AP8802EV2 Ver la hoja de datos (PDF) - Diodes Incorporated.
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AP8802EV2 Datasheet PDF : 8 Pages
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AP8802EV2
VIN 8V ~ 48V DC
CTRL
R2
C2 C1
C3
VIN
SET
AP8802
C4
R1
D1
GND
GND
L1
SW
AP8802 OPERATION
Figure 2: Schematic of the Evaluation Board
In normal operation, when voltage is applied at VIN, the AP8802’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 rate being determined by the input voltage VIN and inductor L1. This rising current
produces a voltage ramp across R1. The internal circuit of the AP8802 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, the 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 AP8802. 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, AP8802 internal circuits, electrical
characteristics and parameters.
AP8802EV2 EVALUATION BOARD - BILL OF MATERIALS
Ref
Value
Package
Part Number
Manufacturer
Notes
U1
AP8802
SOP8LEP
AP8802SPG
DIODES inc
DC-DC
converter
D1
100V, 2A
SMB
B2100
DIODES inc Schottky
diode
R1
0R2
1206
SR732ETTDR200F
KOA
+/-1%,
+/-100ppm
R2
0R0
0805
Generic
-
+/-1%
C1
4.7uF 50V
1210
C1210X475K5RAC
KEMET
X7R +/-10%
GRM32ER71H475KA88L
Murata
C2
-
-
Not Fitted
-
-
C3 100nF,100V
0805
Generic
-
X7R +/-20%
C4 100nF 100V
1206
Generic
-
X7R +/-20%
L1
68uH
-
MSS1038-683ML
Coilcraft
68uH
NPIS104F680MTRF
NIC
NPIS24H680MTRF
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 AP8802 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 1A output, the board temperature rises by around 60C from
ambient after 30 minutes of operation.
Issue 5 August 2009
© Diodes Incorporated 2009
4
www.diodes.com
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