SP6685_06 Datasheet, PDF (12/16 Pages) Sipex Corporation – 700mA Buck/Boost Charge Pump LED Driver

When in Flash mode, (Flash = V_IN), the FB
regulation voltage is set by the resistor R_SET
connected between the R_SET pin and S_GND
and the equation:
V_FB = (1.26V/ R_SET)*11.2KΩ (Flash Mode)
Where 1.26V is the internal bandgap refer-
ence voltage and 11.2KΩ is an internal
resistance used to scale the R_SET current.
Typical values of R_SET are 40KΩ to 180KΩ
for a range of V_FB = 300mV to 75mV in Flash
mode.
The output current is then set in either Flash
or Torch mode by the equation:
I_OUT = V_FB / R_SENSE
_____________O_VERTEMPERATURE
PROTECTION
When the temperature of the SP6685 rises
above 145 degrees Celsius, the over tem-
perature protection circuitry turns off the
output switches to prevent damage to the
device. If the temperature drops back down
below 135 degrees Celsius, the part auto-
matically recovers and executes a soft start
cycle.
__________________O_VERVOLTAGE
PROTECTION
The SP6685 has over voltage protection. If
the output voltage rises above the 5.5V
threshold, the over voltage protection shuts
THEORY OF OPERATION
off all of the output switches to prevent the
output voltage from rising further. When the
output decreases below 5.5V, the device
resumes normal operation.
___________________OVERCURRENT
PROTECTION
The over current protection circuitry moni-
tors the average current out of the V_OUT =
50mV (Torch Mode) pin. If the average
output current exceeds approximately
1Amp, then the over current protection cir-
cuitry shuts off the output switches to pro-
tect the chip.
_____________________COMPONENT
SELECTION
The SP6685 charge pump circuit requires 3
capacitors: 4.7μF input, 1μF output and 1μF
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 sur-
face mount ceramic for low lead inductance
necessary at the 2.4MHz switching frequency
of the SP6685 and to obtain low ESR, which
improves bypassing on the input and output
and improves output voltage drive by reduc-
ing output resistance. Ceramic capacitors
with X5R or X7R temperature grade are
recommended for most applications. A se-
lection of recommended capacitors is in-
cluded in Table 1 below.
Manufacturers
Website
TDK/www.tdk.com
TDK/www.tdk.com
TDK/www.tdk.com
Murata/www.murata.com
Murata/www.murata.com
Murata/www.murata.com
Part Number
C1005X5R0J105M
C1608X5R0J475K
C2012X5R0J106M
GRM155R60J105KE19B
GRM188R60J475KE19
GRM21BR60J106KE19L
Capacitance/
Voltage
1uF/6.3V
4.7uF/6.3V
10uF/6.3V
1uF/6.3V
4.7uF/6.3V
10uF/6.3V
Table 1: Recommended Capacitors
Capacitor
Size/Type/Thickness
0402/X5R/0.5mm
0603/X5R/0.9mm
0805/X5R/1.35mm
0402/X5R/0.55mm
0603/X5R/0.9mm
0805/X5R/1.35mm
ESR at
100KHz
0.03
0.02
0.02
0.03
0.02
0.02
Date: 7/6/06 Rev B
SP6685, 700mA Buck/BoostCharge Pump LED Driver
12
© 2006 Sipex Corporation