ADP1109 Datasheet PDF - Analog Devices
| Part Number | ADP1109 | |
| Description | Micropower Low Cost Fixed 3.3 V/ 5 V/ 12 V and Adjustable DC-to-DC Converter | |
| Manufacturers | Analog Devices | |
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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 12 V
Fixed 3.3 V, 5 V, 12 V and Adjustable Output
Minimum External Components Required
Ground Current: 320 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 ADP1109 is a versatile step-up switching regulator. The
device requires only minimal external components to operate as
a complete switching regulator.
The ADP1109-5 can deliver 100 mA at 5 V from a 3 V input
and the ADP1109-12 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.
ADP1109
FUNCTIONAL BLOCK DIAGRAMS
VIN SENSE
1.25V
REFERENCE
R2
250k⍀
ADP1109-3.3: R1 = 152k⍀
ADP1109-5: R1 = 83k⍀
ADP1109-12: R1 = 29k⍀
COMPARATOR
+
A1
120kHz
OSCILLATOR
Q1
SW
DRIVER
R1
GND
SHUTDOWN
Fixed Output
VIN FB
1.25V
REFERENCE
COMPARATOR
+
A1
ADP1109
SW
120kHz
OSCILLATOR
Q1
DRIVER
GND
SHUTDOWN
Adjustable Output
TYPICAL APPLICATION
L1
33H
D1
VIN
5V
VIN SW SENSE
ADP1109-12
SHUTDOWN
GND
SHUTDOWN/PROGRAM
+ C1
22F
16V
VOUT
12V
60mA
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., 1998
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ADP1109
APPLICATION INFORMATION
THEORY OF OPERATION
The ADP1109 is a flexible, low power switch-mode power sup-
ply (SMPS) controller for step-up dc/dc converter applications.
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 450 µA.
A functional block diagram of the ADP1109 is shown on page 1.
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 provides base
drive to the internal power switch, and the switching action
raises the output voltage. When the voltage at the FB pin ex-
ceeds 1.25 V, the oscillator is shut off. While the oscillator is off,
the ADP1109 quiescent current is only 450 µA. The comparator
includes a small amount of hysteresis, which ensures loop stabil-
ity without requiring external components for frequency com-
pensation.
A shutdown feature permits the oscillator to be shut off. Hold-
ing SHUTDOWN low will disable the oscillator, and the
ADP1109’s quiescent current will remain 450 µA.
The output voltage of the ADP1109 is set with two external
resistors. Three fixed-voltage models are also available: the
ADP1109-3.3 (+3.3 V), ADP1109-5 (+5 V) and ADP1109-12
(+12 V). The fixed-voltage models are identical to the ADP1109,
except that laser-trimmed voltage-setting resistors are included on
the chip. On the fixed-voltage models of the ADP1109, simply
connect the SENSE pin (Pin 8) directly to the output voltage.
COMPONENT SELECTION
General Notes on Inductor Selection
When the ADP1109 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 ADP1109, 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 ADP1109 applications, an in-
ductor of 10 µH to 47 µH, with a saturation current rating of
300 mA to 1 A and dc resistance <0.4 Ω 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 ADP1109 is designed for applications where the input
voltage is fairly stable, such as generating +12 V from a +5 V
logic supply. The ADP1109 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
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 stored in the inductor only while the
ADP1109 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 ADP1109 to regulate the output voltage. When the
internal power switch turns ON, current flow in the inductor
increases at the rate of:
( )IL
t
=
V IN
R'
1−
−R't
e L
(3)
where L is in Henrys and R' is the sum of the switch equivalent
resistance (typically 0.8 Ω 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
L
t
(4)
Replacing t in the above equation with the ON time of the
ADP1109 (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
=
1
L
2
×
I
2
peak
(5)
REV. 0
–5–
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for ADP1109 electronic component. |
| Information | Total 8 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ ADP1109.PDF Datasheet ] | |
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