SP6685 Datasheet, PDF (8/10 Pages) Sipex Corporation – Charge Pump LED Driver For Camera Flash

The SP6685 charge pump circuit requires 3
capacitors: input, output and fly capacitor,
and a 1µ F value is typically recommended.
For the input capacitor, a larger value of
2.2µ F or 4.7µ F will help reduce input volt-
age 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
capacitors is included in Table 1. 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 as possible 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_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:
R_SET = (1.26V/ V_FB)*11.2KΩ (Flash Mode)
For an example of 200mA Torch mode and
600mA Flash mode, the values R_SENSE =
0.25Ω, V_FBREF = 150mV (Flash Mode), and
R_SET = 88.7K are calculated. The power
obtained in the Flash mode would be:
P_FLASH = V_FB *I_OUT = 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
P_FLASH can be calculated from the resistor
size selected. The R_SENSE resistor is recom-
mended to be size 0603 for most applica-
tions.
Part Reference
U1
CIN
COUT, CF
RSET
RSENSE
Part Number
SP6685ER
GRM188R0J475KE19
GRM155R60J105KE19B
-
-
Value
4.7uF/6.3V
1uF/6.3V
88.7K
0.22ohms
Size
3x3mm DFN - 10 pin
0603/X5R/0.9mm ht
0402/X5R/0.5mm ht
0402
0603
Manufacturers/ Website
Sipex/www.sipex.cpm
Murata/www.murata.com
Murata/www.murata.com
any
any
Date: 12/15/04
SP6685 Charge Pump LED Driver for Camera Flash
8
© Copyright 2004 Sipex Corporation