BA6820 ROHM [Rohm], BA6820 Datasheet - Page 6

• Manufacturer Part Number: BA6820
• Description: LED level meter driver, 12-point x 2 channel, VU scale, bar display
• Manufacturer: ROHM [Rohm]

FAttached components
S C
for the square-root compression amplifier. The rectified
voltage output from pins 2 and 4 is attenuated by 1.5dB
at the frequency determined by the following formula (re-
fer to the data for the relationship between the pin 2 and
4 DC voltage frequency characteristics and the LED
lighting level).
FCircuit operation
(1)
There are 12 LEDs each for the left and right channels,
and these are divided into 4 groups of six. A dynamic-
drive technique is used to drive the LEDs in order, and
provide 12 display points for each channel. A 12-point
VU-scale bar display is produced over the display range
*38dB to +10dB. The top eight points have a peak hold
function which may be cancelled if required (there is no
peak hold function for DC mode).
Independent AC (two channels) and DC (one channel)
inputs are provided, and a control input pin is used to
switch between them.
In DC mode, only channel 2 operates.
A power-on mute circuit is provided, so no measures are
required to prevent erroneous lighting of the LEDs when
power is applied.
Audio ICs
When the LEDs light due to low-frequency mechanical
noise or induced hum, reduce the values of C
to cut the cut the low-frequency frequency characteris-
tic.
S VR
sitivity and L / R balance adjustment (refer to item 2 of
Circuit operation).
S C
S R
These resistors set the attack and release times (refer
to item 6 of the Circuit operation).
S C
R
This resistor sets the oscillator frequency (refer to the
Operation notes).
S C
used as a ripple filter. The positive lead should be con-
nected close to V
close to the junction of pins 10 and 11.
1
3
fC =
: 39k carbon-film resistor.
and C
Function
3
1
5
6
: 0.01 F mylar capacitor.
: 100 F electrolytic capacitor. This capacitor is
and C
and R
1
and VR
2
2
: 1 F input coupling capacitors (electrolytic)
4
2
: 22 F electrolytic capacitors.
: 47k carbon-film resistors.
S
C
2
: 5k to 100k potentiometers for sen-
1
(R
1
CC
IN
)VR
(pin 22), and the negative lead
1
)
(R
IN
= input resistance)
1
and C
2
S Q
If the current for one LED is I
for each of Q
Choose transistors that have sufficient margin for I
P
S R
These resistors limit the base current for transistors Q
to Q
h
region, h
so that sufficient base current flows.
S LED
S R
set the LED current. Four LEDs are connected to each
resistor, but as the LEDs light sequentially, only the cur-
rent for one LED flows in a resistor.
The attack and release times for the display can be set
using external components.
(2)
Pins 1 and 3 are the AC inputs, and pin 5 is the DC input.
Pin 6 is used to switch between AC and DC input. When
the pin 6 input is “H”, AC input is selected (pins 1 and 3),
and when it is “L”, DC input (pin 5) is selected. Therefore,
if pins 1 and 3 are used for audio input, and pin 5 as the
input for signal meter output (DC) from a tuner, the switch
input (pin 6) can be used to make LED display do two
jobs.
Pins 1 and 3 have low input impedance, so we recom-
mend that you connect potentiometers (VR
5k to 100k ) in series with the inputs to adjust the bal-
ance between ch1 and ch2 and set the levels.
FE
C
.
, but as the transistors are operated in the saturation
4
8
1
2
to R
. The base current is the collector current divided by
to Q
to R
I
P
R8X13 =
V
Input block (pins 1, 3 and 5)
C
1
C
DL
= 6 I
to LED
= 6 I
FE
7
13
= Display switch output “L” voltage.
4
BA6820F / BA6822S / BA6822F
: 2.2k carbon-film resistors.
: 2SA854S Transistors for display switching.
: 330
will drop considerably. Choose the resistors
1
LED
to Q
LED
12
: SLB-26
(for duty cycle of 7 / 32)
carbon-film resistors. These resistors
4
V
when all LEDs are lit are given by:
V
sat
CC*
V
32
LED*
7
LED
V
, the values of I
sat
I
LED
(Q
1*
Q
4
) *V
1
and VR
C
DL
and P
C
667
and
2
C
1
: