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ADP3050AR-ADP3050AR-3.3-ADP3050AR-5
200 kHz, 1 A High-Voltage Step-Down Switching Regulator
REV.0
200 kHz, 1 A High-Voltage
Step-Down Switching Regulator
FUNCTIONAL BLOCK DIAGRAM
BOOSTFB
GND
BIAS
SWITCH
COMP
FEATURES
Wide Input Voltage Range: 3.6 V to 30 V
Adjustable and Fixed (3.3 V, 5 V) Output Options
Integrated 1 A Power Switch
Uses Small Surface-Mount Components
Cycle-By-Cycle Current Limiting
Peak Input Voltage (100 ms): 60 V
Thermally Enhanced 8-Lead SOIC Package
Configurable as a Buck, Buck-Boost and SEPIC
Regulator
APPLICATIONS
Industrial Power Systems
PC Peripheral Power Systems
Preregulator for Linear Regulators
Distributed Power Systems
Automotive Systems
Battery Chargers
GENERAL DESCRIPTIONThe ADP3050 is a current-mode monolithic buck (step-down)
PWM switching regulator that contains a high current 1 A power
switch and all control, logic, and protection functions. It uses a
unique compensation scheme that allows the use of any type of
output capacitor (tantalum, ceramic, electrolytic, OS-CON).
Unlike some buck regulators, the design is not restricted to using
a specific type of output capacitor or ESR value.
A special boosted drive stage is used to saturate the NPN power
switch, providing a system efficiency higher than conventional
bipolar buck switchers. Further efficiency improvements are ob-
tained by using the low voltage regulated output to provide the
device's internal operating current. A high switching frequency
allows the use of small external surface-mount components. A
wide variety of standard off-the-shelf devices can be used, pro-
viding a great deal of design flexibility. A complete regulator
design requires only a few external components.
The ADP3050 includes a shutdown input that places the device
in a low-power mode, reducing the total supply current to under
20 µA. Internal protection features include thermal shutdown
circuitry and a cycle-by-cycle current-limit for the power switch
to provide complete device protection under fault conditions.
The ADP3050 provides excellent line and load regulation,
maintaining typically less than ±3% output voltage accuracy
over temperature and under all input voltage and output current
conditions.
The ADP3050 is specified over the industrial temperature range of
–40°C to +85°C and is available in a thermally enhanced 8-lead
SOIC package.
ADP3050–SPECIFICATIONS(VIN = 10 V, TA = –40�C to +85�C, unless otherwise noted) ADP3050
ADP3050-3.3
ADP3050-5
ERROR AMPLIFIER
ADP3050
SWITCH
SHUTDOWN
SUPPLY
NOTESAll limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC).Transconductance and voltage gain measurements refer to the internal amplifier without the voltage divider. To calculate the transconductance and gain of the fixed
voltage parts, divide the values shown by FB/1.20.The switching frequency is reduced when the feedback pin is lower than 0.8 � FB.See Figure 22 for test circuit.Switch current limit is measured with no diode, no inductor, and no output capacitor.Minimum input voltage is not measured directly, but is guaranteed by other tests. The actual minimum input voltage needed to keep the output in regulation will
depend on output voltage and load current.
Specifications subject to change without notice.
