AP1539
18V 4A 300KHz BUCK CONVERTER
Description
AP1539 consists of step-
down switching regulator with PWM control.
These devices include a reference voltage source, oscillation circuit,
error amplifier, internal PMOS.
AP1539 provides low-rippl
e power, high efficiency, and excellent
transient characteristics. The PWM control circuit is able to vary the
duty ratio linearly from 0 up to 99
%. This converter also contains an
error amplifier circuit as well as a soft-
start circuit that prevents
overs
hoot at startup. An enable function, an over current protect
function and a short circuit protect function are built inside, and when
OCP or SCP happens, the operation frequency will be reduced from
300KHz to 50KHz. Also, an internal compensation block is
built in to
minimum external component count. 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 p
ortable devices when
coupled with the SOP-8L-DEP mini-
package, providing such
outstanding features as low current consumption. Since this converter
can accommodate an input voltage up to 18
V, it is also suitable for the
operation via an AC adapter.
Features
Input voltage: 3.6V to 18V
Output voltage: 0.8V to VCC
Output current: up to 4A
Duty ratio: 0% to 99% PWM control
Oscillation frequency: 300KHz typ.
Soft-start like, Current limit and Enable function
Thermal Shutdown function
Built-in internal SW P-channel MOS
SOP-8L-DEP: Available in GreenMolding Compound (No Br, Sb)
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
For automotive applications requiring specific change control
(i.e. parts qualified to AEC-
Q100/101/200, PPAP capable, and
manufactured in IATF 16949 certified facilities), please
contact
us or your local Diodes representative.
https://www.diodes.com/quality/product-definitions/
Pin Assignments
1
2
3
4
8
7
6
5
FB
Output
OCSET
Output
EN
Vss
Vss
VCC
1
2
( Top View )
(Note 4 )
SOP-8L-DEP (Dual Exposed Pads)
Note: 4. Exposed pad 1 is connected to VSS and exposed pad 2 is connected to
Output. The board layout for exposed pads needs to be considered to
avoid short circuit.
Applications
PC Motherboard
LCD Monitor
Graphic Card
DVD-Video Player
Telecom Equipment
ADSL Modem
Printer and other Peripheral Equipment
Microprocessor core supply
Notes: 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS), 2011/65/EU (RoHS 2) & 2015/863/EU (RoHS 3) compliant.
2. See https://www.diodes.com/quality/lead-free/ for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and
Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
NOT RECOMMENDED FOR NEW DESIGN
CONTACT US
AP1539
Document number: DS31477 Rev. 6 - 3
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AP1539
Typical Application Circuit
AP 1539
+
-
V
SS
EN
Cc R
A
R
B
D1
**
FB
Vcc Output
CVcc
V
OUT
= 5V/4A
V
IN
R
OCSET
OCSET C
OUT
C
IN
Option
*
C
OCSET
C
EN
R
EN
Option
100K
VOUT
=
VFB x (1+RA/RB)
RB= 0.7K~5K ohm
L1
22uH
6.8K
1.3K
3.9K
0.1uF
+
-
C
0.1uF 470uF
***
470uF
0.1uF
Notes: * Typical feedback compensation (Cc): 5600pF.
** Suggested DIODES Power Schottky P/N: B540 series or PDS540.
*** Suggested C
OUT
for V
OUT
< 1V; 680uF.
Pin Descriptions
Pin Name Pin No. Description
FB 1 Feedback pin
EN 2
Power-off pin
H: Normal operation (Step-down operation)
L: Step-down operation stopped (All circuits deactivated)
OCSET 3 Add an external resistor to set max output current
VCC 4 IC power supply pin
Output 5, 6 Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin to
reduce EMI
VSS 7, 8 GND Pin
Suggested Diodes Incorporated Power Schottky P/N: B540 series or PDS540.
