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ADP1110AR-33 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP1110AR-33
Beschreibung Micropower/ Step-Up/Step-Down Switching Regulator; Adjustable and Fixed 3.3 V/ 5 V/ 12 V
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADP1110AR-33 Datasheet, Funktion
Micropower, Step-Up/Step-Down Switching
a Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V
ADP1110
FEATURES
Operates at Supply Voltages From 1.0 V to 30 V
Step-Up or Step-Down Mode
Minimal External Components Required
Low-Battery Detector
User-Adjustable Current Limiting
Fixed or Adjustable Output Voltage Versions
8-Pin DIP or SO-8 Package
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
FUNCTIONAL BLOCK DIAGRAMS
SET
ADP1110
A2
VIN
GAIN BLOCK/
ERROR AMP
220mV
REFERENCE
A1 OSCILLATOR
A0
ILIM
SW1
Q1
COMPARATOR
R2
R1 300k
DRIVER
GND
SENSE
SW2
ADP1110 Block Diagram—Fixed Output Version
SET
ADP1110
GENERAL DESCRIPTION
The ADP1110 is part of a family of step-up/step-down switch-
ing regulators that operate from an input voltage supply as little
as 1.0 V. This very low input voltage allows the ADP1110 to be
used in applications that use a single cell as the primary power
source.
The ADP1110 can be configured to operate in either step-up or
step-down mode, but for input voltages greater than 3 V, the
ADP1111 would be a more effective solution.
An auxiliary gain amplifier can serve as a low battery detector or
as a linear regulator.
The quiescent current of 300 µA makes the ADP1110 useful in
remote or battery powered applications.
A2
VIN
GAIN BLOCK/
ERROR AMP
220mV
REFERENCE
A1 OSCILLATOR
A0
ILIM
SW1
Q1
COMPARATOR
DRIVER
GND
FB
SW2
ADP1110 Block Diagram—Adjustable Output Version
The 70 kHz frequency operation also allows for the use of
surface-mount external capacitors and inductors.
Battery protection circuitry limits the effect of reverse current to
safe levels at reverse voltages up to 1.6 V.
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






ADP1110AR-33 Datasheet, Funktion
ADP1110
400
350
BIAS CURRENT
300
250
200
150
100
50
0
0 25 70
TEMPERATURE – ؇C
Figure 14. Set Pin Bias Current vs. Temperature
220
219
218
217
216
215
214
213
212
211
0
REFERENCE VOLTAGE
25
TEMPERATURE – ؇C
70
Figure 15. Reference Voltage vs. Temperature
THEORY OF OPERATION
The ADP1110 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 ADP1110 is shown on the
first page. The internal 220 mV 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
220 mV, the 70 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
220 mV, the oscillator is shut off. While the oscillator is off, the
ADP1110 quiescent current is only 300 µA. The comparator
includes a small amount of hysteresis, which 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 800 ns. If an
external resistor is not used, connect ILIM to VIN. Further informa-
tion on ILIM is included in the “Applications” section of this data
sheet.
The ADP1110 internal oscillator provides 10 µs ON and 5 µs
OFF times, which is ideal for applications where the ratio between
VIN and VOUT is roughly a factor of three (such as generating +5 V
from a single 1.5 V cell). Wider range conversions, as well as
step-down converters, can also be accomplished with a slight
loss in the maximum output power that can be obtained.
An uncommitted gain block on the ADP1110 can be connected
as a low–battery detector. The inverting input of the gain block
is internally connected to the 220 mV 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 ADP1110 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 ADP1110 is set with two external
resistors. Three fixed-voltage models are also available:
ADP1110–3.3 (+3.3 V), ADP1110–5 (+5 V) and ADP1110-12
(+12 V). The fixed-voltage models are identical to the
ADP1110 except that laser-trimmed voltage-setting resistors are
included on the chip. Only three external components are
required to form a +3.3 V, +5 V or +12 V converter. On the
fixed-voltage models of the ADP1110, simply connect the
SENSE pin (Pin 8) directly to the output voltage.
COMPONENT SELECTION
General Notes on Inductor Selection
When the ADP1110 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
transferred to the load when the switch turns off. Because both
the collector and the emitter of the switch transistor are
accessible on the ADP1110, the output voltage can be higher,
lower, or of opposite polarity than the input voltage.
To specify an inductor for the ADP1110, 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 ADP1110 applications, an inductor of
15 µH to 100 µH with a saturation current rating of 300 mA to
1A 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.
–6– REV. 0

6 Page









ADP1110AR-33 pdf, datenblatt
ADP1110
The internal structure of the ILIM circuit is shown in Figure 27.
Q1 is the ADP1110’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.
RLIM
(EXTERNAL)
VIN VIN
ILIM
Q3
ADP1110
72kHz
OSC
R1
80
(INTERNAL)
IQ1 SW1
DRIVER 200
Q1
Q2 POWER
SWITCH
SW2
Figure 27. ADP1110 Current Limit Operation
The delay through the current limiting circuit is approximately
800 ns. 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 800 ns or less will produce
spurious responses in the switch ON time; however, the
ADP1110 will still provide a properly-regulated output voltage.
PROGRAMMING THE GAIN BLOCK
The gain block of the ADP1110 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
ADP1110’s 220 mV reference, while the noninverting input is
available at the SET pin. The NPN output transistor will sink
about 300 µA.
Figure 28 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 – 220
220 mV
mV
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.
VLOGIC
VBAT
ADP1110
R1 220V
VREF
SET
AO
R2
33k
GND
RHYS
RL
Figure 28. Setting the Low Battery Detector Trip Point
The circuit of Figure 28 may produce multiple pulses when
approaching the trip point due to noise coupled into the SET
input. To prevent multiple interrupts to the digital logic,
hysteresis can be added to the circuit. Resistor RHYS, with a
value of 1 Mto 10 M, provides the hysteresis. The addition
of RHYS will change the trip point slightly, so the new value for
R1 will be:
R1 = V LOBATT – 220 mV
220 mV
R2
VRL L
220 mV
+ RHYS

where VL is the logic power supply voltage, RL is the pull-up
resistor, and RHYS creates the hysteresis.
The gain block can also be used as a control element to reduce
output ripple. The ADP3000 is normally recommended for low-
ripple applications, but its minimum input voltage is 2 V. The
gain-block technique using the ADP1110 can be useful for step-
up converters operating down to 1 V.
A step-up converter using this technique is shown in Figure 29.
This configuration uses the gain block to sense the output
voltage and control the comparator. The result is that the
comparator hysteresis is reduced by the open loop gain of the
gain block. Output ripple can be reduced to only a few millivolts
with this technique, versus a typical value of 90 mV for a +5 V
converter using just the comparator. For best results, a large
output capacitor (1000 µF or more) should be specified. This
technique can also be used for step-down or inverting applica-
tions, but the ADP3000 is usually a more appropriate choice.
See the ADP3000 data sheet for further details.
INPUT
CINPUT
10µF
270k
L1 D1
15µH
CTX15-4 1N5818
12
ILIM VIN SW1 3
ADP1110
R1
300k
SET 7
AO FB GND SW2
685 4
R2
13.8k
OUTPUT
CL
1000µF
Figure 29. Using the Gain Block to Reduce Output Ripple
–12–
REV. 0

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