11

Video ICs

BA7746S / BA7746FS

(1) preamplifier

The preamplifier in this IC is a high-gain amplifier for

FM audio. This amplifier has been carefully designed

for stability. However, the design of the PCB greatly

effects the stability of the preamplifier. A list of general

precautions are given below. Take note when design-

ing the PCB.

1)The oscillation margin is reduced when the input

and output patterns are physically close.

The input and output wiring should not come out of

the same side of tha IC.

Good example

Bad example

2)The GND pattern should be connected at one point

to the main IC GND (pin 16). In addition, the pream-

plifier input-side GND and output-side GND should

be as close as possible to the main IC GND.

Good example

Bad example

3)A large GND pattern under the IC has a shielding

effect, and reduced the chance of picking up exter-

nal noise.

4)When the preamplifier is connected to a capacitive

load such as shilded wire, or when the output cur-

rent is large, the output may oscillate. In this case,

connect a resistor to the preamplifier output (approx.

390

Ω).

IC

Input

Output

PRE

GND

MAIN

IC

GND

GND

Output

Output

Input

390

REC

PRE

HEAD AMP

BA7746S / FS

BH780XK series

REC

LPF

REC

LPF

MOD

MOD

FM

BPF

DE

MOD

Connection example for BA7746S / BA7746FS and BH780XK series.

Hi-Fi AUDIO

IC

Output

Input

PRE

GND

MAIN

IC

GND

GND

Output

Output

Input