SP6685_06 Datasheet, PDF (13/16 Pages) Sipex Corporation – 700mA Buck/Boost Charge Pump LED Driver

The input and output capacitors should be
located as close to the V_IN and V_OUT pins as
possible to obtain best bypassing, and the
returns should be connected directly to the
P_GND pin or to the thermal pad ground located
under the SP6685. The fly capacitor should
be located as close to the C1 and C2 pins as
possible. See typical circuit layout (page 13)
for details on the recommended layout.
COMPONENT SELECTION
for Torch mode, the V_FB voltage can be
selected for Flash mode using the following
equation:
V_FB = I_OUT * R_SENSE (Flash Mode) where I_OUT is
for Flash Mode.
Next, the R_SET resistor can be selected for
Flash mode using the following equation:
To obtain lower output ripple, the C_OUT value
can be increased from 1μF to 2.2μF or 4.7μF
R_SET = (1.26V/ V_FB)*11.2KΩ (Flash Mode)
with a corresponding decrease in output For an example of 200mA Torch mode and
ripple as shown in the Typical Performance
Characteristic curves. For output currents of
500mA to 700mA, the recommended C_FC fly
capacitor value of 1μF should be used. Out-
600mA Flash mode, the values R_SENSE =
0.25Ω, V_FB = 150mV (Flash Mode), and R_SET
= 94KΩ are calculated. The power obtained
in the Flash mode would be:
put currents in Flash of 100mA to 400mA
can use a 0.47μF C_FC but a minimum 1μF
P_FLASH = V_FB *I_OUT = 150mV*600mA = 90mW.
C_OUT is still needed.
_______________________ RESISTOR
SELECTION
The typical 0603 surface mount resistor is
The sense resistor R_SENSE is determined by
the value needed in the Torch mode for the
desired output current by the equation:
R_SENSE = V_FB/ I_OUT where V_FB = 50mV (Torch
Mode)
rated 1/10 Watt continuous power and 1/5
Watt pulsed power, more than enough for
this application. For other applications, the
P_FLASH power can be calculated and resistor
size selected. The R_SENSE resistor is recom-
mended to be size 0603 for most applica-
tions. The range of typical resistor values
Once the R_SENSE resistor has been selected
and sizes are shown here in Table 2.
Part Reference
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSET
RSENSE
RSENSE
RSENSE
RSENSE
RSENSE
Value
68k
75k
82k
91k
100k
110k
120k
130k
140k
150k
0.22
0.27
0.33
0.39
0.47
Tolerance
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
5%
Size
0402
0402
0402
0402
0402
0402
0402
0402
0402
0402
0603
0603
0603
0603
0603
Manufacturers
any
any
any
any
any
any
any
any
any
any
Panasonic or Vishay
Panasonic or Vishay
Panasonic or Vishay
Panasonic or Vishay
Panasonic or Vishay
Table 2: Resistor values and sizes
Date: 7/6/06 Rev B
SP6685, 700mA Buck/BoostCharge Pump LED Driver
13
© 2006 Sipex Corporation