Diodes AP8803 User Manual

A

P8803

30V 1A BUCK LED DRIVER

Description

The AP8803 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 30V. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness and eliminating
the need for ballast resistors. The AP8803 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 AP8803 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 1A

• High Efficiency Up to 92%

• Operating Input Voltage Up to 30V

• High Switching Frequency Up to 700kHz

• 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.

Pin Assignments

SW

GND

CTRL

1

2

3

Top View

V

IN

45SET

Typical Applications Circuit

AP8803

Document number: DS31970 Rev. 5 - 2

12V_DC

C1

V

IN

CTRL

SET

AP8803

GND

SW

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R

L1

SET

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Pin Descriptions

Pin Name Function

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.

Dimming and On/Off Control Input.

• Leave floating for normal operation.
(V

= V

CTRL

CTRL

= 1.25V giving nominal average output current I

REF

• Drive to voltage below 0.2V to turn off output current

• Drive with DC voltage (0.3V < V

< 1.25V) to adjust output current from 25% to 100% of I

CTRL

OUTnom

= 0.1/RS)

• Input voltage of 0.2V or lower forces the device into low current standby mode and shuts off the output. A PWM signal
allows the output current to be adjusted above or below the level set by the resistor connected to SET input pin.

VIN Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor.

Functional Block Diagram

OUTnom

P8803

Absolute Maximum Ratings (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Rating Unit

VIN

VSW

V

CTRL

Continuous V
Transient (t < 0.5s) 40
SW voltage -0.3 to +30
Transient (t < 0.5s) 40

CTRL pin input voltage -0.3 to +6 V

pin voltage -0.3 to +30

IN

V

V

ISW Switch current 1.25 A

ESD

Human Body Model ESD 500 V

HBM

ESDMM Machine Model ESD <100 V

TJ Junction Temperature 150 °C

T

Lead Temperature Soldering 300 °C

LEAD

T

Storage Temperature Range -65 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;

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

AP8803

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P8803

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

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Symbol Parameter Min Max Unit

VIN Operating Input Voltage 8.0 30 V

V

Voltage High 0.3 2.5 V

CTRLH

V

Voltage Low 0.25 V

CTRLL

ISW Continuous Switch Current (Note 5) 1 A

TA Ambient Temperature Range -40 +125 °C

Duty Cycle Using Inductor ≥ 100µH (Note 4) 0.1 0.95

Notes: 4. 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.

5. Refer to Figure 8 for the device derating curve.

Electrical Characteristics (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Conditions Min Typ Max Unit

V

Internal Regulator Start-Up Threshold VIN rising 5.65 V

INSU

V

Internal Regulator Shutdown Threshold VIN falling 5.55 V

INSD

IQ Quiescent Current CTRL pin floating f = 250kHz 1.8 5 mA

V

Internal Threshold Voltage 92 100 108 mV

THD

I

SET Pin Input Current V

SET

V

Internal Reference Voltage 1.25 V

REF

R

On Resistance of MOSFET ISW = 1A 0.5 1 Ω

DS(on)

SET

= V

-0.1 1.25 10 µA

IN

ISW Continuous Switch Current (Note 5) 1 A

I

SW_Leakage

Notes: 5. Refer to Figure 8 for the device derating curve.

6. Test condition for TSOT25: Device mounted on FR-4 PCB, 25mm x 25mm, 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 Leakage Current 8 µA

f

Switching Frequency 0.7 MHz

OSC

θ

Thermal Resistance Junction-to-

JA

Ambient

TSOT25 (Note 6) 125 °C/W

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P8803

Application Information

AP8803 Operation

The AP8803 is a hysteretic LED current switching regulator sometimes known as an equal ripple switching regulator. In normal operation, 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

12V_DC

(See

IN

CTRL

AP8803

Figure 1), the AP8803 internal switch is turned on. Current starts to flow through sense resistor R1, inductor L1,

, and the inductor L1 (See Figure 2).

IN

V

IN

R

SET

SET

C1

L1

GND

SW

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 by the forward

SET

voltage drop of the LEDs and the schottky diode.
This decaying current produces a falling voltage at R

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

SET

on 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.

. The internal circuit of the AP8803 senses the voltage across R

SET

, which is sensed by the AP8803. A voltage proportional to the sense voltage across

SET

LED Current Control

The LED current is controlled by the resistor R
Connected between V

and SET the nominal average output current in the LED(s) is defined as:

IN

in Figure 1.

SET

V

I = where V

LED

TH

R

SET

is nominally 100mV

TH

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Figure 2 Typical switching waveform

and applies a

SET

with a switching current

SET,

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P8803

Application Information (cont.)

Inductor Selection

A 33μH inductor (or higher) is recommended for most AP8803 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.

In particular, the graph in Figure 3 gives values of nominal switching frequency for several values of inductors (L1) in the typical application
circuit shown on Figure 1, for different input voltages and load condition. It can be used to determine the inductor v alue based on the desired
switching frequency and the input and load conditions.

