AP8801SG [DIODES]
The evaluation board does not have reverse polarity protection;
| 型号： | AP8801SG |
| 厂家： | 
DIODES INCORPORATED |
| 描述： | The evaluation board does not have reverse polarity protection |
| 文件： | 总8页 (文件大小：214K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AP8801EV1 USER GUIDE
DESCRIPTION
The AP8801EV1, Figure 1, is a PCB constructed using an FR4 base for evaluating the AP8801 LED
driver with internal switch in SOP-8L package. The evaluation board can be used to drive an external
choice of LEDs; the total forward voltage across the LEDs depending on the number and type
connected. [1]
The suggested operating voltage for the evaluation board ranges from 8V to 45V maximum.
Higher voltage means lower supply current.
The nominal current for the evaluation board is set at 460mA with a 0R43 sense resistor, R1.
Test point CTRL provides a connection point for DC or PWM dimming and shutdown.
Note: The evaluation board does not have reverse polarity protection
Warning: with 500mA output, the connected LED will be hot and very bright
Figure 1: AP8801EV1 Evaluation Board
AP8801 DEVICE 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 largely 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 eliminates the need for ballast resistors. The AP8801 switches at
frequencies 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.
The device includes the output switch and a current sense circuit, which requires an external sense
resistor to set the nominal current up to 500mA.
Issue 5 – August 2009
© Diodes Incorporated, 2009
www.diodes.com
AP8801EV1
AP8801 DEVICE FEATURES
DEVICE APPLICATIONS
•
•
•
•
Commercial & industrial lighting
Small LCD panel backlighting
Appliance interior lighting
Architecture detail lighting
•
•
•
•
LED driving current up to 500mA
Input voltage from 8V to 48V
High efficiency up to 92%
High switching frequency up to 500KHz
minimum
•
•
•
•
PWM/DC input for dimming control
Built-in soft-start function
Built-in output open-circuit protection
SOP-8L, MSOP-8L are available in “Green”
Molding Compound (No Br, Sb)
Lead Free Finish/RoHS Compliant (Note 1)
•
AP8801 Device Packages, Pin and Definitions
(1) SOP-8L
(2) MSOP-8L
( Top View )
( Top View )
SET 1
8
7
6
5
CTRL
GND
SW
SET 1
8
7
6
5
CTRL
GND
SW
GND
NC
2
3
4
GND 2
AP8801
SOP-8L
AP8801
NC
VIN
3
4
VIN
SW
SW
MSOP-8L
Pin Description
Name
Description
Switch Pin. Connect inductor/freewheeling diode here. Minimize trace area at this pin to reduce
EMI.
SW
GND
SET
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 shut 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 50kΩ, and if the pin is left open VCTRL = VREF
Input Supply Pin. Must be locally bypassed with a capacitor.
No connection
CTRL
VIN
NC
ORDERING INFORMATION
EVALBOARD ORDER
DEVICE ORDER NUMBER
Package
NUMBER
Device
Tape &
Reel
-13
AP8801EV1
S (SOP8L)
M8 (MSOP-8L)
AP8801
Please note: Evaluation boards are subject
to availability and qualified leads.
-13
Issue 5 – August 2009
© Diodes Incorporated 2009
www.diodes.com
2
AP8801EV1
AP8801EV1 EVALUATION BOARD
REFERENCE DESIGN
The AP8801EV1 is an evaluation board configured to be used with the AP8801 in SOP-8L package.
The target application is a driver for one or more series-connected LEDs for luminaires in both
commercial and automotive applications.
The suggested maximum operating voltage for the evaluation board is 45V, and a 0R43 sense
resistor R1 sets the nominal current at 460mA.
An accurate way of determining the current, avoiding the need to insert an ammeter in the current
path, is to measure the voltage on the sense resistor. A 10K resistor and a 1uF capacitor can be used
to form a low pass filter and the voltage across the capacitor represents a more stable dc reading of
current. Using this method, 200mV represents 0.46 Amp when using a 0R43 sense resistor.
The CTRL pin connects to a low pass filter within the AP8801 chip to provide some decoupling, but
the external capacitor C2 (100nF) is used to provide additional decoupling to reduce any high
frequency noise as well as providing soft start function.
Both DC and PWM dimming can be achieved by driving the CTRL pin. For DC dimming, the CTRL pin
may be driven between 0.3V and 1.25V. Driving the CTRL pin below 0.2V will shut down the output
current. For PWM dimming, an external open-collector NPN transistor or open-drain N-channel
MOSFET can be used to drive the CTRL pin. The PWM frequency can be around 100Hz to 1kHz.
For better resolution, PWM capacitor C2 should be removed on the evaluation board, to give a more
accurate duty cycle.
Shorting R2 will connect the test pin CTRL to device pin CTRL if needed. The external capacitor C2
on the CTRL pin sets the soft start time. The amount of soft start time achievable is approximately
0.2ms/nF.
For other reference designs or further applications information, please refer to the AP8801 datasheet.
