LA7577N

No. 4037—10/16

RF AGC Variable Resistor (Pin 4)

The operating point of the RF AGC can be adjusted using

a variable resistor connected to pin 4 as shown in Figure

11. When pin 4 is pulled to 0.5V or lower, both the FM

and video outputs are muted.

VIF Input (Pins 5 and 6)

The VIF amplifier inputs on pins 5 and 6 should be capac-

itively coupled to block DC. The input signal is the aver-

age of the signals on these inputs. The input resistance is

approximately 1.5k

Ω and the input capacitance is approxi-

mately 3pF.

1st SIF Input (Pin 8)

The 1st SIF amplifier input on pin 8, shown in Figure 13,

should be capacitively coupled to block DC. If a SAW fil-

ter is used, an inductor should also be connected as shown

in Figure 14. This matches the SAW filter output capaci-

tance to the LA7577N input capacitance and increases the

sensitivity. The inductor typically would be 0.62

µH (for

Japan), 1.0

µH (for the USA) or 1.3µH (for PAL countries).

Figure 11. RF AGC adjustment

Figure 12. VIF stage

RF AGC Output (Pin 10)

The RF AGC output on pin 10 is an emitter follower with a

200

Ω series protection resistor as shown in Figure 15. The

value of the bleeder resistor connected between pin 10 and

the tuner, shown in Figure 16, should be chosen based on

the tuner maximum gain.

Figure 13. 1st SIF stage

Figure 14. SAW filter matching

Figure 15. RF AGC output

Figure 16. Bleeder resistor connection