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AP8801
500mA LED Step-down Converter
Features
* * * * * * * * LED driving current up to 500mA Operating input voltage up to 48V High efficiency up to 92% High switching frequency up to 500kHz PWM/DC input for dimming control Built-in output open-circuit protection SOP-8L and MSOP-8L are available in "Green" Molding Compound (No Br, Sb) Lead Free Finish/RoHS Compliant (Note 1)
General 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 500kHz. 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 VIN 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 shuts down the output at SW and puts the device into a low-current standby state.
Applications
* * * * Commercial & industrial lighting Small LCD panel backlight Appliances interior lighting Architecture Detail lighting
Typical Application Circuit
24V_DC VIN CTRL
SET
RSET = 0.43
D1
AP8801
C1 = 2.2F
GND SW
L1 = 100H
Figure 1: Typical Application Circuit
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AP8801
500mA LED Step-down Converter
Ordering Information
AP 8801 XX G - 13
Package S : SOP-8L M8 : MSOP-8L Green G : Green Packing
13 : Tape & Reel
Device
AP8801SG-13 AP8801M8G-13
Notes:
Package Code
S M8
Packaging (Note 2)
SOP-8L MSOP-8L
13" Tape and Reel Quantity Part Number Suffix
2500/Tape & Reel 2500/Tape & Reel -13 -13
1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at http://www.diodes.com/products/lead_free.html. 2. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf.
Pin Assignments
(1) SOP-8L (2) MSOP-8L
( Top View ) SET 1 GND NC 2 3
AP8801
( Top View ) 8 7 6 5 CTRL GND SW SW SET 1 GND NC 2 3
AP8801
8 7 6 5
CTRL GND SW SW
VIN 4
VIN 4
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Pin Descriptions
Pin Name SW GND SET CTRL VIN NC Description Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. GND pin Set Nominal Output Current Pin. Configure the output current of the device. 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. A PWM signal allows the output current to be adjusted above or below the level set by the resistor connected to SET input pin. The input impedance is about 50k, and if the pin is left open VCTRL = VREF Input Supply Pin. Must be locally bypassed. No connection
Block Diagram
SET SW
VIN Sensing Block Comparator
Voltage Regulator
5V
CTRL
PWM/DC Control
VREF 1.25V
AP8801
R
GND
Figure 2: AP8801 Block Diagram
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500mA LED Step-down Converter
Absolute Maximum Ratings
Symbol VIN VSW TJ TLEAD TST
Caution:
Parameter VIN pin voltage SW voltage Junction Temperature Lead Temperature Soldering Storage Temperature Range
Rating -0.3~50 -0.3~50 150 300 -65 to +150
Unit V V
o o o
C C C
The absolute maximum ratings are rated values exceeding which the product could suffer physical damage. These values must therefore not be exceeded under any condition. 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
Recommended Operating Conditions
Symbol Parameter TA Ambient Temperature Range Duty Cycle Using Inductor 100H (Note 3)
Notes:
Min -40 0.1
Max 105 0.95
Unit C
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.
Electrical Characteristics
Symbol VIN IOUT IQ FOSC VTHD VREF SET Rds(on) ISW
Leakage
(VIN =24V, TA=25oC, unless otherwise specified) Conditions (Note 4) 184 1.25 78 200 1.25 7 0.7 88 128 58 90 Min 8.0 Typ. Max 48 500 120 0.5 216 1.15 8 0.2 Unit V mA A MHz mV V A A V V C/W C/W C/W C/W
EN EN
JA JC
Notes:
Parameter Operating Input Voltage Continuous switch current Quiescent Current Switching Frequency Internal Threshold Voltage Internal Reference Voltage SET pin input current On Resistance of MOSFET Switch leakage current Voltage High Voltage Low Thermal Resistance Junction-to-Ambient Thermal Resistance Junction-to-Case
VSET=VIN-0.2 ISW=0.4A ON OFF SOP-8L (Note 5) MSOP-8L (Note 5) SOP-8L (Note 5) MSOP-8L (Note 5)
4. Refer to figure 6 for the device derating curve. 5. Test condition for SOP-8L and MSOP-8L: 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.
