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PDF ( 数据手册 , 数据表 ) ADP1111

零件编号 ADP1111
描述 Micropower/ Step-Up/Step-Down SW Regulator; Adjustable and Fixed 3.3 V/ 5 V/ 12 V
制造商 Analog Devices
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ADP1111 数据手册, 描述, 功能
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 pdf, 数据表
ADP1111
As previously mentioned, the switch voltage is higher in step-
down mode than in step-up mode. VSW is a function of switch
current and is therefore a function of VIN, L, time and VOUT.
For most applications, a VSW value of 1.5 V is recommended.
The inductor value can now be calculated:
L = VIN(MIN)
V SW
I PEAK
VOUT
tON
(Equation 7)
where tON = switch ON time (7 µs).
If the input voltage will vary (such as an application that must
operate from a 9 V, 12 V or 15 V source), an RLIM resistor
should be selected from Figure 6. The RLIM resistor will keep
switch current constant as the input voltage rises. Note that
there are separate RLIM values for step-up and step-down modes
of operation.
For example, assume that +5 V at 300 mA is required from a
+12 V to +24 V source. Deriving the peak current from
Equation 6 yields:
I PEAK
=
2
300
0.5
mA
12
5 + 0.5
1.5 + 0.5
= 600 mA
Then, the peak current can be inserted into Equation 7 to
calculate the inductor value:
L
=
12 1.5 5
600 mA
7
µs
=
64
µH
Since 64 µH is not a standard value, the next lower standard
value of 56 µH would be specified.
To avoid exceeding the maximum switch current when the
input voltage is at +24 V, an RLIM resistor should be specified.
Using the step-down curve of Figure 6, a value of 560 will
limit the switch current to 600 mA.
INDUCTOR SELECTION–POSITIVE-TO-NEGATIVE
CONVERTER
The configuration for a positive-to-negative converter using the
ADP1111 is shown in Figure 22. As with the step-up converter,
all of the output power for the inverting circuit must be supplied
by the inductor. The required inductor power is derived from
the formula:
( ) ( )PL = VOUT + VD IOUT
(Equation 8)
The ADP1111 power switch does not saturate in positive-to-
negative mode. The voltage drop across the switch can be
modeled as a 0.75 V base-emitter diode in series with a 0.65
resistor. When the switch turns on, inductor current will rise at
a rate determined by:
( )IL
t
=
VL
R'
R't
1 e L 
(Equation 9)
where: R' = 0.65 + RL(DC)
VL = VIN – 0.75 V
For example, assume that a –5 V output at 50 mA is to be
generated from a +4.5 V to +5.5 V source. The power in the
inductor is calculated from Equation 8:
PL = (|5V|+0.5V|)(50 mA) = 275 mW
During each switching cycle, the inductor must supply the
following energy:
PL
f OSC
=
275 mW
72 kHz
= 3.8 µJ
Using a standard inductor value of 56 µH with 0.2 dc
resistance will produce a peak switch current of:
I PEAK
=
4.5V 0.75
0.65 Ω + 0.2
V
0.85 Ω • 7 µs
1e 56 µH

=
445 mA
Once the peak current is known, the inductor energy can be
calculated from (Equation 9):
EL
=
1
2
(56
µH
)
(445
mA)2
=
5.54
µJ
Since the inductor energy of 5.54 µJ is greater than the PL/fOSC
requirement of 3.82 µJ, the 56 µH inductor will work in this
application.
The input voltage only varies between 4.5 V and 5.5 V in this
application. Therefore, the peak current will not change enough
to require an RLIM resistor and the ILIM pin can be connected
directly to VIN. Care should be taken, of course, to ensure that
the peak current does not exceed 650 mA.
CAPACITOR SELECTION
For optimum performance, the ADP1111’s output capacitor
must be selected carefully. Choosing an inappropriate capacitor
can result in low efficiency and/or high output ripple.
Ordinary aluminum electrolytic capacitors are inexpensive but
often have poor Equivalent Series Resistance (ESR) and
Equivalent Series Inductance (ESL). Low ESR aluminum
capacitors, specifically designed for switch mode converter
applications, are also available, and these are a better choice
than general purpose devices. Even better performance can be
achieved with tantalum capacitors, although their cost is higher.
Very low values of ESR can be achieved by using OS-CON
capacitors (Sanyo Corporation, San Diego, CA). These devices
are fairly small, available with tape-and-reel packaging and have
very low ESR.
The effects of capacitor selection on output ripple are demon-
strated in Figures 15, 16 and 17. These figures show the output
of the same ADP1111 converter that was evaluated with three
different output capacitors. In each case, the peak switch
current is 500 mA, and the capacitor value is 100 µF. Figure 15
shows a Panasonic HF-series 16-volt radial cap. When the
switch turns off, the output voltage jumps by about 90 mV and
then decays as the inductor discharges into the capacitor. The
rise in voltage indicates an ESR of about 0.18 . In Figure 16,
the aluminum electrolytic has been replaced by a Sprague 293D
series, a 6 V tantalum device. In this case the output jumps
about 30 mV, which indicates an ESR of 0.06 . Figure 17
shows an OS-CON 16–volt capacitor in the same circuit, and
ESR is only 0.02 .
–8– REV. 0







ADP1111 equivalent, schematic
–16–










页数 16 页
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