ACT6311
Rev 3, 22-Feb-11
ERROR
AMPLIFIER
Figure 3. Functional Block Diagram
FUNCTIONAL DESCRIPTION
The ACT6311 is a high efficiency step-up DC/DC
converter that employs a current-mode, fixed
frequency pulse-width modulation (PWM)
architecture with excellent line and load regulation.
Figure 3 shows the functional block diagram of the
IC. The flip-flop is set at the start of each oscillator
cycle, and turns on the power switch. During this on
time, the switch current level is sensed and added
to a ramp signal, and the resulting sum is compared
with the output of the error amplifier. If the error
comparator output is high, the flip-flop is reset and
the power switch turns off. Thus, the peak inductor
current level is controlled by the error amplifier
output, which is integrated from the difference
between FB input and the 1.24V reference point.
The ACT6311 operates at a constant switching
frequency for output current higher than 4mA. If the
output current decreases further, the IC will enter
frequency modulation mode, resulting in some low
frequency ripple.
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