Diodes AT5503 User Manual

18V, 3A Synchronous DC-DC Buck Converter AT5503

Preliminary Datasheet

General Description

The AT5503 is a 500kHz 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
AT5503 exhibits high efficiency at light load. The
device integrates N-channel power MOSFET switch
with low on-resistance. Current mode control
provides fast transient response and cycle-by-cycle
current limit.

The AT5503 employs complete protection to ensure
system security, including output Over Voltage
Protection, input Under Voltage Lock Out,
programmable soft-start, Over Temperature
Protection and hiccup mode Short Circuit Protection.

This IC is available in PSOP-8 package.

Features

• Input Voltage Range: 4.5V to 18V

• Fixed 500kHz Frequency

• High Efficiency at Light Load

• 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

• Hiccup Mode SCP

Applications

• Monitor

• TV

• STB

• Datacom

PSOP-8

Figure 1. Package Type of AT5503

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Pin Configuration

MP Package

(PSOP-8)

BS

SW

GND

Figure 2. Pin Configuration of AT5503 (Top View)

IN

1

2

EP

3

4

8

SS

EN

7

COMP

6

FB

5

Pin Description

Pin Number Pin Name Function

Bootstrap pin. A bootstrap capacitor is connected between the

1 BS

2 IN

3 SW

4 GND Ground pin

5 FB

6 COMP

7 EN

8 SS

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

BS pin and SW pin. The voltage across the bootstrap
capacitor drives the internal high-side NMOS switch.
Supply input pin. A capacitor should be connected between
the IN pin and GND pin to keep the DC input voltage
constant.
Power switch output pin. This pin is connected to the inductor
and bootstrap capacitor.

Feedback pin. This pin is connected to an external resistor
divider to program the system output voltage. When the FB
pin voltage exceeds 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. This pin is used to compensate the control loop.
Connect a series RC network from this pin to GND pin. In
some cases, an additional capacitor from this pin to GND pin
is required.
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. Pull up with 100kΩ resistor for automatic startup.
Soft-start control input pin. SS controls the soft start period.
Connect 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.

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Functional Block Diagram

Figure 3. Functional Block Diagram of AT5503

Ordering Information

Circuit Type G1: Green

Package
MP: PSOP-8

Package

PSOP-8

Temperature

Range

-40 to 85°C

AT5503 -

Blank: Tube
TR: Tape & Reel

Part Number Marking ID

AT5503MP-G1 5503MP-G1 Tube

AT5503MPTR-G1 5503MP-G1 Tape & Reel

Packing

Type

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

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

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

Operating Junction Temperature TJ 150 ºC

Storage Temperature T

Lead Temperature
(Soldering, 10sec)
Thermal Resistance
(Junction to Ambient)

ESD (Human Body Model) V

ESD (Machine Model) VMM 200 V

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.

-0.3 to 6 V

COMP

-65 to 150 ºC

STG

260 ºC

T

LEAD

PSOP-8 60 ºC/W

θ

JA

2000 V

HBM

Recommended Operating Conditions

Parameter Symbol Min Max Unit

Input Voltage VIN 4.5 18 V

Operating Ambient Temperature TA -40 85 ºC

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Electrical Characteristics

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

Shutdown Supply Current I

UNDER VOLTAGE LOCKOUT

=3.3V, TA=25ºC, unless otherwise specified.

OUT

=1V,

V

FB

=3.3V

V

EN

VEN=0V 0.1 1.0 µA

SHDN

1.2 1.4 mA

Input UVLO Threshold V

Input UVLO Hysteresis V

VIN Rising 3.65 4.0 4.25 V

UVLO

0.2 V

HYS

ENABLE (EN PIN)

EN Shutdown Threshold
Voltage
EN Shutdown Threshold
Voltage Hysteresis (Note 2)

EN Lockout Threshold Voltage

EN Lockout Hysteresis

1.1 1.5 2 V

350

2.2 2.5 2.7 V

210

mV

mV

VOLTAGE REFERENCE (FB PIN)

Feedback Voltage VFB 0.784 0.8 0.816 V

Feedback Over Voltage
Threshold

Feedback Bias Current IFB V

1.1 V

V

FBOV

=1V -0.1 0.1 µA

FB

MOSFET

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

R

R

ISW=0.2A&0.7A 100 mΩ

DSONH

ISW=-0.2A&-0.7A 100 mΩ

DSONL

CURRENT LIMIT

High-side Switch Leakage
Current

High-side Switch Current Limit I

Low-side Switch Current Limit I

I

LEAKH

4.3 5.6 A

LIMH

LIML

=18V,

V

IN

=0V, VSW=0V

V

EN

From Drain to
Source

0.1 10 μA

50 mA

SWITCHING REGULATOR

Oscillator Frequency f

Short Circuit Oscillator
Frequency

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

410 500 590 kHz

OSC1

180 kHz

f

OSC2

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Electrical Characteristics (Continued)

VIN=VEN=12V, V

Parameter Symbol Conditions Min Typ Max Unit

=3.3V, TA=25ºC, unless otherwise specified.

