808

Audio ICs

BA6800AF

FCircuit operation

(1)

Input block

The AC input pins are pins 1 and 3, and the DC input pins

are pins 5 and 6. Pin 7 is used to switch between the AC

and DC inputs. When the input to pin 7 is “H”, AC input

is selected (pins 1 and 3). Therefore, by using pin 7 to

switch between the AC and DC modes, the IC can do two

jobs. For example, pins 1 and 3 can be used for audio sig-

nal input, and pins 5 and 6 can be used as the input for

the signal meter output from a tuner (DC).

The AC input impedance of pins 1 and 3 is a low 250

Ω

ries with the inputs to adjust the sensitivity and ch1 and

ch2 balance.

(2)

Peak hold circuit

The BA6800AF have peak hold circuits that temporarily

holds peak signal levels in AC input mode.

The peak hold function can be used with the upper 12

points (5 to 16). The peak hold time depends on the oscil-

lator frequency. It is 2 sec. (Typ.) for an oscillator frequen-

cy of 2kHz.

DC mode does not have a peak hold function.

(3)

Grid output

The pin 9 and 10 grid outputs are open-collector NPN

transistors. The logic is active low (the fluorescent tube

lights when the output is “L”), so connect two PNP tran-

circuit to drive the fluorescent tubes (see Fig. 3).

(4)

Segment output block

Pins 11 to 26 are the segment outputs. The output circuits

are open-collector PNP transistors. When grid 1 is “L”,

the ch1 level is output (pin 1 or 5 input level), and when

grid 2 is “L”, the ch2 level is output (pin 3 or 6 input level).

Refer to Fig. 4.

(5)

Grid and segment output timing chart. The grid and

segment output timing for an oscillator frequency of 2kHz

is shown in Fig. 5.

(6)

Attack and release times

The response characteristic for AC input signals is set by

Ω and

µF, the attack time is about 4ms, and the release

time is about 1sec. (same for ch2).

Attack time

: Time for the voltage on pins 2 and 4

to rise from 1V to 2.5V when the in-

put goes from no input to 2.6Vrms,

then back to no input.

Release time : Time for the voltage on pins 2 and 4

to fall from 2.5V to 1V when the input

goes from 2.6Vrms to no input.

(7)

Oscillator frequency

termine the oscillator frequency.

are related as follows :