AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Features
• Input voltage: 4V to 23V
• Output voltage: 0.8V to V
• Output current: 1.8A up to peak 2A
• 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: Available in “Green” Molding Compound
(No Br, Sb)
• Lead Free Finish/ RoHS Compliant (Note 1)
CC
Applications
• PC Motherboard
• LCD Monitor
• Graphic Card
• DVD-Video Player
• Telecom Equipment
• ADSL Modem
• Printer and other Peripheral Equipment
• Microprocessor core supply
General Description
AP1533 consists of step-down switching regulator with PWM
control. These devices include a reference voltage source,
oscillation circuit, error amplifier, internal PMOS.
AP1533 provides low-ripple 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 overshoot 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 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 up to 23V, it is also suitable for the operation via an
AC adapter.
Typical Application Circuit
V
=5V/1.8A
L1
33uH
C
Optional
D1*
R
C
A
6.8K
R
B
1.3K
C
OCSET
Option
EN
EN
Vcc
Output
AP1533
1+
FB
V
SS
R
/R
)
B
A
OCSET
EN
V
OUT
x (
V
FB
=
= 0.7K~5K ohm
R
B
Suggested DIODES Power Schottky P/N: B340 series or PDS340.
*
V
IN
R
OCSET
3.3K
C
IN
470uF
CVcc
0.1uF
R
100K
C
0.1uF
AP1533 Rev. 4 1 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
OUT
+
+
C
0.1uF 470uF
-
-
C
OUT
Ordering Information
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
AP 1 5 3 3 S G - 13
Device
Package Packing
S : SOP-8L
Package
Code
Packaging
(Note 2)
Green
G : Green
13 : Tape & Reel
13” Tape and Reel
Quantity Part Number Suffix
AP1533SG-13 S SOP-8L 2500/Tape & Reel -13
Notes: 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.
2. 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.
Pin Assignments
FB
EN
OCSET
V
CC
1
2
3
4
( Top View )
AP1533
SOP-8L
8
7
6
5
V
SS
V
SS
Output
Output
Pin Descriptions
Pin Name Pin No. Description
FB 1 Feedback pin
Power-off pin
H: Normal operation
EN 2
OCSET 3 Add an external resistor to set max output current
VCC 4 IC power supply pin
(Step-down operation)
L: Step-down operation stopped
(All circuits deactivated)
Output 5, 6
Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin
to reduce EMI
VSS 7, 8 GND Pin
AP1533 Rev. 4 2 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
A
Block Diagram
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Output
Oscillation
Circuit
V
CC
PWM-Switched
Control Circuit
Thermal
Shutdown
V
EN
EN
Voltage Source
90uA
OCSET
Reference
+
-
FB
V
SS
Absolute Maximum Ratings
Symbol Parameter Rating Unit
ESD HBM Human Body Model ESD Protection
8
ESD MM Machine Model ESD Protection 500 V
V
VCC Pin Voltage V
CC
V
Feedback Pin Voltage V
FB
V
EN Pin Voltage V
EN
V
Switch Pin Voltage VSS - 0.3 to VIN + 0.3 V
OUT
P
Power Dissipation Internally limited mW
D
T
Operating Junction Temperature Range -20 to +125
J
T
Storage Temperature Range -65 to +150
ST
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.
