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ADP1108AN PDF 데이터시트 : 부품 기능 및 핀배열

부품번호 ADP1108AN
기능 Micropower DC-DC Converter Adjustable and Fixed 3.3 V/ 5 V/ 12 V
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ADP1108AN 데이터시트, 핀배열, 회로
a
Micropower DC-DC Converter
Adjustable and Fixed 3.3 V, 5 V, 12 V
ADP1108
FEATURES
Operates at Supply Voltages From 2.0 V to 30 V
Consumes Only 110 A Supply Current
Step-Up or Step-Down Mode Operation
Minimum External Components Required
Low Battery Detector Comparator On-Chip
User-Adjustable Current Limit
Internal 1 A Power Switch
Fixed or Adjustable Output Voltage Versions
8-Pin DIP or SO-8 Package
APPLICATIONS
Notebook/Palm Top Computers
3 V to 5 V, 5 V to 12 V Converters
9 V to 5 V, 12 V to 5 V Converters
LCD Bias Generators
Peripherals and Add-On Cards
Battery Backup Supplies
Cellular Telephones
Portable Instruments
GENERAL DESCRIPTION
The ADP1108 is a highly versatile micropower switch-mode
dc-dc converter that operates from an input voltage supply as
low as 2.0 V and typically starts up from 1.8 V.
The ADP1108 can be programmed into a step-up or step-down
dc-to-dc converter with only three external components. The
fixed outputs are 3.3 V, 5 V and 12 V. An adjustable version is
also available. In step-up mode, supply voltage range is 2.0 V to
12 V, and 30 V in step-down mode. The ADP1108 can deliver
150 mA at 5 V from a 2 AA cell input and 300 mA at 5 V from
a 9 V input in step-down mode. Switch current limit can be
programmed with a single resistor.
For battery operated and power conscious applications, the
ADP1108 offers a very low power consumption of less than
110 µA.
The auxiliary gain block available in ADP1108 can be used
as a low battery detector, linear post regulator, under voltage
lockout circuit or error amplifier.
FUNCTIONAL BLOCK DIAGRAMS
SET
VIN
1.245V
REFERENCE
A2
GAIN BLOCK/
ERROR AMP
ADP1108
A1 OSCILLATOR
AO
ILIM
SW1
COMPARATOR
DRIVER
GND
FB
SW2
SET
VIN
1.245V
REFERENCE
ADP1108-3.3
ADP1108-5
ADP1108-12
A2
GAIN BLOCK/
ERROR AMP
A1 OSCILLATOR
R1
GND
COMPARATOR
DRIVER
R2
753k
ADP1108-3.3: R1 = 456k
ADP1108-5: R1 = 250k
ADP1108-12: R1 = 87.4k
SENSE
AO
ILIM
SW1
SW2
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., 1997




ADP1108AN pdf, 반도체, 판매, 대치품
ADP1108–Typical Performance Characteristics
1.2
1
VIN = 3.0V
0.8
VIN = 2.0V
0.6 VIN = 5.0V
0.4
0.2
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
SWITCH CURRENT – Amps
Figure 1. Saturation Voltage vs. ISWITCH
Current in Step-Up Mode
1.6
1.4
1.2
1
VCE (SAT)
0.8
0.6
0.4
0.2
0
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75
SWITCH CURRENT – Amps
Figure 2. Switch ON Voltage vs.
Switch Current In Step-Down Mode
1100
1000
VIN = 24V WITH L = 500µH @ VOUT = 5V
900
800
700
600
500
400
300 VIN = 12V WITH L = 250µH @ VOUT = 5V
200
100
10
100
RLIM
1k
Figure 4. Maximum Switch Current
vs. RLIM In Step-Down Mode
100
90
80
70
60 VIN = 5V
50
40
30
20 VIN = 2V
10
0
0 100 200 300 400 500 600 700 800 900
SWITCH CURRENT – mA
Figure 5. Supply Current vs. Switch
Current
22
21
20
19
18
17
16
15
14
13
–40
0 25 70
TEMPERATURE – °C
85
Figure 7. Oscillator Frequency vs.
Temperature
67
66
65
64
63
62
61
60
59
58
57
–40
0 25 70
TEMPERATURE – °C
85
Figure 8. Duty Cycle vs. Temperature
1100
1000
900
800
700
2V < VIN < 5V
600
500
400
300
200
100
10
100
RLIM
1k
Figure 3. Maximum Switch Current
vs. RLIM In Step-Up Mode
120
110
100
90
80
70
60
50
40
–40
0 25 70
TEMPERATURE – °C
85
Figure 6. Quiescent Current vs.
Temperature
35
34.5
34
33.5
33
32.5
32
31.5
31
30.5
30
–40
0 25 70
TEMPERATURE – °C
85
Figure 9. Switch ON Time vs.
Temperature
–4– REV. 0

