Diodes AP8800 User Manual

A

P8800

350mA LED STEP-DOWN CONVERTER

Description

The AP8800 is a step-down DC/DC converter designed to drive LEDs
with a constant current. The device can drive up to seven 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 eliminates
the need for ballast resistors. The AP8800 switches at frequency up
to 0.6MHz. This allows the use of small size external components,
hence minimizing the PCB area needed.

Maximum output current of AP8800 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 shuts down the output
at SW and puts the device into a low-current standby state.

and SET input pins. Dimming is achieved

IN

Features

• LED driving current up to 350mA

• Compatible with 12V & 24V standard systems

• High efficiency up to 92%

• High switching frequency up to 0.6MHz

• PWM/DC input for dimming control

• Built-in soft-start function

• Built-in output open-circuit protection

• SO-8, MSOP-8 and U-DFN3030-10: 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)

Applications

• Commercial & Industrial Lighting

• Small LCD Panel Backlight

• Architecture Detail Lighting

• Appliances Interior Lighting

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.

Pin Assignments

CTRL

RSVD

SW

GND

CTRL

RSVD

GND

CTRL

RSVD

SW

GND

SO-8

( Top View )

1

2
3

AP8800

8
7
6

45

MSOP-8

( Top View )

SW

1
2

3

AP8800

8
7
6

45

U-DFN3030-10

( Top View )

NC

1

2

3

4

5

AP8800

10

9

8

7

6

SET

NC

NC

V

SET

NC

NC

V

IN

SET
NC

NC

NC
V

IN

IN

Typical Applications Circuit

AP8800

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Pin Descriptions

Pin Name

SO-8 MSOP-8 U-DFN3030-10

SW 3 3 4

Pin Number

Function

Switch Pin. Connect inductor/freewheeling diode here. Minimize trace area at this pin to
reduce EMI.

GND 4 4 5 GND Pin

SET 8 8 10 Set Nominal Output Current Pin. To 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.

CTRL 1 1 1

• 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 200kΩ, and if the pin is left open V

.

S

CTRL

VIN 5 5 6 Input Supply Pin. Must be locally bypassed.

RSVD 2 2 2 Reserved. Normally connected to Ground

NC 6, 7 6, 7 2, 7, 8, 9 No Connection.

Functional Block Diagram

= V

REF

P8800

Absolute Maximum Ratings (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Rating Unit

V

VIN Pin Voltage -0.3 to +30 V

IN

V

Set Voltage Relative to VIN V

SET

-5 to VIN +0.3 V

IN

VSW SW Voltage -0.3 to +30 V
V

CTRL Pin Input Voltage -0.3 to +5 V

CTRL

T

Maximum Junction Temperature 125 °C

J

T

Maximum Lead Temperature 300 °C

LEAD

T

Storage Temperature Range -55 to +125 °C

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.

AP8800

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P8800

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

A

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 (Note 2) 0.3 2.5 V

CTRLDC

V

Voltage Low for PWM Dimming Relative to GND 0 0.2 V

CTRLL

f

Maximum Switching Frequency 500 kHz

OSC

TA Ambient Temperature Range -40 +85 °C

Duty Cycle Using Inductor ≥ 100µH (Note 3) 0.1 0.95

V

CTRL Input Voltage to Attain 100% LED Current 1.25

ENH

V

CTRL Input Voltage Below Which Device Turns Off 0.2

ENL

Notes: 2. For 100% brightness either leave floating or connect to 1.25V relative to GND.

3. 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.

V

Electrical Characteristics (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Conditions Min Typ Max Unit

I

Continuous Switch Current (Note 4) — — 350 mA

OUT

IQ Quiescient Current — 20 30 μA

V

Internal Current Sense Threshold Voltage V

THD

V

Internal Reference Voltage — 1.25 — V

REF

SET SET Pin Input Current V

– V

92 100 108 mV

IN

SET

= V

-0.1 — 1.3 — μA

SET

IN

RDS(on) On-Resistance of Internal Switch — 1.7 2.2 Ω

I

SW_Leakage

Notes: 4. Refer to figure 8 for the device derating curve.

