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ADP1173AR-12 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP1173AR-12
Beschreibung Micropower DC-DC Converter
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADP1173AR-12 Datasheet, Funktion
a
FEATURES
Operates From 2.0 V to 30 V Input Voltages
Only 110 A Supply Current (Typical)
Step-Up or Step-Down Mode Operation
Very Few External Components Required
Low Battery Detector 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 and Palmtop Computers
Cellular Telephones
Flash Memory Vpp Generators
3 V to 5 V, 5 V to 12 V Converters
9 V to 5 V, 12 V to 5 V Converters
Portable Instruments
LCD Bias Generators
GENERAL DESCRIPTION
The ADP1173 is part of a family of step-up/step-down switching
regulators that operates from an input supply voltage of as little as
2 V to 12 V in step-up mode and to 30 V in step-down mode.
The ADP1173 consumes as little as 110 µA in standby mode,
making it ideal for applications that need low quiescent current.
An auxiliary gain amplifier can serve as a low battery detector,
linear regulator (under voltage lockout) or error amplifier.
The ADP1173 can deliver 80 mA at 5 V from a 3 V input in
step-up configuration or 100 mA at 5 V from a 12 V input in
step-down configuration. For input voltages of less than 2 V use
the ADP1073.
Micropower
DC-DC Converter
ADP1173
FUNCTIONAL BLOCK DIAGRAMS
SET
VIN
1.245V
REFERENCE
A2
GAIN BLOCK/
ERROR AMP
ADP1173
A1 OSCILLATOR
COMPARATOR
DRIVER
AO
ILIM
SW1
GND
FB
SW2
SET
VIN
1.245V
REFERENCE
ADP1173-3.3
ADP1173-5
ADP1173-12
A2
GAIN BLOCK/
ERROR AMP
A1 OSCILLATOR
AO
ILIM
SW1
R1
GND
COMPARATOR
DRIVER
R2
753k
ADP1173-3.3: R1 = 456k
ADP1173-5: R1 = 250k
ADP1173-12: R1 = 87.4k
SENSE
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






ADP1173AR-12 Datasheet, Funktion
ADP1173
When the internal power switch turns ON, current flow in the
inductor increases at the rate of:
I
L
(t
)
=
V IN
R
1–
e
Rt
L

(3)
where L is in henrys and R' is the sum of the switch equivalent
resistance (typically 0.8 at +25°C) and the dc resistance of
the inductor. In most applications, where the voltage drop across
the switch is small compared to VIN , 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
ADP1173 (23 µs, typical) will define the peak current for a
given inductor value and input voltage. At this point, the
inductor energy can be calculated as follows:
EL
=
1
2
LI
2PEAK
(5)
As previously mentioned, EL must be greater than PL/fOSC so the
ADP1173 can deliver the necessary power to the load. For best
efficiency, peak current should be limited to 1 A or less. Higher
switch currents will reduce efficiency, because of increased
saturation voltage in the switch. High peak current also increases
output ripple. As a general rule, keep peak current as low as pos-
sible to minimize losses in the switch, inductor and diode.
In practice, the inductor value is easily selected using the equa-
tions above. For example, consider a supply that will generate
9 V at 50 mA from a 3 V source. The inductor power required
is, from Equation 1:
PL = (9V + 0.5V – 3V )×(50 mA) = 325 mW
On each switching cycle, the inductor must supply:
PL
f OSC
=
325 mW
24 kHz
=13.5 µJ
The required inductor power is fairly low in this example, so the
peak current can also be low. Assuming a peak current of 500 mA
as a starting point, Equation 4 can be rearranged to recommend
an inductor value:
L
=
I
V IN
L(MAX
)
t
=
3V
500 mA
23
µs
=
138
µH
Substituting a standard inductor value of 100 µH, with 0.2 dc
resistance, will produce a peak switch current of:
I PEAK
=
3V
1.0
1–
e
–1.0 Ω × 23
100 µH
µs

