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Regulator ICs
Power supply for CD radio cassette players
BA3924
The BA3924 is a system reference power supply for use in CD radio cassette players. Outputs dedicated to a microprocessor (5.0V), CD player (7.5V), audio system (7.5V), and motor drive (9V) are built in. Also built in is a VCC)B output that allows turning ON and OFF the supply voltage by HIGH and LOW levels of the standby pin.
FApplications CD radio cassette players
FFeatures 1) With outputs dedicated to a microcontroller, CD player, audio system, and motor drive, the IC is best suited for CD radio cassette players. 2) Zero standby current (typ.). 3) Output current limit circuit protects the IC against short-circuiting damage.
4) Compact 12-pin package allows large power dissipation. 5) Thermal shutdown circuit protects the IC against thermal damage. 6) VCC)B output allows turning ON and OFF the power supply voltage by HIGH and LOW levels of the standby pin.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
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FBlock diagram
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FPin descriptions
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FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 12V)
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FMeasurement circuits
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FCircuit operation
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FApplication example
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FOperation notes (1) Operating power supply voltage When operating within the proper ranges of power supply voltage and ambient temperature, most circuit functions are guaranteed. Although the rated values of electrical characteristics cannot be absolutely guaranteed, characteristic values do not change drastically within the proper ranges. When the supply voltage becomes less than the sum of the minimum I / O voltage differential and each output voltage, the reference power supply will not function any more. However, there will be no sudden drop in voltage or output current. (2) Power dissipation (Pd) Refer to the power dissipation characteristics (Fig. 7) and the rough estimation of IC power dissipation given on a separate page. Make sure to consider the power dissipation of the external PNP transistors, through which power is supplied to the AUCIO, CD, and COMMON circuits. Leave a sufficient margin in your application. S Power dissipation Except under transitional conditions, the power dissipation of this IC is 3W per unit at 25_C. Use the following equations and Fig. 1 to roughly calculate the allowable power dissipation and decide if a heat sink is needed or what kind of a heat sink is needed. (Basic equation) Pd = P * PO where P = power supplied from the power supply PO = power supplied to the load from the IC
BA3924
(Rough estimation) S Power consumed by the AUDIO output P1 = (VOMO * VO1) IO1 S Power consumed by the CD output P2 = (VOMO * VO2) IO2 S Power consumed by the COMMON output P3 = (VOMO * VO3) IO3 S Power consumed by the VCC+B output P4 = (VCC * VO4) IO4 S Power consumed by the circuit current P5 = VCC IQ S Power consumed by the MOTOR output where P6 = (VCC * VF) IBMO Pd = P1 ) P2 ) P3 ) P4 ) P5 ) P6 VCC is the maximum constant supply voltage VOMO is the minimum MOTOR output voltage VO1 is the minimum AUDIO output voltage VO2 is the minimum CD output voltage VO3 is the minimum COMMON output voltage VO4 is the minimum VCC)B output voltage VCC * VF = (minimum constant supply voltage) * 0.7V IQ is the maximum circuit current IO1 is the maximum AUDIO constant output current IO2 is the maximum CD constant output current IO3 is the maximum COMMON constant output current IO4 is the maximum VCC)B constant output current IO5 is the maximum constant base drive current
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(3) Preventing oscillation at each output To stop output oscillation, make sure to connect a capacitor between GND and each of the MOTOR (pin 3), AUDIO (pin 5), COMMON (pin 6), and CD (pin 8) output pins. Use capacitors whose valve are not below the values denoted in the application circuit (Fig. 4) and not susceptible to temperature. (4) Ground pins Pre GND (pin 10) and Pow GND (pin 12) are the ground pins of the IC. Pin 10 is the reference ground pin for power supplies, including the built-in reference power supply, and the comparators. Voltage and threshold values may shift if the potential of pin 10 is unstable. Take sufficient care when designing the conductor pattern near this pin. The source current from this pin is in the level of a few milliamperes. Pin 12, which is connected to the ground traces other than those connected to pin 10, is connected with the IC substrate and the back metal. (5) External PNP transistors ROHM's 2SB1370 (E- or F-rank) is recommended. This is a TO-220FP type transistor. (6) Overvoltage protection circuit Although the absolute maximum voltage is 22V, a peak voltage of 30V for 200ms is assured only during the standby state (pin 11 is LOW). The overvoltage circuit is activated when the VCC voltage exceeds 23V. When the circuit is activated, a standby circuit current (IST) of a few milliamperes flows in the IC. The overvoltage protection circuit is also activated if a voltage exceeding the absolute maximum rating is applied while the STANDBY pin is HIGH. As a result all the output voltage is turned off.
BA3924
(7) Overcurrent protection circuit If the output current of any of the MOTOR (pin 3), AUDIO (pin 5), COMMON (pin 6), and CD (pin 8) exceeds the current capacity, the built-in current limit circuit limits the current to a set level. If the potential of each pin is about the same as that of Pow GND (pin 12), the output current is reduced to the level of the ground short-circuit current given in the "Electrical Characteristics." (8) Thermal protection The circuit current, the limit current of each power supply output, and the ground short-circuit current decrease gradually with increasing temperature. For further protection, the thermal shutdown circuit turns off all outputs when the IC is overheated, and brings back to normal operation when the temperature is decreased to a certain level.
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FElectrical characteristic curve
BA3924
FExternal dimensions (Units: mm)
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