5. Test condition for SO-8, MSOP-8 and U-DFN3030-10: Device mounted on FR-4 PCB, 2”x 2”, 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.

Switch Pin Leakage Current — — 5 μA

SO-8 (Note 5) — 92 —

θ

Thermal Resistance Junction-to-Ambient

JA

MSOP-8 (Note 5) —
U-DFN3030-10 (Note 5) —
SO-8 (Note 5) —

θ

Thermal Resistance Junction-to-Case

JC

MSOP-8 (Note 5) —
U-DFN3030-10 (Note 5) —

120

46
60
98
32

—
—
—
—
—

°C/W
°C/W
°C/W
°C/W
°C/W
°C/W

AP8800

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P8800

Application Information

AP8800 Operation

The AP8800 is a hysteretic LED current switching regulator sometimes known as an equal ripple switching regulator. In normal ope ration, when
voltage is applied at +V
and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +V

(See Figure 1), the AP8800 internal switch is turned on. Current starts to flow through sense resistor R1, inductor L1,

IN

, and the inductor L1 (See Figure 2).

IN

Figure 1 Typical Configuration

This rising current produces a voltage ramp across R
proportional voltage to the input of the internal comparator.

When this voltage reaches an internally set upper threshold, the internal switch is turned off. The inductor current continues to flow through R
L1, the LEDs and the schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined b y the for ward voltage drop
of the LEDs and the schottky diode.

This decaying current produces a falling voltage at R

is applied at the input of the internal comparator. When this voltage falls to the internally set lower threshold, the internal switch is turned on

R

SET

again. This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R
determined by the input voltage and LED chain voltage.

In normal operation the off time is relatively constant (determined mainly by the LED chain voltage) with only the on-time varying as the input
voltage changes. At duty cycles up to around 80% the ramp of the LED/switch current is very linear; however, as the duty cycle approaches 95%
the LED current ramp starts to become more exponential. This has two effects:

1. The overall on time starts to increase lowering the overall switching frequency.

2. The average LED current starts to increase – which may impact accuracy.

AP8800

Document number: DS31764 Rev. 7 - 2

. The internal circuit of the AP8800 senses the voltage across R

SET

, which is sensed by the AP8800. A voltage proportional to the sense voltage across

SET

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Figure 2 Typical Switching Waveform

SET

with a switching current

SET,

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and applies a

SET

August 2012

,

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P8800

Application Information (cont.)

Inductor Selection

A 100μH inductor is recommended for most AP8800 applications with input voltage at 24V.
Figure 3 displays the resulting switching frequency varying the main circuit parameters: Supply voltage, Inductor value and number of LEDs to be
driven.

Switching Frequency

700

600

500

400

300

Frequency [kHz]

200

100

0

0 50 100 150 200 250 300 350 400 450 500

47

100

150

68

220

100

150

220

Inductor Value [uH]

470

470

12V - 1LED
24V - 3 LEDs
28V - 4LEDs

Figure 3 Switching Frequency vs. Supply Voltage, Inductor, and Number of LEDs

Capacitor Selection

The small size of ceramic capacitors makes them ideal for AP8800 applications. X5R and X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges than other types such as Z5U. A 1μF input capacitor is sufficient for most intended
applications of AP8800.

Diode Selection

Schottky diode, e.g. B140, with their low forward voltage drop and fast reverse recovery, is the ideal choice for AP8800 applications.

Miscellaneous

To ensure optimal performance, RSVD pin should be connected to the GND pin with the shortest trace length.

AP8800

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P8800

Application Information (cont.)

LED Current Dimming

The LED current can be dimmed in two ways;

1. Analog Dimming: Where a dc voltage is applied to the CTRL pin
or

2. PWM Dimming: Where a Pulse Width Modulated (PWM) signal is applied to the CTRL pin.

Analog Dimming

If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current in this case is:

V

I ×=

LED

CTRL

V

A DC signal from 0.3V to 2.5V applied to the CTRL pin will vary the LED current from 24% to 200% of nominal LED current. This gives an
approximate 8:1 dimming range; care, should be exercised when overdriving the CTRL pin to 200% of nominal LED current not to exceed the
power dissipation of the package.

The graph in Figure 4 shows values of nominal average output current for 3 values of current setting resistor (R
circuit shown on Figure 1, for different voltages applied on the CTRL pin.

REF

V

TH

R

SET

) in the typical application

SET

400

350

300

250

200

150

LE D Curren t [mA]

100

50

0

0 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3

0.3

0.3

0.33

0.39

0.39

0.47

0.47

AP8800

Document number: DS31764 Rev. 7 - 2

0.56

0.56

0.56

LED current Versus RSET and VCTRL

0.68

0.75

0.82
1

0.68

0.68

0.82

0.82

1.2

1

1.2

1

1.2

R SET value [ Ohm s]

1.5

1.5

1.5

Figure 4 LED Current Setting vs. R

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LED current @
VCTR L = 1.25V

LED current @
VCTR L = 2.5V

LED current @

2
2

2

3
3

3

VCTR L = 0.625V

SET

and V

CTRL

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P8800

Application Information (cont.)

PWM Dimming

A PWM signal with a max resolution of 8bit can be applied to CTRL regulate the output current to a value below the nominal average value set
by resistor R
applying DC voltage to the CTRL pin to achieve average LED current dimming.

Figure 5 shows the typical PWM response of the AP8800A. An internal filter produces a rump.

. PWM dimming gives a wider average LED current variation and is more accurate at lower average LED currents than by

SET

Figure 5 Typical PWM Dimming Waveform

The recommended method of driving the CTRL pin and controlling the amplitude of the PWM waveform is to use a small NPN switching
transistor as shown below:

Figure 6 Open Collector PWM Dimming Circuit

This scheme uses the 200k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor eg
MMBT3904.

Soft-Start

An external capacitor from the CTRL pin to ground will provide soft-start delay, by increasing the time taken for the voltage on this pin to rise to
the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator.

The soft-start time is 0.5ms/nF.

AP8800

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P8800

Application Information (cont.)

Fault conditions

The AP8800 is inherently protected against open-LED conditions. If one LED becomes open circuit the device automatically stops switching and
will only retart if the open-LED fault is removed.

If one or more LEDs should become shorted together then the s witching frequency and duty cycle will change. If one or m ore LEDs get shorted
together, the ramp-up time of LED current will become shorter due to there being a larger voltage across the inductor. However, the ramp-down
time of the LED current will increase due to the voltage across the inductor becoming smaller.

Figure 7 below shows the AP8800 driving 3 LEDs when all 3 LEDs become shorted togethe r. Due to the large voltage change across the
inductor during both LED current ramp-up and ramp-down we see a large difference in switching frequency.

Figure 7 LED Short Fault Condition

Thermal Considerations

The graph below in Figure 8, gives details for power derating. This assumes the device to be mounted on a 2 5 x 25mm PCB with 1oz copper
standing in still air.

2

1.8

1.6

1.4

1.2
1

0.8

POWER (W)

0.6

0.4

0.2
0

0 25 50 75 100 125 150

MSOP-8

DFN3030-10

SO-8

MBIENT TEMPERATURE (°C)

Figure 8 Power Dissipation Derating Curve

AP8800

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Ordering Information

P8800

AP 8800 XX G - X

Package Packing

S : SO-8

M8 : MSOP-8

Green

G : Green

7/ 13 : Tape & Reel

FN : U-DFN3030-10

Part Number Package Code Packaging

AP8800SG-13 S SO-8 2500/Tape & Reel -13

AP8800M8G-13 M8 MSOP-8 2500/Tape & Reel -13

AP8800FNG-7 FN U-DFN3030-10 3000/Tape & Reel -7

Quantity Part Number Suffix

7”/13” Tape and Reel

Marking Information

SO-8

( Top View )

5

G : Green

: Year : 08, 09,10~

YY

X

X

41

WW : Week : 01~52; 52
represents 52 and 53 week
X

: Internal Code

MSOP-8

Logo

Part Number

8

AP8800
YY

WW

( Top View )

