1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Data Sheet
General Description
The AP3431 is a high efficiency step-down DC-DC
voltage converter. The chip operation is optimized
by peak-current mode architecture with built-in
synchronous power MOS switchers. The oscillator
and timing capacitors are all built-in providing an
internal switching frequency of 1MHz that allows
the use of small surface mount inductors and
capacitors for portable product implementations.
Integrated Soft Start (SS), Under Voltage Lock Out
(UVLO), Thermal Shutdown Detection (TSD) and
short circuit protection are designed to provide
reliable product applications.
The device is available in adjustable output voltage
versions ranging from 0.8V to 0.9
voltage range is from 2.7V to 5.5V , and is able to
deliver up to 2.0A.
The AP3431 is available in SOIC-8 package.
×
VIN when input
Features
• High Efficiency Buck Power Converter
• Output Current: 2A
• Low R
• Adjustable Output Voltage from 0.8V to 0.9×V
• Wide Operating Voltage Range: 2.7V to 5.5V
•
Built-in Power Switches for Synchronous
Rectification with High Efficiency
• Feedback Voltage: 800mV
• Switching Frequency: 1.0MHz
• Thermal Shutdown Protection
• Internal Soft Start
Internal Switches : 120mΩ(VIN=5V)
DS(ON)
IN
Applications
• LCD TV
• Set Top Box
• Post DC-DC Voltage Regulation
• PDA and Notebook Computer
Figure 1. Package Type of AP3431
SOIC-8
Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Pin Configuration
M Package
(SOIC-8)
1
2
3
4
Figure 2. Pin Configuration of AP3431 (Top View)
8
7
6
5
Pin Description
Pin Number Pin Name Function
1 VCC Supply input for the analog circuit
2 NC No connection
3 GND Ground pin
4 FB
5 EN
6 PGND Power switch ground pin
7 SW Switch output pin
8 VIN
Feedback pin. Receives the feedback voltage from a resistive
divider connected across the output
Chip enable pin. Active high, internal pull-high with
200kΩ resistor
Power supply input for the MOSFET switch
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Functional Block Diagram
Figure 3. Functional Block Diagram of AP3431
Ordering Information
AP3431 A -
Circuit Type
Package
M: SOIC-8
Package
Temperature
Range
Part Number Marking ID Packing Type
AP3431M-G1 3431M-G1
SOIC-8 -40 to 80°C
AP3431MTR-G1 3431M-G1
BCD Semiconductor's Pb-free products, as designated with "G1" in the part number, are RoHS compliant and
green.
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G1:Green
Blank: Tube
TR: Tape & Reel
Tube
Tape & Reel
Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Absolute Maximum Ratings (Note 1)
Parameter Symbol Value Unit
Supply Input for the Analog Circuit VCC
Power Supply Input for the MOSFET Switch VIN
SW Pin Switch Voltage VSW
Enable Voltage VEN -0.3 to VIN+0.3 V
SW Pin Switch Current ISW 2.9 A
Power Dissipation (on PCB, TA=25°C) PD 1.45 W
Thermal Resistance (Junction to Ambient, Simulation) θJA 68.63 °C/W
Junction Temperature TJ 160 °C
Operating Temperature TOP -40 to 85 °C
Storage temperature T
ESD (Human Body Model) V
ESD (Machine Model) VMM
Note 1: Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to
the device. These are stress ratings only, and functional operation of the device at these or any other conditions
beyond those indicated under “Recommended Operating Conditions” is not implied. Exposure to “Absolute
Maximum Ratings” for extended periods may affect device reliability.
-55 to 150 °C
STG
HBM
0 to 6.0
0 to 6.0
-0.3 to V
2000
200
IN
+0.3
V
V
V
V
V
Recommended Operating Conditions
Parameter Symbol Min Max Unit
Supply Input Voltage VIN 2.7 5.5 V
Junction Temperature Range TJ -40 125 °C
Ambient Temperature Range TA -40 80 °C
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Electrical Characteristics
VIN=VCC=VEN=5V, V
specified.
