Audio ICs
Fluorescent display tube level meter
driver, 16-point 2 channel, VU scale,
bar display
BA6800AS
The BA6800AS is a two-channel, 16-point fluorescent display tube driver for VU-scale bar-level meters. It uses a dynam-
ic-drive system and has both AC and DC inputs. The AC input mode has a peak hold circuit. The IC features a power-on
mute, and the output block can directly drive fluorescent display tubes, so few external components are required. The
grid output duty cycle is 1 / 8.
FApplications
Level meters for all types of AV equipment
FFeatures
1) Uses dynamic-drive system to display two 16-point
channels. 30-pin SDIP package.
2) AC and DC inputs provided. Switching function al-
lows two-mode display.
3) Upper 12 points have peak hold function in AC mode
(two seconds).
FAbsolute
maximum ratings (Ta = 25_C)
4) Power-on mute function.
5) Dynamic-drive system reduces the power dissipa-
tion of the fluorescent display tube power supply.
6) Square root compression amplifier built in.
797
Audio ICs
FCircuit
operation
(1) Input block
The AC input pins are pins 1 and 3, and the DC input pins
are pins 6 and 7. Pin 8 is used to switch between the AC
and DC inputs. When the input to pin 8 is “H”, AC input
is selected (pins 1 and 3). Therefore, by using pin 8 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 6 and 7 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 250Ω (typ.), so con-
nect potentiometers (VR
1
and VR
2
) in series with the in-
puts to adjust the sensitivity and ch1 and ch2 balance.
(2) Peak hold circuit
The BA6800AS features a peak hold circuit that tempo-
rarily 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 oscillator
frequency. It is 2 sec. (typ.) for an oscillator frequency of
2kHz. DC mode does not have a peak hold function.
(3) Grid output
The pin 10 and 11 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-
sistors Q1 and Q2 as shown in the application example
circuit to drive the fluorescent tubes (see Fig. 3).
BA6800AS
(4) Segment output block
Pins 12 to 28 are the segment outputs. The output cir-
cuits are open-collector PNP transistors. When grid 1 is
“L”, the ch1 level is output (pin 1 or 6), and when grid 2
is “L”, the ch2 level is output (pin 3 or 7). Refer to Fig. 4.
(5) Grid and segment output timing chart
The grid and segment output timing is shown in Fig. 5.
(6) Attack and release times
The response characteristic for AC input signals is set by
resistor R1 and capacitor C
3
for ch1 and resistor R
2
and
capacitor C
4
for ch2 (pins 2 and 4). When R
1
= 47kΩ and
C
3
= 22µF, 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 input
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
The resistor R
26
and capacitor C
5
connected to pin 30 de-
termine the oscillator frequency. The oscillator frequency
(f
osc
) and grid output period (T) are related as follows :
T (ms) = 16 / f
osc
(kHz)
801
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