Diodes AP8800A User Manual

A

Description

The AP8800A is a step-down DC/DC converter designed to drive LEDs with a constant current. The device can drive up to 7 LEDs, depending on the forward voltage of the LEDs, in series from a voltage source of 8V to 28V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The AP8800A switches at frequency up to 600kHz. This allows the use of small size external components, hence minimizing the PCB area needed.

Maximum output current of AP8800A is set via an external resistor connected between the V by applying either a DC voltage or a PWM signal at the CTRL input pin. An input voltage of 0.2V or lower at CTRL switches off the output MOSFET simplifying PWM dimming.

and SET input pins. Dimming is achieved

IN

Features

COST EFFECTIVE 28V BUCK 1-W LED DRIVER

Pin Assignments

SW

GND

CTRL

Applications

(Top View)

1

2

3

5V

IN

4 SET

P8800A

• LED driving current up to 370mA

• Better than 5% accuracy

• High efficiency up to 95%

• Operating input voltage from 8V to 28V

• Simple, versatile solution requiring only 4 components

• PWM/DC input for dimming control

• Built-in output open-circuit protection

• TSOT25: Available in “Green” Molding Compound (No Br, Sb)

with lead Free Finish/ RoHS Compliant

 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 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.

• MR16 Lamps

• General Illumination Lamps

Typical Applications Circuit

AP8800A

Document number: DS35100 Rev. 3 - 2

1 of 13

www.diodes.com

August 2012

A

Pin Descriptions

Pin Name Pin Number Function

SW 1 Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI.

GND 2 GND Pin

Dimming and On/Off Control Input.

• Input voltage of 0.2V or lower forces the device into low current standby mode and shuts off the output.

CTRL 3

SET 4

VIN 5

An open-drain/collector PWM signal allows the output current to be adjusted below the level set by the resistor connected to SET input pin.

• The input impedance is about 50kΩ, and if the pin is left open V

• Drive with DC voltage (0.3V < V

< 2.5V) to adjust output current from 24% to 200% of I

CTRL

= V

REF

.

Set Nominal Output Current Pin. Configures the output current of the device.

Input Supply Pin. Must be locally decoupled to GND with >

2.2µF X7R ceramic capacitor – see applications

section for more information.

Functional Block Diagram

P8800A

OUTnom

Absolute Maximum Ratings (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Ratings Unit

VIN Continuous VIN Pin Voltage Relative to GND -0.3 to +30 V

V

Set Voltage Relative to VIN V

SET

-5 to VIN +0.3 V

IN

VSW SW Voltage Relative to GND -0.3 to +30 V

V

CTRL Pin Input Voltage -0.3 to +5 V

CTRL

ISW Switch Current 0.45 A

TJ Junction Temperature 105 °C

T

Lead Temperature Soldering 300 °C

LEAD

T

Storage Temperature Range -55 to +150 °C

ST

Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;

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.

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.

AP8800A

Document number: DS35100 Rev. 3 - 2

2 of 13

www.diodes.com

August 2012

A

P8800A

Recommended Operating Conditions (@T

Symbol Parameter Min Max Unit

VIN Operating Input Voltage Relative to GND 8.0 28 V

V

Voltage Range for 24% to 200% DC Dimming Relative to GND 0.3 2.5 V

CTRLDC

V

Voltage Low for PWM Dimming Relative to GND 0.2 V

CTRLL

ISW Continuous Average Switch Current (Note 4) 370 mA

D

Duty Cycle Range Applied to CTRL (f < 500Hz) 0.01 1

PWM

fSW Switching Frequency 600 kHz TA Ambient Temperature Range -40 105 °C

Note: 4. Dependent on junction and ambient temperature.

Electrical Characteristics (@T

Symbol Parameter Conditions Min Typ Max Unit

IQ Quiescent Current V

ISD Shutdown Current V

V

Internal Threshold Voltage 95 100 105 mV

THD

V

Internal Reference Voltage 1.25 V

REF

I

SET Pin Input Current V

SET

R

On Resistance of MOSFET 1.5 2.2 Ω

DS(ON)

I

Switch Leakage Current 5 µA

SW-LKG

fSW Switching Frequency with L = 100µH

tSS Soft-Start Time

tPD Internal Comparator Propagation Delay 55 ns

θ

Thermal Resistance Junction-to-Ambient TSOT25 (Note 5) 200 °C/W

JA

Note: 5. Test condition for TSOT25: Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed.

= +25°C, VIN = 12V, unless otherwise specified.)

A

= +25°C, unless otherwise specified.)

A

= 1.25V, fSW = 250kHz 300 650 µA

CTRL

= 0V 20 30 µA

CTRL

= VIN-0.1 1.3 µA

SET

ADJ pin floating L = 100H I

= 350mA @ 1 LED (V

OUT

= 3.4V)

LED

Time taken for output current to reach 90% of final value after V

CTRL

= 0.3V

250 kHz

500 µs

AP8800A

Document number: DS35100 Rev. 3 - 2

3 of 13

www.diodes.com

August 2012

A

0

5

Typical Characteristics

50

400

T= 25°C

A

2

20

T = 25°C

A

P8800A

300

200

Quiescent Current (µA)

100

0

04 812 16 20 24 28

Input Voltage (V)

Quiescent Current (Switching) vs. Input Voltage

1.242

Reference Voltage (V)

T = 25°C

A

15

10

Shutdown Current (µA)

5

0

048121620 24 28

Input Voltage (V)

Shutdown Current (Non-Switching) vs. Input Voltage

1.25

1.245

REF

V (V)

1.24

V = 12V

IN

1.2415 4812 16 20 24 28

Input Voltage (V)

Reference Voltage vs. Input Voltage

1.4

1.2

1

0.8

0.6

Reference Voltage (V)

0.4

T = 25°C

A

1.235

-40 -15 10 35 60 85 1 10 Ambient Temperature ( °C)

Reference Voltage vs. Ambient Temperature

2.4

V = 12V

IN

2.2

2

1.8

1.6

1.4

Power Switch On-Resistance ( )Ω

0.2

0

012345678910

Input Voltage (V)

Reference Voltage vs. Input Voltage (Low Voltage)

1.2

1

-40 -15 10 35 60 85 Ambient Temperature (°C)

Power Switch On-Resistance vs. Ambient Temperature

110

AP8800A

Document number: DS35100 Rev. 3 - 2

4 of 13

www.diodes.com

August 2012