AP5101SG-13 [DIODES]
1.5A Step-Down Converter with 1.4MHz Switching Frequency; 1.5A降压转换器具有1.4MHz的开关频率
| 型号： | AP5101SG-13 |
| 厂家： | 
DIODES INCORPORATED |
| 描述： | 1.5A Step-Down Converter with 1.4MHz Switching Frequency |
| 文件： | 总15页 (文件大小：376K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Description
Pin Assignments
The AP5101 is a current mode step-down converter with a
built-in power MOSFET to enable smallest solution size
power conversion.
( Top View )
1
2
3
4
8
7
6
5
SW
IN
GND
BST
COMP
FB
With the low series resistance power switch it enables a
constant output current of up to 1.5A over a wide input supply
range. The load and line regulation has excellent response
time over the operating input voltage and temperature range.
EN
GND
The AP5101 is self protected, through a cycle-by-cycle
current limiting algorithm and an on chip thermal protection.
SO-8
The AP5101 will provide the voltage conversion with a low
count of widely available standard external components.
The AP5101 is available in SO-8 package.
Features
Applications
•
•
•
•
Distributed Power Systems
Battery Charger
•
•
•
•
•
•
•
•
•
•
•
VIN 4.75 to 22V
1.5A Peak Output Current
Pre-Regulator for Linear Regulators
WLED Driver
Stable with Low ESR Ceramic Output Capacitors
External compensation
Up to 92% Efficiency
0.1µA Shutdown Mode
Fixed 1.4MHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Output Adjustable from 0.81V to 15V
SO-8: Available in “Green” Molding Compound
(No Br, Sb)
•
Lead Free Finish/ RoHS Compliant (Note 1)
Note: 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at
http://www.diodes.com/products/lead_free.html.
Typical Application Circuit
Input
4.75V to 22V
C4
C1
2
7
L1
IN
BST
1
5
ON
3
SW
FB
EN
OFF
Output
3.3V 1.5A
AP5101
R1
COMP
GND
D1
6
4,8
C2
R2
C3
R3
Figure 1 Typical Application Circuit
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Typical Application Circuit (continiued)
C4
10nF
Input
4.75V to 22V
C1
10uF/25V
CERAMIC
R4
100k
L1
7
2
4.7uH
IN
3
BST
1
5
Output
3.3V
1.5A
SW
FB
EN
R1
AP5101
49.9k 1%
GND
COMP
C2
6
22µF/6.3V
CERAMIC
X2
4,8
R2
16.2k 1%
D1
B340A
C3
3nF
R3
5.6k
Figure 2. 1.4MHz, 3.3V Output at 1.5A Step-Down Converter
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Pin Descriptions
( Top View )
1
2
3
4
8
7
6
5
SW
IN
GND
BST
COMP
FB
EN
GND
SO-8
Pin Name
Pin Number
Descriptions
SW
1
Switch Output. This is the reference for the floating top gate driver.
Supply Voltage. The AP5101 operates from a +4.75V to +22V unregulated
input. A decoupling capacitor C1 is required to prevent large voltage spikes
from appearing at the input. Place this capacitor near the IC.
2
IN
On/Off Control Input. Do not leave this pin floating. To turn the device ON, pull
EN above 1.2V and to turn it off pull below 0.4V.
3
4
EN
If enable/disable is not used, connect a 100kΩ resistor between EN to VIN.
Ground. This pin is the voltage reference for the regulated output voltage. For
this reason care must be taken in its layout. This node should be placed
outside of the D1 to C1 ground path to prevent switching current spikes from
inducing voltage noise into the part.
GND
Feedback. To set the output voltage, connect this pin to the output resistor
divider or directly to VOUT. To prevent current limit run away during a current
limit condition, the frequency foldback comparator lowers the oscillator
frequency when the FB voltage is below 400mV.
FB
COMP
BST
5
6
7
Compensation. COMP is used to compensate the regulation control loop.
Connect a series RC network from COMP to GND.
Bootstrap. To form a boost circuit, a capacitor is connected between SW and
BST pins to form a floating supply across the power switch driver. This
capacitor is needed to drive the power switch’s gate above the supply voltage.
Typical values for CBST range from 0.1uF to 1uF.
Ground. This pin is the voltage reference for the regulated output voltage. All
control circuits are referenced to this pin. For this reason care must be taken in
its layout.
