SP6685ER-L/TR 데이터 시트보기 (PDF) - Exar Corporation
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SP6685ER-L/TR Datasheet PDF : 14 Pages
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SP6685
700mA Buck/Boost Charge Pump LED Driver
RESISTOR SELECTION
The sense resistor RSENSE is determined by the
value needed in the Torch mode for the
desired output current by the equation:
RSENSE = VFB/IOUT
Where VFB = 50mV (Torch Mode)
Once the RSENSE resistor has been selected for
Torch mode, the VFB voltage can be selected
for Flash mode using the following equation:
VFB = IOUT * RSENSE (Flash Mode)
Where IOUT is for Flash Mode.
Next, the RSET resistor can be selected for
Flash mode using the following equation:
RSET = (1.26V/ VFB)*11.2KΩ (Flash Mode)
For an example of 200mA Torch mode and
600mA Flash mode, the values RSENSE =
0.25Ω, VFB = 150mV (Flash Mode), and RSET
= 94KΩ are calculated. The power obtained in
the Flash mode would be:
PFLASH = VFB *IOUT = 150mV*600mA = 90mW.
The typical 0603 surface mount resistor is
rated 1/10 Watt continuous power and 1/5
Watt pulsed power, more than enough for this
application. For other applications, the PFLASH
power can be calculated and resistor size
selected. The RSENSE resistor is recommended
to be size 0603 for most applications. The
range of typical resistor values and sizes are
shown in table 2.
Part Ref.
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSENSE
RSENSE
RSENSE
RSENSE
RSENSE
Value
68KΩ
75KΩ
82KΩ
91KΩ
100KΩ
110KΩ
120KΩ
130KΩ
140KΩ
150KΩ
0.22Ω
0.27Ω
0.33Ω
0.39Ω
0.47Ω
Tolerance
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
Table 2: Resistor Value and Sizes
Size
0402
0402
0402
0402
0402
0402
0402
0402
0402
0402
0603
0603
0603
0603
0603
EVALUATION BOARD CIRCUIT LAYOUT
© 2009 Exar Corporation
12/14
Rev. 2.0.0
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