Parameter Symbol Conditions Min Typ Max Unit
Input Voltage Range VIN 2.7 5.5 V
=1.2V, VFB=0.8V, L=2.2µH, CIN=10µF, C
OUT
=22µF, TA=25°C, unless otherwise
OUT
Shutdown Current I
Active Current ION V
Regulated1Feedback
Voltage
Regulated Output
Voltage Accuracy
∆V
Peak Inductor
Current
Oscillator Frequency f
PMOSFET RON R
NMOSFET RON R
EN High-level Input
Voltage
EN Low-level Input
Voltage
V
OFF
For Adjustable Output Voltage 0.784 0.8 0.816 V
V
FB
OUT/VOUT
I
PK
OSC
ON(P)
ON(N)
V
EN_H
V
EN_L
2.9 A
V
VIN = 5V 120 mΩ
VIN = 5V 120 mΩ
1.5 V
0.4 V
=0V 4 µA
EN
= 0.95V 460 µA
FB
=2.7V to 5.5V,
V
IN
=0 to 2.0A
I
OUT
= 2.7V to 5.5V 1.0 MHz
IN
-3 3 %
EN Input Current IEN 2 µA
Soft-start Time tSS 450 µs
Maximum Duty
Cycle
90 %
D
MAX
Rising 2.4 V
Under Voltage Lock
Out Threshold
Falling 2.3 V
Hysteresis 0.1 V
Thermal Shutdown TSD Hysteresis=30°C 160 °C
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics
Figure 4. Efficiency vs. Output Current Figure 5. Efficiency vs. Output Current
Figure 6. 2.5V Load Regulation Figure 7. 1.8V Load Regulation
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 8. 2.5V Line Regulation Figure 9. 1.8V Line Regulation
Figure 10. Efficiency vs. Output Current
Figure 11. Efficiency vs. Output Current
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 12. 1.2V Load Regulation Figure 13. 1.0V Load Regulation
Figure 14. 1.2V Line Regulation
Figure 15. 1.0V Line Regulation
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 16. Efficiency vs. Output Current Figure 17. Frequency vs. Input Voltage
Figure 18. 3.3V Load Regulation
Figure 19. Temperature vs. Output Current
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 20. EN Pin Threshold vs. Input Voltage Figure 21. FB Voltage vs. Output Current
Figure 22. V
(VIN=5V, V
OUT
Ripple Figure 23. Dynamic Mode
OUT
=3.3V, I
=500mA) (Load=200mA to 1200mA, VIN=5V, V
OUT
OUT
=3.3V)
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 24. V
(VIN=5V, V
Ripple Figure 25. Dynamic Mode (Rising)
OUT
OUT
=3.3V, I
=1A)
OUT
Figure 26. V
(VIN=5V, V
OUT
Ripple Figure 27. Dynamic Mode (Falling)
OUT
=3.3V, I
=2A)
OUT
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 28. EN Pin, Low to High Figure 29. Soft Start
(VIN=5V, V
OUT
=3.3V, I
=100mA) (VIN=5V, V
OUT
OUT
=3.3V, I
=0A)
OUT
Figure 30. EN Pin, Low to High Figure 31. Soft Start
(VIN=5V, V
OUT
=3.3V, I
=1A) (VIN=5V, V
OUT
OUT
=3.3V, I
OUT
=1A)
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Performance Characteristics (Continued)
Figure 32. EN Pin, High to Low Figure 33. OTP
(VIN=5V, V
OUT
=3.3V, I
=1A)
OUT
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Application Information
The basic AP3431 application circuit is shown in Figure
35, external components selection is determined by the
load current and is critical with the selection of inductor
and capacitor values.
1. Inductor Selection
For most applications, the value of inductor is chosen
based on the required ripple current with the range of
1µH to 6.8µH.