Switching Frequency @ I

600

500

400

300

200

Frequency [kHz]

100

0

0 50 100 150 200 250 300 350 400 450 500

33

47

68

33

47

100

150

68

100

150

220

220

Inductor Value [uH]

LE D

=1A

12V - 1 LED
24V - 3 LED s
30V - 5 LED s

470

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

Capacitor Selection

The small size of ceramic capacitors makes them ideal for AP8803 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 2.2μF input capacitor is sufficient for most
intended applications of AP8803.

Diode Selection

Schottky diodes, e.g. B240 or DFLS240L in the proprietary PowerDI123 package, with their low forward voltage drop and fast reverse recovery,
are the ideal choice for AP8803 applications.

In addition, Super Barrier Rectifier devices (as SBR2A40P1) can be used for their enhanced thermal performances.

AP8803

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P8803

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 is:

V

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 setti ng resistor (R
circuit shown on Figure 1, for different voltages applied on the CTRL pin.

It can be used to determine the R
external DC voltage lower than 2.5V and higher than 0.2V).

REF

THD

R

SET

) in the typical application

SET

value based on the desired LED current and the condition of the CTRL pin (floating o r driven with an

SET

1200

1000

800

600

400

LED Cu rrent [mA]

200

0

0.2

0.3

0.1

0.39

0.15

0.3

0.47

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

AP8803

Document number: DS31970 Rev. 5 - 2

0.47

LED current Versus RSET and VCTRL

0.75

0.82

0.75

0.82

1

1

RSET valu e [Ohms]

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 @
VCTR L = 0.625V

2
2

3
3

SET

and V

CTRL

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P8803

Application Information (cont.)

PWM Dimming

A Pulse Width Modulated (PWM) signal with a max resolution of 8-bit, can be applied to the CTRL pin to change the output current to a value
above or below the nominal average value set by resistor R

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

. To achieve this resolution the PWM frequency has to be lower than 500Hz.

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 internal 200kΩ resistor between the CTRL 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.

AP8803

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P8803

Application Information (cont.)

Fault Condition Operation

The AP8803 has by default open LED protection. If the LEDs should become open circuit the AP8803 will stop oscillating; the SET pin will rise

and the SW pin will then fall to GND. No excessive voltages will be seen by the AP8803.

to V

IN

If the LEDs should become shorted together the AP8803 will continue to switch however the duty c ycle at which it will operate will change
dramatically and the switching frequency will most likely decrease. The on-time of the internal power MOSFET switch will be significantly
reduced because almost all of the input voltage is now developed across the inductor. The off-time will be significantly increased because the
reverse voltage across the inductor is now just the Schottky diode voltage (See Figure 7) causing a much slower decay in inductor current.
During this condition the inductor current will remain within its controlled levels and so no excessive heat will be generated within the AP8803.

Figure 7 Switching Characteristics (normal open to short LED ch ain)

Thermal Considerations

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

1.2

1

0.8

0.6

0.4

Power dissipat ion (W)

0.2

0

-50 -25 0 25 50 75 100 125 150

Ambient Temperat ure (°C)

Figure 8 Power Dissipation Derating Curve

The maximum power dissipation is affected by PCB area and the area of copper associated with the LX pin as well as other components on the
PCB generating heat – such as the inductor, capacitor or rectifiers.

AP8803

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θ

Ordering Information

Part Number Package Code Packaging

AP8803WTG-7 WT TSOT25 3000/Tape & Reel -7

Quantity Part Number Suffix

7” Tape and Reel

Marking Information

XX : Identification Code
Y : Year 0~9
W : Week: A~Z: 1~26 week
a~z: 27~52 week;
z represents 52 and 53 week

Part Number Package Identification Code

AL8803WT-7 TSOT25 AY

Package Outline Dimensions (All dimensions in mm.)

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

E1

A2

A

A1

AP8803

Document number: DS31970 Rev. 5 - 2

D

e1

E

c

L

4x 1

e

5x b

θ

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L2

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TSOT25

Dim Min Max Typ

A

A1 0.01 0.10
A2 0.84 0.90

D
E

E1

b 0.30 0.45
c 0.12 0.20
e

e1

L 0.30 0.50

L2

θ 0° 8° 4°

θ1 4° 12°

All Dimensions in mm

1.00

−

− −

− −

− −

− −

− −

− −

−

−

−

2.90

2.80

1.60

−

−

0.95

1.90

0.25

−

P8803

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P8803

Suggested Pad Layout

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

C C

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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).

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

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Copyright © 2012, Diodes Incorporated

www.diodes.com

Y1

Y (5x)

X (5x)

IMPORTANT NOTICE

LIFE SUPPORT

Dimensions Value (in mm)

C
X
Y

Y1

0.950

0.700

1.000

3.199

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