ML4833

8

The oscillator frequency is determined by the following

equations:

F

tt

OSC

CHG

DIS

=

+

1

(3)

and

tR C In

VI

R

V

VI

R

V

CHG

T T

REF

CH

T

TL

REF

CH

T

TH

=

+−

+−









(4)

where:

F

RC

OSC

TT

≅

×

1

051

.

(5)

Figure 4 shows the output configuration for the

operational transconductance amplifiers.

CURRENT

MIRROR

IN

OUT

CURRENT

MIRROR

IN

OUT

IQ +

2

IQ –

2

Figure 4. Output Configuration

transconductance amplifiers will introduce an offset error.

The magnitude of the offset voltage that will appear at the

of 0.05 µ

Capacitor C1 as shown in Figure 3 is used to block the

DC current to minimize the adverse effect of offsets.

Slew rate enhancement is incorporated into all of the

operational transconductance amplifiers in the ML4833.

This improves the recovery of the circuit in response to

power up and transient conditions. The response to large

signals will be somewhat non-linear as the transconductance

amplifiers change from their low to high transconductance

mode. This is illustrated in Figure 5.

Linear Slope Region

0

Figure 5. Transconductance Amplifier Characteristics

BALLAST OUTPUT SECTION

The IC controls output power to the lamps via frequency

modulation with non-overlapping conduction. This means

that both ballast output drivers will be low during the

OSCILLATOR

The VCO frequency ranges are controlled by the output

to increase, thereby causing the oscillator frequency to

increase. Since the ballast output network attenuates high

frequencies, the power to the lamp will be decreased.

17

+

–

1.25/3.75

7

CONTROL

5.5mA

CLOCK

Figure 6. Oscillator Block Diagram and Timing