4페이지










ADP1108AN 전자부품, 판매, 대치품
ADP1108
where: DC = duty cycle (0.7 for the ADP1108)
VSW = voltage drop across the switch
VD = diode drop (0.5 V for a 1N5818)
IOUT = output current
VOUT = the output voltage
VIN = the minimum input voltage
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
=V IN(MIN) V SW
I PEAK
V OUT
× tON
(Equation 7)
where: tON = switch ON time (36 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 4. 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 250 mA is required from a +9 V
to +18 V source. Deriving the peak current from Equation 6
yields:
I PEAK
=
2 × 250 mA
0.7

9
5 + 0.5
1.5 + 0.5

= 491 mA
The peak current can than be inserted into Equation 7 to cal-
culate the inductor value:
L
=
9 – 1.5 – 5
491 mA
×
36
µs
=
183
µH
Since 183 µH is not a standard value, the next lower standard
value of 150 µH would be specified.
To avoid exceeding the maximum switch current when the in-
put voltage is at +18 V, an RLIM resistor should be specified. Us-
ing Figure 4, a value of 160 will limit the switch current to
500 mA.
Inductor Selection—Positive-to-Negative Converter
The configuration for a positive-to-negative converter using the
ADP1108 is shown in Figure 19. 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|+ V D × IOUT
(Equation 8)
The ADP1108 power switch does not saturate in positive-to-
negative mode. The voltage drop across the switch can be mod-
eled 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
1e L 
(Equation 9)
where: R' = 0.65 + RL (DC)
VL = VIN – 0.75 V
For example, assume that a –5 V output at 100 mA is to be gen-
erated from a +4.5 V to +5.5 V source. The power in the induc-
tor is calculated from Equation 8:
PL = (|– 5V|+ 0.5V ) × (100 mA) = 550 mW
During each switching cycle, the inductor must supply the fol-
lowing energy:
PL
f OSC
=
550 mW
19 kHz
= 28.9 µ J
Using a standard inductor value of 220 µH with 0.3 dc resis-
tance will produce a peak switch current of:
I PEAK
=
4.5V – 0.75 V
0.65 Ω + 0.3
–0.95 Ω × 36 µs
1 e 220 µH  = 568 mA
Once the peak current is known, the inductor energy can be cal-
culated from Equation 9:
( )EL
=
1
2
 220
µH
×
568 mA
2
=
35.5
µ
J
The inductor energy of 35.5 µJ is greater than the PL/fOSC re-
quirement of 28.9 µJ, so the 220 µH inductor will work in
this application.
To avoid exceeding the maximum switch current when the in-
put voltage is at +5.5 V, an RLIM resistor should be specified.
Referring to Figure 4, a value of 150 is appropriate in this
application.
Capacitor Selection
For optimum performance, the ADP1108’s output capacitor
must be carefully selected. 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 Equiva-
lent 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 Corpora-
tion, 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 12, 13, and 14. These figures show the output
of the same ADP1108 converter, which 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 12
shows a Panasonic HF-series* radial aluminum electrolytic.
When the switch turns off, the output voltage jumps by about
90 mV and then decays as the inductor discharges into the ca-
pacitor. The rise in voltage indicates an ESR of about 0.18 . In
Figure 13, the aluminum electrolytic has been replaced by a
Sprague 593D-series* tantalum device. In this case the output
jumps about 35 mV, which indicates an ESR of 0.07 . Figure
14 shows an OS-CON SA series capacitor in the same circuit,
and ESR is only 0.02 .
*All trademarks are the property of their respective holders.
REV. 0
–7–

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