669

Audio ICs

BA6820F / BA6822S / BA6822F

These are open-collector outputs that drive the LEDs

(see Fig. 5).

(pin 21) is as follows: if the channel 1 input is higher than

comparator level 1 during the first-point period for chan-

nel 1, a “L” level is output. Next, if the channel 1 input is

higher than comparator level 2 during the second-point

period for channel 1, a “L” level is output, if the channel

2 input is higher than comparator level 1 during the first-

point period for channel 2, a “L” level is output, and then

if the channel 2 input is higher than comparator level 2

during the second-point period for channel 2, a “L” level

(5)

Mode switch pins (pins 6, 7 and 8)

S AC/DC mode switch pin (pin 6)

When “H” AC input (pins 1 and 3) is selected, and when

“L” DC input (pin 5) is selected.

“H”: 1, 3pin “L”: 5pin

S Mute (pin 7)

When “H”, mute is applied, and no display is output. Nor-

mally “L”.

S Peak hold (pin 8)

When “H”, peak hold for AC input is cancelled.

The circuit for these three mode switches is given in Fig.

6.

Pins 6 to 8 are pulled down by a 50k

Ω resistor, so there

is no need for the inputs to be connected to GND for a “L”

input.

(6)

Attack and release times (pins 2 and 4)

The output response to AC input signals is set by the RC

Attack time: the time for pins 2 and 4 to go from 0V to 2V

(when all 12 LEDs are lit) when the input signal goes from

no signal to a 1.8V input signal with f = 1kHz (the input

level at which the 12th LED lights is +6dB).

Release time: the time for pins 2 and 4 to go from 2V to

120mV (the level at which the first LED lights) when the

input signal goes from a 1.8V input signal to no signal (the

input level at which the 12th LED lights is +6dB).

The recommended values are 10k

tack and release times are zero seconds regardless of

the RC circuits (see Fig. 7).

(7)

Oscillator frequency (pin 9)

quency.

The relationship between the oscillator frequency and

the display switching period is as follows:

The LED drive output, display switch output period, peak

hold time, and mute time when power is applied are all

determined by the oscillation frequency, and are varied

when the frequency is changed.