Diodes AP8801 User Manual

Description

The AP8801 is a step-down DC/DC converter designed to drive LEDs with a constant current. The device can drive up to thirteen LEDs, depending on the forward voltage of the LEDs, in series from a voltage source of 8V to 48V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The AP8801 switches at frequency up to 700kHz. This allows the use of small size external components, hence minimizing the PCB area needed.

Maximum output current of AP8801 is set via an external resistor connected between the V applying either a DC voltage or a PWM signal at the CTRL input pin. An input voltage of 0.2V or lower at CTRL shuts down the output at SW and puts the device into a low-current standby state.

Features

• LED driving current up to 500mA

• Operating input voltage up to 48V

• High efficiency up to 92%

• High switching frequency up to 700kHz

• PWM/DC input for dimming control

• Built-in output open-circuit protection

• SO-8 and MSOP-8 are in “Green” Molding Compound (No Br, Sb)

 Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)  Halogen and Antimony Free. “Green” Device (Note 3)

and SET input pins. Dimming is achieved by

IN

AP8801

500mA LED STEP-DOWN CONVERTER

Pin Assignments



SET

GND GND

NC

V

IN

SET

GND GND

NC

V

IN

Applications

• Commercial & industrial lighting

• Small LCD panel backlight

• Appliances interior lighting

• Architecture Detail lighting

(Top View)

1 2

AP8801

3 45

SO-8

8 7 6

CTRL

SW

(Top View)

1 2

AP8801

3 45

MSOP-8

8 7 6

CTRL

SW

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.

Typical Application Circuit

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AP8801

Document number: DS31765 Rev. 7 - 2

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500mA LED STEP-DOWN CONVERTER

Pin Descriptions

Pin Name Functions

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

GND GND pin

SET Set Nominal Output Current Pin. Configure the output current of the device.

Dual Function Dimming Control Pin.

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

• A PWM signal (driven by an open-drain/collector source) allows the output current to be adjusted over a wide

CTRL

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

VIN

NC No connection

Input Supply Pin. Must be locally bypassed.

range up to 100%.

• An analog voltage between 0.3V and 2.5V adjusts the output current between 25% and 200% of the current set by 0.2V/R

.

S

= V

CTRL

REF

Functional Block Diagram

AP8801

Fig. 1 Block Diagram

Absolute Maximum Ratings

Symbol Parameter Rating Unit

VIN VIN pin voltage

VSW

V

CTRL

V

SENSE

TJ

T

LEAD

T

ST

Caution: 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.

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.

AP8801

Document number: DS31765 Rev. 7 - 2

SW voltage -0.3 to +50 V

CTRL Pin Input Voltage -0.3 to +6 V

SET Voltage +0.3 to -5 V Junction Temperature 150 Lead Temperature Soldering 300 Storage Temperature Range -65 to +150

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-0.3 to +50 V

o

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C C C

AP8801

500mA LED STEP-DOWN CONVERTER

Recommended Operating Conditions

Symbol Parameter Min Max Unit

VIN

V

CTRLDC

V

CTRLL

f

OSC

TA

Duty Cycle Using Inductor ≥ 100µH (Note 6) 0.10 0.95 —

Notes: 4. For 100% brightness either leave floating or connect to 1.25V relative to GND.

5. AP8801 will operate at higher frequencies but accuracy will be affected due to propagation delays.

6. For most applications the LED current will be within 8% over the duty cycle range specified. Duty cycle accuracy is also dependent on propagation delay. Smaller size inductors can be used but LED current accuracy may be greater than 8% at extremes of duty cycle. This is most noticeable at low duty cycles (less than 0.1) or when the input voltage is high and only one LED is being driven.

Electrical Characteristics (T

Symbol Parameter Conditions Min Typ Max Unit

I

OUT

IQ

V

THD

V

SENSEHYS

V

REF

SET SET pin input current

R

DS(ON)

I

SW_LEAKAGE

θ

JA

θ

JC

Notes: 7. Refer to figure 6 for the device derating curve.

8. Test condition for SO-8 and MSOP-8: Device mounted on FR-4 PCB, 2”x2”, 2oz 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.

