SP6685 Datasheet, PDF (7/10 Pages) Sipex Corporation – Charge Pump LED Driver For Camera Flash

regulation point for more than 32 cycles of
the internal clock, the SP6685 automati-
cally switches to the 2X mode. The SP6685
remains in the 2X mode until one of four
things happens: the enable pin EN has
been toggled, the Flash pin has changed
from high to low, V_IN is cycled or a thermal
fault occurs. The 2X mode is the charge
pump mode where the output can be pumped
as high as two times the input voltage,
provided the output does not exceed the
maximum voltage for the SP6685, which is
internally limited to about 4.3V. In the 2X
mode, as in the 1X mode, the output current
is regulated by the voltage at the FB pin.
In the Torch mode, (Flash = GND) the Flash
pin is set to logic low and the SP6685 FB pin
regulates to 50mV output:
THEORY OF OPERATION
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 100K to 500K for
a range of V_FB = 150mV to 30mV in Flash
mode.
The output current is then set in either Flash
or Torch mode by the equation:
I_OUT = V_FB / R_SENSE
V_FB = 50mV (Torch Mode)
OVERTEMPERATURE PROTECTION
When the temperature of the SP6685 rises above 145 degrees Celsius, the over temperature
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 automatically recovers
and executes a soft start cycle.
OVERVOLTAGE PROTECTION
The SP6685 has over voltage protection. If the output voltage rises above the 4.3V 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 4.3V, 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 current exceeds approximately 1Amp, then the over
current protection circuitry shuts off the output switches to protect the chip.
Date: 12/15/04
SP6685 Charge Pump LED Driver for Camera Flash
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© Copyright 2004 Sipex Corporation