Diodes AP3503 User Manual

Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

General Description

The AP3503 is a 340kHz fixed frequency, current
mode, PWM synchronous buck (step-down) DC-DC
converter, capable of driving a 3A load with high
efficiency, excellent line and load regulation. The
device integrates N-channel power MOSFET
switches with low on-resistance. Current mode
control provides fast transient response and
cycle-by-cycle current limit.

The AP3503 employs complete protection to ensure
system security. Including output Over Voltage
Protection, input Under Voltage LockOut,
programmable soft-start, Over Temperature
Protection to safeguard the circuit.

This IC is available in PSOP-8 package.

Figure 1. Package Type of AP3503

PSOP-8

Features

• Input Voltage Range: 4.5V to 18V

• Fixed 340kHz Frequency

• High Efficiency: up to 95%

• Output Current: 3A

• Current Mode Control

• Built-in Over Current Protection

• Built-in Thermal Shutdown Function

• Built-in UVLO Function

• Built-in Over Voltage Protection

• Programmable Soft-start

Applications

• LCD TV

• Set Top Box

• Portable DVD

• Digital Photo Frame

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Pin Configuration

MP Package
(PSOP-8)

1

2

3

4

8

7

6

5

Figure 2. Pin Configuration of AP3503 (Top View)

Pin Description

Pin Number Pin Name Function

Bootstrap pin. A bootstrap capacitor is connected between the BS pin

1

2

3
4

5

6

7

8

BS

and SW pin. The voltage across the bootstrap capacitor drives the
internal high-side power MOSFET

IN

SW

Supply power input pin. A capacitor should be connected between the
IN pin and GND pin to keep the input voltage constant
Power switch output pin. This pin is connected to the inductor and
bootstrap capacitor

GND Ground pin

Feedback pin. This pin is connected to an exte rnal resistor divider to
program the system output voltage. When the FB pin voltage exceeds

FB

1.1V, the over voltage protection is triggered. When the FB pin
voltage is below 0.3V, the oscillator frequency is lowered to realize
short circuit protection
Compensation pin. This pin is the output of the transconductance
error amplifier and the input to the current comparator. It is used to

COMP

compensate the control loop. Connect a series RC network from this
pin to GND. In some cases, an additional capacitor from this pin to
GND pin is required
Control input pin. EN is a digital in put that turns the regulator on or

EN

off. Drive EN high/low to turn on/off the regulator. Pull up with
100kΩ resistor for automatic startup
Soft-start control input pin. SS controls the soft-start period. Connect

SS

a capacitor from SS to GND to set the soft-start period. A 0.1µF
capacitor sets the soft-start period to 15ms. To disable the soft-start
feature, leave SS unconnected

EP Exposed pad. It should be connected to GND in PCB layout

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Functional Block Diagram

2

IN

EN

7

1.5V

SHUTDOWN
COMPARATOR

0.3V

LOCK
COMPARATOR

SCP

INTERNAL

REGULATOR

OSCILLATOR

90k/340k

CLK

VA
VB

SLOP

COMP

CURRENT

SENSE

AMPLIFIER

PWM

COMPARATOR

VA

+

1

BS

M1

Q

S

Q

R

M2

3

SW

2.5 V

SS

VB

6

8

A

EA

5

FB

0.

925V

6

COMP

1.3V

4

GND

Figure 3. Functional Block Diagram of AP3503

Ordering Information

AP3503 -

Package

Temperature

PSOP-8

Circuit Type

Package
MP: PSOP-8

Range

-40 to 85°C

Part Number Marking ID Packing Type

AP3503MP-G1 3503MP-G1 Tube
AP3503MPTR-G1 3503MP-G1 Tape & Reel

G1: Green

TR: Tape & Reel
Blank: Tube

BCD Semiconductor's Pb-free products, as designated with "G1" suffix in the part number, are RoHS compliant
and green.

