L6599A STMicroelectronics, L6599A Datasheet - Page 18

• Manufacturer Part Number: L6599A
• Description: IMPROVED HIGH-VOLTAGE RESONANT CONTROLLER
• Manufacturer: STMicroelectronics

Specifications of L6599A

• Two-level Ocp: frequency-shift and latched shutdown

Application information
7.1
18/36
Figure 21. Typical system block diagram
Oscillator
The oscillator is programmed externally by means of a capacitor (CF), connected from pin 3
(CF) to ground, that will be alternately charged and discharged by the current defined with
the network connected to pin 4 (RFmin). The pin provides an accurate 2 V reference with
about 2 mA source capability and the higher the current sourced by the pin is, the higher the
oscillator frequency will be. The block diagram of
circuit that explains the operation.
The network that loads the RFmin pin generally comprises three branches:
1.
2.
3.
A resistor RFmin connected between the pin and ground that determines the minimum
operating frequency;
a resistor RFmax connected between the pin and the collector of the (emitter-
grounded) phototransistor that transfers the feedback signal from the secondary side
back to the primary side; while in operation, the phototransistor will modulate the
current through this branch - hence modulating the oscillator frequency - to perform
output voltage regulation; the value of RFmax determines the maximum frequency the
half-bridge will be operated at when the phototransistor is fully saturated;
an R-C series circuit (CSS+RSS) connected between the pin and ground that enables
to set up a frequency shift at start-up (see
contribution of this branch is zero during steady-state operation.
Doc ID 15308 Rev 5
Section 7.3:
Figure 22
shows a simplified internal
Soft-start). Note that the
L6599A