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| Regulator ICs System power supply for car stereos BA3918 The BA3918 is a single-chip power supply IC for use in car audio systems. One 5.6V output for a microcontroller, three 8.7V outputs, and two outputs interlocked by BACKUP and ACC systems are built in. FApplications Car audio systems FFeatures 1) All outputs except AMP and ANT use a PNP transistor with a low saturation voltage. 2) Output current limit circuit prevents damage to the IC due to short-circuiting. 3) Overvoltage protection circuit provides protection against surges from the ACC or BACKUP input. 4) Compact 12-pin POWER package allows large power dissipation. 5) Thermal protection circuit prevents heat damage to the IC. FBlock diagram 242 Regulator ICs FAbsolute maximum ratings (Ta = 25_C) BA3918 FRecommended operating conditions (Ta = 25_C) FPin descriptions 243 Regulator ICs FInput / output circuits BA3918 244 Regulator ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 13.2V) BA3918 245 Regulator ICs BA3918 FInput / output timing chart 246 Regulator ICs FEstimate of allowable power dissipation Except under transitional conditions, the power dissipation of this IC is 3W per unit at 25_C. See Fig. 4 for thermal derating characteristics, including some cases where heat sinks are used. BA3918 A = maximum voltage for VCC I1 = maximum output current for VDD I2 = maximum output current for COM I3 = maximum output current for AMP I4 = maximum output current for ANT I5 = maximum output current for AM I6 = maximum output current for FM S Power consumed by VDD 5.6V S Power consumed by COM 8.7V S Power consumed by AMP S Power consumed by ANT S Power consumed by AM 8.7V S Power consumed by FM 8.7V S Power consumed internally by each circuit P1 = (A * 5.6V) I1 ) (I1 / 20 ) I1 / 10) I2 ) (I2 / 30 ) I2 / 10) P2 = (A * 8.7V) P3 = 1V I3 ) (22mA) A I4 ) (22mA) A P4 = 1V I5 ) (I5 / 30 ) I5 / 10) P5 = (A * 8.7V) I6 ) (I2 / 50 ) I6 / 10) P6 = (A * 8.7V) circuit current (about 5mA) P7 = VCC A A A A PMax. = P1 ) P2 ) P3 ) P4 ) (P5 or P6, whichever is greater) ) P7 247 Regulator ICs FApplication example BA3918 248 Regulator ICs FOperation notes (1) Example of application The application circuit of Fig. 3 is recommended for use. Make sure to confirm the adequacy of parts characteristics. When using the circuit with changes to external circuit constants, make sure to leave sufficient margins in consideration of fluctuations in the IC and external components including static and transitional characteristics. Note that ROHM has not carried out extensive survey regarding the patent right of this application. (2) 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. (3) Power dissipation (Pd) Refer to the power dissipation curves (Fig. 4) and the rough estimation of IC power dissipation given on a separate page. Make sure your design allows a maximum power within the operating temperature range. (4) Overvoltage protection circuit The overvoltage protection circuit turns OFF all outputs when the potential difference between VCC (pin 7) and GND (pin 12) is more than about 26V at normal temperature. Make sure to use the IC within this voltage limit. (5) Preventing oscillation at each output To stop output oscillation, make sure to connect a capacitor having a capacitance of 10F or greater between GND and each of the VDD (pin 5), COM (pin 9), AM (pin 10), and FM (pin 11) output pins. We recommend using a tantalum electrolytic capacitor whose capacitance is unsusceptible to temperature. (6) Overcurrent protection circuit An overcurrent protection circuit is installed on the VDD (pin 5), AMP (pin 6), ANT (pin 8), COM (pin 9), AM (pin 10), and FM (pin 11) outputs, based on the respective output current. This prevents IC destruction due to overcurrent, by limiting the current with a curve shape of "7" in the voltage-current graph. The IC is designed with margins so that current flow will be restricted and latching will be prevented even if a large current suddenly flows through a large capacitor. The circuit should be carefully set because output current is further restricted when output voltage is less than 1VF (considered as short mode). BA3918 (7) Thermal protection circuit A built-in thermal protection circuit prevents thermal damage to the IC. All outputs except VDD are switched OFF when the circuit operates, and revert to the original state when temperature drops to a certain level. (8) Grounding Each ground trace in the application circuit of Fig. 3 must be adequately short from GND (pin 12). Make sure to arrange the ground traces in a pattern that prevents mutual interference. (9) Although the quality of this IC is rigorously controlled, the IC may be destroyed when the supply voltage or the operating temperature exceeds their absolute maximum ratings. Because short mode or open mode cannot be specified when the IC is destroyed, be sure to take physical safety measures, such as fusing, if any of the absolute maximum ratings might be exceeded. (10) We recommend installing a bypass line in your application if there is a mode where potential difference between each output and input (VCC) or GND is reversed from the normal state. FThermal derating characteristic curve 249 Regulator ICs FElectrical characteristic curves BA3918 FExternal dimensions (Units: mm) 250 |
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