ANP020

ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
Contents
1.
AP1605 Specifications
1.1 Features
1.2 General Descriptions
1.3 Pin Assignments
1.4 Pin Descriptions
1.5 Block Diagram
1.6 Absolute Maximum Ratings
2.
Design Procedure
2.1 Programming Output Voltage
2.2 Inductor Selection
2.3 Output Capacitor Selection
2.4 Output Rectifier Selection
2.5 Input Capacitor Selection
3. Design Example
3.1 Summary of Target Specifications
3.2 Calculating and Components Selection
3.3 Demo Board Efficiency Calculation
4. Hardware
4.1 Introduction
4.2 Demo Board Schematic
4.3 Board of Materials
4.4 Board Layout
This application note contains new product information. Diodes, Inc. reserves the right to modify the product specification without notice. No liability is
assumed as a result of the use of this product. No rights under any patent accompany the sale of the product.
1/9
ANP020 – App. Note 1
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
1. AP1605 Specifications
1.1 Features
- Low Current Consumption:
In Operation: 100µA max.
Power Off: 2µA max.
- Input Voltage: 2.5V to 7V
Adjustable Version (+2.5%)
- PWM/PFM Dual Mode
- Oscillation Frequency: 300 kHz (Typ.)
- With a Power-off Function
- Built-in Internal SW P-Channel MOS
- SOP-8L/TSSOP-8L Package
1.2 General Descriptions
AP1605 consists of CMOS step-down switching regulator with PWM/PFM dual mode control. These
devices include a reference voltage source, oscillation circuit, error amplifier, internal PMOS and etc.
AP1605 provides low-ripple power, high efficiency, and excellent transient characteristics. The
PWM/PFM control circuit is able to vary the duty ratio linearly 0%~0.25% (PFM) and 25%~100% (PWM).
With the addition of an internal P-channel Power MOS, a coil, capacitors, and a diode connected
externally, these ICs can function as step-down switching regulators. They serve as ideal power supply
units for portable devices when coupled with the SOP–8L mini-package, providing such outstanding
features as low current consumption. Since this converter can accommodate an input voltage of up to 7V,
it is also ideal when operating via an AC adapter.
1.3 Pin Assignments
FB
CE
1
8 Vss
2
7 Vss
AP1605
Vcc 3
6 SW
PVcc 4
5 SW
Vss
1
CE
2
CE
3
FB
4
(SOP-8L)
AP1605
8
SW
7
PVcc
6
PVcc
5
Vcc
(TSSOP-8L)
2/9
ANP020 – App. Note 1
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
1.4 Pin Descriptions
Pin
Pin No.
Name SOP TSSOP
FB
1
4
CE
2
2, 3
Vcc
3
5
PVcc
4
6, 7
SW
5, 6
8
Vss
7, 8
1
Description
Feedback pin
Chip Enable:
H: Enable
L: Disable
IC Signal Power Supply
Pin, add a 10Ω Resistor
to PVcc and a 0.1µF
Capacitor to GND.
IC Power Supply Pin
Switch Pin. Connect
External Inductor/Diode
Here. Minimize Trace
Area at this Pin to
Reduce EMI.
GND Pin
1.5 Block Diagram
SW
PV CC
FB
AP1605
V CC
PWM /PFM -Switched
Control Circuit
+
-
CE
Oscillation
Circuit
Reference Voltage
Source
V SS
3/9
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
1.6 Absolute Maximum Ratings
Symbol
Rating
Unit
VCC Pin Voltage
VSS - 0.3 to VSS + 8
V
PVCC Pin Voltage
VSS - 0.3 to VSS + 8
V
FB
FB Pin Voltage
VSS - 0.3 to VSS + 8
V
VCE
ON/OFF Pin Voltage
VSS - 0.3 to VSS + 8
V
VSW
Switch Pin Voltage
V
PD
Power Dissipation
VSS - 0.3 to VIN + 0.3
1200
700
-20 to +85
VCC
Parameter
*1
PVCC
SOP-8L
TSSOP-8L
Operating Temperature Range
TOPR
TSTG
Storage Temperature Range
-20 to +125
mW
o
C
o
C
2. Design Procedure (refer to “Demo Board Schematic” on page 8)
2.1 Programming Output Voltage
The output voltage is programmed by selection of the divider R1 and R2. The designer should
use resistors R1 and R2 with ±1% tolerance in order to obtain best accuracy of the output voltage.
