669
Audio ICs BA6820F / BA6822S / BA6822F
(2) LED drive outputs (pins 16 to 21)
These are open-collector outputs that drive the LEDs
(see Fig. 5).
One complete cycle of the timing chart starting from O
1
(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
is output.This cycle is then repeated for outputs O
2 to O6.
(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 50kΩ 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
circuits connected to pins 2 and 4 (R
1 and C3 for channel
1, and R
2 and C4 for channel 2).
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 10kΩ to 47kΩ for R
1 and
R
2 and 10µF to 22µF for C3 and C4. In DC mode, the at-
tack and release times are zero seconds regardless of
the RC circuits (see Fig. 7).
(7) Oscillator frequency (pin 9)
R
3 and C5 connected to pin 9 determine the oscillator fre-
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.