PIN FUNCTION DESCRIPTION
ABSOLUTE MAXIMUM RATINGS*IN Voltage
Steady State . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V to +30 V
Peak (<100 ms) . . . . . . . . . . . . . . . . . . . . .–0.3 V to +60 V
BOOST Voltage
Steady State . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V to +45 V
Peak (<100 ms) . . . . . . . . . . . . . . . . . . . . .–0.3 V to +65 V
SD, BIAS Voltage . . . . . . . . . . . . . . . . .–0.3 V to IN + 0.3 V
FB Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V to +8 V
COMP Voltage . . . . . . . . . . . . . . . . . . .–0.3 V to IN + 0.3 V
SWITCH Voltage . . . . . . . . . . . . . . . . .–0.3 V to IN + 0.3 V
Operating Ambient Temperature Range . . . .–40°C to +85°C
Operating Junction Temperature Range . . .–40°C to +125°C
Storage Temperature Range . . . . . . . . . . . .–65°C to +150°C
θJA (2-Layer PCB) . . . . . . . . . . . . . . . . . . . . . . . . . .108°C/W
θJA (4-Layer PCB) . . . . . . . . . . . . . . . . . . . . . . . . . . .81°C/W
PIN CONFIGURATION
8-Lead SOIC
(R-Suffix)
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although this device features proprietary ESD protection circuitry, permanent damage may occur
on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
ADP3050
– Typical Characteristics Figure 1.Quiescent Operating Current vs. Temperature
Figure 2.Shutdown Quiescent Current vs. Supply Voltage
Figure 3.Quiescent Operating Current vs. Supply Voltage
Figure 4.Average Output Current Limit vs. Temperature
Figure 5.Boost Current vs. Load Current
Figure 6.5 V Output Efficiency
Figure 7.3.3 V Output Efficiency
Figure 8.Output Voltage Change vs. Temperature
INPUT VOLTAGE –V
0.6�0.6
010
OUTPUT VOLTAGE CHANGE 30
0.0�0.4
�0.2
Figure 9.5 V Output Voltage Change vs. Input Voltage
Figure 10.3.3 V Output Voltage Change vs. Input Voltage
Figure 11.Minimum Input Voltage vs. Load Current
Figure 12.Load Regulation
ADP3050
LOAD CURRENT – A
SWITCH SATURATION VOLTAGE
0.5Figure 13.Switch Saturation Voltage vs. Load Current
Figure 14.Switching Frequency vs. Temperature
NORMALIZED FEEDBACK VOLTAGE – V
SWITCHING FREQUENCY
kHz
VIN = 10V
COMP = 0.4VFigure 15.Frequency Foldback
Figure 16.Continuous Conduction-Mode Waveforms
Figure 17.Discontinuous Conduction-Mode Waveforms
Figure 18.Transient Response
Figure 19.Start-Up from Shutdown
Figure 20.Error Amplifier Transconductance vs. Temperature
THEORY OF OPERATIONThe ADP3050 is a fixed-frequency, current-mode buck regulator.
Current mode systems provide excellent transient response, and
are much easier to compensate than voltage-mode systems. (Refer
to the functional block diagram.) At the beginning of each clock
cycle, the oscillator sets the latch, turning on the power switch.
The signal at the noninverting input of the comparator is a replica
of the switch current (summed with the oscillator ramp). When
this signal reaches the appropriate level set by the output of the
error amplifier, the comparator resets the latch and turns off the
power switch. In this manner, the error amplifier sets the correct
current trip level to keep the output in regulation. If the error
amplifier output increases, more current is delivered to the
output; if it decreases, less current is delivered to the output.
The current sense amplifier provides a signal proportional to
switch current to both the comparator and to a cycle-by-cycle
current limit. If the current limit is exceeded, the latch will be
reset, turning the switch off until the beginning of the next clock
cycle. The ADP3050 has a foldback current limit that reduces
the switching frequency under fault conditions to reduce stress
to the IC and to the external components.
Most of the control circuitry is biased from the 2.5 V internal
ADP3050 is drawn from the input supply. When the BIAS pin
is above 2.7 V, the majority of the operating current is then
drawn from this pin (usually tied to the regulator's low-voltage
output) instead of from the higher-voltage input supply. This
can provide substantial efficiency improvements at light-load
conditions, especially for systems where the input voltage is
much higher than the output voltage.
The ADP3050 uses a special drive stage that allows the power
switch to saturate. An external diode and capacitor provide a
boosted voltage to the drive stage that is higher than the input
supply voltage. Overall efficiency is dramatically improved by
using this type of saturating drive stage.
Pulling the SD pin below 0.4 V puts the device in a low-power
mode, shutting off all internal circuitry and reducing the supply
current to under 20 µA.
Figure 22.Typical Application Circuit
Setting the Output VoltageThe output of the adjustable version (ADP3050AR) can be set
to any voltage between 1.25 V and 12 V by connecting a resistor
divider to the FB pin as shown in Figure 23.