The output voltage can be calculated from the following formula: Vout = 1.2 x (1 + R1 / R2), select a
value for R2 between 100K and 200KΩ. The higher resistor values minimize leakage current pickup
in the feedback pin.
2.2 Inductor Selection
A. The minimum inductor
L
(min)
can be calculated from the following design formula table:
Calculation
T
T
L
V
V
ON
OFF
[V
V
IN (min)
IN (min)
− V SAT − V OUT
]
− V SAT − V OUT × T ON (max)
2 × I LOAD (min)
(min)
= Internal Driver dropout Voltage of the AP1605 = ILoad * 120mΩ
SAT
F
Step-down (buck) Converter
(V OUT + V F )
= Forward voltage drop of output rectifier D1 = 0.4V
B. The inductor must be designed so that it does not saturate or significantly saturate at DC current
bias of
.
PK
I
I
PK
= Peak inductor or switch current =
I
LOAD (max)
+ I LOAD (min)
4/9
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
2.3 Output Capacitor Selection
A. The Output Capacitor is required to filter the output and provide regulator loop stability. When
selecting an Output Capacitor, the important capacitor parameters are; the 100kHz Equivalent
Series Resistance (ESR), the RMS ripples current rating, voltage rating, and capacitance value.
For the output capacitor, the ESR value is the most important parameter. The ESR can be
calculated from the following formula:
⎞
⎛
ESR = ⎜ V RIPPLE ⎟
⎟
⎜ 2× I
LOAD (min) ⎠
⎝
B. It is important to select the Vout capacitor value by AP1605. The Vout capacitor value cannot be
above 68uF. The larger capacitor value could make Vout over-shoot.
2.4 Output Rectifier Selection
A. The Output Rectifier D1 current cannot be less than the peak switch current IPK. The reverse
voltage rating of the Output Rectifier D1 should be at least 1.25 times of the Maximum Input
Voltage.
B. The Output Rectifier D1 must be fast (short reverse recovery time) and must be located close to
the AP1605 using short leads and short printed circuit traces. Because of their fast switching
speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency,
and should be the first choice, especially in low output voltage applications.
2.5 Input Capacitor Selection
A. The RMS current rating of the input capacitor can be calculated from the following formula table.
The capacitor manufacturers data sheet must be checked to assure that this current rating is not
exceeded.
Calculation
δ
I
I
ΔI
Step-down (buck) Converter
Ton/(Ton+Toff)
I
I
PK
m
I
LOAD (max)
+ I LOAD (min)
LOAD (max)
− I LOAD (min)
2 × I LOAD(min)
L
IN ( rms )
δ × ⎢(I PK × I m ) +
⎡
⎣
1
(Δ I L )2 ⎤⎥
3
⎦
B. This capacitor should be located close to the IC using short leads and the voltage rating should
be approximately 1.5 times of the maximum input voltage.
5/9
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
3. Design Example
3.1 Summary of Target Specifications
V
V
V
Input Power
Regulator Output Power
Output Ripple Voltage
Efficiency
Switching Frequency
IN (max)
OUT
= +7V;
= +3.3V;
V
I
IN (min)
= +4V
LOAD(max)
= 3A;
I
LOAD(min)
= 0.2A
≤ 100 mV peak-to-peak
RIPPLE
85% minimum at full load
f = 300kHz ± 15 %
3.2 Calculating and Components Selection
Calculation Formula
Vout = Vref x ((R1/R2) + 1)
L(min) ≥
I
PK
=
I
[V
IN (min)
]
− V SAT − V OUT × T ON (max)
2 × I LOAD (min)
LOAD (max)
+ I LOAD (min)
⎞
⎛
ESR = ⎜ V RIPPLE ⎟
⎟
⎜ 2× I
LOAD (min) ⎠
⎝
V WVDC ≥ 1.5 ×V OUT
V
I
RRM
PK
=
≥ 1.25 ×V IN (max)
I
LOAD (max)
+ I LOAD (min)
1
2⎤
⎡
= δ × ⎢(I PK × I m ) + (Δ I L ) ⎥
3
⎣
⎦
V WVDC ≥ 1.5 ×V IN (max)
I
IN ( rms )
Select Condition
100KΩ ≤ R2 ≤ 200KΩ
L
I
≥ 4.1UH
(min)
≥
rms
I
PK
= 3A
ESR ≤ 300mΩ
RRM
PK
I
V
≥ 11.25V
≥
WVDC
I
IN ( rms )
Select L = 4.7uH / 5A
"Viking
Tech"
Select D1 = 40V/3A
= 3A
ripple
R1 = 180KΩ; R2 = 100KΩ
Select C8 from
68uF/6.3V*1pcs
V WVDC ≥ 5V
V
I
Component spec.
