AL8807AEV3 データシートの表示（PDF） - Diodes Incorporated.
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AL8807AEV3 Datasheet PDF : 8 Pages
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AL8807AEV3
AL8807A Operation
In normal operation, when a voltage is applied at +Vin, the AL8807A internal NDMOS switch is turned
on. Current starts to flow through sense resistor R1, inductor L1, and the LED. The current ramps up
linearly, the ramp rate being determined by the input voltage +Vin and the inductor L1. This rising
current produces a voltage ramp across R1. The internal circuit of the AL8807A senses the voltage
across R1 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, the LED and the Schottky diode D1, and back to the supply
rail, but it 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
AL8807A. 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 the average LED current set by the sense
resistor R1. Please refer to the datasheets for the threshold limits, AL8807A internal circuits, electrical
characteristics and parameters.
AL8807AEV3 Component list
Ref
U1
D1
R1
R2
R3
C1, C5
C2, C3
C4
C6, C7,
C8, C9
C12
C10, C11
L1
Value
AL8807A
60V, 2A
0R1
Package
MSOP
1206
1k0
4.7uF 50V
100nF, 100V
0805
1210
0805
1uF 100V
1206
0805
1n5, 100V
68uH
0805
Part Number
AL8807AMP-13
DFLS260
NOT FITTED
C1210X475K5RAC
NMC0805X7R104K100 PF
GRM21BR71H104KA01L
NMC1206X7R104K100
NOT FITTED
MSS1038-683ML
NPIS24H680MTRF
NPIS104F680MTRF
Manufactu
rer
Diodes
Zetex
Diodes
Zetex
Generic
Generic
Generic
KEMET
Generic
NIC Comps
MURATA
Generic
NIC Comps
Generic
Generic
Coilcraft
NIC Comps
Notes
DC-DC converter
Schottky diode
1% 250mW
Fit with R1 to
adjust LED
current if
required
1% 125mW
X7R
X7R
X7R
Fit to improve
EMC
performance if
required
C0G
Note: The component part numbers are correct at the time of publication. Diodes Inc reserves the
right to substitute other parts where necessary, without further notification.
Issue 2 – October 2012
© Diodes Incorporated 2012
4
www.diodes.com
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