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Audio ICs
6V / 330mW single-channel power amplifier
BA546
The BA546 is a monolithic power amplifier designed for use in portable radios, tape recorders and interphones. With a 6V power supply voltage, it has a rated output of 330mW into an 8 load (THD = 10%), and a maximum output of 550mW. It comes in a compact 9-pin SIP package with no heatsink fins.
FApplications Portable radios, cassette recorders, and interphones.
FFeatures 1) High output. POUT = 330mW (VCC = 6V and an 8 load (THD = 10%)). See Fig. 2. 2) Good low voltage characteristics. Begins operating at less than 2V (see Fig. 1).
3) 9-pin SIP package; around the same size as a preamplifier. 4) Pin compatible with the Rohm BA526 and BA527 power ICs. Choose to suit your application. 5) Low current dissipation (4.8mA Typ.).
FBlock diagram
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Audio ICs
FInternal circuit configuration
BA546
FAbsolute maximum ratings (Ta = 25_C)
FElectrical characteristics (unless otherwise noted, Ta = 25C, VCC = 6V, RL = 8 and f = 1kHz)
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Audio ICs
FMeasurement circuit
BA546
FAttached components (see Fig. 1) C1: input coupling capacitor The recommended value is 10F. This capacitor and RIN determine the bass cutoff frequency fLC1 for the input stage according to the following formula: 2C1RIN If the capacitance value of C1 is too small, the signal source reactance will increase, and cause the noise to increase and fLC1 will become higher. Conversely, if it is too large, the startup time after power is applied will be longer, and if the potentiometer is adjusted while the capacitor is charging, the charging current will flow through the slider current, and cause noise. DC cutoff resistor for the feedback circuit The recommended value is 47F. This capacitor and RNF determine feedback circuit bass cutoff frequency fLC2. fLC2 is given by the following formula: 1 [Hz] 2C2RNF Fig. 7 illustrates how changing C2 varies the bass characteristics. ripple filter capacitor The recommended value is 47F. fLC2 = fLC1 = 1 [Hz]
C4:
Phase compensation capacitor This capacitor determines the treble cutoff frequency fHC. fHC is given by the following formula: [kHz] C4 [pF] (however, GVC = 50dB) If GVC is not 50dB, fHC doubles for each decrease in GVC of 6dB. Fig. 7 illustrates how changing C4 varies the treble characteristics. ripple filter and pre-driver bypass capacitor The recommended value is 100F. If this capacitor is made too small, the ripple rejection and power output will deteriorate. Output coupling capacitor The recommended value is 470F. Power supply filter capacitor Determine based on the amount of power supply ripple and the regulation. fHC = 4000
C5:
C2:
C6: C7:
C3:
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Audio ICs
FCircuit construction (See Fig. 2) (1) Voltage amplification stage This circuit is comprised of a differential amplifier (Q1 and Q4), a constant current source (Q5), and an active load (Q2 and Q3). This active load is the input to the pre-driver (via Q8 and Q9). (2) Pre-driver The pre-driver is an earthed-emitter amplifier with transistors Q8 and Q9 forming a Darlington PNP transistor. The Q9 collector load is the input impedance looking from the base of Q14 and the constant-current load due to Q12. (3) Idling loop The idling loop is the Q13, Q10, Q11 and Q14 loop. The VBE of Q13 is subtracted from the VF of Q10 and Q11 and is biased by Q14. (4) Power stage The power stage is a quasi-complementary circuit made up of a Darlington PNP transistor (Q13 and Q15), and an NPN transistor (Q14).
BA546
(5) The AC gain is determined by the ratio between R6 (24k) and RNF connected to pin 7. The formula is as follows: [dB] RNF Variation of GVC and THD with RNF is shown in Fig. 12. GVC 20log 24k
FApplication example
The BA546 will generally be used as a power amplifier for portable cassette players and similar equipment, and will usually have a preamplifier before it, so insert the volume control between the stages. The gain of the power stage alone is determined by RNF. Use Fig. 12 to choose a value for RNF that gives the required gain.
When RNF is 68, the standard GVC is 50dB. When combining the BA546 with an ALC-equipped preamplifier as the previous stage, the control voltage for the ALC can be taken from pin 4, and the power supply for the preamplifier from pin 9.
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Audio ICs
FElectrical characteristics curves
BA546
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Audio ICs
FExternal dimensions (Units: mm)
BA546
410

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