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| Audio ICs ALS headphone driver BA3570F / BA3570FS The BA3570F and BA3570FS are stereo headphone amplifiers with ALS (Auto Loudness System) which have been designed for use as headphone drivers in audio equipment. FApplications Stereo headphones FFeatures 1) The use of ALS (Auto Loudness System) makes it possible to obtain a dynamic sound regardless of the volume level. 2) Built-in power mute circuit. 3) Built-in bypass circuit. FBlock diagram 554 Audio ICs FPin descriptions (pin numbers are for 22-pin BA3570F) BA3570F / BA3570FS FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 555 Audio ICs BA3570F / BA3570FS FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 3.0V, RL = 16, f = 1kHz, and the measurement circuit is as shown in Fig. 1) 556 Audio ICs FMeasurement circuit BA3570F / BA3570FS FExplanation of ALS operation and attached components (pin numbers are for 22-pin BA3570F) (1) ALS ON When ALS is on, the signal circuit (including external connections) is as shown in Fig. 2. 557 Audio ICs 1) Bass signal transmission and gain vs. frequency BA3570F / BA3570FS 2) Treble signal transmission and gain vs. frequency The gain and cutoff frequency of each block is as follows: 1 LPF1 cutoff frequency : fCL1= (Hz) 2 S (R3//R4) S C4 Amp E gain : GV(E) = 20log R15+R16 R15 (dB) z15dB Amp A gain ATT attenuation Amp B gain Amp B cutoff frequency : GV(A) = 0 : GV(ATT) = 20log : GV(B) = 20log : fCL3 = 1 2 S R7 S C11 1 2 S R12 S C12 EVR R10)EVR R7)R11 R7 (dB) (dB) (dB) (Hz) In this case, R3 = R4 = 2SR12 (= 100k) and C4 = C12 (= 0.1F), therefore fCL1 = fCL2 (= 32Hz), and the frequency characteristic is bass boost (*12 dB / OCT) as shown in Fig. 4. Also, R14 = 2SR13, therefore GV(D) = 6 (dB) and the EVR MAX total gain GLMAX when signals are input from both channels is GLMAX = GV(A)+GV(B)+GV(C)+GV(D) GLMAX = +GV(MUTE)+GV(E) GLMAX = GV(B)+6+15 (dB) The gain and cutoff frequency of each block is as follows: HPF cutoff : fCH1 = frequency 1 1 2 S (R6+R8) S C10 LPF2 cutoff frequency : fCL2 = Amp C gain Amp D gain Mute switch gain (Hz) (dB) R14 R13 (Hz) : GV(C) = 0 : GV(D) = 20log : GV(MUTE) = 0 (dB) (dB) 558 Audio ICs R8+R9 HPF cutoff : fCH2 = 2 S (R6R8+R8R10+R6R10) S C10 frequency 2 Amp D gain : GV(D) = 20log R13 R13+R14 BA3570F / BA3570FS (Hz) Amp D' gain: GV(D) = 20log R19+R20 R19 (dB) (dB) As R17 = R18 and R19 = R20, the total gain GV(OFF) when ALS is off is GV (OFF) = GV (ATT2) +GV (D) +GV (MUTE) +GV (E) = 15 *6 )6 0 15 (dB) Furthermore, as R14 = 2R13, GV(D) = +9.5 (dB) The total gain GH1 for the frequency band ftfCH1 is GH1 = 20log R9 R8+R9 +9.5+15 (dB) and it is flat as shown in Fig. 8. and the total gain GH2 for the frequency band fCH2tf is GH2 = 20log R9 R6 / / R8+R9 +9.5+15 (dB) 3) Combined frequency characteristics As shown in Fig. 6, the ALS characteristics can be obtained from the bass characteristics (Fig. 4) and the treble characteristics (Fig. 6). (2) ALS OFF The signal circuit when ALS is off is shown in Fig. 7. The gain and cutoff frequency of each block is as follows: ATT2 attenuation: GV(ATT2) = 20log R18 R17+R18 (dB) 559 Audio ICs FExplanation of ALS operation and attached components (1) ALS system control circuit The ALS system control circuit is shown in Fig. 9. BA3570F / BA3570FS FMute amplifier (pin numbers are for 22-pin BA3570F) The output muting can be switched on or off. FMute switching table S ALS mode switching table S ALS SW external connection value: C13 By increasing the capacitance of C13, the switching sound made when ALS is turned on or off can be reduced, however, the switching time will increase. Set the value appropriately for the application. S ALS external connection value: C14 The ALC attack and recovery time for ALS is determined by C14 connected to the pin (Pin 9). FMUTE SW external connection value: C8 By increasing the capacitance of C8, the switching sound made when the mute is turned on or off can be reduced, however, the switching time will increase. Set the value appropriately for the application. 560 Audio ICs FApplication example BA3570F / BA3570FS FElectrical characteristic curves 561 Audio ICs BA3570F / BA3570FS 562 Audio ICs FExternal dimensions (Units: mm) BA3570F / BA3570FS 563 |
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