Part Number

U-DFN3030-10

AP8800

Document number: DS31764 Rev. 7 - 2

8765

Logo

AP8800

234

1

Y W X

A~Z : Green

: Year : 0~9

Y

W

: Week : A~Z : 1~26 week;
a~z : 27~52 week; z represents
52 and 53 week

( Top View )

XX : Identification Code

Y

X X

W

XY

: Year : 0~9
: Week : A~Z : 1~26 week;

W

a~z : 27~52 week; z represents

52 and 53 week

X

: A~Z : Green

Part Number Package Identification Code

AP8800FNG-7 U-DFN3030-10 A4

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Package Outline Dimensions (All dimensions in mm.)

Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.

Package Type: SO-8

Package Type: MSOP-8

e

b

D

E1

A2

E

A1

Detail ‘A’

h

°

45

A3

A

L

0.254

Gaug e Plane
Seating Plane

7°~9

°

Detail ‘A’

D

4

x

4

x

1

0

Detail C

1

°

0

°

a

L

c

See Detail C

E

Gauge Plane
Seating Plane

0.25

x

y

A2

A1

1

b

A3

A

e

E3

E1

Package Type: U-DFN3030-10

Pin#1 ID

A

A1

E

E2

z

AP8800

Document number: DS31764 Rev. 7 - 2

D

D2

e

b

A3

SEATING PLANE

L

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Dim Min Max

Dim Min Max Typ

A - 1.10 ­A1 0.05 0.15 0.10
A2 0.75 0.95 0.86
A3 0.29 0.49 0.39

b 0.22 0.38 0.30
c 0.08 0.23 0.15

D 2.90 3.10 3.00

E 4.70 5.10 4.90
E1 2.90 3.10 3.00
E3 2.85 3.05 2.95

e - - 0.65

L 0.40 0.80 0.60

a 0° 8° 4°

x - - 0.750

y - - 0.750
All Dimensions in mm

Dim Min Max Typ

A 0.57 0.63 0.60

A1 0 0.05 0.02
A3

b 0.20 0.30 0.25
D 2.90 3.10 3.00

D2 2.30 2.50 2.40

e
E 2.90 3.10 3.00

E2 1.50 1.70 1.60

L 0.25 0.55 0.40
z

All Dimensions in mm

SO-8

A - 1.75
A1 0.10 0.20
A2 1.30 1.50
A3 0.15 0.25

b 0.3 0.5

D 4.85 4.95

E 5.90 6.10
E1 3.85 3.95

e 1.27 Typ

h - 0.35

L 0.62 0.82

0° 8°

θ

All Dimensions in mm

MSOP-8

U-DFN3030-10

⎯ ⎯

⎯ ⎯

⎯ ⎯

0.15

0.50

0.375

P8800

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Suggested Pad Layout

Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.

Package Type: SO-8

X

Dimensions Value (in mm)

X 0.60

C1

C2

Y

Y 1.55
C1 5.4
C2 1.27

Package Type: MSOP-8

Y1

X C

Y

Dimensions Value (in mm)

C 0.650
X 0.450
Y 1.350

Y1 5.300

Package Type: U-DFN3030-10

AP8800

Document number: DS31764 Rev. 7 - 2

Y

X

C

X1

G

G

Z

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Dimensions Value (in mm)

Z 2.60

G 0.15

X 1.80
X1 0.60

Y 0.30

C 0.50

P8800

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Tape Orientation (Note 6)

For U-DFN3030-10

P8800

Notes: 6. The taping orientation of the other package type can be found on our website at http://www.diodes.com/datasheets/ap02007.pdf.

AP8800

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P8800

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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).

Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.

Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorize d application, Customers shall indemnify and
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indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.

Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.

Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:

A. Life support devices or systems are devices or systems which:

1. are intended to implant into the body, or

2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the

labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the

failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and

acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.

Copyright © 2012, Diodes Incorporated

www.diodes.com

IMPORTANT NOTICE

LIFE SUPPORT

AP8800

Document number: DS31764 Rev. 7 - 2

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