8
GND
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Absolute Maximum Ratings (Note 2)
Symbol
VIN
Parameter
Rating
26
Unit
V
Supply Voltage
VSW
VBS
Switch Voltage
Boost Voltage
–0.3 to VIN + 0.3
VSW + 6
V
V
All Other Pins
–0.3 to +6
-65 to +150
+150
V
TST
TJ
TL
Storage Temperature
Junction Temperature
Lead Temperature
°C
°C
°C
+260
ESD Susceptibility
HBM
MM
Human Body Model
Machine Model
2
kV
V
200
Note: 2. Exceeding these ratings may damage the device.
Thermal Resistance (Note 3)
Rating
Symbol
Parameter
Junction to Ambient
Junction to Case
Unit
θJA
θJC
120
15
°C/W
°C/W
Note: 3. Test condition for SO-8: Measured on approximately 1” square of 1 oz copper.
Recommended Operating Conditions (Note 4)
Symbol
Parameter
Min
Max
Unit
VIN
TA
Supply Voltage
22
+85
15
V
°C
V
4.75
-40
Operating Ambient Temperature Range
Output Voltage
VOUT
0.81
Note: 4. The device function is not guaranteed outside of the recommended operating conditions.
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Electrical Characteristics (VIN = 12V, TA = +25°C, unless otherwise noted)
Symbol
Parameter
Feedback Voltage
Test Conditions
Min
Typ.
Max
Unit
VFB
IFB
R DS(ON)
4.75V ≤ VIN ≤ 22V
0.790
0.810
0.1
0.830
V
µA
Ω
Feedback Current
VFB = 0.8V
Switch-On Resistance (Note 5)
Switch Leakage
0.35
10
µA
A
VEN = 0V, VSW = 0V
Current Limit (Note 5)
Current Sense Transconductance
Output Current to Comp Pin Voltage
2.5
1.3
A/V
GCS
AVEA
GEA
fSW
400
850
V/V
Error Amplifier Voltage Gain (Note 5)
Error Amplifier Transconductance
uA/V
ΔIC = ±10μA
VFB = 0.6V
VFB = 0V
Oscillator Frequency
Fold-back Frequency
Maximum Duty Cycle
1.1
1.4
500
65
1.7
MHz
kHz
%
VFB = 0.6V
tON
Minimum On-Time (Note 5)
Under Voltage Lockout
Threshold Rising
Under Voltage Lockout Threshold
Hysteresis
EN Input Low Voltage
EN Input High Voltage
100
ns
3.8
1.2
4.0
4.2
0.4
V
100
mV
V
V
2.1
0.1
0.1
0.5
150
µA
µA
µA
mA
°C
V
EN = 2V
EN Input Current
VEN = 0V
IS
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown (Note 5)
1.0
0.7
VEN = 0V
IQ
VEN = 2V, VFB = 1V
Note: 5. Guaranteed by design
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Typical Performance Characteristics
VIN =12V, VOUT =3.3V, L =4.7uH, C1=10uF, C2=22uF, Ta=+25•C, unless otherwise noted.
Steady State Test
IOUT=0.5A
Load Transient Test
IOUT=0.2A to 0.8A. Step at 0.8A/us
Time- 1us/div
Time- 100us/div
Start-up Through Enable (No Load)
Start-up through Enable (IOUT=1A, resistive load)
Time- 50us/div
Time- 50us/div
Shutdown Through Enable (No Load)
Shutdown Through Enable (IOUT=1A, resistive)
Time- 50us/div
Time- 50us/div
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Typical Performance Characteristics (continued)
VIN =12V, VOUT =3.3V, L =4.7uH, C1=10uF, C2=22uF, Ta=+25•C, unless otherwise noted.
Short Circuit Entry Short Circuit Recovery
Time- 100us/div
Time- 50us/div
Current Sense Transconductance (Gcs)
Gcs= 1.5A/(comp2-comp1)=1.5A/(1.8-0.65) =1.3A/V
Time- 2us/div
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Applications Information
Operation
The AP5101 is a current mode control, asynchronous buck regulator. Current mode control assures excellent line and load
regulation and a wide loop bandwidth for fast response to load transients. Figure. 3 depicts the functional block diagram of
AP5101.
The operation of one switching can be explained as follows. At the beginning of each cycle, HS (high-side) MOSFET is off. The
EA output voltage is higher than the current sense amplifier output, and the current comparator’s output is low. The rising edge
of the 1.4MHz oscillator clock signal sets the RS Flip-Flop. Its output turns on HS MOSFET.