AP1539
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AP1539
Block Diagram
Oscillation
Circuit
Reference Voltage
Source with Soft Start
PWM-Switched
Control Circuit
+
-
VssV
EN
EN
90uA
OCSET
FB
Vcc
Thermal
Shutdown
Output
Absolute Maximum Ratings
Symbol Parameter Rating Unit
ESD HBM Human Body Model ESD Protection 5.5 KV
ESD MM Machine Model ESD Protection 200 V
VCC VCC Pin Voltage VSS - 0.3 to VSS + 20 V
VFB Feedback Pin Voltage VSS - 0.3 to VCC V
VEN EN Pin Voltage VSS - 0.3 to VCC V
VOUT Switch Pin Voltage VSS - 0.3 to VCC V
PD Power Dissipation Internally limited mW
TJ Operating Junction Temperature Range -40 to +125 oC
TST Storage Temperature Range -65 to +150 oC
Caution: The absolute maximum ratings are rated values exceeding which the product could suffer physical damage.
These values must therefore not be exceeded under any conditions.
Recommended Operating Conditions
Symbol Parameter Min Max Unit
Input Voltage (Note 5)
3.6
18
V
Output Current
0
4
A
Operating Ambient Temperature
-20
+85
oC
Note: 5. For the operations in low input voltage, AP1539 can tolerate down to 3.6V but max output current loading will be less than 4A. For nominal applications in
such low input voltage range, especially lower than 4V, a higher ROCSET with larger heat sink is recommended.
AP1539
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AP1539
Electrical Characteristics
(VIN = 12V, TA = +25°C, unless otherwise specified)
Symbol Parameter Conditions Min Typ. Max Unit
VFB
Feedback Voltage
IOUT = 0.1A
0.784
0.8
0.816
V
IFB
Feedback Bias Current
IOUT = 0.1A
0.1
0.5
µA
ISHDN
Current Consumption During Power
Off
VEN = 0V 10 µA
VOUT
/ VIN Line Regulation VIN = 5V~18V 1 2 %
V
OUT
/ VOUT
Load Regulation IOUT = 0.1 to 4A 0.2 0.5 %
fOSC
Oscillation Frequency
Measure waveform at SW pin
240
300
400
KHz
fOSC1
Frequency of Current Limit or Short
Circuit Protection
Measure waveform at SW pin 50 KHz
VIH
EN Pin Input Voltage
Evaluate oscillation at SW pin
2.0
V
VIL
Evaluate oscillation stop at SW pin
0.8
ISH
EN Pin Input Leakage Current
EN Pin High
20
µA
ISL
EN Pin Low
-10
µA
IOCSET
OCSET Pin Bias Current
75
90
105
µA
RDS(ON) Internal MOSFET RDS(ON)
VIN = 5V, VFB = 0V
90
mΩ
VIN = 12V, VFB = 0V
50
EFFI Efficiency VIN = 12V, VOUT = 5V
IOUT = 4A
92 %
TSHDN
Thermal shutdown threshold
+150
°C
THYS
Thermal shutdown hysteresis
+55
°C
θJC Thermal Resistance Junction-to-Case
SOP-8L-DEP (Note 6) 26 oC/W
Note: 6. Test condition for SOP-8L-DEP: Devices mounted on 2oz copper, minimum recommended pad layout on top & bottom layer with thermal vias, double
sided FR-4 PCB.
