SGM3140 Datasheet, PDF (8/14 Pages) SG Micro Corp – Charge Pump LED Driver

SGM3140
OPERATION
The SGM3140 is a charge pump regulator designed for
converting a Li-ion battery voltage of 2.7V to 4.2V to drive
a white LED used in digital still camera flash and torch
applications. The SGM3140 has two modes of operation
which are pin selectable for either Flash or Torch. Flash
mode is usually used with a pulse of about 200 to 300
milliseconds to generate a high intensity Flash. Torch can
be used continuously at a lower output current than Flash
and is often used for several seconds in a digital still
camera “movie” mode.
The SGM3140 also has two modes of operation to
control the output current: the 1× mode and 2× mode.
Operation begins after the enable pin EN receives a logic
high, the band-gap reference wakes up after 50μs, and
then SGM3140 goes through a soft-start mode designed
to reduce inrush current. The SGM3140 starts in the 1×
mode, which acts like a linear regulator to control the
output current by continuously monitoring the feedback
pin FB. In 1× mode, if the SGM3140 auto detects a
dropout condition, which is when the FB pin is below the
regulation point for more than 15μs, the SGM3140
automatically switches to the 2× mode. The SGM3140
remains in the 2× mode until one of four things happens:
1) The enable pin EN has been toggled.
2) The FLASH pin has changed from high to low.
3) V_IN is cycled or V_IN is at least 1V above V_OUT.
4) A thermal fault occurs.
500mA Buck/Boost
Charge Pump LED Driver
The 2× 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 SGM3140, which is internally limited to
about 5.5V. In the 2× mode, as in the 1× 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 SGM3140 FB pin is regulated to
47mV output:
V_FB = 47mV (Torch Mode)
When in Flash mode (FLASH = “High”), the FB regulation
voltage is set by the resistor R_SET connected between the
RSET pin and SGND pin with the equation:
V_FB = (1.26V/R_SET) × 10.2kΩ (Flash Mode)
Where 1.26V is the internal band-gap reference voltage
and 10.2kΩ is an internal resistance used to scale the
RSET current. Typical values of R_SET are 42kΩ to 170kΩ
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
SG Micro Corp
8
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