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AP65353
3A, 18V, 650kHz ADAPTIVE COT STEP-DOWN CONVERTER
Description
The AP65353 is an adaptive constant on-time mode synchronous
buck converter providing high efficiency, excellent transient response
and high DC output accuracy for low-voltage regulation in digital
TV and monitor.
The constant-on-time control scheme handles wide input/output
voltage ratios and provides low external component count. The
internal proprietary circuit enables the device to adopt both low
equivalent series resistance (ESR) output capacitors, such as
SP-CAP or POSCAP and ultra-low ESR ceramic capacitors.
The adaptive on-time control supports seamless transition between
continuous conduction mode (CCM) at higher load conditions and
discontinuous conduction mode (DCM) at lighter load conditions.
Pin Assignments
( Top View )
EN 1
FB 2
VREG5 3
SS 4
Exposed
Pad
9
SO-8EP
8 VIN
7 BS
6 SW
5 PGND
DCM allows AP65353 to maintain high efficiency at light load
conditions. The AP65353 also features programmable soft-start,
UVLO, OTP, OVP and OCP to protect the circuit.
This IC is available in SO-8EP package.
Features
Fixed Frequency Emulated Constant On-Time Control
Good Stability Independent of the Output Capacitor ESR
Fast Load Transient Response
Synchronous Rectification: 90mΩ Internal High-side Switch and
57mΩ Internal Low-Side Switch
Wide Input Voltage Range: 4.5V to 18V
Output Voltage Range: 0.76V to 6V
3A Continuous Output Current
650kHz Switching Frequency
Built-in Over Current Limit
Built-in Over Voltage Protection
Built-in Thermal Shutdown Protection
Programmable Soft-Start
Pre-biased Start-Up
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html 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.
AP65353
Document number: DS37925 Rev. 1- 2
1 of 15
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June 2015
© Diodes Incorporated

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Typical Applications Circuit
INPUT
VIN
12V
C1
20μF
OFF
C4
8.2nF
8
IN
ON 1
EN
4
SS
7
BST
6
SW
AP65353
5
GND
2
FB
3
VREG5
C5 L1
0.1µF 1.5μH
R1
8.25kΩ
R2
22.1kΩ
C3
1µF
OUTPUT
VOUT
1.05V
C2
44μF
Figure 1 Typical Application Circuit
AP65353
Pin Descriptions
Pin
Name
Pin Number
EN 1
FB
VREG5
SS
2
3
4
SW 6
BS
VIN
PGND
7
8
5, 9 (Exposed Pad)
Function
Enable Input
EN is a digital input that turns the regulator on or off. Drive EN high to turn on the
regulator, drive it low to turn off. It can be safely connected to VIN directly for automatic
startup.
Feedback Input
FB senses the output voltage and regulates it. Drive FB with a resistive voltage divider
connected to it from the output voltage.
Internal power supply output pin to connect an additional capacitor. Connect a 1μF
(typical) capacitor as close as possible to the VREG5 and GND. This pin is not active
when EN is low.
Soft-Start Control Input Pin
SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-
start period.
Power Switching Output
SW is the switching node that supplies power to the output. Connect the output LC filter
from SW to the output load. Note that a capacitor is required from SW to BS to power the
high-side switch.
Bootstrap Pin
A bootstrap capacitor is connected between the BS pin and SW pin. The voltage across
the bootstrap capacitor drives the internal high-side NMOS switch. A 0.1μF (typical)
capacitor is required for proper operation.
Supply Input
A capacitor should be connected between the VIN pin and GND pin to keep the DC input
voltage constant.
Power Ground
Exposed pad must be connected to GND plane and connected to PGND for maximum
power dissipation.
