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| 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 9mVrms to 380mVrms (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 applications 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 allowing different types of LEDs to be used in combination. FBlock diagram 4) Built-in half-wave rectifier amplifier. 5) With bar-type display, by connecting four LEDs in series, power dissipation is reduced. 651 Audio ICs FAbsolute maximum ratings (Ta = 25_C) BA683A FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 12V, and f = 1kHz) 652 Audio ICs FMeasurement circuit BA683A FComparator level vs. AC and DC input levels FApplication example 653 Audio ICs FAttached 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 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 27k. 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 BA683A to external input circuits. The recommended value is 2.2F. (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 10k. (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 = 10k and C2 = 10F. BA683A (5) Input offset adjustment resistors (R4 and VR1) These resistors are used to adjust the input offset for the rectifier amplifier. The recommended values are R4 = 240k, and VR1 = 500. If the value of VR1 is too high, adjustment becomes difficult, and if it is too small, adjustment may not be possible. (6) Power supply capacitor (C3) This capacitor stabilizes the power supply line. The recommended value is 10F. This capacitor will have no effect if its value is 1F 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 L1 to L8 and L9 to L12 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 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 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 VR1 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. 654 Audio ICs FTape deck application example BA683A FExternal dimensions (Units: mm) 655 |
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