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ADP1111 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP1111
Beschreibung Micropower/ Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V/ 5 V/ 12 V
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADP1111 Datasheet, Funktion
Micropower, Step-Up/Step-Down SW
a Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V
ADP1111
FEATURES
Operates from 2 V to 30 V Input Voltage Range
72 kHz Frequency Operation
Utilizes Surface Mount Inductors
Very Few External Components Required
Operates in Step-Up/Step-Down or Inverting Mode
Low Battery Detector
User Adjustable Current Limit
Internal 1 A Power Switch
Fixed or Adjustable Output Voltage
8-Pin DIP or SO-8 Package
APPLICATIONS
3 V to 5 V, 5 V to 12 V Step-Up Converters
9 V to 5 V, 12 V to 5 V Step-Down Converters
Laptop and Palmtop Computers
Cellular Telephones
Flash Memory VPP Generators
Remote Controls
Peripherals and Add-On Cards
Battery Backup Supplies
Uninterruptible Supplies
Portable Instruments
GENERAL DESCRIPTION
The ADP1111 is part of a family of step-up/step-down switch-
ing regulators that operates from an input voltage supply of 2 V
to 12 V in step-up mode and up to 30 V in step-down mode.
The ADP1111 can be programmed to operate in step-up/step-
down or inverting applications with only 3 external components.
The fixed outputs are 3.3 V, 5 V and 12 V; and an adjustable
version is also available. The ADP1111 can deliver 100 mA at
5 V from a 3 V input in step-up mode, or it can deliver 200 mA
at 5 V from a 12 V input in step-down mode.
FUNCTIONAL BLOCK DIAGRAMS
SET
ADP1111
A2
VIN
GAIN BLOCK/
ERROR AMP
1.25V
REFERENCE
A1 OSCILLATOR
COMPARATOR
DRIVER
A0
ILIM
SW1
GND
FB
SET
SW2
VIN
1.25V
REFERENCE
R1
A2
GAIN BLOCK/
ERROR AMP
ADP1111-5
ADP1111-12
A0
ILIM
SW1
A1 OSCILLATOR
COMPARATOR
R2 220k
DRIVER
SW2
GND
SENSE
Maximum switch current can be programmed with a single
resistor, and an open collector gain block can be arranged in
multiple configuration for low battery detection, as a post linear
regulator, undervoltage lockout, or as an error amplifier.
If input voltages are lower than 2 V, see the ADP1110.
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., 1996






ADP1111 Datasheet, Funktion
ADP1111
350
300
250 BIAS CURRENT
200
150
100
50
0
–40
0 25 70
TEMPERATURE – ؇C
85
Figure 14. Set Pin Bias Current vs. Temperature
THEORY OF OPERATION
The ADP1111 is a flexible, low-power, 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 very high performance
with low quiescent current.
A functional block diagram of the ADP1111 is shown on
the first page of this data sheet. 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 72 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 1.25 V, the oscillator is shut off. While
the oscillator is off, the ADP1111 quiescent current is only
300 µA. The comparator includes a small amount of hysteresis,
which ensures loop stability without requiring external compo-
nents 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 1 µs. If an
external resistor is not used, connect ILIM to VIN. Further
information on ILIM is included in the “APPLICATIONS”
section of this data sheet.
The ADP1111 internal oscillator provides 7 µs ON and 7 µs
OFF times that are ideal for applications where the ratio
between VIN and VOUT is roughly a factor of two (such as
converting +3 V to + 5 V). However, wider range conversions
(such as generating +12 V from a +5 V supply) can easily be
accomplished.
An uncommitted gain block on the ADP1111 can be connected
as a low-battery detector. The inverting input of the gain block
is internally connected to the 1.25 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 300 µA.
The ADP1111 provides external connections for both the
collector and emitter of its internal power switch that permit
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 ADP1111 is set with two external
resistors. Three fixed-voltage models are also available:
ADP1111–3.3 (+3.3 V), ADP1111–5 (+5 V) and ADP1111–12
(+12 V). The fixed-voltage models are identical to the
ADP1111, except that laser-trimmed voltage-setting resistors
are included on the chip. On the fixed-voltage models of the
ADP1111, simply connect the feedback pin (Pin 8) directly to
the output voltage.
COMPONENT SELECTION
General Notes on Inductor Selection
When the ADP1111 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 transferred
to the load when the switch turns off. Since both the collector
and the emitter of the switch transistor are accessible on the
ADP1111, the output voltage can be higher, lower, or of
opposite polarity than the input voltage.
To specify an inductor for the ADP1111, the proper values of
inductance, saturation current and dc resistance must be
determined. This process is not difficult, and specific equations
for each circuit configuration are provided in this data sheet. In
general terms, however, the inductance 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 values. The inductor
must also store enough energy to supply the load, without
saturating. Finally, the dc resistance of the inductor should be
low so that excessive power will not be wasted by heating the
windings. For most ADP1111 applications, an inductor of
15 µH to 100 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.
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 three step
process:
1. Define the operating parameters: minimum input voltage,
maximum input voltage, output voltage and output current.
2. Select the appropriate conversion topology (step-up, step-
down, or inverting).
3. Calculate the inductor value using the equations in the
following sections.
–6– REV. 0

