Audio ICs Stereo sound controller IC BA3853BFS The BA3853BFS is a dual-channel electronic volume controller built around a low-noise, low-distortion VCA. It is suited for car-audio applications, and has performance that rivals mechanical-type volume controllers. In addition to volume control, the IC includes all functions required for controlling sound quality, to allow more compact designs with far fewer components. Applications Car audio systems Features 1) Provides electronic control for volume, balance, fader, tone (bass and treble), and loudness. 2) The volume control circuit is a low-distortion, lownoise VCA circuit that uses DC voltage for control. The IC uses an internally-generated, temperaturecompensated reference voltage and is capable of dual-channel control with the addition of a single potentiometer. 3) Available in an SSOP-24 package that is ideal for compact designs. Absolute maximum ratings (Ta = 25C) Recommended operating conditions (Ta = 25C) 791 Audio ICs Block diagram 792 BA3853BFS Audio ICs BA3853BFS Pin descriptions and input / output circuits 793 Audio ICs 794 BA3853BFS Audio ICs BA3853BFS Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 8V, f = 1kHz, BW = 20Hz to 20kHz, VOL / C = MAX, TONE = ALL FLAT, FAD / C = FLAT, BAL / C = FLAT, LOUD = OFF, and MUTE = OFF) Operating specifications (1) Input and output signals have the same phase. (2) Maximum loudness control variation occurs at 30dB ATT. At 10dB ATT, the variation is 0dB. (3) For loudness operation during tone adjustment, arithmetic processing is performed with the maximum tone variation amount. 795 Audio ICs Measurement circuit 796 BA3853BFS Audio ICs BA3853BFS Measurement circuit switch operation A, B and C in the table refer to the following: A: Max. volume B: 1 / 2 volume C: Min. volume 797 Audio ICs Circuit operation (1) As shown is the block diagram, the main circuit blocks are the main volume (front and rear), tone control (bass and treble), and balance and fader. Signal control for each block is possible with a DC voltage. (2) The main volume is comprised of a front volume and rear volume controller. The front volume controller has 18dB of attenuation. Application example 798 BA3853BFS (3) The tone filter is an external CR circuit. Refer to item 5 of the application notes regarding the component values. (4) The loudness is set by a calculation based on the tone control current. Refer to control curves item 3 of the application notes. (5) The control curves for the balance and fader are given in the measurement data. Audio ICs External components (1) Mute and loudness circuit components Select the values for the mute and loudness on / off pin components to suit the product that you are designing. The value of the resistor should be 2.2MΩ or less. Set the circuit time constant as follows: BA3853BFS When using a switch as illustrated in the circuit diagram, set the values for C and R in the time-constant circuit as follows: (1) When the switch is on (rise) V = Vreg EXP (* t ) CR12 / (R1)R2) (2) When the switch is off (fall) V = Vreg (1 * EXP ( * t R1C2 )) V: pin 3 or pin 4 voltage (2) External filter circuits The filter circuits are built using passive components, and the resistors for both the bass and treble filters are on the chip. Construct the circuits shown below. (1) Bass filter cutoff frequency 1 1 fc1 = = 2πC1R1 2πC1 20kΩ (2) Treble filter cutoff frequency High-pass filter side 1 1 fc2 = = 2πC2R2 2πC2 10kΩ Low-pass filter side 1 = fc3 = 2πC3R3 2πc3 Filter cutoff frequencies The circuits given above have the following frequency characteristics. 1 100pF 20kΩ = 80kHz The tone control circuit is designed to give a change of ±15dB (Typ.) for the frequency that you wish to boost or cut at the peak and bottom of the frequency characteristic. Design the filter with due consideration to the frequency characteristics. The values for the filter given in the application circuit have been selected to give sufficient boost and cut at f = 100Hz and f = 10kHz. 799 Audio ICs BA3853BFS Application notes (1) Power supply voltage range Operation of the basic functions of the application example circuit are guaranteed if operated within the stipulated power supply voltage and ambient temperature ranges. Rohm cannot guarantee the ratings for the electrical characteristics, but these will not change radically if the circuit is operated within the stipulated power supply voltage and ambient temperature ranges. (2) Mute circuits Both the main volume and fader volume circuits have a built-in mute circuit. Mute is applied to all output pins. Mute logic (3) Loudness control (1) The loudness circuit is designed to work together with the main volume. (2) Maximum loudness change occurs when the signal attenuation is 30dB or lower. Up to a signal attenuation of 10dB, the circuit is designed to have a change in loudness of 0dB. (3) For signal attenuation between 10dB to 30dB, the change in loudness is smaller approaching 10dB, and gets larger approaching 30dB. (4) When loudness is operated during tone adjustment, if the amount of boost due to the combined tone boost and loudness exceeds the maximum boost, the circuit design ensures that the amount of loudness change will not exceed the maximum amount of tone boost (see Figs. 6 and 7). (5) Loudness is on when the pin voltage is below 2.5V, and off above 2.5V. 800 (4) Balance / fader (1) Balance control curve The balance control curve has been designed so that at above 2.8V, channel 1 (1-Fr, 1-Rr) is attenuated, and at below 2.2V, channel 2 (2-Fr, 2-Rr) is attenuated. (2) Fader control curve The fader control curve has been designed so that at below 2.2V, the front (1-Fr, 2-Fr) is attenuated, and at above 2.8V, the rear (1-Rr, 2-Rr) is attenuated. (5) Input / output circuits Buffers are used before and after the signal input and output pins. Audio ICs BA3853BFS External dimensions (Units: mm) 801