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ADP2147 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADP2147
Beschreibung Buck Regulator
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADP2147 Datasheet, Funktion
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FEATURES
Input voltage: 2.3 V to 5.5 V
Peak efficiency: 95%
3 MHz fixed frequency operation
Low quiescent current: 23 μA
Ultralow shutdown current: 0.2 μA (typical)
VSEL pin for simple dynamic voltage scaling (DVS)
100% duty cycle low dropout mode
Internal synchronous rectifier, compensation, and soft start
Current overload and thermal shutdown protection
Small, 6-ball, 1 mm × 1.5 mm WLCSP package
APPLICATIONS
PDAs and palmtop computers
Wireless handsets
Digital audio portable media players
Digital cameras, GPS navigation units
Low power portable medical equipment
Compact, 800 mA, 3 MHz,
Simple DVS, Buck Regulator
ADP2147
GENERAL DESCRIPTION
The ADP2147 is a high efficiency, low quiescent current, step-
down (buck) dc-to-dc regulator with an output voltage that can
be switched between two different settings under the control of
a select pin. The total solution requires only three tiny external
components.
The buck regulator automatically switches operating modes,
depending on the load current level, to maximize efficiency. At
high output loads, the buck regulator operates in PWM mode.
When the load current falls below a predefined threshold, the
regulator operates in power save mode (PSM), improving the
light-load efficiency.
The ADP2147 runs on input voltages of 2.3 V to 5.5 V, which
allows for single lithium or lithium polymer cells, multiple
alkaline or NiMH cells, PCMCIA, USB, and other standard
power sources. The maximum load current of 800 mA is
achievable across the input voltage range.
The ADP2147 is available with fixed output voltages from 0.8 V
to 3.3 V. All versions include an internal power switch and
synchronous rectifier for minimal external part count and high
efficiency. The ADP2147 has an internal soft start and is
internally compensated. During logic controlled shutdown, the
input is disconnected from the output, and the ADP2147 draws
less than 0.2 μA (typical) from the power source.
Other key features include undervoltage lockout to prevent deep
battery discharge and soft start to prevent input current over-
shoot at startup. The ADP2147 is available in a 6-ball WLCSP.
TYPICAL APPLICATIONS CIRCUIT
2.3V TO 5.5V
4.7µF
VIN SW
ADP2147
1.0µH
VOUT
4.7µF
ON
OFF
EN
VOUT
VOUT_H
VOUT_L
VSEL
GND
Figure 1.
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2011 Analog Devices, Inc. All rights reserved.






ADP2147 Datasheet, Funktion
ADP2147
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 3.6 V, TA = 25°C, VEN = VIN, unless otherwise noted.
100
90
80
70
60
50
40
30
20
10
0
0.001
0.01
IOUT (A)
0.1
VIN = 2.3V
VIN = 3.6V
VIN = 4.2V
VIN = 5.5V
1
Figure 3. Efficiency vs. Load Current, Across Input Voltage,
VOUT = 1.8 V
100
90
80
70
60
50
40
30
20
10
0
0.001
0.01
IOUT (A)
0.1
VIN = 2.3V
VIN = 3.6V
VIN = 4.2V
VIN = 5.5V
1
Figure 4. Efficiency vs. Load Current, Across Input Voltage,
VOUT = 0.8 V
100
90
80
70
60
50
40
30
20
10
0
0.001
0.01
IOUT (A)
0.1
VIN = 3.9V
VIN = 4.2V
VIN = 5.5V
1
Figure 5. Efficiency vs. Load Current, Across Input Voltage,
VOUT = 3.3 V
1.825
1.815
1.805
VIN = 2.3V
VIN = 3.6V
VIN = 4.2V
VIN = 5.5V
1.795
1.785
1.775
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
IOUT (A)
Figure 6. Load Regulation Across Input Voltage, VOUT = 1.8 V
0.815
0.810
0.805
VIN = 2.3V
VIN = 3.6V
VIN = 4.2V
VIN = 5.5V
0.800
0.795
0.790
0.785
0.780
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
IOUT (A)
Figure 7. Load Regulation Across Input Voltage, VOUT = 0.8 V
3.378
3.358
3.338
VIN = 3.9V
VIN = 4.2V
VIN = 5.5V
3.318
3.298
3.278
3.258
3.238
3.218
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
IOUT (A)
Figure 8. Load Regulation Across Input Voltage, VOUT = 3.3 V
Rev. 0 | Page 6 of 16

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ADP2147 pdf, datenblatt
ADP2147
SIMPLE DYNAMIC VOLTAGE SCALING (DVS)
The ADP2147 has a VSEL pin that allows the user to force the
output voltage to change from one level (the default VOUT
setting) when VSEL is low and to another level (the alternate
VOUT setting) when VSEL is high. Transition between VOUT
levels is achieved within 40 μs when VOUT is commanded to go
from a lower voltage to a higher voltage. When VOUT is com-
manded to go from a higher VOUT voltage to a lower one, the
transition time depends on the load current present at that time.
SHORT-CIRCUIT PROTECTION
The ADP2147 includes frequency foldback to prevent output
current runaway on a hard short. When the voltage at the
feedback pin falls below half the target output voltage, indi-
cating the possibility of a hard short at the output, the switching
frequency is reduced to half the internal oscillator frequency.
The reduction in the switching frequency allows more time for
the inductor to discharge, preventing a runaway of output current.
UNDERVOLTAGE LOCKOUT
To protect against battery discharge, undervoltage lockout
(UVLO) circuitry is integrated on the ADP2147. If the input
voltage drops below the 2.15 V UVLO threshold, the ADP2147
shuts down, and both the power switch and the synchronous
rectifier turn off. When the voltage rises above the UVLO
threshold, the soft start period is initiated, and the part is
enabled.
THERMAL PROTECTION
In the event that the ADP2147 junction temperature rises above
150°C, the thermal shutdown circuit turns off the regulator.
Extreme junction temperatures can be the result of high current
operation, poor circuit board design, or high ambient temperature.
A 20°C hysteresis is included so that when thermal shutdown
occurs, the ADP2147 does not return to operation until the on-
chip temperature drops below 130°C. When coming out of
thermal shutdown, a soft start is initiated.
SOFT START
The ADP2147 has an internal soft start function that ramps the
output voltage in a controlled manner upon startup, thereby
limiting the inrush current. The soft start minimizes input
voltage drop when a battery or a high impedance power source is
connected to the regulator’s input.
After the EN pin is driven high, internal circuits begin to power
up. Start-up time in the ADP2147 is the measure of when the
output is in regulation after the EN pin is driven high. Start-up
time consists of the power-up time plus the soft start time.
CURRENT LIMIT
The ADP2147 has protection circuitry to limit the amount of
positive current flowing through the PFET switch and the
synchronous rectifier. The positive current limit on the power
switch controls the amount of current that can flow from the
power source to the output. The negative current limit prevents
the inductor current from reversing direction and flowing out
of the load.
100% DUTY OPERATION
With a drop in VIN or with an increase in ILOAD, the ADP2147
eventually reaches a limit where, even with the pFET switch on
100% of the time, VOUT drops below the desired output voltage.
At this limit, the ADP2147 smoothly transitions to a mode
where the PFET switch stays on 100% of the time. When the input
conditions change again and the required duty cycle falls, the
ADP2147 immediately restarts PWM regulation without
allowing overshoot on VOUT.
Rev. 0 | Page 12 of 16

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