6 Page









ADP1111 pdf, datenblatt
ADP1111
This occurs in the step-up mode when the following condition is
met:
VOUT + VDIODE
VIN VSW
<
1
1
DC
where DC is the ADP1111’s duty cycle. When this relationship
exists, the inductor current does not go all the way to zero
during the time that the switch is OFF. When the switch turns
on for the next cycle, the inductor current begins to ramp up
from the residual level. If the switch ON time remains constant,
the inductor current will increase to a high level (see Figure 24).
This increases output ripple and can require a larger inductor
and capacitor. By controlling switch current with the ILIM
resistor, output ripple current can be maintained at the design
values. Figure 25 illustrates the action of the ILIM circuit.
RLIM
(EXTERNAL)
VIN
VIN
ILIM
Q3
ADP1111
72kHz
OSC
R1
80
(INTERNAL)
IQ1
200 SW1
DRIVER
Q1
Q2 POWER
SWITCH
SW2
Figure 26. ADP1111 Current Limit Operation
The delay through the current limiting circuit is approximately
1 µs. If the switch ON time is reduced to less than 3 µs, accuracy
of the current trip-point is reduced. Attempting to program a
switch ON time of 1 µs or less will produce spurious responses
in the switch ON time; however, the ADP1111 will still provide
a properly regulated output voltage.
200mA/div
Figure 24.
200mA/div
PROGRAMMING THE GAIN BLOCK
The gain block of the ADP1111 can be used as a low-battery
detector, error amplifier or linear post regulator. The gain block
consists of an op amp with PNP inputs and an open-collector
NPN output. The inverting input is internally connected to the
ADP1111’s 1.25 V reference, while the noninverting input is
available at the SET pin. The NPN output transistor will sink
about 300 µA.
Figure 27a shows the gain block configured as a low-battery
monitor. Resistors R1 and R2 should be set to high values to
reduce quiescent current, but not so high that bias current in
the SET input causes large errors. A value of 33 kfor R2 is a
good compromise. The value for R1 is then calculated from the
formula:
R1
=
V
LOBATT 1.25
1.25 V
V
R2
where VLOBATT is the desired low battery trip point. Since the
gain block output is an open-collector NPN, a pull-up resistor
should be connected to the positive logic power supply.
5V
Figure 25.
The internal structure of the ILIM circuit is shown in Figure 26.
Q1 is the ADP1111’s internal power switch that is paralleled by
sense transistor Q2. The relative sizes of Q1 and Q2 are scaled
so that IQ2 is 0.5% of IQ1. Current flows to Q2 through an
internal 80 resistor and through the RLIM resistor. These two
resistors parallel the base-emitter junction of the oscillator-
disable transistor, Q3. When the voltage across R1 and RLIM
exceeds 0.6 V, Q3 turns on and terminates the output pulse. If
only the 80 internal resistor is used (i.e. the ILIM pin is
connected directly to VIN), the maximum switch current will be
1.5 A. Figure 6 gives RLIM values for lower current-limit values.
VBAT
VIN
ADP1111
R1 1.25V
REF
AO
SET
RL
47k
TO
PROCESSOR
33k R2
GND
R1= –V–L3–B5––.–11–µ.2–A5–V–
VLB = BATTERY TRIP POINT
Figure 27a. Setting the Low Battery Detector Trip Point
–12–
REV. 0

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