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500mA LED Step-down Converter
Application Information
LED Current Control The LED current is controlled by the resistor RSET in Figure 1 connected between VIN and SET. The nominal average output current in the LED(s) is defined as:
I LED =
VTHD RSET
If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current is:
ILED =
VCTRL VTHD VREF RSET
LED current Versus RSET and VCTRL
600
500 LED Current [mA]
0.4 0.47 0.56
0.82 1 1.2 0.82 1.5 1 1.2 0.68 0.82 1.5 1 2 1.2 1.5 3 2 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3 3 3 2 LED current @ VCTRL = 0.625V 0.68 LED current @ VCTRL = 1.25V LED current @ VCTRL = 2.5V
400
300 0.47
200
100
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 RSET value [Ohms ]
Figure 3: LED Current setting Vs RSET and VCTRL
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Application Information
Inductor Selection
(Continued)
This section highlights how to select the inductor suitable for the application requirements in terms of switching frequency, LED current accuracy and temperature.
Switching Frequency @ ILED = 500mA
600 47 500 68 100
Frequency [kHz]
400
150 12V - 1 LED 100 220 150 100 220 150 220 470 470 470
300
47 68
24V - 3 LEDs 48V - 6 LEDs
200
100
0 0 50 100 150 200 250 300 350 400 450 500 Inductor Value [uH]
Figure 4: Switching Frequency Vs Inductor Value
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500mA LED Step-down Converter
Application Information
(Continued)
The inductor influences the LED current accuracy that the system is able to provide. The following section highlights how to select the inductor in relation to the device packages and the LED current, while maintaining the chip temperature below 70C.
Figure 5: Minimum recommended inductor with 500mA LED current Capacitor Selection The small size of ceramic capacitors makes them ideal for AP8801 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 2.2F input capacitor is sufficient for most intended applications of AP8801. A 4.7F input capacitor is suggested for application with an input voltage equal or higher than 40V. Diode Selection Schottky diodes, e.g. B1100, with their low forward voltage drop and fast reverse recovery, are the ideal choice for AP8801 applications. PWM Dimming A Pulse Width Modulated (PWM) signal with a max resolution of 8bit, 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 RSET. To achieve this resolution the PWM frequency has to be lower than 500Hz.
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500mA LED Step-down Converter
Application Information
Thermal Considerations
(Continued)
The graph below in figure 6, gives details for power derating. This assumes the device to be mounted on a 25x25mm PCB with 1oz copper standing in still air.
Maximum Power Dis ipation s
1.4 1.2 1
SOP8L
0.8 Power (W ) 0.6
MSOP8L
0.4 0.2 0 0 25 50 75 100 125 150
Ambient Temperature (D C eg )
Figure 6: AP8801 derating curves Package Selection The device comes with a wide selection of packages. The suggested package is able to provide a case temperature below 70C (with an ambient temperature of 25C) for the combination of input voltage and load requested.
Figure 7: Suggested package for a 500mA application
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500mA LED Step-down Converter
Marking Information
(1) SOP-8L
( Top View )
8 5
Logo Part Number
AP8801 YY WW X X
1 4
G : Green YY : Year : 08, 09,10~ WW : Week : 01~52; 52 represents 52 and 53 week X : Internal Code
(2) MSOP-8L
( Top View )
8 Logo Part Number 7 6 5 A~Z : Green Y : Year : 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week
YWX
AP8801
1 2 3 4
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Package Information
(1) Package Type: SOP-8L
(All Dimensions in mm)
3.85/3.95
5.90/6.10
0.10/0.20
0.254 0.62/0.82
Gauge Plane Seating Plane
Detail "A"
7~9 1.30/1.50 1.75max. 0.15/0.25
0.35max. 45
7~9
Detail "A"
0/8
1.27typ 4.85/4.95
0.3/0.5
8x-0.60 5.4 6x-1.27 8x-1.55
Land Pattern Recommendation (Unit: mm)
(2) Package Type: MSOP-8L
8x-0.45 2.9/3.1 4.7/5.1 4.4 6x-0.65 1 0.75/0.95 0.65Bsc. 0.22/0.38 0.15Typ. 0.05/0.15 8x-1.4 Land Pattern Recommendation (Unit:mm) "A" 0/0.15 0.25 Gauge plane
0/8
0.05 2.9/3.1
0.4/0.8 DETAIL "A" 0.95Ref.
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500mA LED Step-down Converter
IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDING 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). 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 unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or 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. LIFE SUPPORT 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 information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright (c) 2009, Diodes Incorporated www.diodes.com
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