When the HS MOSFET is on, inductor current starts to increase. The Current Sense Amplifier senses and amplifies the
inductor current. Since the current mode control is subject to sub-harmonic oscillations that peak at half the switching
frequency, Ramp slope compensation is utilized. This will help to stabilize the power supply. This Ramp compensation is
summed to the Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the
sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS Flip-
Flop is reset and HS MOSFET is turned off. The external Schottky rectifier diode (D1) conducts the inductor current.
For one whole switching cycle, if the sum of the Current Sense Amplifier output and the Slope Compensation signal does not
exceed the EA output, then the falling edge of the oscillator clock resets the Flip-Flop. The output of the Error Amplifier
increases when feedback voltage (VFB) is lower than the reference voltage of 0.81V. This also increases the inductor current
as it is proportional to the EA voltage.
2
IN
CURRENT SENSE AMPLIFIER
-
RSEN
25mO
+
RAMP
REGULATOR
GENERATOR
BST
SW
7
1
OSCILLATOR
1.4MHz/500KHz
3
REGULATOR
EN
Q
S
R
R
DRIVER
+
-
CURRENT LIMIT
COMPARATOR
REFERENCE
GND
FB
4
5
8
6
GND
+
-
+
EA
PWM
-
COMPARATOR
ERROR AMPLIFIER
COMP
Figure 3. Functional Block Diagram
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Applications Information (Continued)
Component Selection
The output voltage can be adjusted from 0.81V to 15V using an external resistor divider. Table 1 shows a list of resistor
selection for common output voltages. Resistor R1 is selected based on a design tradeoff between efficiency and output
voltage accuracy. For high values of R1 there is less current consumption in the feedback network. However the trade off is
output voltage accuracy due to the bias current in the error amplifier. R2 can be determined by the following equation:
V
⎛
⎞
OUT
⎜
⎜
⎟
R
= R
×
2
− 1
1
⎟
⎠
0.81
⎝
VOUT (V)
R1 (kΩ)
R2 (kΩ)
1.8
2.5
3.3
5.0
80.6 (1%)
49.9 (1%)
49.9 (1%)
49.9 (1%)
64.9 (1%)
23.7 (1%)
16.2 (1%)
9.53 (1%)
Table 1. Resistor Selection for Common Output Voltage
Compensation Components
The AP5101 has an external COMP pin through which system stability and transient response can be controlled. COMP pin is
the output of the internal trans-conductance error amplifier. A series capacitor-resistor combination sets a pole-zero
combination to control the characteristics of the control system. The DC gain of the voltage feedback loop is given by:
V
FB
A
= R
× G
× A
×
VEA
VDC
LOAD
CS
V
OUT
Where VFB is the feedback voltage (0.810V), RLOAD is the load resistor value, GCS is the current sense trans-conductance and
VEA is the error amplifier voltage gain.
A
The control loop transfer function incorporates two poles. One is due to the compensation capacitor (C3) and the output
resistor of error amplifier, and the other is due to the output capacitor and the load resistor. These poles are located at:
G
EA
f
=
=
P1
2π × C3 × A
VEA
1
f
P2
2π × C2 × R
LOAD
Where GEA is the error amplifier trans-conductance.
One zero is present due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at:
1
f
=
Z1
2π × C3 × R3
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Applications Information (Continued)
The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover
frequency where the feedback loop has the unity gain is crucial.
A rule of thumb is to set the crossover frequency to below one-tenth of the switching frequency. Use the following procedure to
optimize the compensation components:
1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following
equation:
2π × C2 × fc
V
2π × C2 × 0.1× fs
V
OUT
OUT
R3 =
×
<
×
G
× G
CS
V
G
V
EA
FB
×G
CS
FB
EA
Where fC is the crossover frequency, which is typically less than one-tenth of the switching frequency.
2. Choose the compensation capacitor (C3) to achieve the desired phase margin. Set the compensation zero, fZ1, to below
one-fourth of the crossover frequency to provide sufficient phase margin. Determine the C3 value by the following equation:
2
C3 >
π × R3 × fc
Where R3 is the compensation resistor value.
Inductor
Calculating the inductor value is a critical factor in designing a buck converter. For most designs, the following equation can be
used to calculate the inductor value;
V
× (V − V )
IN OUT
OUT
L =
V
× ΔI × f
IN
L
SW
Where ΔI is the inductor ripple current.
L
And fsw is the buck converter switching frequency.
Choose the inductor ripple current to be 30% of the maximum load current. The maximum inductor peak current is calculated
from:
ΔI
L
I
= I +
L(MAX) LOAD
2
Peak current determines the required saturation current rating, which influences the size of the inductor. Saturating the
inductor decreases the converter efficiency while increasing the temperatures of the inductor, the MOSFET and the diode.
