Audio ICs Fluorescent display tube level meter driver, 12-point 2 channel, VU scale, bar display BA6810S The BA6810S is a two-channel, 12-point fluorescent display tube driver for VU-scale bar-level meters. It uses a dynamic-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, allowing cost and space savings while improving reliability. The grid output duty cycle is 1 / 8. Applications Level meters for all types of AV equipment Features 1) Uses dynamic-drive system to display two 12-point channels. 30-pin SDIP package. 2) AC and DC inputs provided. Switching function allows two-mode display. 3) Upper 8 points have peak hold function in AC mode (two seconds Typ.). 4) Power-on mute function. 5) Forced-mute function. 6) Terminal for meter sensitivity adjustment provided (adjustment with one terminal is possible). 7) I2L injector current terminal provided. 8) Square root compression amplifier built in. 9) Dynamic-drive system reduces the power dissipation of the fluorescent display tube power supply. Block diagram 783 Audio ICs FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions 784 BA6810S Audio ICs BA6810S FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5.0V) 785 Audio ICs 786 BA6810S Audio ICs BA6810S Measurement circuit Application example 787 Audio ICs Circuit operation (1) Input block The AC input pins are pins 2 and 4, and the DC input pins are pins 6 and 7. Pin 9 is used to switch between the AC and DC inputs. When the input to pin 9 is “H”, AC input is selected (pins 2 and 4). Therefore, by using pin 9 to switch between the AC and DC modes, the IC can do two jobs, using one fluorescent tube. For example, pins 2 and 4 can be used for audio signal input, and pins 6 and 7 can be used as the input for the signal meter output from a tuner (DC). (2) Peak hold circuit The BA6810S features a peak hold circuit that temporarily holds peak signal levels in AC input mode. The peak hold function can be used with the upper 8 points (5 to 12). The peak hold time depends on the oscillator frequency. It is 2 sec. (Typ.) for an oscillator frequency of 2kHz. (3) MUTE function The display can be turned off by driving the MUTE terminal “H”. (4) Meter sensitivity adjustment terminal Connect a potentiometer of about 10kΩ, and adjust it so that the 8th point lights when the for an AC input of 400mVrms. The dispersion between L and R channels is ±1.0dB. (5) Grid output The pin 13 and 14 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 transistors Q1 and Q2 as shown in the application example circuit to drive the fluorescent tubes (see Fig. 4). (6) Segment output block Pins 15 to 28 are the segment outputs. The output circuits are open-collector PNP transistors. When grid 1 is “L”, the ch1 level is output (pin 2 or 6 input level), and when grid 2 is “L”, the ch2 level is output (pin 4 or 7 input level). (Refer to Fig. 5.) 788 BA6810S (7) Grid and segment output timing chart. The grid and segment output timing is shown in Fig. 6. (8) Attack and release times The output response characteristic for AC input signals is set by pins 3 and 5. The comparator level may change somewhat due to the sag of the CR circuit discharge. (9) Oscillator frequency The resistor and capacitor connected to pin 30 determine the oscillator frequency. The oscillator frequency (fosc) and grid output period (T) are related as follows: T (ms) = 16 / fosc (kHz) Audio ICs BA6810S Electrical characteristics curves External dimensions (Units: mm) 789