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Absolute Maximum Ratings (Note 1)

Parameter Symbol Value Unit

IN Pin Voltage VIN -0.3 to 20 V
EN Pin Voltage VEN -0.3 to VIN V
SW Pin Voltage VSW 21 V
BS Pin Voltage VBS -0.3 to VSW+6 V
FB Pin Voltage VFB -0.3 to 6 V
COMP Pin Voltage V
SS Pin Voltage VSS -0.3 to 6 V
Thermal Resistance
Operating Junction Temperature TJ 150 ºC
Storage Temperature T
Lead Temperature (Soldering, 10sec) T
ESD (Human Body Model) VHBM 2000 V
ESD (Machine Model) VMM 200 V

-0.3 to 6 V

COMP

θ

JA

-65 to 150 ºC

STG

260 ºC

LEAD

60 ºC/W

Note 1: Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to
the device. These are stress ratings only, and functional operation of the device at these or any other conditions
beyond those indicated under “Recommended Operating Conditions” is not implied. Exposure to “Absolute
Maximum Ratings” for extended periods may affect device reliability.

Recommended Operating Conditions

Parameter Symbol Min Max Unit

Input Voltage VIN 4.5 18 V
Operating Ambient Temperature TA -40 85 ºC

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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µ

Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Electrical Characteristics

TA=25ºC, VIN=VEN=12V, V

Parameter Symbol Conditions Min Typ Max Unit

SUPPLY VOLTAGE (IN PIN)

Input Voltage VIN 4.5 18 V

Quiescent Current IQ VFB=1V,VEN=3V 1.2 1.4 mA
Shutdown Supply Current I

UNDER VOLTAGE LOCKOUT

Input UVLO Threshold V
Input UVLO Hysteresis V

ENABLE (EN PIN)

EN Shutdown Threshold Voltage 1.1 1.5 2 V
EN Shutdown Threshold Voltage Hysteresis

(Note 2)
EN Lockout Threshold Voltage 2.2 2.5 2.7 V
EN Lockout Hysteresis 210 mV

VOLTAGE REFERENCE (FB PIN)

Feedback Voltage VFB 0.907 0.925 0.943 V
Feedback Over Voltage Threshold V
Feedback Bias Current IFB VFB=1V -0.1 0.1

MOSFET

High-side Switch On-resistance(Note 3) R
Low-side Switch On-resistance(Note 3) R

CURRENT LIMIT

High-side Switch Leakage Current I
High-side Switch Current Limit I
Low-side Switch Current Limit I

SWITCHING REGULATOR

Oscillator Frequency f
Short Circuit Oscillator Frequency f
Max. Duty Cycle D
Min. Duty Cycle D

ERROR AMPLIFIER

Error Amplifier Voltage Gain (Note 2) AEA 400 V/V
Error Amplifier Transconductance GEA 800
COMP to Current Sense Transconductance GCS 5.2 A/V

THERMAL SHUTDOWN

Thermal Shutdown (Note 2) T
Thermal Shutdown Hysteresis (Note 2) T

SOFT START (SS PIN)

=3.3V, unless otherwise specified.

OUT

VEN=0V 0.1 10

SHDN

UVLO

VIN Rising 3.65 4.00 4.25 V

200 mV

HYS

350 mV

1.1 V

FBOV

DSONHISW
DSONLISW

LEAKH

LIMH

LIML

OSC1
OSC2

MAX

MIN

OTSD

HYS

=0.2A/0.7A
=-0.2A/-0.7A

VIN=18V,VEN=VSW=0V 0.1 10

4.3 5.6 A
From drain to Source 1.4 A

280 340 400 kHz
90 kHz

VFB=0.85V 90 %

VFB=1V 0 %

160 ºC

20 ºC

100
100

µA

µA

mΩ
mΩ

µA

A/V

Soft-start Time (Note 2) tSS

C

SS

=0.1µF

Soft-start Current VSS=0V 6

15 ms

µA

Note 2: Not tested, guaranteed by design.