AP8801

Document number: DS31765 Rev. 7 - 2

Operating Input Voltage relative to GND 8.0 48.0 V Voltage range for 24% to 200% DC dimming relative to GND (Note 4) 0.3 2.5 V Voltage Low for PWM dimming relative to GND 0 0.2 V Maximum Switching Frequency (Note 5) — 625 kHz Ambient Temperature Range -40 +105 ºC

= 25°C, VIN = 24V; unless otherwise specified.)

A

Continuous switch current (Note 7) — — 500 mA Quiescent Current — 78 120 μA Internal Threshold Voltage 184 200 216 mV Sense threshold hysteresis — 15 — % Internal Reference Voltage — 1.25 — V

V

= V

IN

= 0.4A

-0.2

SET

On Resistance of MOSFET Switch leakage current — — 8 μA

Thermal Resistance Junction-to-Ambient

Thermal Resistance Junction-to-Case

I

SW

SO-8 (Note 8) — 88 — °C/W MSOP-8 (Note 8) — 128 — °C/W SO-8 (Note 8) — 58 — °C/W MSOP-8 (Note 8) — 90 — °C/W

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— 7 — μA — 0.70 1.15 Ω

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NON

T

C

HIN

G SUPPLY CUR

REN

T

CTR

OLTAG

R

CUR

REN

T

C

URRENT

TCH

N

G

F

R

Q

U

N

C

Y

H

Typical Characteristics

0.9

(mA)

0.8

0.7

AP8801

500mA LED STEP-DOWN CONVERTER

1.256

1.254

0.6

0.5

0.4

0.3

0.2

-SWI

0.1 0

06055510 15 20 25 30 35 40 5045

Figure. 2 Supply Current (not switching) vs. Input Voltage

1.2

1.0

0.8

Ω

()

0.6

DS(ON)

0.4

0.2

0

-40 -25 -10 5 20 35 50 65 80 95 110 125

600

INPUT VOLTAGE (V)

AMBIENT TEMPERATURE (C)

Figure. 4 R vs Ambient Temperature

DS(ON)

1.252

E (V)

1.250

L V

1.248

1.246

1.244

-40 125-25 110-10 5 20 35 50 65 9580 AMBIENT TEMPERATURE (°C)

500 450 400 350

(mA)

300 250

200

LED

150 100

Figure. 3 V vs. Ambient Temperature

50

0

0 0.5 1.5 2.01.0

800

CTRL

R RESISTANCE ( )

SET

Figure. 5 LED Current vs. R

Ω

SET

500

400

(mA)

300

200

LED

100

0

02.50.5 1.0 1.5 2.0

Figure. 6 LED Current vs. V

R = 0.56

CTRL VOLTAGE (V)

AP8801

Document number: DS31765 Rev. 7 - 2

SET

Ω

R = 0.68

SET

R = 1.33

SET

CTRL

Ω

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700

z) (k

600

500

E E

400

300

I

200

SWI

100

0

02.50.5 1.0 1.5 2.0

Figure. 7 Switching Frequency vs. V

CTRL VOLTAGE (V)

CTRL

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F

FIC

C

Y

UTY CYC

Typical Characteristics (T

10

8 6

4 2 0

-2

-4

-6

OUTPUT CURRENT DEVIATION (%)

-8

-10 61218 4824 30 36 42

SUPPLY VOLTAGE (V)

Figure . 8 LED Current vs. In put Volt age

700

600

500

500mA LED STEP-DOWN CONVERTER

= +25°C, VIN = 60V, L =68µH unless otherwise stated.)

A

100

95 90 85

(%)

80 75

IEN

70

E

65 60

55 50

61218 4824 30 36 42

SUPPLY VOLTAGE (V)

100

90 80

70

Figure. 9 Efficiency vs. Input Voltage

AP8801

400

300

200

100

SWITCHING FREQUENCY (kHz)

0

61218 4824 30 36 42

Figure. 10 Sw i tching Frequency vs. Input Voltage

SUPPLY VOLTAGE (V)

60

LE (%)

50 40

D

30 20 10

0

61218 4824 30 36 42

SUPPLY VOLTAGE (V)

Figure. 11 Duty Cycle vs. Input Voltage

Figure. 12 Steady State Waveforms

AP8801

Document number: DS31765 Rev. 7 - 2

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Figure.13 Start-Up Showing LED Current Soft -Start

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