Functional description L5986
The L5986 device is based on a “voltage mode”, constant frequency control. The output voltage V
OUT
is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing an error signal that, compared to a fixed frequency sawtooth, controls the ON and
OFF time of the power switch.
The main internal blocks are shown in the block diagram in
Figure 3
. They are:
A fully integrated oscillator that provides sawtooth to modulate the duty cycle and the synchronization signal. Its switching frequency can be adjusted by an external resistor.
The voltage and frequency feedforward are implemented.
The soft-start circuitry to limit inrush current during the startup phase
The voltage mode error amplifier
The pulse width modulator and the relative logic circuitry necessary to drive the internal power switch
The high-side driver for embedded P-channel Power MOSFET switch
The peak current limit sensing block, to handle overload and short-circuit conditions
A voltage regulator and internal reference. It supplies internal circuitry and provides a fixed internal reference.
A voltage monitor circuitry (UVLO) that checks the input and internal voltages
A thermal shutdown block, to prevent thermal runaway.
Figure 3. Block diagram
8/42 DocID14971 Rev 5
