BA3308 ROHM

Document overview

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Technical content

Features

1) Built-in ALC rectifier diode. 2) Wide operating power supply voltage range (V CC = 4.5V to 14V). 3) Low current dissipation (IQ = 3.5mV). 4) High gain (GVO = 80dB). 5) Low distortion (THD = 0.1%). 6) Low noise (VNIN = 1µVrms) 7) Input coupling capacitors and not necessary. 8) Good ALC channel balance. 9) Power-on mute circuit. 10) ALC dynamic range can be varied by the addition of an external input resistor. Absolute maximum ratings (Ta = 25C) Recommended operating conditions (Ta = 25C)

Audio ICs BA3308 / BA3308F / BA3308FV Block diagram Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 7.0V, f = 1kHz and BPF: 20Hz to 20kHz)

Audio ICs BA3308 / BA3308F / BA3308FV Measurement circuit Application example Application example circuit PCB (copper side)

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 cou- pling capacitors C 1 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 C 3 and R3 (C4 and R4) in the ap- plication example circuit diagram, or values close to these, and adjust the voltage gain with R 5 (R6). R5 (R6) is also the DC bias feedback resistor, and is connected be- tween pin 3 (7), and the output capacitor C 5 (C6). (2) ALC (See Fig. 6) The BA3308 includes a signal rectifier block and elec- tronic 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 4.5V F (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 C The operating point of the amplifier’s ch1 and ch2 output 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 poten- tiometer control are generated, and the ALC starts oper- ating. The electronic potentiometers are connected between the input lines (pins 2 and 8) and GND, and the input sig- nals is attenuated by the ratio of the electronic potentiom- eter resistances and the external resistors R 1 and R2. The range of the ALC can be varied by the values of R1 and R 2, but if they are too large the S/N ratio will worsen. Suf- ficient ALC range should be obtained with R1 and R2 val- ues 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 BA3308 / BA3308F / BA3308FV (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 nega- tive-feedback section to give the NAB characteristics. The voltage gain is given by: G V =  R 11 R9 / (I jϖ C 9 /C0083 R9)  /R3 In the same way as for recording, the NAB time constant circuit is adjusted to give the required gain (to prevent 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 R 1 and R2 that are connected to the input pins (2 and 8) for recording are switched out.

Audio ICs BA3308 / BA3308F / BA3308FV Operation notes The BA3308 has a built-in power-on mute circuit to pre- vent generation of a “pop” sound when the power is ap- plied. The generation of the “pop” sound is prevented by the DC blocking capacitors C 3 and C4 connected to pins 1 and 9, and the charge time required for the ripple filter 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, C 8 and R8. Application board component layout (component side)

Audio ICs BA3308 / BA3308F / BA3308FV Electrical characteristics curves

External dimensions (Units: mm) 200 Audio ICs BA3308 / BA3308F / BA3308FV