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Audio ICs
Audio sound controller
BH3857AFV
The BH3857AFV is a signal-processing IC for controlling audio quality in CD radio-cassette players and mini-component
stereo systems. Three-line serial control is available making it easy to adjust tone and volume using a microprocessor .
Applications
Mini-component stereo systems, CD radio cassette play-
ers, car audio systems and TVs.
Features
1) Volume (main volume) and tone (bass and treble)
control possible by direct serial link to a microproces-
sor. DC control is also possible.
2) Volume control is done with a low-distortion, low-
noise VCA, and step noise is suppressed.
3) The gain of the input amplifier can be adjusted, and
two surround matrixes are available to expand the
sound.
4) The IC includes a stable reference voltage source
and input buffer to reduce external component re-
quirements, and comes in a compact 40-pin SSOP
package that is perfect for compact designs.
5) Four open-collector outputs are provided to make
logic control possible.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions (Ta = 25C)
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Audio ICs BH3857AFV
Block diagram
Control of volume, bass, treble and surround 2 can also be done by external application of a DC voltage to the VC (volume), BC (bass), TC (treble) and SC
(surround 2) terminals.
The impedance of the VC, TC, and BC terminals is 10kΩ (Typ.).
The impedance of the SC terminal is 200kΩ (Typ.).
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Audio ICs BH3857AFV
Pin descriptions
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Audio ICs BH3857AFV
Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 8V, f = 1kHz, BW = 20Hz to 20kHz,
VOL = MAX, Tone = ALL FLAT, Rg = 600Ω, RL = 10kΩ, INPUT_AMP_GAIN = 0dB)
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Audio ICs BH3857AFV
Measurement circuit
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Audio ICs BH3857AFV
FCircuit operation
(1) About the data format
As shown in Fig. 2, there are 32 bits of data. When the
power is applied, a reset is applied to switch ports 1 to 4
off, but the reset is not applied to the other ports, so they
are unstable. For this reason, it is necessary to input the
data at least once while the set mute circuit is on.
SSurround is on when the bit data is 0, and of f when it
is 1.
SWith regard to the port 1 to 4 outputs, when the power
is on, if no data is input the transistors for each output
are set to off. The outputs are on when the bit data is
1, and off when it is 0.
∗Apply the following data for chip select and parity.
∗D18 : Surround matrix 1 control
D19 : Surround matrix 2 control
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Audio ICs BH3857AFV
(2) Logic input terminals
Logic input terminals have a bipolar construction, so take
care with regard to source current.
(3) T iming chart
The timing chart is shown in Fig. 3.
T iming (recommended conditions)
Timing chart constants
Fig.3
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Audio ICs BH3857AFV
(4) Data table
The transmission data is given in the table below.
Volume data settings (reference values)
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Audio ICs BH3857AFV
Bass and treble settings (reference values)
T reble data Bass data
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Audio ICs BH3857AFV
Application example
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Audio ICs BH3857AFV
FAttached components
(1) Input buffer
(2) Bass filter
SThe input impedance is 47kΩ.
SA buffer if R and C1 are not present.
SThe gain can be set by R and the 20kΩ.
GVC = (R 20kΩ)/R
Note: Set C2 (input coupling) and C1 (used to set the
gain) depending on the frequency band used.
SA band-pass filter is constructed using a multiple-feedback type active filter.
f0 can be changed using the C valve.
(Theoretical formula)
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Audio ICs BH3857AFV
(3) Treble filter
The bypass filter cutoff frequency (fc1) can be altered
by changing the value of the external capacitor C3.
The recommended value for is about 8kHz.
The bandwidth of the internal amplifier is determined
by (about 100kHz).
The tone control provides gain boost or cut over a fre-
quency range that you decide. At the peak and bottom of
the frequency characteristic the boost is 15dB, and the
cut is *15dB (Typ.). Take the frequency characteristic
into consideration when designing the filter.
(1) Amount of tone boost
When the amount of volume attenuation is large, the tone
control width will change. Reference values are given be-
low.
Note, however , that the actual values will vary due to dif-
ferences in individual components.
Reference values :
Tone control width at 0dB volume attenuation :
±15.0dB
Tone control width at *40dB volume attenuation :
±13.5dB
Tone control width at *60dB volume attenuation :
±12.0dB
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Audio ICs BH3857AFV
(4) Surround matrix
(1) Surround 1
Circuit example
Gain setting
Mixing signal frequency characteristic settings
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Audio ICs BH3857AFV
(2) Surround 2 The surround matrix construction is shown in the dia-
gram on the left.
The gain calculations are given by the formulas in the dia-
gram.
FOperation notes
We guarantee the application example, but recommend
that you thoroughly check its characteristics and pay
attention to the points of caution given below.If you
change any of the external component values, check
both the static and transient characteristics of the circuit,
and allow sufficient margin in your selections to take into
account variations in the components and ICs.
(1) Operating power supply voltage range
The basic circuit functions are guaranteed to operate if
the circuit is operated within the recommended tempera-
ture and supply voltage ranges. Please confirm the val-
ues of the circuit constants, voltage setting, and tempera-
ture in actual use.
(2) Step switching noise
The VC (pin 37), TC (pin 36), BC (pin 35), and SC (pin 25)
terminals have components connected to them in the ap-
plication example. The values of these components may
need to be changed depending on the signal level setting
and PCB pattern. Investigate carefully before deciding
on the values of the various circuit constants.
The equivalent circuit for these terminals is given below
(an integrator circuit is set at the first stage to slow the
variation).
(3) Volume and tone level settings
This specification sheet gives reference values for the
amount of attenuation and gain with respect to the serial
control data.
The internal D/A convertor is an R-2R circuit, and data
exists for the places where continuous variation does not
occur between data.
Use this when fine setting is required. The setting limits
are up to 8 bits for volume (256 steps) and 5 bits (32
steps) for tone.
(4) Digital / analog separation
The digital and analog power supplies and grounds are
completely separate. The digital circuits are supplied
from a stable reference source that is on the chip (Vref (pin
31)). For this reason, there is no need to worry about tim-
ing shifts, or interference due to digital noise.
(5) Output ports
Ports 1 to 4 (pins 26 to 29), are reset when the power is
applied. The reset state continues until the next serial
data is input.
Note: The CK, DATA and LATCH line data must be held
low up until the next data is input after power is ap-
plied.
SDo not apply more than 15V to the output ports.
(6) DC control
An internal impedance of 10kΩ is seen from the VC (pin
37), TC (pin 36), and BC (pin 35) terminals, and 200kΩ
is seen from the SC (pin 25) terminal, so with regard to
DC control, we recommend direct control with the voltage
source.
When using variable volume, take the impedance into
consideration when making the setting.
Note: The DC control voltage range is 0V to Vref.
Do not apply voltages above Vref to the terminals.
External dimensions (Units: mm)
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Audio ICs BH3857AFV
Electrical characteristic curves