Issue 5 – August 2009
© Diodes Incorporated 2009
www.diodes.com
3
AP8801EV1
AP8801 OPERATION
In normal operation, when voltage is applied at VIN, the AP8801’s internal NDMOS switch is turned
on. Current starts to flow through sense resistor R1, inductor L1, and the LED(s). The current ramps
up linearly. The ramp rate is determined by the input voltage VIN and inductor L1. This rising current
produces a voltage ramp across R1. The internal circuit of the AP8801 senses this voltage and
applies a proportional voltage to the input of the internal comparator. When this voltage reaches an
internally set upper threshold, the NDMOS switch is turned off. The inductor current continues to flow
through R1, L1, LED(s), Schottky diode D1, and back to the supply rail. The current decays, with the
rate of decay determined by the forward voltage drop of the LEDs and the Schottky diode. This
decaying current produces a falling voltage at R1 which is sensed by the AP8801. A voltage
proportional to the sense voltage across R1 is applied at the input of the internal comparator. When
this voltage falls to the internally set lower threshold, the NDMOS switch is turned on again. This
switch-on-and-off cycle continues to provide an average current (set by the sense resistor R1) to the
LEDs. Please refer to the datasheet for the threshold limits, AP8801 internal circuits, electrical
characteristics and parameters.
AP8801EV1 Evaluation Board - BOM
Ref
U1
Value
AP8801
Package
SOP-8L
Part Number
AP8801SG
Manufacturer
DIODES inc
Notes
DC-DC
converter
Schottky
diode
D1
100V, 2A
SMB
B2100
DIODES inc
R1
0R43
1206
SR732BTTDR430F
Generic
KOA
+/-1%,
+/-100ppm
R2
C1
0R0
4.7uF 50V
0805
1210
Generic
-
+/-1%
+/-10%
C1210C475K5RAC
GRM32ER71H475K
Not fitted
Kemet
Murata
--
Kemet
NIC
Kemet
Murata
NIC
Coilcraft
NIC
C2
C3
-
-
-
100nF, 100V
0805
C0805C104K1RAC
NMC0805X7R104K100
C1206C104K1RAC
GRM319R72A104K
NMC1206X7R104K100
MSS1038-683ML
NPIS104F680MTRF
NPIS24H680MTRF
+/-10%
C4
L1
100nF, 100V
68uH
1206
-
+/-10%
68uH
NIC
The FR4 PCB design, with adequate copper top and bottom and plated through vias for thermal
coupling, guarantees a good thermal dissipation for the AP8801 device. Other sources of heat are the
Schottky diode, the inductor and the sense resistor, therefore care must be taken in their placement.
Warning: At 45V operation with 500mA output, the board temperature rises by around 60C
from ambient after 30 minutes of operation.
Issue 5 – August 2009
© Diodes Incorporated 2009
www.diodes.com
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AP8801EV1
Figure 3: Component layout and circuit board view
AP8801EV1 Connection Point Definition
Name
VIN
GND
Description
Positive supply voltage.
Supply Ground (0V).
CTRL
Internal voltage ref. pin (1.25V). This pin can be used to achieve dimming and
soft-start, and for switching the output current off.
•
•
Leave floating for normal operation.
See 'Circuit Features' section to achieve dimming, soft-start and for
switching the output current off.
LED A
LED K
LED A connects tCo4the external LED anode
LED K connects to the external LED cathode
AP8801EV1 BASIC OPERATION AT FULL VOLTAGE
1. Connect external LEDs across test pins ‘LED A’ (anode) and ‘LED K’ (cathode). The number
of external LEDs that can be connected depends on their operating power and forward
voltage drop, but typically 12 x 3.2V LEDs can be connected using a 45V rail. For an external
load other than LEDs, the positive terminal of the load should be connected to the anode and
the negative to the cathode.
2. Connect VIN and GND.
Warning: The board does not have reverse battery/supply protection.
3. Set the PSU to the desired input voltage (usually between 12V and 45V)
4. Turn on the PSU. The external LEDs will illuminate and the current should be approximately
500mA
5. The switching waveform on the SW pin can be acquired using the test point J1
Warning: Do not stare at the LEDs directly.
Issue 5 – August 2009
© Diodes Incorporated 2009
www.diodes.com
5
AP8801EV1
CIRCUIT FEATURES
N.B. Remove power whilst changing components!
Soft-start
1. The AP8801 has a in-built soft start function. A capacitor, C2 may be fitted to the evaluation
board to increase the soft start time by slowing the rise time of the adjust pin at start-up at the
rate of 0.2ms/nF. The board is supplied with a zero-ohm resistor in position R2. Please see
the data sheet for further details.
PWM
1. Remove the soft start capacitor C2
2. Refer to the datasheet for instructions on how to perform PWM
Switching off the output current
3. Shorting the CTRL pin to GND will cause the LED current to go to zero. Releasing this pin will
switch on the system (creating a soft-start power up sequence if the C2 capacitor is used).
Changing the LED current
1. refer to the datasheet for the derating curve and the power dissipation capability of the
package
2. Remove R1
3. Calculate and fit a new sense resistor, R1, the value of which is based on the required LED
current without dimming. R1 can be calculated using following equation :
R1= 0.2V / ILED where ILED = the LED current.
R1 = the sense resistors value in ohms.
0.2V is the nominal sense voltage with CTRL open circuit or
set to 1.25V.
PERFORMANCE
The system efficiency depends on the sense resistor, supply voltage, switching inductor, and the
number of LEDs.
With a 45V supply and 12 LEDs, the switching frequency is typically 320 kHz and efficiency levels
>90% are achievable.
Visit our website www.diodes.com to find useful tools for circuit design and simulation.
REFERENCE
[1] AP8801 Datasheet – www.diodes.com
Issue 5 – August 2009
© Diodes Incorporated 2009
www.diodes.com
6
AP8801EV1
INTENTIONALLY BLANK
Issue 5 – August 2009
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7
AP8801EV1
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Copyright © 2009, Diodes Incorporated
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