- 0.3 to VSS + 24 V
SS
- 0.3 to VCC V
SS
- 0.3 to VIN + 0.3 V
SS
Recommended Operating Conditions
Symbol Parameter Min Max Unit
VIN Input Voltage 4 23 V
I
Output Current 0 1.8
OUT
TA Operating Ambient Temperature -25 85
KV
o
C
o
C
o
C
AP1533 Rev. 4 3 of 9 JULY 2009
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A
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Electrical Characteristics
(V
IN = 12V, T
Symbol Parameter Conditions Min Typ. Max Unit
VFB Feedback Voltage I
IFB Feedback Bias Current I
I
SHDN
∆V
OUT
/ VIN
∆V
OUT
/ V
OUT
f
Oscillation Frequency Measure waveform at SW pin 240 300 400 KHz
OSC
f
OSC1
VIH
VIL Evaluate oscillation stop at SW pin - - 0.8
ISH
ISL EN Pin Low - -10 - µA
I
OCSET
R
DS(ON)
EFFI Efficiency
T
SHDN
T
Thermal shutdown hysteresis - 55 - °C
HYS
θJA
θJC
Notes: 3. Test condition: Device mounted on FR-4 PCB, 2”x2”, 2oz copper, minimum recommended pad layout, single side.
AP1533 Rev. 4 4 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
= 25°C, unless otherwise specified)
A
= 0.1A 0.784 0.8 0.816 V
OUT
= 0.1A - 0.1 0.5 µA
Current Consumption During
Power Off
Line Regulation V
Load Regulation I
Frequency of Current Limit or
Short Circuit Protection
EN Pin Input Voltage
EN Pin Input Leakage Current
OUT
V
= 0V - 10 - µA
EN
= 5V~23V - 1 2 %
IN
= 0.1 to 1.8A - 0.2 0.5 %
OUT
Measure waveform at SW pin - 50 - KHz
Evaluate oscillation at SW pin 2.0 - -
V
EN Pin High - 20 - µA
OCSET Pin Bias Current -- 75 90 105 µA
V
=5V, VFB=0V - 110 150
Internal MOSFET R
DS(ON)
IN
VIN=12V, VFB=0V - 80 110
=12V, V
V
IN
I
OUT
=1.8
OUT
= 5V
- 91 - %
mΩ
Thermal shutdown threshold - 150 - °C
Thermal Resistance
Junction-to-Ambient
Thermal Resistance
Junction-to-Case
For better thermal performance, larger copper pad for heatsink is needed.
SOP-8L (Note 3) - 134 -
SOP-8L (Note 3) - 22 -
o
C/W
o
C/W
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Typical Performance Characteristics (Continued)
VIN vs. Frequency
OUT
320
318
316
314
312
(kHz)
310
OSC
308
F
306
304
302
300
0 2 4 6 8 10 12 14 16 18 20 22 24
(V
=3.3V ; I
V
OUT
=0.2A)
IN
(V)
0.820
0.815
0.810
0.805
(V)
0.800
FB
V
0.795
0.790
0.785
0.780
0 2 4 6 8 1012141618202224
OUT
(V
VIN vs. V
OUT
=3.3V; I
V
IN
(V)
AP1533
FB
=0.2A)
Line Regulation
OUT
3.40
3.35
3.30
3.25
(V)
3.20
OUT
V
3.15
3.10
3.05
3.00
0 2 4 6 8 1012141618202224
100%
90%
80%
70%
60%
50%
40%
30%
Efficiency (%)
20%
10%
0%
00.511.52
(V
=3.3V; I
V
Efficiency
OUT
I
OUT
IN
=0.2A)
(V)
VOUT=3.3V
VOUT=5V
(A)
Load Regulation
3.25
3.24
3.23
3.22
3.21
(V)
3.20
OUT
3.19
V
3.18
3.17
3.16
3.15
0 0.5 1 1.5 2
(VIN=12V)
OUT
(A)
I
AP1533 Rev. 4 5 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
V
V
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Typical Performance Characteristics (Continued)
Ripple
( V
IN
= 12V; V
OUT
= 3.3V; I
OUT
= 0.1A )
OUT
(V
= 12V; V
IN
OUT
= 3.3V; I
OUT
Ripple
AP1533
= 1.8A )
OUT
Test Circuit
+
-
open
OUTPUT OUTPUT
CC
OCSET
A
EN
V
SS
open
FBV
Oscillation
A
V
CC
+
-
OCSET
EN
V
Enable function test Feedback function test
V
CC
OCSET
EN
OUTPUT
FB
V
V
SS
+
-
FB
SS
Operation fun c tion test
AP1533 Rev. 4 6 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
Functional Description
PWM Control
The AP1533 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 AP1533 assures that the
high-side MOSFET driver remains in the off state whenever the
supply voltage drops below 3.3V. Normal operation resumes
once V
Current Limit Protection
The current limit threshold is set by external resistor R
connected from V
current I
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:
where,
I
resistance; f
inductor value will affect the ripple current ΔI.