AP65353
Document number: DS37925 Rev. 1- 2
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Functional Block Diagram
AP65353
Figure 2 Functional Block Diagram
AP65353
Document number: DS37925 Rev. 1- 2
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AP65353
Absolute Maximum Ratings (Note 4) (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
VIN Supply Voltage
VREG5
VREG5 Pin Voltage
VSW
Switch Node Voltage
VBS
Bootstrap Voltage
VFB
Feedback Voltage
VEN
Enable/UVLO Voltage
VSS
Soft-start PIN
VGND
GND Pin Voltage
TST Storage Temperature
TJ Junction Temperature
TL Lead Temperature
ESD Susceptibility (Note 5)
HBM
Human Body Model
MM Machine Model
Rating
-0.3 to 20
-0.3V to +6.0
-1.0 to VIN +0.3
-0.3 to VSW +6.0
-0.3V to +6.0
-0.3V to VIN
-0.3V to +6.0
-0.3 to 0.3
-65 to +150
+160
+260
2
200
Unit
V
V
V
V
V
V
V
V
°C
°C
°C
kV
V
Notes:
4. Stresses greater than the 'Absolute Maximum Ratings' specified above may cause permanent damage to the device. These are stress ratings only;
functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may
be affected by exposure to absolute maximum rating conditions for extended periods of time.
5. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when
handling and transporting these devices.
Thermal Resistance (Note 6)
Symbol
Parameter
θJA Junction to Ambient
Rating
SO-8EP
38.56
Unit
°C/W
θJC Junction to Case
SO-8EP
6.85 °C/W
Recommended Operating Conditions (Note 7) (@TA = +25°C, unless otherwise specified.)
Notes:
Symbol
VIN
TJ
TA
Parameter
Supply Voltage
Operating Junction Temperature Range
Operating Ambient Temperature Range
Min Max
4.5 18.0
-40 +125
-40 +85
6. Test condition: SO-8: Device mounted on 1"x1" FR-4 substrate PCB, 2oz copper, with minimum recommended pad layout.
7. The device function is not guaranteed outside of the recommended operating conditions.
Unit
V
°C
°C
AP65353
Document number: DS37925 Rev. 1- 2
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AP65353
Electrical Characteristics (@TA = +25°C, VIN = 12V, unless otherwise specified.)
Parameter
SUPPLY VOLTAGE (VIN PIN)
Input Voltage
Quiescent Current
Shutdown Supply Current
UNDER VOLTAGE LOCKOUT
UVLO Threshold
UVLO Hysteresis
ENABLE (EN PIN)
EN High-level Input Voltage
EN Low-level Input Voltage
VOLTAGE REFERENCE (FB PIN)
Feedback Voltage
Feedback Bias Current
VREG5 OUTPUT
VREG5 Output Voltage
Source Current Capability
Load Regulation
Line Regulation
MOSFET
High-side Switch On-resistance
Low-side Switch On-resistance
CURRENT LIMIT
High Level Current Limit
ON-TIME TIMER
On Time
Minimum Off Time
THERMAL SHUTDOWN
Thermal Shutdown
Thermal Shutdown Hysteresis
SOFT START (SS PIN)
Soft-Start Source Current
Soft-Start Discharge Current
OVERVOLTAGE PROTECTION
OVP Trip Threshold
Symbol
Conditions
VIN
IQ
ISHDN
VFB = 0.85V
VEN = 0V
VUVLO
VHYS
VENH
VENL
VIN Rising Test VREG5 Voltage
VIN Falling Test VREG5 Voltage
VFB VOUT = 1.05V
IFB VFB = 0.8V
VVREG5
RDSONH
RDSONL
6.0V < VIN < 18V 0 < IVREG5 < 5mA
VIN = 6V, VVREG5 = 4V
0 < IVREG5 < 5mA
6.0V < VIN < 18V IVREG5 = 5mA
ILIM-H
L = 1.5μH
tON
tOFF-MIN
TOTSD
THYS
VIN = 12V, VOUT = 1.05V
VFB = 0.7V
ISS-SOURCE
ISS-DISCHARGE
VSS = 1.0V
VSS = 0.5V
Min
4.5
3.6
0.16
1.25
0.753
-0.1
4.8
3.9
4.2
0.1
115
Typ
0.6
1
3.85
0.35
0.765
0
5.1
100
0.090
0.057
4.5
150
260
150
25
6.0
0.2
120
Max
18
0.75
10
4.1
0.47
18
0.85
0.777
0.1
5.4
100
20
5.5
310
7.8
125
Unit
V
mA
μA
V
V
V
V
V
μA
V
mA
mV
mV
A
ns
ns
°C
°C
μA
mA
%
AP65353
Document number: DS37925 Rev. 1- 2
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June 2015
© Diodes Incorporated