Audio ICs Dual preamplifier with ALC BA3308 / BA3308F / BA3308FV The BA3308, BA3308F and BA3308FV are dual preamplifier ICs with built-in ALC circuits, and have been designed for use in stereo radio-cassette recorders and tape recorders. They come in compact 9-pin SIP (BA3308), 14-pin MF (BA3308F) and 14-pin SSOP (BS3308FV) packages, and have two record / playback preamplifiers, and an ALC circuit. The preamplifiers have high gain and low distortion, and can be directly coupled to the tape head without coupling capacitors. This prevents tape head magnetization and "pop" noise generation. A built-in rectifier means that an ALC circuit with good channel balance and large dynamic range can be constructed with addition of just an external time constant circuit. The ICs also include power-on mute circuits that suppress "pop" noise generation. Applications Stereo radio cassette recorders, cassette decks and home stereo systems and music centers Features 1) Built-in ALC rectifier diode. 2) Wide operating power supply voltage range (VCC = 4.5V to 14V). 3) Low current dissipation (IQ = 3.5mV). 4) High gain (GVO = 80dB). 5) Low distortion (THD = 0.1%). 6) 7) 8) 9) 10) Low noise (VNIN = 1Vrms) Input coupling capacitors and not necessary. Good ALC channel balance. Power-on mute circuit. ALC dynamic range can be varied by the addition of an external input resistor. Absolute maximum ratings (Ta = 25C) Recommended operating conditions (Ta = 25C) 193 Audio ICs BA3308 / BA3308F / BA3308FV Block diagram Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 7.0V, f = 1kHz and BPF: 20Hz to 20kHz) 194 Audio ICs BA3308 / BA3308F / BA3308FV Measurement circuit Application example Application example circuit PCB (copper side) 195 Audio ICs BA3308 / BA3308F / BA3308FV Total application circuit Circuit operation (1) Recording (1) Recording amplifier (See Fig. 5) The channel 1 and 2 amplifier input stages of the BA3308 (pins 8 and 2) can be direct-coupled, and the input coupling capacitors C1 and C2 are not particularly required. The voltage gain of the recording amplifier is given by GV = R5 / R3, but as a "pop" noise is generated when power is applied, (see "operation notes"), use the time constant circuit values given for C3 and R3 (C4 and R4) in the application example circuit diagram, or values close to these, and adjust the voltage gain with R5 (R6). R5 (R6) is also the DC bias feedback resistor, and is connected between pin 3 (7), and the output capacitor C5 (C6). (2) ALC (See Fig. 6) The BA3308 includes a signal rectifier block and electronic potentiometers required for the ALC. In the signal rectifier block, a comparator compares the DC output voltage component of the output stage signal (pins 3 and 7) to a voltage of 4.5VF (1VF is about 0.7V, so 4.5VF is approximately 3V), and if it is above this, the comparator switches on, and charges the smoothing capacitor C7. The operating point of the amplifier's ch1 and ch2 output 196 stages is fixed at 3VF, so when the signal output voltage is 1.5VF (an effective value of approximately 0.75V), the comparator goes on, DC signals for electronic potentiometer control are generated, and the ALC starts operating. The electronic potentiometers are connected between the input lines (pins 2 and 8) and GND, and the input signals is attenuated by the ratio of the electronic potentiometer resistances and the external resistors R1 and R2. The range of the ALC can be varied by the values of R1 and R2, but if they are too large the S / N ratio will worsen. Sufficient ALC range should be obtained with R1 and R2 values of around several kohms. C7 and R7 connected to pin 5 set the ALC attack and recovery times. The larger the values of these constants, the longer the recovery time, and the smaller the value of C7 the shorter the attack time. Audio ICs (2) Playback (See Fig. 7) During playback, the ch1 and ch2 amplifiers are used as NAB equalizer amplifiers, and time constant circuits are connected between pins 1 and 3, and 7 and 9 in the negative-feedback section to give the NAB characteristics. The voltage gain is given by: GV = R11 R9 / (I jC9 R9) / R3 In the same way as for recording, the NAB time constant circuit is adjusted to give the required gain (to prevent BA3308 / BA3308F / BA3308FV generation of a "pop" noise when power is applied). The output stage (pins 3 and 7) operating point is fixed at 3VF. Therefore, as indicated in the VMax. vs, VCC characteristic (see Fig. 19), even if the VCC voltage is made larger than 5V, the maximum output voltage will not exceed 1.2V (typ.). The ALC circuit is not required for playback, so pin 5 is grounded. The S / N ratio during playback is better if the external resistors R1 and R2 that are connected to the input pins (2 and 8) for recording are switched out. 197 Audio ICs Operation notes The BA3308 has a built-in power-on mute circuit to prevent generation of a "pop" sound when the power is applied. The generation of the "pop" sound is prevented by the DC blocking capacitors C3 and C4 connected to pins 1 and 9, and the charge time required for the ripple filter Application board component layout (component side) 198 BA3308 / BA3308F / BA3308FV capacitor C8 that is connected to pin 6. To ensure correct operation of this circuit, use the values given in the application example circuit for C3, C4, R3, R4, C8 and R8. Audio ICs BA3308 / BA3308F / BA3308FV Electrical characteristics curves 199 Audio ICs External dimensions (Units: mm) 200 BA3308 / BA3308F / BA3308FV Product Designation Page 1 of 2 ROHM-logo Product Designation l l l When ordering, specify the part number. Check each code against the tables shown below. Fill in from the left, leaving any extra boxes empty on the right. Product Designation Ordering information Packing and forming information only required for SOP, and QFP parts that are required in tape and reel containers. For example, to order part BA4558F on paper tape type E2, order number is BA4558F-E2, when required in tube container, order number is BA4558F. Quick reference of packaging specifications Package Container type DIP/SDIP Tube container SIP/HSIP/ZIP/SZIP/RSIP-A3 Tube container SOP/SSOP/HSOP/WSOP-10/WSOPL10 Packaging specification code Tube container Embossed E1, E2 tape file://F:\export\projects\bitting1\imaging\BITTING\cpl\20010105\01042001\ROHM...\7form.htm 1/5/01 Product Designation SSOP-A54 Page 2 of 2 Embossed E2 tape Tray Tray (dry QFP/SQFP/VQFP/UQFP/TQFP/PBGA pack) VP Embossed E1, E2 tape Bulk TO220FP Tube container SMP5 Embossed TL, TR tape TO252 Embossed E1, E2 tape RSLP8 Embossed E2(Sprocket 1pin, tape Horizontal) RSIP13 E2(Sprocket 1pin, Embossed Horizontal), E4 tape (Sprocket 1pin, Vertical) Note: SOP type can be delivered in tube, paper tape, or embossed tape. BGA/CSP package | SIP/ZIP package QFP package | Photo package SOP package | Product Designation DIP package | Packaging Specification [LSI Package Assemblies] [HOME | Selection Guide] file://F:\export\projects\bitting1\imaging\BITTING\cpl\20010105\01042001\ROHM...\7form.htm 1/5/01