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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. FApplications Mini-component stereo systems, CD radio cassette players, car audio systems and TVs. FFeatures 1) Volume (main volume) and tone (bass and treble) control possible by direct serial link to a microprocessor. DC control is also possible. 2) Volume control is done with a low-distortion, lownoise 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 requirements, 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. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 664 Audio ICs FBlock diagram BH3857AFV 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 10k (Typ.). The impedance of the SC terminal is 200k (Typ.). 665 Audio ICs FPin descriptions BH3857AFV 666 Audio ICs BH3857AFV FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 8V, f = 1kHz, BW = 20Hz to 20kHz, VOL = MAX, Tone = ALL FLAT, Rg = 600, RL = 10k, INPUT_AMP_GAIN = 0dB) 667 Audio ICs FMeasurement circuit BH3857AFV 668 Audio ICs 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. BH3857AFV D18 : Surround matrix 1 control D19 : Surround matrix 2 control S Surround is on when the bit data is 0, and off when it is 1. S With 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. 669 Audio ICs (2) Logic input terminals Logic input terminals have a bipolar construction, so take care with regard to source current. (3) Timing chart The timing chart is shown in Fig. 3. Timing (recommended conditions) BH3857AFV Fig.3 Timing chart constants 670 Audio ICs (4) Data table The transmission data is given in the table below. Volume data settings (reference values) BH3857AFV 671 Audio ICs BH3857AFV Bass and treble settings (reference values) Treble data Bass data 672 Audio ICs FApplication example BH3857AFV 673 Audio ICs FAttached components (1) Input buffer BH3857AFV S The input impedance is 47k. S A buffer if R and C1 are not present. S The gain can be set by R and the 20k. GVC = (R ) 20k) / R Note: Set C2 (input coupling) and C1 (used to set the gain) depending on the frequency band used. (2) Bass filter S A band-pass filter is constructed using a multiple-feedback type active filter. f0 can be changed using the C valve. (Theoretical formula) 674 Audio ICs (3) Treble filter BH3857AFV S The bypass filter cutoff frequency (fc1) can be altered by changing the value of the external capacitor C3. The recommended value for fc1 is about 8kHz. S The bandwidth of the internal amplifier is determined by fc2 (about 100kHz). The tone control provides gain boost or cut over a frequency 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 below. Note, however, that the actual values will vary due to differences 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 675 Audio ICs (4) Surround matrix (1) Surround 1 Circuit example BH3857AFV S Gain setting S Mixing signal frequency characteristic settings 676 Audio ICs (2) Surround 2 BH3857AFV The surround matrix construction is shown in the diagram on the left. The gain calculations are given by the formulas in the diagram. 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 temperature and supply voltage ranges. Please confirm the values of the circuit constants, voltage setting, and temperature 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 application 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 timing 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 applied. SDo not apply more than 15V to the output ports. (6) DC control An internal impedance of 10k is seen from the VC (pin 37), TC (pin 36), and BC (pin 35) terminals, and 200k 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. 677 Audio ICs FElectrical characteristic curves BH3857AFV FExternal dimensions (Units: mm) 678 |
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