Instruction Manual

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AP8800A

Document number: DS35100 Rev. 3 - 2

1 of 13

www.diodes.com

August 2012

P8800A

COST EFFECTIVE 28V BUCK 1-W LED DRIVER

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

and SET input pins. Dimming is 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 switches off the output

MOSFET simplifying PWM dimming.

Features

• 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)

Pin Assignments

4 SET

CTRL

GND

(Top View)

Applications

• MR16 Lamps

• General Illumination Lamps

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 Applications Circuit

Summary of content (13 pages)

PAGE 1
AP8800A COST EFFECTIVE 28V BUCK 1-W LED DRIVER Description Pin Assignments The AP8800A is a step-down DC/DC converter designed to drive (Top View) 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.
PAGE 2
AP8800A Pin Descriptions Pin Name SW GND Pin Number 1 2 CTRL 3 SET 4 VIN 5 Function Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. 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. 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.
PAGE 3
AP8800A Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Symbol Min Max Unit Operating Input Voltage Relative to GND 8.0 28 V VCTRLDC Voltage Range for 24% to 200% DC Dimming Relative to GND 0.3 2.5 V VCTRLL Voltage Low for PWM Dimming Relative to GND 0.2 V 370 mA VIN ISW DPWM Parameter Continuous Average Switch Current (Note 4) Duty Cycle Range Applied to CTRL (f < 500Hz) fSW Switching Frequency TA Ambient Temperature Range Note: 0.
PAGE 4
AP8800A Typical Characteristics 25 500 TA = 25°C TA = 25°C 20 Shutdown Current (µA) Quiescent Current (µA) 400 300 200 15 10 100 0 0 5 0 4 0 12 16 20 24 28 Input Voltage (V) Shutdow n Current (Non-Sw itching) vs. Input Voltage 1.255 8 12 16 20 24 28 Input Voltage (V) Quiescent Current (Switching) vs. Input Voltage 1.2425 4 TA = 25°C 8 V IN = 12V V REF (V) Reference Voltage (V) 1.25 1.242 1.245 1.24 1.2415 4 8 12 16 20 24 Input Voltage (V) Reference Voltage vs.
PAGE 5
AP8800A Typical Characteristics (cont.) 350 RS = 0.3 Ω V IN = 12V L = 100µH R S = 0.33 Ω 300 R S = 0.56 Ω 1 250 IOUT Mean (mA) Deviation From Nominal Set Current(%) 2 0 200 RS = 1 Ω 150 100 -1 50 -2 -40 0 -15 10 35 60 85 110 Ambient Temperature (°C) Change in LED Current vs. Ambient Temperature AP8800A Document number: DS35100 Rev. 3 - 2 0 5 of 13 www.diodes.com 0.5 1.5 2 V CTRL (V) Output Current vs. VCT RL 1 2.
PAGE 6
AP8800A Application Information (@TA = +25°C, VIN = 12V, unless otherwise specified.) AP8800A Operation The AP8800A is a hysteretic LED current switching regulator sometimes known as an equal ripple switching regulator. In normal operation, when voltage is applied at +VIN (See Figure 1), the AP8800A internal switch is turned on. Current starts to flow through sense resistor R1, inductor L1, and the LEDs.
PAGE 7
AP8800A Application Information (cont.) (@TA = +25°C, VIN = 12V, unless otherwise specified.) Inductor Selection A 68μH inductor or higher, is recommended for most AP8800A applications with input voltage at 12V. Figure 3 displays the resulting switching frequency with various main circuit parameters: Supply voltage, Inductor value and number of LEDs to be driven.
PAGE 8
AP8800A Application Information (cont.) (@TA = +25°C, VIN = 12V, unless otherwise specified.) 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 V ILED = CTRL × TH VREF R SET A DC signal from 0.3V to 2.
PAGE 9
AP8800A Application Information (cont.) (@TA = +25°C, VIN = 12V, unless otherwise specified.) 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 RSET. PWM dimming gives a wider average LED current variation and is more accurate at lower average LED currents than by applying dc voltage to the CTRL pin to achieve average LED current dimming. Figure 5 shows the typical PWM response of the AP8800A.
PAGE 10
AP8800A Application Information (cont.) (@TA = +25°C, VIN = 12V, unless otherwise specified.) Fault Conditions The AP8800A 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 switching frequency and duty cycle will change.
PAGE 11
AP8800A Application Information (cont.) (@TA = +25°C, VIN = 12V, unless otherwise specified.) Application Example SET CTRL GND VIN SW The typical application for the AP8800A is the MR16 application driving 1W rated LEDs from a 12V ac supply. AP8800A Component List Quantity PCB Ident Value 1 U1 AP8800A LED Driver IC Diodes Inc. 1 D1, D2, D3, D4, D5 SBR1A40 Input bridge & freewheeling diode Diodes Inc.
PAGE 12
AP8800A Ordering Information Part Number Package Code Packaging AP8800AWT-7 WT TSOT25 Quantity 3000/Tape & Reel 7” Tape and Reel Part Number Suffix -7 Marking Information (1) TSOT25 (Top View) 4 7 5 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 X : A~Z : Internal code XX Y W X 1 2 3 Part Number AP8800AWT-7 Package TSOT25 Identification Code AZ Package Outline Dimensions (All dimensions in mm.
PAGE 13
AP8800A Suggested Pad Layout Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. C C Dimensions Value (in mm) C 0.950 X 0.700 Y 1.000 Y1 3.199 Y1 Y (5x) X (5x) IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, 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).