L6699DTR STMicroelectronics, L6699DTR Datasheet - Page 13

• Manufacturer Part Number: L6699DTR
• Description: AC/DC Switching Converters Enhanced High Volt Res CTRL 600V
• Manufacturer: STMicroelectronics

Specifications of L6699DTR

• Product Category: AC/DC Switching Converters

L6699
6.1
Oscillator
The oscillator is programmed externally by means of a capacitor (CF), connected from pin 3
(CF) to ground, that is alternately charged and discharged by the current defined with the
network connected to pin 4 (
2 mA source capability; the higher the current sourced by the pin, the higher the oscillator
frequency. The block diagram of
operation.
The network that loads the
1.
2.
3.
Figure 5.
The following approximate relationships hold for the minimum and the maximum oscillator
frequency respectively:
Equation 1
a resistor
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 modulates the current
through this branch - therefore modulating the oscillator frequency - to perform output
voltage regulation; the value of RFmax determines the maximum frequency the half
bridge is operated at when the phototransistor is fully saturated.
an R-C series circuit (C
the setting up of a frequency shift at startup (see
Note that the contribution of this branch is zero during steady-state operation.
Oscillator's internal block diagram
RF
f
min
min
=
connected between the pin and ground that determines the minimum
· 3
CF
RF
SS
RF
1
·
Doc ID 022835 Rev 2
min
+ R
RF
min
Figure 5
pin generally comprises three branches:
). The pin provides an accurate 2 V reference with about
min
SS
) connected between the pin and ground that enables
;
shows a simplified internal circuit that explains the
f
max
=
· 3
CF
Section 6.3: Safe-start procedure
·
(
RF
1
min
//
Application information
RF
max
)
13/38
).