Audio ICs
LED level meter driver, 12-point,
power scale, dot or bar display
BA683A
The BA683A is a monolithic IC for LED power meter applications. The display level range is 9mV
rms
to 380mV
rms
(Typ.)
divided into 12 points with interval spacings of 3dB. The constant current outputs can be set using an external resistor.
FApplications
Level meters for all types of audio equipment applica-
tions
FFeatures
1) 12-point power meter driver for bar / dot displays.
2) Fixed-current outputs that can directly drive LEDs.
3) Output current can be set using external resistors al-
lowing different types of LEDs to be used in combina-
tion.
FBlock
diagram
4) Built-in half-wave rectifier amplifier.
5) With bar-type display, by connecting four LEDs in se-
ries, power dissipation is reduced.
651
Audio ICs
FAttached
components
(1) LED current setting resistor (R
1
)
This resistor sets the LED current value. Refer to Fig. 3
for the relationship between the value of this resistor and
the current value. The ratio of the current for outputs 1 to
8 and 9 to 12 is about 2: 1. The recommended value is
for this resistor is 27kΩ. If the LED current is set too high,
the allowable power dissipation of the package may be
exceeded, so exercise due caution.
(2) Input coupling capacitor (C
1
)
This capacitor connects the BA683A to external input cir-
cuits. The recommended value is 2.2µF.
(3) Input bias resistor (R
2
)
This resistor is the input impedance. If the value is set too
large, the DC bias voltage will increase, and the input off-
set will increase and have an effect on the comparators.
The recommended value is 10kΩ.
(4) Resistor and capacitor that set the LED operation
level discharge time constant (R
3
and C
2
)
These components set the discharge time constant for
LED operation level. The recommended values are R
3
=
10kΩ and C
2
= 10µF.
BA683A
(5) Input offset adjustment resistors (R
4
and VR
1
)
These resistors are used to adjust the input offset for the
rectifier amplifier. The recommended values are R
4
=
240kΩ, and VR
1
= 500Ω. If the value of VR
1
is too high,
adjustment becomes difficult, and if it is too small, adjust-
ment may not be possible.
(6) Power supply capacitor (C
3
)
This capacitor stabilizes the power supply line. The rec-
ommended value is 10µF. This capacitor will have no ef-
fect if its value is 1µF or less.
FOperation
notes
(1) LED connection
Connect the LEDs as indicated in Fig. 2 (1) and Fig 2 (2).
Note that the connection methods are different for bar
and dot displays, and that in the case of bar display, pin
18 is open, while for dot display, pin 18 is connected to
GND.
For the BA683A, the ratio of the current for LEDs L
1
to L
8
and L
9
to L
12
is about 2: 1. If you want the current ratio for
some of the L1 to L8 LEDs to be 1, reduce the current by
connecting a resistance in parallel with the LED. Short
any LED that are unused. Connect the LEDs that are not
used from the lowest level LED (except when the 12th
LED is not used for display alignment).
(2) LED current adjustment
The LED current is set using R
1
. The relationship be-
tween the value of R
1
and the typical LED current is given
in Fig. 3.
(3) Comparator voltage
In the case of the BA683A, the comparator voltage is the
input voltage when about half LED current setting value
(Typ.) starts flowing in an LED.
Therefore, if the LED current is set to 16mA, when the
third LED starts to light and 8mA is flowing in the LED,
this input voltage is the third comparator voltage.
(4) 0dB and input offset adjustment
First, adjust the input signal so that the 10th LED lights.
This is the 0dB input signal level. Next, lower the input
signal level to
*27dB,
and adjust the offset adjustment
potentiometer VR
1
so that the first LED lights. Repeat the
0dB and
*27dB
adjustments alternately to accurately
set the levels. The input level at which an LED lights is the
comparator voltage.
(5) Earthing
The BA683A GND (pin 9) and the external component
earths should connected together at one point.
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MCU
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