BA3835S

Audio ICs Band-pass filter for spectrum analyzer BA3835S / BA3835F The BA3835S and BA3835F are 5-band, band-pass filter ICs that use microprocessor time division to produce serial output for spectrum analyzer displays. To minimize the number of external components required and enable compact and reliable designs, all of the capacitors for the filters are on the chip. FApplications CD radio cassette players, mini-component stereo systems, car stereos FFeatures 1) Five band-pass filter elements for spectrum analyzer displays. 2) High-speed readout (output response time : 5µsec. Typ.). 3) Discharge time constant circuit for each band is on the chip. 4) Differential input amplifier rejects common-mode noise. 5) Single 5V power supply. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 601 Audio ICs FBlock diagram 1 (BA3835S) BA3835S / BA3835F 602 Audio ICs FBlock diagram 2 (BA3835F) BA3835S / BA3835F 603 Audio ICs BA3835S / BA3835F FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V, RL = 10MΩ, VAIN = *30dBV and SEL = 1) 604 Audio ICs FMeasurement circuit (BA3835S) BA3835S / BA3835F 605 Audio ICs FOutput select logic table BA3835S / BA3835F FTiming chart 606 Audio ICs FApplication example (BA3835S) BA3835S / BA3835F 607 Audio ICs FOperation notes (1) Frequency characteristics The frequency characteristics of this IC are determined by the resistor connected between the RREF terminal and GND. For the specification conditions, the value of this resistor is 100kΩ. If it is necessary to set the frequency characteristics accurately, use a variable resistor (note : all bands will shift together). (2) Load characteristics To convert the bias sense output signal to the GND sense signal, the IC performs a V / I conversion, and then an I / V conversion using a 10kΩ resistor (typ.) for the output. Therefore, if the load circuit connected to the A OUT pin has a MOS structure there is no problem (eg. microprocessor input port), but if the connected circuit has a low input impedance, it may cause the output level to drop. (3) External resistor for the control pin When using a common port for the output select control and FL drive, you must add a diode and resistor as shown in Fig. 4 to prevent the FL drive “L” voltage from destroying the IC. BA3835S / BA3835F And from this, the following condition is obtained : R < 30kΩ In this case, the “L” level voltage V2 for the IC will be : V2 < 0.75V (4) Recommended operating ranges Provided that the IC is operated within the recommended operating conditions and the recommended temperature range, the basic circuit functions are guaranteed. Within these ranges, ratings for electrical characteristics for conditions other than those stipulated cannot be guaranteed, but the inherent function of the bandpass filter will be maintained. (5) Application circuit Provided the recommended circuit constants are used, the application circuit should function correctly. However, we recommend that you confirm the characteristics of the circuits in actual use and pay due attention to the cautionary notes given below. If you change the circuit constants, check both the static and transient characteristics of the circuit, and allow sufficient margin to accommodate variations between both ICs and external components. Note, also, that Rohm has not been able to conduct a sufficient study into patent rights. In this case, the “L” voltage applied to the internal comparator input terminal V1 is given by : V1 = R1)R R1)R2)R Vref To maintain a noise margin of at least 2.5V with respect to the comparator threshold level Vref, the representative values for Vref, R1 and R2 are 1.5V, 20kΩ, and 10kΩ respectively. This gives : 20kΩ)R 20kΩ)10kΩ)R 1.5V)0.25V