Figure 21.Error Amplifier Gain
ADP3050Figure 23.Adjustable Output Application Circuit
APPLICATION INFORMATIONThe complete process for designing a step-down switching regu-
lator using the ADP3050 is given in the following sections. Each
section includes a list of recommended devices. These lists do
not include every available device, nor every available manufac-
turer. They contain only surface-mount devices, but equivalent
through-hole devices can be substituted if needed. In choosing
components, keep in mind what is most important to the design
(efficiency, cost, size, etc.) as these things will ultimately deter-
mine which components are used. Also, make sure the design
specifications are clearly defined and that they reflect the worst-
case conditions. Key specifications include the minimum and
maximum input voltage, the output voltage and ripple, and the
minimum and maximum load current.
INDUCTOR SELECTIONThe inductor value will determine the mode of operation for the
regulator: continuous mode, where the inductor current flows
continuously; or discontinuous mode, where the inductor current
reduces to zero during every switch cycle. Continuous mode is
the best choice for many applications. It provides higher output
power, lower peak currents in the switch, inductor, and diode,
and a lower inductor ripple current (which means lower output
ripple voltage). Discontinuous mode does allow the use of smaller
magnetics, but at a price: lower available load current, and higher
peak and ripple currents. Designs with a high input voltage or a
low load current often operate in discontinuous mode to mini-
mize inductor value and size. The ADP3050 is designed to work
well in both modes of operation.
Continuous ModeThe inductor current in a continuous mode system is a triangular
waveform (equal to the ripple current) centered around a dc value
(equal to the load current). The amount of ripple current is deter-
mined by the inductor value, and is usually between 20% and 40%
of the maximum load current. To reduce the inductor size, ripple
currents between 40% and 80% are often used in continuous
mode designs with a high input voltage or a low output current.
The inductor value can be calculated using the following equation:
Where VIN(MAX) is the maximum input voltage, VOUT is the regu-
lated output voltage, and fSW is the switching frequency (200 kHz).
The initial choice for the amount of ripple current may seem arbi-
trary, but it will serve as a good starting point for finding a standard
off-the-shelf inductor value (i.e., 10 µH, 15 µH, 22 µH, 33 µH, and
47 µH). If a specific inductance value is to be used, simply rearrange
the above equation to find the ripple current. For an 800 mA, 12 V
to 5 V system, and a ripple current of 320 mA (40% of 800 mA) is
chosen, the inductance would be:
A 47 µH inductor is the closest standard value, which gives a ripple
current of about 310 mA. The peak switch current is equal to the
load current plus one-half the ripple current (this is also the peak
current for the inductor and the catch diode):
Pick an inductor with a dc (or saturation) current rating about
20% larger than ISW(PK) to ensure that the inductor is not running
near the edge of saturation. For this example, 1.20 � 0.95 A =
1.14 A, so use an inductor with a dc current rating of at least 1.2 A.
The maximum switch current is internally limited to 1.5 A, and
this limit, along with the ripple current, will determine the maxi-
mum load current the system can provide.
If the load current decreases to below one-half the ripple current,
the regulator will operate in discontinuous mode.
Discontinuous ModeFor load currents less than around 0.5 A, discontinuous mode
operation can be used. This will allow the use of a smaller induc-
tor, but the ripple current will be much higher (which means a
higher output ripple voltage). If a larger output capacitor must be
used to reduce the output ripple voltage, the overall system may
actually take up more board area than if a larger inductor was
used. The operation and equations for the two modes are quite
different, but the boundary between these two modes occurs
when the ripple current is equal to twice the load current (when
IRIPPLE = 2 � IOUT). From this we can use Equation 2 to find the
minimum inductor value needed to keep the system in continu-
ous mode operation (solve for the inductor value with IRIPPLE =
2 � IOUT).
Using an inductor below this value will cause the system to operate
in discontinuous mode. For a 400 mA, 24 V to 5 V system:
If the chosen inductor value is too small, the internal current
limit will trip each cycle and the regulator will have trouble
providing the necessary load current.
Inductor Core Types and Materials