= 616 mA
Once the peak current is known, the inductor energy can be
calculated from Equation 5:
EL
=
1
(100
2
µH )×
(616
mA)2
= 19
µJ
The inductor energy of 19 µJ is greater than the PL/fOSC re-
quirement of 13.5 µJ, so the 100 µH inductor will work in this
application. By substituting other inductor values into the same
equations, the optimum inductor value can be selected.
When selecting an inductor, the peak current must not exceed
the maximum switch current of 1.5 A. If the equations shown
above result in peak currents > 1.5 A, the ADP1073 should be
considered. This device has a 72% duty cycle, so more energy is
stored in the inductor on each cycle. This results in greater
output power.
The peak current must be evaluated for both minimum and
maximum values of input voltage. If the switch current is high
when VIN is at its minimum, then the 1.5 A limit may be ex-
ceeded at the maximum value of VIN. In this case, the ADP1173’s
current limit feature can be used to limit switch current. Simply
select a resistor (using Figure 4) that will limit the maximum
switch current to the IPEAK value calculated for the minimum
value of VIN. This will improve efficiency by producing a con-
stant IPEAK as VIN increases. See the Limiting the Switch Current
section of this data sheet for more information.
Note that the switch current limit feature does not protect the
circuit if the output is shorted to ground. In this case, current is
only limited by the dc resistance of the inductor and the forward
voltage of the diode.
Inductor Selection—Step-Down Converter
The step-down mode of operation is shown in Figure 15. Unlike
the step-up mode, the ADP1173’s power switch does not
saturate when operating in the step-down mode. Therefore,
switch current should be limited to 650 mA in this mode. If the
input voltage will vary over a wide range, the ILIM pin can be
used to limit the maximum switch current. If higher output
current is required, the ADP1111 should be considered.
The first step in selecting the step-down inductor is to calculate
the peak switch current as follows:
I PEAK
= 2IOUT
DC
V
V
IN
OUT +V D
V SW +V
D

(6)
where DC = duty cycle (0.55 for the ADP1173)
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 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
(7)
where tON = switch ON time (23 µs)
If the input voltage will vary (such as an application that must
operate from a 12 V to 24 V source) an RLIM resistor should be
selected from Figure 5. The RLIM resistor will keep switch cur-
rent constant as the input voltage rises. Note that there are separate
RLIM values for step-up and step-down modes of operation.
–6– REV. 0

6 Page









ADP1173AR-12 pdf, datenblatt
ADP1173
Typical Circuit Applications
2 x 1.5V
CELLS
L1*
68µH
R1
100
12
ILIM VIN SW1 3
ADP1173
FB 8
GND SW2
54
1N5818
1N4148
2.21M
1%
4.7µF
0.1µF
118k
1%
1N5818
*L1 = GOWANDA GA10-682K
COILTRONICS CTX68-4
FOR 5V INPUT CHANGE R1 TO 47
CONVERTER WILL DELIVER –22V AT 40mA
22µF
220k
–22V OUTPUT
7mA AT 2.0V INPUT
70% EFFICIENCY
Figure 24. 3 V–22 V LCD Bias Generator
L1*
82µH
2 x 1.5V
CELLS
12
ILIM VIN
SW1 3
ADP1173-5
GND SW2 SENSE 8
54
1N5818
+
100µF
5V OUTPUT
150mA AT 3V INPUT
60mA AT 2V INPUT
*L1 = GOWANDA GA10-822K
Figure 25. 3 V to 5 V Step-Up Converter
9V
BATTERY
100
12
ILIM VIN SW1 3
ADP1173-5
SENSE 8
GND SW2
54
L1*
47µH
1N5818
+
100µF
5V OUTPUT
150mA AT 9V INPUT
50mA AT 6.5V INPUT
*L1 = GOWANDA GA10-472K
COILTRONICS CTX50-1
FOR HIGHER OUTPUT CURRENTS SEE ADP1073 DATASHEET
Figure 27. 9 V to 5 V Converter
+VIN
12V-28V
100
12
ILIM VIN SW1 3
ADP1173-5
SENSE 8
GND SW2
54
L1*
220µH
1N5818
+
100µF
*L1 = GOWANDA GA10-223K
5V OUTPUT
300mA
Figure 28. +20 V to 5 V Step-Down Converter
+VIN
5V INPUT
+
22µF 100
12
ILIM VIN SW1 3
ADP1173-5
SENSE 8
GND SW2
54
L1*
100µH
1N5818
+
100µF
*L1 = GOWANDA GA10-103K
COILTRONICS CTX100-1
–5V OUTPUT
75mA
Figure 26. +5 V to –5 V Converter
–12–
REV. 0

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