Audio ICs Fluorescent display tube level meter driver, 12-point 2 channel, VU scale, bar display BA6810F The BA6810F 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. 28-pin SOP 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. Block diagram 790 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. Audio ICs BA6810F FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions 791 Audio ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 5.0V) 792 BA6810F Audio ICs BA6810F 793 Audio ICs Measurement circuit Application example 794 BA6810F Audio ICs Circuit operation (1) Input block The AC input pins are pins 23 and 25, and the DC input pins are pins 27 and 28. Pin 2 is used to switch between the AC and DC inputs. When the input to pin 2 is “H”, AC input is selected (pins 23 and 25). Therefore, by using pin 2 to switch between the AC and DC modes, the IC can do two jobs, using one fluorescent tube. For example, pins 23 and 25 can be used for audio signal input, and pins 27 and 28 can be used as the input for the signal meter output from a tuner (DC). (2) Peak hold circuit The BA6810F 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 left and right channels is "1.0dB. (5) Grid output The pin 6 and 7 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 8 to 19 are the segment outputs. The output circuits are open-collector PNP transistors. When grid 1 is “L”, the ch1 level is output (pin 23 or 27 input level), and when grid 2 is “L”, the ch2 level is output (pin 25 or 28 input level). Refer to Fig. 5. BA6810F (7) Grid and segment output timing chart. The grid and segment output timing is shown in Fig. 6. (8) Attack and recovery times The output response characteristic for AC input signals is set by pins 24 and 26. 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 21 determine the oscillator frequency. The oscillator frequency (fosc) and grid output period (T) are related as follows: 795 Audio ICs Electrical characteristics curves External dimensions (Units: mm) 796 BA6810F