V-V

Note 3: R

DSON

=

SW2SW1

.

I-I

SW2SW1

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Typical Performance Characteristics

T

=25ºC, VIN=12V, V

A

=3.3V, unless otherwise noted.

OUT

100

90

80

70

60

50

Efficiency ( %)

40

30

20

10

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2

V

=3.3V, TA=25oC, L=10µH

OUT

VIN=5V
VIN=12V

Output Current (A)

Figure 4. Efficiency vs. Output Current Figure 5. Quiescent Current vs. Case Temperature

1.2

1.1

1.0

0.9

0.8

Feedback Voltage (V)

0.7

0.6

-50 -25 0 25 50 75 100 125 150

Case Temperature (oC)

1.4

1.3

1.2

1.1

Quiescent Current (mA)

1.0

0.9

-50 -25 0 25 50 75 100 125 150

Case Temperature (oC)

3.6

3.5

3.4

3.3

3.2

Output Voltage (V)

3.1

3.0

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2

Output Current (A)

Figure 6. Feedback Voltage vs. Case Temperature Figure 7. Output Voltag e vs. Output Current

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Typical Performance Characteristics (Continued)

TA=25ºC, VIN=12V, V

=3.3V, unless otherwise noted.

OUT

200

180

160

140

120

100

80

60

High-side Switch On-resistance (mΩ)

40

-60 -40 -20 0 20 40 60 80 100 120 140

Case Temperatur e (oC)

160

140

120

100

80

60

Low-side Switch On-resistance (mΩ)

40

-60 -40 -20 0 20 40 60 80 100 120 140

Case Temperature (oC)

Figure 8. High-side Switch On-resistance Figure 9. Low-side Switch On-resistance

vs. Case Temperature vs. Case Temperature

V

IN_AC

200mV/div

V

20mV/div

10V/div

OUT_AC

2A/div

VSW

IL

200mV/div

V

OUT_AC

1A/div

I

OUT

Time 4µs/div

Time 200µs/div

Figure 10. Output Ripple (I

=3A) Figure 11. Load Transient (I

OUT

=1.5A to 3A)

OUT

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Typical Performance Characteristics (Continued)

TA=25ºC, VIN=12V, V

=3.3V, unless otherwise noted.

OUT

V

EN

2V/div

VSS

2V/div

V

OUT

2V/div

IL

2A/div

VEN

2V/div

VSS

2V/div

V

OUT

2V/div

IL

2A/div

V

OUT

2V/div

IL

2A/div

Time 10ms/div

Figure 12. Enable Turn on Characteristic Figure 13. Enable Turn off Characteristic

(VIN=12V, VEN=3.3V, V

Time 40µs/div

=3.3V, IL=3A) (VIN=12V, VEN=3.3V, V

OUT

V

OUT

2V/div

IL

2A/div

Time 200µs/div

OUT

Time 40µs/div

=3.3V, I

=3A)

L

Figure 14. Short Circuit Protection (I

=0A) Figure 15. Short Circuit Recovery (I

OUT

OUT

=0A)

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Typical Application

Input Voltage=12V

Output Voltage=3.3V

C21
22µF/25V

L 10µH

C22
22µF/25V

R4

100k

1

BS

2

C4
10nF

D1

Optional

Figure 16. Typical Application of AP3503

IN

3

SW

4

GND FB

AP3503

SS

EN

COMP

8

7

6

5

R1

26.1k

C5

0.1µF

C3

3.3nF

R2 10k

C12

10µF/25V

C6

Optional

R3
13k

C11
10µF/25V

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Data Sheet

340kHz, 3A Synchronous DC-DC Buck Converter AP3503

Mechanical Dimensions

PSOP-8 Unit: mm(inch)

3.202(0.126)

3.402(0.134)

May. 2012 Rev. 1. 7 BCD Semiconductor Manufacturing Limited

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