refer to test circuit unless otherwise specified) (continued)

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

K1

Parabola Coefficient

=

, see Figure 2

0.28

Parabola Coefficient

=

, see Figure 2

0.71

– 40

40

mV

Current Source

S1

→ b

100

µA

Saturation Voltage

Io = 400 mA Sink

S2

→ b1

2

V

Saturation Voltage

Io = 100 mA Source

S2

→ cS1 → b

0.8

1.5

V

Forward Voltage

S2

→ dS1 → b

1.2

1.7

V

Frame Sawtooth Current

66

µA

7

R7

R6

10k

Ω

10k

Ω

R2

R8

20k

Ω

a

b

S1

R3

11k

Ω

10k

Ω

R1

S2

a

b

c

d

TDA4950

V

S

V

F

V

SATH

I

O

V

SATL

I

F

-I

O

I

FR

V

REF

V

FR

6

5

8

4

3

1

2

Figure 1 : Test CIrcuit

-60

0

15

30

36

60

V

7F

V

7A

V

7B

V

7C

V

7D

V

7E

V

I

Figure 2 : Parabola Characteristics

CIRCUIT OPERATION

(see the shematic diagram)

A differential amplifier OP1 is driven by a vertical

frequency sawtooth current of

± 33µA which is

produced via an external resistor from the sawtooth

voltage. The non-inverting input of this amplifier is

connected with a reference voltage corresponding

to the DC level of the sawtooth voltage. This DC

voltage should be adjustable for the keystone cor-

rection. The rectified output current of this amplifier

drives the parabola network which provides a para-

bolic output current. This output current produces

the corresponding voltage due to the voltage drop

across the external resistor at pin 7.

If the input is overmodulated (> 40

µA) the internal

current is limited to 40

µA. This limitation can be

used for suppressing the parasitic parabolic current

generated during the flyback time of the frame

sawtooth.

A comparator OP2 is driven by the parabolic cur-

rent. The second input of the comparator is con-

nected with a horizontal frequency sawtooth

voltage the DC level of which can be changed by

the external circuitry for the adjustment of the pic-

ture width.

The horizontal frequency pulse-width modulated

output signal drives the final stage. It consists of a

class D push-pull output amplifier that drives, via

an external inductor, the diode modulator.

TDA4950

3/5