AP1539
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AP1539
Typical Performance Characteristics
V
IN
vs. Frequency
(V
OUT
= 3.3V, I
OUT
= 0.2A)
306
308
310
312
314
316
318
320
322
324
326
0246810 12 14 16 18
V
IN
(V)
F
OSC
(kHz)
VIN vs . VFB
(V
OUT = 3.3V, IOUT = 0.2A)
0.780
0.785
0.790
0.795
0.800
0.805
0.810
0.815
0.820
0246810 12 14 16 18
VIN (V)
VFB (V)
Line Regulation
(V
OUT
= 3.3V, I
OUT
= 0.2A)
3.00
3.05
3.10
3.15
3.20
3.25
3.30
3.35
3.40
0 2 4 6 8 10 12 14 16 18
V
IN
(V)
V
OUT
(V)
Load Regulation
(V
IN
= 12V)
3.25
3.26
3.27
3.28
3.29
3.30
3.31
3.32
3.33
3.34
3.35
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
I
OUT
(A)
V
OUT
(V)
Efficiency
(V
IN
= 12V)
0
10
20
30
40
50
60
70
80
90
100
0.0 1.0 2.0 3.0 4.0
I
OUT
(A)
Efficiency (%)
VOUT=3.3V
V OUT=5V
Switch Current Limit
(TA = 25)
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
0246810 12 14 16 18
VIN (V)
Current Limit (A)
ROCSET=6.8k
ROCSET=4.7k
AP1539
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AP1539
Typical Performance Characteristics (continued)
Current Limit vs. Temperature
(V
IN
= 12V, R
OCSET
= 6.8k)
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
-25 025 50 75 100
Ambient Temperature (C)
Current Limit (A)
V
OUT
Ripple
(VIN=12V, VOUT=3.3V, IOUT=0.1A)
V
OUT
Ripple
(VIN=12V, VOUT=3.3V, IOUT=4.0A)
Load Transient Response
(VIN =12V, VOUT =3.3V, IOUT =0.1~4A)
Ambient Temperature (°C)
AP1539
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AP1539
Test Circuit
A
FBV
CC
V
SS
EN
open
open
FB
EN
+
-
O
scillation
Output Output
A
FB
EN
+
-+
-
V
Output
OCSET
OCSET
OCSET
Enable function test Feedback function test
Operation function test
V
CC
V
CC
V
SS
V
SS
Functional Description
PWM Control
The AP1539 is a DC/DC converter that employs pulse width modulation (PWM) scheme. Its pulse width varies in the range of 0% to 99%, based
on the output current loading. The output ripple voltage caused by the PWM high frequency switching can easily be reduced through an output
filter. Therefore, this converter provides a low ripple output supply over a broad range of input voltage & output current loading.
Under Voltage Lockout
The under voltage lockout circuit of the AP1539 assures that the high-side MOSFET driver remains in the off state whenever the supply voltage
drops below 3.3V. Normal operation resumes once VCC rises above 3.5V.
Current Limit Protection
The current limit threshold is set by external resistor ROCSET connected from VCC supply to OCSET pin. The internal sink current IOCSET (90uA
typical) across this resistor sets the voltage at OCSET pin. When the PWM voltage is less than the voltage at OCSET, an over-current condition is
triggered.
The current limit threshold is given by the following equation:
RIRI
OCSET
OCSETDS(ON)PEAK
×=×
2
)I(
+> II OUT(MAX)PEAK
where,
IN
OUTOUTIN
V
V
Lfs
VV
I×
×
=
IPEAK is the output peak current; RDS (ON) is the MOSFET ON resistance; FS is the PWM frequency (300KHz typical). Also, the inductor value will
affect the ripple current ΔI.
AP1539
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AP1539
Functional Description (continued)
The above equation is recommended for input voltage range of 5V to 18V. For input voltage lower than 5V, higher than 18V or ambient
temperature over +100°C, higher ROCSET is recommended.
The recommended minimum ROCSET value is summarized below:
VOUT
(V)
VIN (V)
5V
12V
18V
0.8
6.8K
3.9K
4.7K
1.0
6.8K
3.9K
4.7K
1.2
6.8K
3.9K
4.7K
1.8
6.8K
3.9K
4.7K
2.5
6.8K
3.9K
4.7K
3.3
6.8K
3.9K
4.7K
5.0
N/A
3.9K
5.6K
Inductor Selection
For most designs, the operates with inductors of 22µH to 33µH. The inductor value can be derived from the following equation:
IN
OUTOUTIN
V
V
fs
VV
L×
×
=
I
Where IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple current. Choose
inductor ripple current approximately 15% of the maximum load current 4A, IL=0.6A. The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple current to prevent core saturation (4A+0.3A).
