The gated oscillator capability eliminates the need for frequency
compensation.
ADP1109A
FUNCTIONAL BLOCK DIAGRAM
VIN SENSE
1.25V
REFERENCE
R2
250k
ADP1109A-3.3: R1 = 152k
ADP1109A-5: R1 = 83k
ADP1109A-12: R1 = 29k
COMPARATOR
SW
A1
R1
120kHz
OSCILLATOR
Q1
DRIVER
GND
SHUTDOWN
PGND
VIN FB
ADP1109A
1.25V
REFERENCE
COMPARATOR
SW
A1
120kHz
OSCILLATOR
Q1
DRIVER
GND
SHUTDOWN
PGND
TYPICAL APPLICATION
L1
33H
D1
3
VIN
1 VIN
SW SENSE 8
VOUT
5V 12V
ADP1109A-12
60mA
7 SHUTDOWN
PGND
GND
4
SHUTDOWN/PROGRAM
5
+ C1
22F
16V
Flash Memory VPP Generator
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: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1997






ADP1109AAR-33 Datasheet, Funktion
ADP1109A
APPLICATION INFORMATION
THEORY OF OPERATION
The ADP1109A is a flexible, low power switch-mode power
supply (SMPS) controller for step-up dc/dc converter applica-
tions. This device uses a gated-oscillator technique to provide
very high performance with low quiescent current. For example,
more than 2 W of output power can be generated from a +5 V
source, while quiescent current is only 360 µA.
A functional block diagram of the ADP1109A is shown on the
front page. The internal 1.25 V reference is connected to one
input of the comparator, while the other input is externally
connected (via the FB pin) to a feedback network connected to
the regulated output. When the voltage at the FB pin falls below
1.25 V, the 120 kHz oscillator turns on. A driver amplifier pro-
vides base drive to the internal power switch, and the switching
action raises the output voltage. When the voltage at the FB pin
exceeds 1.25 V, the oscillator is shut off. While the oscillator is
off, the ADP1109A quiescent current is only 460 µA. The com-
parator includes a small amount of hysteresis, which ensures
loop stability without requiring external components for fre-
quency compensation.
A shutdown feature permits the oscillator to be shut off. Hold-
ing SHUTDOWN low will disable the oscillator, and the
ADP1109A’s quiescent current will remain 460 µA.
The output voltage of the ADP1109A is set with two external
resistors. Three fixed-voltage models are also available: the
ADP1109A-3.3 (+3.3 V), ADP1109A-5 (+5 V) and ADP1109A-12
(+12 V). The fixed-voltage models are identical to the ADP1109A,
except that laser-trimmed voltage-setting resistors are included on
the chip. On the fixed-voltage models of the ADP1109A, simply
connect the SENSE pin (Pin 8) directly to the output voltage.
considered for battery powered and similar applications where
the input voltage varies.
To minimize Electro-Magnetic Interference (EMI), a toroid or
pot core type inductor is recommended. Rod core inductors are
a lower-cost alternative if EMI is not a problem.
Calculating the Inductor Value
Selecting the proper inductor value is a simple two step process:
1. Define the operating parameters: minimum input voltage,
maximum input voltage, output voltage and output current.
2. Calculate the inductor value, using the equations in the fol-
lowing section.
Inductor Selection
In a step-up, or boost, converter (Figure 1), the inductor must
store enough power to make up the difference between the input
voltage and the output voltage. The inductor power is calculated
from the equation:
( ) ( )PL = VOUT +V D VIN (MIN ) × IOUT
(1)
where VD is the diode forward voltage (Ϸ0.5 V for a 1N5818
Schottky). Energy is only stored in the inductor while the
ADP1109A switch is ON, so the energy stored in the inductor
on each switching cycle must be must be equal to or greater
than:
PL
f OSC
(2)
in order for the ADP1109A to regulate the output voltage. When
the internal power switch turns ON, current flow in the inductor
increases at the rate of:
COMPONENT SELECTION
General Notes on Inductor Selection
When the ADP1109A internal power switch turns on, current
begins to flow in the inductor. Energy is stored in the inductor
core while the switch is on, and this stored energy is then trans-
ferred to the load when the switch turns off.
To specify an inductor for the ADP1109A, the proper values of
inductance, saturation current and dc resistance must be deter-
mined. This process is not difficult, and specific equations are
provided in this data sheet. In general terms, however, the induc-
tance value must be low enough to store the required amount of
energy (when both input voltage and switch ON time are at a
minimum) but high enough that the inductor will not saturate
when both VIN and switch ON time are at their maximum val-
ues. The inductor must also store enough energy to supply the
load, without saturating. Finally, the dc resistance of the induc-
tor should be low, so that excessive power will not be wasted by
heating the windings. For most ADP1109A applications, an
inductor of 10 µH to 47 µH, with a saturation current rating of
300 mA to 1 A and dc resistance <0.4 is suitable. Ferrite core
inductors that meet these specifications are available in small,
surface-mount packages. Air-core inductors, as well as RF chokes,
are unsuitable because of their low peak current ratings.
The ADP1109A is designed for applications where the input
voltage is fairly stable, such as generating +12 V from a +5 V
logic supply. The ADP1109A does not have an internal switch
current limiting circuit, so the inductor may saturate if the input
voltage is too high. The ADP1111 or ADP3000 should be
( )IL t
=
V IN
R'
R't
1e L 
(3)
where L is in Henrys and R' is the sum of the switch equivalent
resistance (typically 0.8 at +25°C) and the dc resistance of
the inductor. In most applications, the voltage drop across the
switch is small compared to VIN so a simpler equation can be
used:
( )IL t
= V IN t
L
(4)
Replacing t in the above equation with the ON time of the
ADP1109A (5.5 µs, typical) will define the peak current for a
given inductor value and input voltage. At this point, the induc-
tor energy can be calculated as follows:
EL
=
1L
2
×
I
2
peak
(5)
As previously mentioned, EL must be greater than PL/fOSC so
that the ADP1109A can deliver the necessary power to the load.
For best efficiency, peak current should be limited to 1 A or
less. Higher switch currents will reduce efficiency because of
increased saturation voltage in the switch. High peak current
also increases output ripple. As a general rule, keep peak current
as low as possible to minimize losses in the switch, inductor and
diode.
–6– REV. 0

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