I −
1
=∆
V
OUTL
Lf
×
The largest ripple current occurs at the highest input
voltage. Having a small ripple current reduces the ESR
loss in the output capacitor and improves the efficiency.
The highest efficiency is realized at low operating
frequency with small ripple current. However, larger
value inductors will be required. A reasonable starting
point for ripple current setting is △I
maximum ripple current stays below a specified
value, the inductor should be chosen according to the
following equation:
=
L
V
[
OUT
MAXIf
∆×
L
The DC current rating of the inductor should be at
least equal to the maximum output current plus half
the highest ripple current to prevent inductor core
saturation. For better efficiency, a lower
DC-resistance inductor should be selected.
2. Capacitor Selection
The input capacitance, CIN, is needed to filter the
trapezoidal current at the source of the top MOSFET.
To prevent large ripple voltage, a low ESR input
capacitor sized for the maximum RMS current must
be used. The maximum RMS capacitor current is
given by:
It indicates a maximum value at V
I
RMS=IOUT
commonly used for design because even significant
Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited
II
×=
OMAXRMS
/2. This simple worse-case condition is
V
OUT
)1(
V
IN
=40%I
L
V
1][
)(
V
OUT
−
MAXV
IN
VVV
)]([ −
OUTINOUT
IN
=2V
IN
1
2
MAX
]
)(
OUT
. For a
, where
qw
deviations do not much relieve. The selection of C
is determined by the Effective Series Resistance
(ESR) that is required to minimize output voltage
ripple and load step transients, as well as the amount
of bulk capacitor that is necessary to ensure that the
control loop is stable. Loop stability can be also
checked by viewing the load step transient response
as described in the following section. The output
ripple, △V
, is determined by:
OUT
[
ESRIV
LOUT
+∆≤∆
8
1
××
]
Cf
OUT
The output ripple is the highest at the maximum input
voltage since △I
increases with input voltage.
L
3. Load Transient
A switching regulator typically takes several cycles to
respond to the load current step. When a load step
occurs, V
to △I
resistance of output capacitor. △I
charge or discharge C
signal used by the regulator to return V
immediately shifts by an amount equal
OUT
×ESR, where ESR is the effective series
LOAD
also begins to
LOAD
generating a feedback error
OUT
OUT
steady-state value. During the recovery time, V
can be monitored for overshoot or ringing that would
indicate a stability problem.
4. Output Voltage Setting
The output voltage of AP3431 can be adjusted by a
resistive divider according to the following formula:
VV
REFOUT
R
1
R
2
V
The resistive divider senses the fraction of the output
voltage as shown in Figure 34.
VOUT
R1
R2
FB
AP3431
GND
Figure 34. Setting the Output Voltage
14
R
+×=+×=
R
OUT
to its
OUT
1
)1(8.0)1(
2
+×=
Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Application Information (Continued)
5. Short Circuit Protection
When the AP3431 output node is shorted to GND, as
V
drop under 0.4V, the chip will enter soft-start
FB
mode to protect itself, when short circuit is removed,
and V
rise over 0.4V, the AP3431 recover back to
FB
normal operation again. If the AP3431 reach OCP
threshold while short circuit, the AP3431 will enter
soft-start cycle until the current under OCP threshold.
6. Efficiency Considerations
The efficiency of switching regulator is equal to the
output power divided by the input power times 100%.
It is usually useful to analyze the individual losses to
determine what is limiting efficiency and which
change could produce the largest improvement.
Efficiency can be expressed as:
Efficiency=100%-L1-L2-…..
Where L1, L2, etc. are the individual losses as a
percentage of input power.
Although all dissipative elements in the regulator
produce losses, two major sources usually account for
most of the power losses: V
2
I
R losses. The VIN quiescent current loss dominates
the efficiency loss at very light load currents and the
2
R loss dominates the efficiency loss at medium to
I
heavy load currents.