Hence choosing an inductor with appropriate saturation current rating is important.
A 1µH to 10µH inductor with a DC current rating of at least 25% percent higher than the maximum load current is
recommended for most applications.
For highest efficiency, the inductor’s DC resistance should be less than 200mΩ. Use a larger inductance for improved
efficiency under light load conditions.
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Applications Information (Continued)
Input Capacitor
The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. The input
capacitor has to sustain the ripple current produced during the on time on the upper MOSFET. It must hence have a low ESR
to minimize the losses.
Due to large dI/dt through the input capacitors, electrolytic or ceramics should be used. If a tantalum must be used, it must be
surge protected. Otherwise, capacitor failure could occur. For most applications, a 4.7µF ceramic capacitor is sufficient.
Output Capacitor
The output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the
output voltage. The output capacitor is a basic component for the fast response of the power supply. In fact, during load
transient, for the first few microseconds it supplies the current to the load.
The converter recognizes the load transient and sets the duty cycle to maximum, but the current slope is limited by the inductor
value.
Maximum capacitance required can be calculated from the following equation:
ΔI
inductor 2
)
L(I
+
out
2
C
=
o
2
2
(Δ V + V
)
− V
out
out
Where ΔV is the maximum output voltage overshoot.
ESR of the output capacitor dominates the output voltage ripple. The amount of ripple can be calculated from the equation
below:
Vout
= ΔI
× ESR
inductor
capacitor
An output capacitor with ample capacitance and low ESR is the best option. For most applications, a 22µF ceramic capacitor
will be sufficient.
External Diode
The external diode’s forward current must not exceed the maximum output current. Since power dissipation is a critical factor
when choosing a diode, it can be calculated from the equation below:
V
OUT
P
= (1−
)×I
× 0.3V
OUT
diode
V
IN
Note: 0.3V is the voltage drop across the Schottky diode. A diode that can withstand this power dissipation must be chosen.
PC Board Layout
This is a high switching frequency converter. Hence attention must be paid to the switching currents interference in the layout.
Switching current from one power device to another can generate voltage transients across the impedances of the
interconnecting bond wires and circuit traces. These interconnecting impedances should be minimized by using wide, short
printed circuit traces. The input capacitor needs to be as close as possible to the IN and GND pins. The external feedback
resistors should be placed next to the FB pin.
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Applications Information (Continued)
External Bootstrap Diode
It is recommended that an external bootstrap diode be added when the input voltage is no greater than 5V or the 5V rail is
available in the system. This helps improve the efficiency of the regulator. The bootstrap diode can be a low cost one such as
IN4148 or BAT54.
5V
BOOST
DIODE
7
BST
10nF
AP5101
1
SW
Figure 4. External Bootstrap Diode
Current
Rating (A)
Dimensions
L x W x H (mm3)
Max DCR
Manufacturer
Part Number
Inductance(µH)
(Ω)
Toko
Sumida
A921CY-4R7M
CDRH4D28C/LD
7440530047
4.7
4.7
4.7
0.027
0.036
0.038
1.66
1.50
2.00
6.0 x 6.3 x 3.0
5.1 x 5.1 x 3.0
5.8 x 5.8 x 2.8
Wurth Electronics
Table 2. Suggested Surface Mount Inductors
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Ordering Information
AP5101 S G - 13
Green
G : Green
Packing
Package
S : SO-8
13 : Tape & Reel
13” Tape and Reel
Package
Code
Packaging
(Note 6)
Device
Quantity
2500/Tape & Reel
Part Number Suffix
AP5101SG-13
S
SO-8
-13
Note: 6. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at
http://www.diodes.com/datasheets/ap02001.pdf.
Marking Information
( Top View )
5
8
YY : Year : 10, 11, 12~
WW : Week : 01~52;
52 represents 52 and 53 week
X : Internal Code
Logo
AP5101
YYWWX X
Part No
G : Green
1
4
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
Package Outline Dimensions (All Dimensions in mm)
Gauge Plane
Seating Plane
0.62/0.82
Detail "A"
7°~9°
7°~9°
0.35max.
45°
Detail "A"
0°/8°
0.3/0.5
1.27typ
4.85/4.95
8x-0.60
6x-1.27
Land Pattern Recommendation
(Unit: mm)
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AP5101
Document number: DS32258 Rev. 1 - 2
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
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the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided
in the labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected
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Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes
Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2010, Diodes Incorporated
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AP5101
Document number: DS32258 Rev. 1 - 2
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