OUT

Maximum Duty Cycle D

Minimum Duty Cycle D

VFB=0.7V 90 %

MAX

VFB=1V 0 %

MIN

ERROR AMPLIFIER

Error Amplifier Voltage Gain
(Note 2)
Error Amplifier
Transconductance
COMP to Current Sense
Transconductance

400 V/V

A

EA

800 μA/V

G

EA

5.2 A/V

G

CS

THERMAL SHUTDOWN

Thermal Shutdown (Note 2) T

Thermal Shutdown Hysteresis
(Note 2)

160 ºC

OTSD

30 ºC

T

HYS

SOFT START (SS PIN)

Soft-start Time (Note 2) tSS CSS=0.1μF 15 ms

Soft-start Current 5 μA

Note 2: Not tested, guaranteed by design.

V-V

Note 3: R

DSON

=

SW2SW1

I-I

SW2SW1

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Typical Performance Characteristics

VIN=12V, V

=3.3V, L=4.7µH, TA=25°C, unless otherwise noted.

OUT

100

90

80

70

60

50

40

Efficiency (%)

30

20

10

0.01 0.1 1

VIN=12V

V

=3.3V, L=4.7μH

OUT

V

=5.0V, L=6.8μH

OUT

Output Current (A)

1.30

1.25

1.20

1.15

1.10

1.05

1.00

0.95

Quiescent Current (mA)

0.90

0.85

0.80

-50-25 0 255075100125150

Temperature (oC)

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

VSW

(10V/div)

V

OUT-AC

(20mV/div)

I
(1A/div)

(200mV/div)

L

V

OUT-AC

I

OUT

(1A/div)

Time(1µs/div)

Time(100µs/div)

Figure 6. Output Ripple (I

=2.5A) Figure 7. Load Transient Response (I

OUT

=0.2A to 2.5A)

OUT

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Typical Performance Characteristics (Continued)

VIN=12V, V

=3.3V, L=4.7µH, TA=25°C, unless otherwise noted.

OUT

V

V

OUT-AC

(100mV/div)

I

OUT

(1A/div)

(10V/div)

V

OUT

(2V/div)

I
(1A/div)

IN

L

Figure 8. Load Transient Response (I

Time(100µs/div)

Time(3.20ms/div)

=1A to 2.5A) Figure 9. Power On from VIN (I

OUT

OUT

=2.5A)

VIN

(10V/div)

V

(2V/div)

I
(1A/div)

OUT

L

(2V/div)

(2V/div)

I
(1A/div)

V

VEN

OUT

L

Time(3.20ms/div)

Time(3.20ms/div)

Figure 10. Power Off from VIN (I

=2.5A) Figure 11. Power On from EN (I

OUT

OUT

=2.5A)

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Typical Performance Characteristics (Continued)

VIN=12V, V

VEN

(2V/div)

V

OUT

(2V/div)

I

L

(1A/div)

Figure 12. Power Off from EN (I

VSS

(2V/div)

V

OUT

(2V/div)

V

SW

(10V/div)

I

L

(2A/div)

=3.3V, L=4.7µH, TA=25°C, unless otherwise noted.

OUT

(2V/div)

(2V/div)

(10V/div)

(2A/div)

Time(3.20ms/div)

=2.5A) Figure 13. Short Circuit Protection (I

OUT

V

VSS

OUT

V

SW

I

L

Time(64ms/div)

OUT

Time(64ms/div)

Figure 14. Short Circuit Protection Recovery (I

OUT

=2.5A)

=2.5A)

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Typical Application

Input Voltage=12V

C

IN

10μF*2

Output Voltage=3.3V

L

10nF

4.7μH

R

EN

100kΩ

C

SS

1

2

3

BS

IN

AT5503

SW

COMP

C

BS

SS

EN

8

7

6

0.1μF

C

C

3.3nF

C

P

Optional

R

C

13kΩ

FB

5

R2

10kΩ

R1

31.25kΩ

C

OUT

22μF*2

4

GND

Figure 15. Typical Application Circuit of AT5503

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

18V, 3A Synchronous DC-DC Buck Converter AT5503

Mechanical Dimensions

PSOP-8 Unit: mm(inch)

3.202(0.126)

3.402(0.134)

Mar. 2013 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

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