BA6820F datasheet(6/10 Pages) ROHM | LED level meter driver, 12-point x 2 channel, VU scale, bar display

6 page

π S C1 (RIN)VR1)

VCC*VLED*Vsat (Q1*Q4)

*VDL

ILED

667

Audio ICs

BA6820F / BA6822S / BA6822F

FAttached components

S C1 and C2: 1µF 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 (re-

fer to the data for the relationship between the pin 2 and

4 DC voltage frequency characteristics and the LED

lighting level).

fC =

(RIN = input resistance)

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 characteris-

tic.

S VR1 and VR2: 5kΩ to 100kΩ potentiometers for sen-

sitivity and L / R balance adjustment (refer to item 2 of

Circuit operation).

S C3 and C4: 22µF electrolytic capacitors.

S R1 and R2: 47kΩ carbon-film resistors.

These resistors set the attack and release times (refer

to item 6 of the Circuit operation).

S C5: 0.01µF mylar capacitor.

R3: 39k

Ω carbon-film resistor.

This resistor sets the oscillator frequency (refer to the

Operation notes).

S C6: 100µF electrolytic capacitor. This capacitor is

used as a ripple filter. The positive lead should be con-

nected close to VCC (pin 22), and the negative lead

close to the junction of pins 10 and 11.

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

ILED (for duty cycle of 7 / 32)

PC = 6

ILED

Vsat

Choose transistors that have sufficient margin for IC and

PC.

S R4 to R7: 2.2kΩ 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: 330Ω carbon-film resistors. These resistors

set the LED current. Four LEDs are connected to each

resistor, but as the LEDs light sequentially, only the cur-

rent for one LED flows in a resistor.

X13 =

VDL = Display switch output “L” voltage.

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 dynamic-

drive 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.

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 recom-

mend that you connect potentiometers (VR1 and VR2:

Ω to 100kΩ) in series with the inputs to adjust the bal-

ance between ch1 and ch2 and set the levels.

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