Diodes AP8802 User Manual

AP8802

Description

The AP8802 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 AP8802 switches at frequencies up to 700kHz. This allows the use of small size external components, hence minimizing the PCB area needed.

Maximum output current of AP8802 is set via an external resistor connected between the V achieved 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 shuts down the output at SW and puts the device into a low-current standby state.

and SET input pins. Dimming is

IN

Features

• LED driving current up to 1A

• High efficiency up to 92%

• Operating input voltage up to 48V

• High switching frequency up to 700kHz

• PWM/DC input for dimming control

• Built-in output open-circuit protection

• SO-8, SO-8EP and U-DFN3030-10 are available in “Green”

Molding Compound (No Br, Sb)

• 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.

Typical Application Circuit

Pin Assignments

SET

GND

NC V

IN

Applications

• Commercial & industrial lighting

• Small LCD panel backlight

• Appliances interior lighting

• Architecture Detail lighting

1A LED STEP-DOWN CONVERTER

(Top View)

2

AP8802

3 4

SO-8

SET

GND

NC NC

V

IN

8 7 6 5

CTRL GND

SET

GND SW SW

(Top View)

1 2

AP8802

3 4 5

U-DFN3030-10

NC

V

IN

(Top View)

2 3 4

10

CTRL GND

9 8

NC

7

SW

6

SW

AP8802

SO-8EP

8 7 6 5

CTRL GND

SW SW

AP8802

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1A LED STEP-DOWN CONVERTER

Pin Descriptions

Name SO-8 SO-8EP U-DFN3030-10 Function

SW 6, 5 6, 5 7, 6

GND 2 2 2, 9 GND pin

SET 1 1 1 Set Nominal Output Current Pin. Configure the output current of the device.

CTRL 8 8 10

VIN

NC 3 3 3, 4, 8 No connection

EP - EP EP

4 4 5 Input Supply Pin. Must be locally bypassed.

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

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 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

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

Exposed pad: Internally connected to IC substrate. It should be connected to GND and as large as possible thermal mass for improved

thermal impedance and power dissipation capability. However the exposed pad is not a Power GND return path. The dedicated GND pins must be connected to 0V. See Land Pad diagrams.

.

S

CTRL

Functional Block Diagram

AP8802

= V

REF

AP8802

Document number: DS31766 Rev. 9 - 2

Figure. 1 Functional Block Diagram

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AP8802

Absolute Maximum Ratings (T

Symbol Parameter Rating Unit

VIN VIN pin voltage

VSW

V

CTRL

V

SENSE

TJ

T

LEAD

T

ST

Note: 4 All voltages unless otherwise stated are measured with respect to GND.

5. V

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

SW voltage -0.3 to +50 V

CTRL Pin Input Voltage -0.3 to +6 V

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

is measured with respect to VIN.

SENSE

Recommended Operating Conditions (T

Symbol Parameter Min Max Unit

VIN

V

CTRLDC

V

CTRL

f

OSC

TA

Duty Cycle Using inductor ≥ 100µH (Note 8) 0.10 0.95 —

Notes: 6. For 100% brightness either leave floating or connect to 1.25V relative to GND.

7. AP8802 will operate at higher frequencies but accuracy will be affected due to propagation delays and also increased power dissipation will occur due to increased switching losses.

8. 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.

Operating input voltage relative to GND 8.0 48.0 V Voltage range for 24% to 200% DC dimming relative to GND (Note 6) 0.3 2.5 V Voltage low for PWM dimming relative to GND 0 0.2 V Maximum switching frequency (Note 7) — 625 kHz Ambient temperature range -40 +105 °C

AP8802

Document number: DS31766 Rev. 9 - 2

= +25°C) (Note 4)

A

= +25°C)

A

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-0.3 to +50 V

1A LED STEP-DOWN CONVERTER

o

C

o

C

o

C

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AP8802

Electrical Characteristics (T

Symbol Parameter Conditions Min Typ. Max Unit

I

OUT

IQ

V

THD

V

SENSEHYS

SET SET pin input current V

REF

R

DS(ON)

I

SW_LEAKAGE

θ

Notes: 9. Refer to figure 8 for the device derating curve.

