Typical industrial TL ballasts requires complex

control with dimming or automation interface.

Here the L6569 is a driver between the power

and control blocks. To use it with an external os-

cillator, pin CF is used as an 0-12V logic input,

and the L6569 becomes a high voltage buffer.

Applications with power above 150W require a full

bridge inverter. Figure 6 shows how two L6569

drive such a MOSFET bridge. If no external con-

trol is required, the first L6569 master can control

the switching with its oscillator, and synchronizes

the other driver as (slave).

The L6569 start up

Two versions of the L6569 are available with dif-

ferent start up characteristics. The L6569 drives

the lower MOSFET ON at power-up until the sup-

ply voltage reaches the Under Voltage Lock Out.

The bootstrap capacitor is precharged to 4.6V

and both the lower and the upper MOSFETs will

switch immediately with the oscillator. This is in-

tended for inverters which use only one DC block-

ing capacitor connected to the power ground, as

shown on figure 4 for CFL ballast.

CHARGE PUMP CIRCUIT

LOGIC

L6569

600V

120

Ω

ON

15.6 V

ON

Figure 5: Bootstrap capacitor charge.

L6569

47

47

EXTERNAL

OSCILLATOR

STB9NK50Z

100nF

HV

RF

CF

GND

D02IN1386

L6569

47

47

100nF

BOOT

HVG

OUT

LVG

BOOT

HVG

OUT

LVG

RF

CF

GND

Figure 6: Basic diagram for 2x105 W lamp ballast in full bridge configuration.

AN880 APPLICATION NOTE

3/14