SP6686 Datasheet, PDF (10/13 Pages) Sipex Corporation – 400mA Buck/Boost Charge Pump LED Driver

The SP6686 charge pump circuit requires 3
capacitors: 4.7µF input, 1µF output and
0.47µF fly capacitor are typically recom-
mended. 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 reduc-
ing output resistance. X5R or X7R Ceramic
capacitors are recommended for most ap-
plications. A selection of recommended ca-
pacitors is included in Table 1. The input
and output capacitors should be located as
close to the V_IN and V_OUTpins 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 SP6686. The fly capacitor should be
located as close to the C1 and C2 pins as
possible.
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)
COMPONENT SELECTION
Once the R_SENSE resistor has been selected
for Torch mode, the V_FB voltage can be
selected for Flash mode using the following
equation:
V = I *R (Flash Mode) where I is
FB OUT SENSE
OUT
for Flash Mode
Next, the R_SET resistor can be selected for
Flash mode using the following equation:
R_SET = (1.26V/ V_FB)*11.2KΩ (Flash Mode)
For an example of 150mA Torch mode and
400mA Flash mode, the values R =
SENSE
0.33Ω, V_FB = 135mV (Flash Mode), and R_SET
= 106KΩ are calculated. The power ob-
tained in the Flash mode would be:
P_FLASH = V_FB *I_OUT = 133mV*400mA = 53mW.
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 P_FLASH can be calculated from the resis-
tor size selected. The R_SENSE resistor is
recommended to be size 0603 for most
applications.
Manufacturers/ Website
TDK/www.tdk.com
TDK/www.tdk.com
TDK/www.tdk.com
TDK/www.tdk.com
Murata/www.murata.com
Murata/www.murata.com
Murata/www.murata.com
Murata/www.murata.com
Part Number
C1005X5R0J474K
C1005X5R0J105K
C1608X5R0J225K
C1608X5R0J475K
GRM155R60J474KE19D
GRM155R60J105KE19D
GRM188R60J225KE19D
GRM188R60J475KE19D
Capacitance/
Voltage
0.47uF/6.3V
1uF/6.3V
2.2uF/6.3V
4.7uF/6.3V
0.47uF/6.3V
1uF/6.3V
2.2uF/6.3V
4.7uF/6.3V
Capacitor
Size/Type/Thickness
0402/X5R/0.55mm
0402/X5R/0.55mm
0603/X5R/0.9mm
0603/X5R/0.9mm
0402/X5R/0.55mm
0402/X5R/0.55mm
0603/X5R/0.8mm
0603/X5R/0.8mm
ESR at
100KHz
0.03
0.03
0.03
0.02
0.03
0.03
0.03
0.02
Table 1: Recommended Capacitors
Date: 03/10/06
SP6686 400mA, Buck/Boost Charge Pump LED Driver
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