10. Test condition for SO-8, SO-8EP and U-DFN3030-10: 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.

Continuous switch current (Note 9) — — 1 A Quiescent Current — 75 120 μA Internal Threshold Voltage 184 200 216 mV Sense threshold hysteresis — 15 — %

Internal Reference Voltage — 1.25 — V On Resistance of MOSFET Switch leakage current — — 8 μA

Thermal Resistance Junction-to-

JA

Ambient

Thermal Resistance Junction-to-Case

JC

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

A

V

= V

IN

= 0.8A

-0.2

SET

I

SW

SO-8 (Note 10) — 82 — °C/W SO-8EP (Note 10) — 45 — °C/W U-DFN3030-10 (Note 10) — 38 — °C/W SO-8 (Note 10) — 52 — °C/W SO-8EP (Note 10) — 7 — °C/W U-DFN3030-10 (Note 10) — 24 — °C/W

1A LED STEP-DOWN CONVERTER

— 5 — μA

— 0.65 1.10 Ω

AP8802

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2

R

CUR

RENT

CUR

REN

T

Typical Characteristics

0.9



0.8

0.7

AP8802

1A LED STEP-DOWN CONVERTER

1.256

1.254

0.6

0.5

0.4

0.3

0.2

0.1

NON-SWITCHING SUPPLYCURRENT (mA)

0

0484448121620242832 4036

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

1.

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

Figure. 4 R vs. Ambient Temperature

1200

1000

(mA )

800

INPUT VOLTAGE (V)

AMBIENT TEMPERATURE (°C)

DS(ON)

R = 0.2

Ω

SET

R = 0.3

SET

Ω

1.252

1.250

1.248

CTRL VOLTAGE (V)

1.246

1.244

-40 125-25 110-10520355065 9580 AMBIENT TEMPERATURE (°C)

1000

(mA)

LED

Figure. 3 V vs. Ambient Temperature

900 800 700 600

500 400 300 200 100

0

0 0.5 1.0 1.5 2.0 2.5

800 700

600

500

CTRL

R RESISTANCE ( )

SET

Figure. 5 LED Current vs. R

Ω

SET

600

400

LED

200

0

0 0.5 1 1.5 2 2.5

CTRL VOLTAGE (V)

Figure. 6 LED Current vs. V

AP8802

Document number: DS31766 Rev. 9 - 2

R = 0.68

SET

CTRL

Ω

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400

300

200

SWITCHING FREQUENCY (kHz)

100

0

02.50.5 1 1.5 2

Figure. 7 Switching Frequency vs. V

CTRL VOLTAGE (V)

CTRL

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TCHINGFREQ

U

k

H

UTYCY

C

Typical Characteristics (T

1A LED STEP-DOWN CONVERTER

= +25°C, VIN = 40V, L = 68µH; unless otherwise stated.)

A

AP8802

10

8 6

4 2 0

-2

-4

-6

OUTPUT CURRENT DEVIATION (%)

-8

-10 61218 4824 30 36 42

Figure. 8 LED Current vs. Input Voltage

500

T = +25°C

A

450

R = 0.2

z)

ENCY (

SWI

SET

L = 68µH

400 350 300

250 200

1 LED

150 100

50

0

61218 4824 30 36 42

Figure. 10 Switching Frequency vs. Input Voltage

INPUT VOLTAGE (V)

Ω

3 LEDs

5 LEDs

INPUT VOLTAGE (V)

7 LEDs

61218 4824 30 36 42

100

LE (%)

D

Figure 9. Efficiency vs. Input Voltage

90 80 70

60 50 40 30 20 10

0

61218 4824 30 36 42

Figure. 11 Duty Cycle vs. Input Voltage

INPUT VOLTAGE (V )

SUPPLY VOLTAGE (V)

Fig. 12 Steady State Waveforms

AP8802

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Fig.13 Start-Up Showing LED Current Soft Start

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