Audio ICs
LED level meter driver, 12-point,
linear scale, dot or bar display
The BA689 is a monolithic IC for LED level meter applications. The display level range is 0mVrms to 300mVrms (typ.) divided into 12 equally-spaced points with 25mVrms steps. The constant current outputs can be set using external resistors
to allow use of different color LEDs in various combinations.
Signal meters, battery checkers,
and air conditioner temperature displays
1) 12-point level meter driver for bar / dot displays.
2) Fixed-current outputs that can directly drive LEDs.
3) Output current can be set using external resistors allowing different types of LEDs to be used in combination.
Absolute maximum ratings (Ta = 25C)
4) Built-in half-wave rectifier amplifier.
5) LED on and off timing can be set using an external
capacitor and resistor.
6) With bar-type display, by connecting four LEDs in series, power dissipation is reduced.
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Block diagram
Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 12V, and f = 1kHz)
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Measurement circuit
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Application example
Attached components
(1) LED current setting resistor (R1)
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 recommended value is 27kΩ for
green LEDs, and 39kΩ for red LEDs. 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 (C1)
This capacitor connects the BA689 to external input circuits. The recommended value is 2.2µF.
(3) Input bias resistor (R2)
This resistor is the input impedance. If the value is set too
large, the DC bias voltage will increase, and the input offset 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 (R3 and C2)
These components set the discharge time constant for
LED operation level. The recommended values are R3 =
10kΩ and C2 = 10µF.
(5) Power supply capacitor (C3)
This capacitor stabilizes the power supply line. The recommended value is 10µF. This capacitor will have no effect if its value is 1µF or less.
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Application example (DC input)
DC input is input directly to pin 3 (see Fig. 4). However,
when the input level is high, connect the input directly to
the amplifier output (pin 4) as shown in Fig. 5. When this
is done dispersion of the rectifier amplifier gain ceases to
be a factor, and the comparator dispersion becomes extremely small.
Operation notes
(1) LED connection
Connect the LEDs as indicated in Fig. 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.
When using different color LEDs that have different current values (e.g. green for the lower 10 LEDs and red for
the top two) set the value of the current to the larger LED
current using the external resistor, and adjust the current
value for LEDs that require a smaller current by connecting resistors in parallel them.
If you wish to remove LEDs, be certain to short unused
If the resistance of the 100kΩ VR shown in Fig. 5 becomes too small, the discharge time constant determined by R1 and C1 will change, and the response time
will vary. The maximum input level to pin 4 is 6V.
(2) LED current adjustment
The LED current is set using R1. The relationship between the value of R1 and the typical LED current is given
in Fig. 3.
(3) Comparator voltage
In the case of the BA689, the comparator voltage is the
input voltage when about half LED current setting value
(typ.) is flowing in an LED.
Therefore, if the LED current is set to 16mA, the
comparator voltage is the value when 8mA is flowing in
the LED.
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External dimensions (Units: mm)