= 2.3A
≥ 11.25V
Select C1 from "Viking Tech"
100uF/16V*1pcs
6/9
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
3.3 Demo Board Efficiency Calculation
Vcc (V)
Icc (A)
Vout (V)
Iout (A)
Efficiency (%)
5.00
0.051m
3.311
0
0
5.00
0.216
3.296
0.3
91.56
5.00
0.428
3.295
0.6
92.38
5.00
0.643
3.295
0.9
92.24
5.00
0.865
3.294
1.2
91.39
5.00
1.092
3.292
1.5
90.44
5.00
1.329
3.289
1.8
89.09
5.00
1.565
3.291
2.1
88.32
5.00
1.826
3.285
2.4
86.35
5.00
2.088
3.28
2.7
84.83
5.00
2.373
3.275
3
82.81
4. Hardware
4.1 Introduction
This application note discusses simple ways to select all necessary components to implement a
step-down (BUCK) Switching Regulator and gives a design example. In this example, the AP1605
monolithic IC is used to design a cost-effective and high-efficiency miniature switching regulator. For
more complete information, pin descriptions and specifications for the AP1605 will not be repeated here.
Please refer to the datasheet when designing or evaluating the AP1605.
This demonstration board allows the designer to evaluate the performance of the AP1605 series
buck switching regulator in a typical application circuit. The user needs only to supply an input voltage
and a load. Operation at other voltages and currents may be accomplished by proper component
selection and replacement.
7/9
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ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
4.2 Demo Board Schematic
U2
VIN
4
3
D2
15£[
C1
100uF/16V
2
PVCC
VCC
CE
SW
AP1605-SOP
VSS
VSS
7
8
SW*
FB
5
1
L1
VOUT
2
4.7uH
6
1
D1
B340A
C2
R1
180K
C7
R5
100K
0.1uF
0.1uF
C3
4.7uF
C8
68uF/16V
R2
100K
R6
0.1uF
Vout = 1.2 * (1+R1/R2)
R2 suggest 100K~200K
4.3 Board of Materials
Item
Value
Q’ty
Description
MFG/Dist.
C1
100uF, 16V
1
Aluminum Electrolytic Capacitor
Viking Tech
C2
0.1uF, 25V
1
0805 Ceramic SMD Capacitor
Viking Tech
C3
0.1uF, 25V
1
0805 Ceramic SMD Capacitor
Viking Tech
R6
0.1uF, 25V
1
0805 Ceramic SMD Capacitor
Viking Tech
C7
0.1uF, 25V
1
0805 Ceramic SMD Capacitor
Viking Tech
C8
68uF, 6.3V
1
Solid Tantalum Capacitor
Viking Tech
D1
40V, 3A
1
Schottky Diode
L1
4.7uH, 5A
1
Inductance
Wurth Elektronik
U1
300kHz, 3A
1
Step-down Switching Regulator
Anachip
R1
180KΩ
1
1% 0805 SMD Resistor
Viking Tech
R2
100KΩ
1
1% 0805 SMD Resistor
Viking Tech
R5
100KΩ
1
1% 0805 SMD Resistor
Viking Tech
D2
15Ω
1
1% 0805 SMD Resistor
Viking Tech
Part
Number
B340A
WE-PD3
7445404
AP1605
8/9
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© Diodes Incorporated
ANP020
Application Note
AP1605 300KHz,3A PWM/PFM Dual Mode Step-down Switching Regulator
4.4
PC Board Layout
(1) Top View
(2) Bottom View
9/9
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