The above equation is recommended for input voltage range of
5V to 18V. For input voltage lower than 5V or ambient
temperature over 100°C, higher R
The recommended minimum R
The maximum R
current output.
rises above 3.5V.
CC
supply to OCSET pin. The internal sink
CC
(90μA typical) across this resistor sets the voltage
OCSET
×=×
RIRI
OCSETOCSETDS(ON)PEAK
)I(Δ
II
OUT(MAX)PEAK
−
I ×
=Δ
is the output peak current; R
PEAK
V
(V) V
IN
4 0.8 3.9K
5 3.3 3.3K
12 5 3.3K
18 12 3.3K
23 12 4.7K
is the PWM frequency (300KHz typical). Also, the
S
(V) R
OUT
value should not exceed AP1533 maximum
OCSET
+>
2
V
OUTOUTIN
V
IN
is the MOSFET ON
DS (ON)
is recommended.
OCSET
value is summarized below:
(Ω)
OCSET
VV
×
OCSET
Lfs
OCSET
AP1533 Rev. 4 7 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
Inductor Selection
For most designs, the operation range with inductors is from
22µH to 33µH. The inductor value can be derived from the
following equation:
VV
−
L ×
=
fs
Where ΔI
ripple current and small value inductors result in high ripple
current. Choose inductor ripple current approximately 15% of the
maximum load current 1.8A, ∆I
the inductor should be at least equal to the maximum load current
plus half the ripple current to prevent core saturation
(1.8A+0.135A).
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.
The bulk capacitor’s 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 T
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 as closely as possible and keep away
2. Connect input capacitor to Vcc and Vss pin as closely as
3. Connect R
4. Connect ground side of the input capacitor & Schottky &
is inductor Ripple Current. Large value inductors lower
L
& TJ or large PD (Power Dissipation), The dual
C
from inductor flux for pure V
possible to get good power filter effect.
possible.
output capacitor as closely as possible and use ground
plane for best performance.
to Vcc and OCSET pin as closely as
OCSET
V
OUTOUTIN
Δ×
L
V
I
=0.27A. The DC current rating of
ΔIV
×=
LRIPPLE
.
FB
IN
ESR
Marking Information
(1) SOP-8L
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
( Top View )
8
5
Logo
Part Number
AP1533
WW X
YY
X
41
Package Information ( All Dimensions in mm )
(1) Package Type: SOP-8L
0.254
0.62/0.82
7°~9°
Gauge Plane
Seating Plane
Detail "A"
7°~9°
1.27typ
4.85/4.95
0.3/0.5
3.85/3.95
1.30/1.50
5.90/6.10
1.75max.
0.15/0.25
0.10/0.20
0.35max.
Detail "A"
45°
G : Green
YY
: Year : 08, 09,10~
WW : Week : 01~52; 52
represents 52 and 53 week
X
: Internal Code
0°/8°
8x-0.60
5.4
6x-1.27
8x-1.55
Land Pattern Recommendation
(Unit: mm)
AP1533 Rev. 4 8 of 9 JULY 2009
DS31192 www.diodes.com © Diodes Incorporated
AP1533
PWM CONTROL 1.8A STEP-DOWN CONVERTER
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DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
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Copyright © 2009, Diodes Incorporated
www.diodes.com
IMPORTANT NOTICE
LIFE SUPPORT
AP1533 Rev. 4 9 of 9 JULY 2009
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