Input Capacitor Selection
This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input
voltage. The RMS current rating requirement for the input capacitor of a buck regulator is approximately 1⁄2 the DC load current. A low ESR input
capacitor sized for maximum RMS current must be used. A 470µF low ESR capacitor for most applications is sufficient.
Output Capacitor Selection
The output capacitor is required to filter the output voltage and provides regulator loop stability. 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 output ripple can be calculated from the following formula.
ESR
ΔIV L
RIPPLE
×=
The bulk capacitors ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient.
An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher voltage electrolytic
capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings may be needed to provide the low ESR values
required for low output ripple voltage.
PCB Layout Guide
If you need low TC & TJ or large PD (Power Dissipation), The dual SW pins(5& 6) and VSS pins(7& 8)on the SOP-8L package are internally
connected to die pad, The evaluation board should be allowed for maximum copper area at output (SW) pins.
1. Connect FB circuits (R1, R2, C1) as closely as possible and keep away from inductor flux for pure VFB.
2. Connect C3 to VCC and VSS pin as closely as possible to get good power filter effect.
3. Connect R4 to VCC and OCSET pin as closely as possible.
4. Connect ground side of the C2 & D1 & C4 as closely as possible and use ground plane for best performance.
AP1539
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AP1539
Functional Description (continued)
Top Side Layout Guide
Bottom Side Layout Guide
AP1539
+
-
V
SS
EN
C1 R1
R2
FB
Vcc Output
C3
V
OUT
V
IN
R4
OCSET C4
C2
Option
C7
C6
R5
Option
L1
+
-
C8
D1
Layout numbering comparison
Keep the gap of exposed pads from short circuit.
Use vias to conduct the heat into the backside of
PCB layer. The heat sink at output (SW) pins should
be allowed for maximum solder-painted area.
Recommended exposed-pads gap: 30~40mil
(0.75~1mm)
Brown: IC exposed pads.
Red: recommended layout.
Reference pads layout dimension:
Output: 90 x 50 mil
Vss: 90 x 60 mil
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AP1539
Ordering Information
AP 1539 SDP G - 13
Package Packing
Green
13 : Tape & Reel
G : Green
SDP : SOP-8L-DEP
Device
Package
Code
Packaging
(Note 7)
13” Tape and Reel
Quantity
Part Number Suffix
AP1539SDPG-13
SDP
SOP-8L-DEP
2500/Tape & Reel
-13
Note: 7. Pad layout as shown as shown in Diodes Incorporateds package outline PDFs, which can be found on our website at
http://www.diodes.com/package-outlines.html.
Marking Information
(1) SOP-8L-DEP
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AP1539
Package Outline Dimensions (All Dimensions in mm)
Please see http://www.diodes.com/package-outlines.html for the latest version.
(1) Package type: SOP-8L-DEP
1
9°(all side)
0.35Typ.
45°
4
5
8
R0.1
0.3/0.5
1.27Typ.
4.85/4.95
Seating Plane
Gauge Plane
5.90/6.10
0.62/0.82
0.254
0/0.13
View"A"
View"A"
1.4/1.5
1.63Max.
3.85/3.95
Land Pattem Recommendation
(Unit: mm)
EXPOSED PAD
Bottom view
EXPOSED PAD
14
58
1.15Typ.
2.05Typ.
2.15Typ. 0.685
0.713
0.20
0.9
C
L
1.7 1.7
C
L
14
5
8
8x-0.60
5.4
2.35
6x-1.27
1.8 1.8
1.0
C
L
0.95
1.65
C
L
Top View
0.15/0.25
8x-1.55
0°/8°
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AP1539
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or
indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.
This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
LIFE SUPPORT
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without 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 to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, 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 © 2020, Diodes Incorporated
www.diodes.com
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