SP6685 Datasheet, PDF (11/14 Pages) Sipex Corporation – Charge Pump LED Driver For Camera Flash

SP6685
700mA Buck/Boost Charge Pump LED Driver
In the Torch mode, (Flash = GND) the Flash
pin is set to logic low and the SP6685 IFB pin
regulates to 50mV output:
current exceeds approximately 1Amp, then
the over current protection circuitry shuts off
the output switches to protect the chip.
V_FB = 50mV
(Torch Mode)
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 the 1.26V is the internal bandgap
reference voltage and the 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
OVERTEMPERATURE PROTECTION
When the temperature of the SP6685 rises
above 145°C, the over temperature protection
circuitry turns off the output switches to
prevent damage to the device. If the
temperature drops back down below 135°C,
the part automatically recovers and executes a
soft start cycle.
OVERVOLTAGE PROTECTION
The SP6685 has over voltage protection. If the
output voltage rises above the 5.5V threshold,
the over voltage protection shuts 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 monitors
the average current out of the V_OUT = 50mV
(Torch Mode) pin. If the average output
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 surface
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 reducing
output resistance. Ceramic capacitors with
X5R or X7R temperature grade are
recommended for most applications. A
selection of recommended capacitors is
included in Table 1 below.
Manufacturer Part Number
Value Size/Type
muRata
muRata
muRata
GRM155R60J105K 1µF/6.3V
GRM188R60J475K 4.7µF/6.3V
GRM21BR60J106K 10µF/6.3V
0402/X5R
0603/X5R
0805/X5R
Table 1: Recommended Capacitors
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.
To obtain lower output ripple, the C_OUT value
can be increased from 1μF to 2.2μF or 4.7μF
with a corresponding decrease in output 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. Output
currents in Flash of 100mA to 400mA can use
a 0.47μF C_Fc but a minimum 1μF C_OUT is still
needed.
© 2009 Exar Corporation
11/14
Rev. 2.0.0