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Audio ICs
LED level meter driver, 12-point channel, VU scale, bar display
BA6820F / BA6822S / BA6822F
2
The BA6820F, BA6822S and BA6822F are two-channel, 12-point LED drivers for VU-scale bar-level meters. The ICs are available in 22-pin SOP (BA6820F and BA6822F) and 22-pin shrink-DIP (BA6822S) packages, and use a dynamic-drive system that can drive two 12-point displays. The ICs have independent AC and DC inputs, and the AC input mode has a peak hold circuit (with cancel function). The ICs also feature a power-on mute, so steps to prevent erroneous LED lighting at power on are not required. The input resistance of the AC inputs is 3k (Typ.) for the BA6820F and 0.3k (Typ.) for the BA6822S / F.
FApplications Level meters for VCRs, stereo cassette players, audio amplifiers and karaoke equipment.
FFeatures 1) Uses dynamic-drive system to display two 12-point channels. 22-pin SOP and 22-pin shrink DIP packages. 2) Independent AC and DC inputs provided (one input displays one channel). Switching function allows two-mode display. 3) Upper 8 points have peak hold function in AC mode (two seconds). A peak-hold cancel function is also provided.
4) A mute function is provided, and muting can be applied externally. 5) Power on mute function.
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Audio ICs
FBlock diagram
BA6820F / BA6822S / BA6822F
FAbsolute maximum ratings (BA6820F / BA6822F) (Ta = 25_C)
(BA6822S) (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
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Audio ICs
BA6820F / BA6822S / BA6822F
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5.0V and f = 1kHz)
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Audio ICs
BA6820F / BA6822S / BA6822F
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Audio ICs
FMeasurement circuit
BA6820F / BA6822S / BA6822F
FApplication example
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Audio ICs
FAttached components S C1 and C2: 1F input coupling capacitors (electrolytic) for the square-root compression amplifier. The rectified voltage output from pins 2 and 4 is attenuated by 1.5dB at the frequency determined by the following formula (refer to the data for the relationship between the pin 2 and 4 DC voltage frequency characteristics and the LED lighting level). fC = 1 2 S C1 (RIN)VR1) (RIN = input resistance)
BA6820F / BA6822S / BA6822F
S Q1 to Q4: 2SA854S Transistors for display switching. If the current for one LED is ILED, the values of IC and PC for each of Q1 to Q4 when all LEDs are lit are given by: IC = 6 PC = 6 ILED (for duty cycle of 7 / 32) ILED Vsat 7 32
When the LEDs light due to low-frequency mechanical noise or induced hum, reduce the values of C1 and C2 to cut the cut the low-frequency frequency characteristic. S VR1 and VR2: 5k to 100k potentiometers for sensitivity and L / R balance adjustment (refer to item 2 of Circuit operation). S C3 and C4: 22F electrolytic capacitors. S R1 and R2: 47k carbon-film resistors. These resistors set the attack and release times (refer to item 6 of the Circuit operation). S C5: 0.01F mylar capacitor. R3: 39k carbon-film resistor. This resistor sets the oscillator frequency (refer to the Operation notes). S C6: 100F electrolytic capacitor. This capacitor is used as a ripple filter. The positive lead should be connected close to VCC (pin 22), and the negative lead close to the junction of pins 10 and 11. FCircuit operation (1) Function There are 12 LEDs each for the left and right channels, and these are divided into 4 groups of six. A dynamicdrive technique is used to drive the LEDs in order, and provide 12 display points for each channel. A 12-point VU-scale bar display is produced over the display range *38dB to +10dB. The top eight points have a peak hold function which may be cancelled if required (there is no peak hold function for DC mode). Independent AC (two channels) and DC (one channel) inputs are provided, and a control input pin is used to switch between them. In DC mode, only channel 2 operates. A power-on mute circuit is provided, so no measures are required to prevent erroneous lighting of the LEDs when power is applied.
Choose transistors that have sufficient margin for IC and PC. S R4 to R7: 2.2k carbon-film resistors. These resistors limit the base current for transistors Q1 to Q2. The base current is the collector current divided by hFE, but as the transistors are operated in the saturation region, hFE will drop considerably. Choose the resistors so that sufficient base current flows. S LED1 to LED12: SLB-26 S R8 to R13: 330 carbon-film resistors. These resistors set the LED current. Four LEDs are connected to each resistor, but as the LEDs light sequentially, only the current for one LED flows in a resistor. R8X13 = VCC*VLED*Vsat (Q1*Q4) *VDL ILED
VDL = Display switch output "L" voltage.
The attack and release times for the display can be set using external components. (2) Input block (pins 1, 3 and 5) Pins 1 and 3 are the AC inputs, and pin 5 is the DC input. Pin 6 is used to switch between AC and DC input. When the pin 6 input is "H", AC input is selected (pins 1 and 3), and when it is "L", DC input (pin 5) is selected. Therefore, if pins 1 and 3 are used for audio input, and pin 5 as the input for signal meter output (DC) from a tuner, the switch input (pin 6) can be used to make LED display do two jobs. Pins 1 and 3 have low input impedance, so we recommend that you connect potentiometers (VR1 and VR2: 5k to 100k) in series with the inputs to adjust the balance between ch1 and ch2 and set the levels.
