SP6686ER-L/TR View Datasheet(PDF) - Exar Corporation
Part Name
Description
Manufacturer
SP6686ER-L/TR Datasheet PDF : 12 Pages
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SP6686
400mA Buck/Boost Charge Pump LED Driver
0.47μF fly capacitor are typically
recommended. For the input capacitor, a
larger value of 10μF will help reduce input
voltage ripple for applications sensitive to
ripple on the battery voltage. All the
capacitors should be ceramic to obtain low
ESR, which improves bypassing on the input
and output and improves output voltage drive
by reducing output resistance. X5R or X7R
Ceramic capacitors are recommended for most
applications. A selection of recommended
capacitors is included in Table 1. The input and
output capacitors should be located as close to
the VIN and VOUT pins as possible to obtain best
bypassing, and the returns should be
connected directly to the PGND pin or to the
thermal pad ground located under the SP6686.
The fly capacitor should be located as close to
the C1 and C2 pins as possible. The sense
resistor RSENSE is determined by the value
needed in the Torch mode for the desired
output current by the equation:
Where VFB=50mV in torch mode.
Next, the RSET resistor can be selected for
Flash mode using the following equation:
1.26
11.2 Ω
For an example of 150mA Torch mode and
400mA Flash mode, the values RSENSE=0.33Ω,
VFB=135mV (Flash Mode), and RSET=106kΩ are
calculated. The power obtained in the Flash
mode would be:
133
400
53
The typical 0603 surface mount resistor is
rated at 1/10 Watt continuous power and 1/5
Watt pulsed power, more than enough for this
application. For other applications, the PFLASH
can be calculated from the resistor size
selected. The RSENSE resistor is recommended
to be size 0603 for most applications.
EVALUATION BOARD LAYOUT
Once the RSENSE resistor has been selected for
Torch mode, the VFB voltage can be selected
for Flash mode using the following equation:
Where IOUT is for Flash Mode
© 2009 Exar Corporation
9/12
Rev. 2.0.0
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