6.1 The V
quiescent current loss comprises two
IN
parts: the DC bias current as given in the electrical
characteristics and the internal MOSFET switch gate
charge currents. The gate charge current results from
switching the gate capacitance of the internal power
MOSFET switches. Each cycle the gate is switched
from high to low, then to high again, and the packet
of charge, dQ moves from V
resulting dQ/dt is the current out of V
typically larger than the internal DC bias current. In
continuous mode,
QQfI +×=
Where Q
and QN are the gate charge of power
P
PMOSFET and NMOSFET switches. Both the DC
bias current and gate charge losses are proportional to
Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited
quiescent current and
IN
to ground. The
IN
)(
NPGATE
that is
IN
the V
and this effect will be more serious at higher
IN
input voltages.
2
6.2 I
R losses are calculated from internal switch
resistance, R
and external inductor resistance RL.
SW
In continuous mode, the average output current
flowing through the inductor is chopped between
power PMOSFET switch and NMOSFET switch.
Then, the series resistance looking into the SW pin is
a function of both PMOSFET and NMOSFET R
resistance and the duty cycle (D) are as follows:
R
Therefore, to obtain the I
R
resistance and the duty cycle (D):
DS(ON)
−×
() ()
2
R losses, simply add RSW to
and multiply the result by the square of the
L
1
NONDSPONDSSW
average output current.
Other losses including C
and C
IN
ESR dissipative
OUT
losses and inductor core losses generally account for
less than 2 % of total additional loss.
7. Thermal Characteristics
In most applications, the part does not dissipate much
heat due to its high efficiency. However, in some
conditions when the part is operating in high ambient
temperature with high R
resistance and high
DS(ON)
duty cycles, such as in LDO mode, the heat
dissipated may exceed the maximum junction
temperature. To avoid the part from exceeding
maximum junction temperature, the user should do
some thermal analysis. The maximum power
dissipation depends on the layout of PCB, the thermal
resistance of IC package, the rate of surrounding
airflow and the temperature difference between
junction and ambient.
8. PCB Layout Considerations
When laying out the printed circuit board, the
following checklist should be used to optimize the
performance of AP3431.
1) The power traces, including the GND trace, the SW
trace and the VIN trace should be kept direct, short
and wide.
2) Put the input capacitor as close as possible to the V
15
DS(ON)
)(
DRDRR
Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Application Information (Continued)
-IN and GND pins.
3) The FB pin should be connected directly to the
feedback resistor divider.
4) Keep the switching node, SW, away from the
sensitive FB pin and the node should be kept small
area.
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Typical Application
Note 2:
R
1
)1(
VV
FBOUT
+×= .
R
2
Figure 35. Typical Application Circuit of AP3431
Table 1. Component Guide
V
(V)
OUT
3.3 31.25 10 2.2
2.5 21.5 10 2.2
1.8 12.5 10 2.2
1.2 5 10 2.2
1.0 3 10 2.2
R1(kΩ) R2(kΩ)L1(µH)
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Data Sheet
1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431
Mechanical Dimensions
SOIC-8 Unit: mm(inch)
1.000(0.039)
4.700(0.185)
5.100(0.201)
7
°
7
°
1.270(0.050)
TYP
0.100(0.004)
0.300(0.012)
1.350(0.053)
1.750(0.069)
0.675(0.027)
0.725(0.029)
R0.150(0.006)
3.800(0.150)
4.000(0.157)
0.320(0.013)
°
8
°
8
D
2
0
°
8
°
D
1
:
0
5.800(0.228)
6.200(0.244)
0.800(0.031)
0.200(0.008)
0.330(0.013)
0.510(0.020)
0.190(0.007)
0.250(0.010)
0.900(0.035)
1°
5°
0.450(0.017)
0.800(0.031)
)
6
0
0
.
0
(
0
5
1
.
0
R
Note: Eject hole, oriented hole and mold mark is optional.
Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited
18
BCD Semiconductor Manufacturing Limited
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