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Audio ICs
(3) Peak hold The peak hold circuit momentarily holds the maximum signal level in AC input mode. The peak hold function applies to comparator levels 5 to 12 (8 points). When the oscillator frequency is 4kHz, the peak hold time is two seconds (Typ.), and can be changed by changing the oscillator frequency. The peak hold function can be turned off by setting pin 8 high. The peak hold function does not operate in DC input mode. (4) Output block The two sets of 12 LEDs for the BA6820F and BA6822S / F are divided into 4 groups of six. A dynamicdrive technique is used to drive the LEDs in order, and display the input level. Group 1 Channel 1 LEDs 1, 3, 5, 7, 9 and 11 (odd-numbered LEDs) Group 2 Channel 1 LEDs 2, 4, 6, 8, 10 and 12 (even-numbered LEDs) Group 3 Channel 2 LEDs 1, 3, 5, 7, 9 and 11 (odd-numbered LEDs) Group 4 Channel 2 LEDs 2, 4, 6, 8, 10 and 12 (even-numbered LEDs) Therefore, six LED drive outputs, and four display switch terminals are provided. The output timing chart for when all LEDs are lit is shown in Fig. 3. In DC input mode, only channel 2 operates. D1 to D4 in the timing chart operate in the same way as for AC mode (i.e. D1 and D2 operate), but O1 to O6 are high for the channel 1 period.
BA6820F / BA6822S / BA6822F
(1) Display switch outputs (pins 12 to 15) To successively switch between the four LED groups, these outputs are active low (see Fig. 4). The outputs are pulled up by 36k resistors (between the base and emitter of Q1 to Q4), so leak current bypass resistors are not required.
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Audio ICs
(2) LED drive outputs (pins 16 to 21) These are open-collector outputs that drive the LEDs (see Fig. 5). One complete cycle of the timing chart starting from O1 (pin 21) is as follows: if the channel 1 input is higher than comparator level 1 during the first-point period for channel 1, a "L" level is output. Next, if the channel 1 input is higher than comparator level 2 during the second-point period for channel 1, a "L" level is output, if the channel 2 input is higher than comparator level 1 during the firstpoint period for channel 2, a "L" level is output, and then if the channel 2 input is higher than comparator level 2 during the second-point period for channel 2, a "L" level is output.This cycle is then repeated for outputs O2 to O6. (5) Mode switch pins (pins 6, 7 and 8) S AC / DC mode switch pin (pin 6) When "H" AC input (pins 1 and 3) is selected, and when "L" DC input (pin 5) is selected. "H": 1, 3pin "L": 5pin S Mute (pin 7) When "H", mute is applied, and no display is output. Normally "L". S Peak hold (pin 8) When "H", peak hold for AC input is cancelled. The circuit for these three mode switches is given in Fig. 6. Pins 6 to 8 are pulled down by a 50k resistor, so there is no need for the inputs to be connected to GND for a "L" input. (6) Attack and release times (pins 2 and 4) The output response to AC input signals is set by the RC circuits connected to pins 2 and 4 (R1 and C3 for channel 1, and R2 and C4 for channel 2).
BA6820F / BA6822S / BA6822F
Release time: the time for pins 2 and 4 to go from 2V to 120mV (the level at which the first LED lights) when the input signal goes from a 1.8V input signal to no signal (the input level at which the 12th LED lights is +6dB). The recommended values are 10k to 47k for R1 and R2 and 10F to 22F for C3 and C4. In DC mode, the attack and release times are zero seconds regardless of the RC circuits (see Fig. 7). (7) Oscillator frequency (pin 9) R3 and C5 connected to pin 9 determine the oscillator frequency. The relationship between the oscillator frequency and the display switching period is as follows:
The LED drive output, display switch output period, peak hold time, and mute time when power is applied are all determined by the oscillation frequency, and are varied when the frequency is changed.
Attack time: the time for pins 2 and 4 to go from 0V to 2V (when all 12 LEDs are lit) when the input signal goes from no signal to a 1.8V input signal with f = 1kHz (the input level at which the 12th LED lights is +6dB).
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Audio ICs
BA6820F / BA6822S / BA6822F
(8) GND terminal (pins 10 and 11) Pin 11 is the GND for the pin 12 to pin 21 driver circuits, and pin 10 is the GND for the other signal circuits (see Fig. 8). Pins 10 and 11 are not connected internally, so both must be connected to GND. The large LED current that flows from pin 11 has a large high-frequency component, so care must be taken with regard to the PCB layout to avoid faulty operation of the IC, and incorrect lighting of the LEDs due to noise. FOperation notes (1) Use the potentiometers VR1 and VR2 connected to pins 1 and 3 to set the 0dB levels and adjust the channel 1 and channel 2 balance. (2) The recommended oscillator frequency is 4kHz (pin 9). The external component values for C5 and R3 are 0.01F and 41k (or 39k). If you wish to use other values, they should be in the ranges 0.001F to 0.1F and 10k to 100k. (see Fig. 9). (3) The dynamic ranges for the BA6820F and BA6822S / F comparators are large, and the comparators will operate even with low-level signals. For this reason, noise may cause the LEDs to light when they should not, and to prevent this, GND line noise should be kept sufficiently low. (4) Take care to ensure the none of the pins have a voltage applied to them that is higher than VCC or lower than GND (e.g. supply the LED current from a source other than VCC). (5) In general, the level meter output block is switched on and off in the range GND to VCC, and a large voltage with a large high-frequency component is generated. Therefore, if the input and output lines are close, the out-
put may be fed back to the input and cause oscillation, incorrect LED lighting, or faulty operation of the IC. Design the PCB artwork so that there is no coupling between the input and output lines or with other units, in the same way as for linear amplifier PCB design. If they must be physically close, insert a capacitor between the input and GND to reduce the AC input impedance, and prevent noise from entering the input.
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Audio ICs
FElectrical characteristic curves
BA6820F / BA6822S / BA6822F
FExternal dimensions (Units: mm)
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