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| Regulator ICs System power supply for CD radio cassette players BA3936 The BA3936 is a system power supply for use in CD radio cassette players. With two 8V outputs, two 5V outputs, one 7.8V output, one POWER CONTROL output, the IC is best suited for CD radio cassette players. FApplications CD radio cassette players FFeatures 1) Two 8V outputs, two 5V outputs, one 7.8V output, and a POWER CONTROL output are built in. 2) Precise output voltage is obtained by using external reference voltage input (only AUDIO 8V and LIMIT 7.8V outputs have an internal reference voltage system). 3) Output current limit circuit protects the IC against short-circuiting damage. 4) Compact SIP-M12 package allows a large power dissipation. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 175 Regulator ICs FBlock diagram BA3936 176 Regulator ICs FInput / output circuits BA3936 177 Regulator ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 12.0V, and REF = 5V) BA3936 178 Regulator ICs BA3936 179 Regulator ICs BA3936 FCircuit operation LIMIT 7.8V rises regardless of VREF, STB, and MODE SW. AUDIO 8V and POWER CONTROL rises when STB is HIGH, regardless of MODE SW (Vref 5V is also required for POWER CONTROL). RADIO 5V rises when MODE SW is 1.4V (Typ.), and CD 5V and CD 8V rise when MODE SW is 3.2V (Typ.). 180 Regulator ICs BA3936 FEstimate of allowable power dissipation Except under transitional conditions, the power dissipation of this IC is 3W per unit at 25_C. See Fig. 5 for thermal derating curve, including some cases where heat sinks are used. S Power consumed by LIMIT 7.8V P1 = (VCC * 7.8V) maximum output current of LIMIT 7.8V maximum output current of AUDIO 8.0V S Power consumed by AUDIO 8.0V P2 = (VCC * 8.0V) maximum output current of CD 8.0V S Power consumed by CD 8.0V P3 = (VCC * 8.0V) maximum output current of CD 5.0V S Power consumed by CD 5.0V P4 = (VCC * 5.0V) maximum output current of RADIO 5.0V S Power consumed by RADIO 5.0V P5 = (VCC * 5.0V) S Power consumed internally by each circuit P6 = VCC circuit current PMAX. = P1 ) P2 ) (P3 ) P4 or P5, whichever is greater) ) P6 181 Regulator ICs FApplication example BA3936 FOperation notes (1) Operating power supply voltage When operating within 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. (2) Power dissipation (Pd) Refer to the heat reduction characteristics (Fig. 5) and the rough estimation of IC power dissipation given on a separate page. Make sure to use the IC within the allowable power dissipation with a sufficient margin. (3) Preventing oscillation at each output and installing a ripple filter capacitor To stop oscillation of output, make sure to connect a capacitor between GND and each of the AUDIO 8V (pin 3), RADIO (pin 5), CD 5V (pin 1), CD 8V (pin 2), and LIMIT 7.8V (pin 8) output pins. We recommend using a tantalum electrolytic capacitor having a capacitance of 10F or greater (100F or greater for AUDIO 8V) with minimal temperature susceptibility. A minimum capacitance val- ue recommended for each electrolytic capacitor is shown in the application circuit. Also, sudden deterioration of the AUDIO 8V ripple rejection during a power drop can be prevented by connecting a capacitor (220F or greater recommended) to the C pin (pin 4). (4) Overcurrent protection circuit An overcurrent protection circuit is installed on the AUDIO 8V (pin 3), RADIO (pin 5), CD 5V (pin 1), CD 8V (pin 2), and LIMIT 7.8V (pin 8) outputs, based on the respective output current. This prevents IC destruction by 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. Note that these protection circuits are only good for preventing damage from sudden accidents. Make sure your design does not cause the protection circuit to operate continuously under transitional conditions (for instance, if output is clamped at 1VF or higher, short mode circuit operates at 1VF or lower). 182 Regulator ICs (5) Reference voltage Because output voltage is dependent on the input reference voltage, unstable input results in output wavering and degradation of ripple rejection. Take care when setting the reference voltage power supply. Note that the AUDIO 8V and LIMIT 7.8V outputs, which have a built-in reference voltage system, are not affected by the external reference voltage. (6) Thermal protection circuit A built-in thermal protection circuit prevents thermal damage to the IC. All outputs except LIMIT 7.8V are switched OFF when the circuit operates, and revert to the original state when temperature drops to a certain level. (7) Grounding Each ground line in the application circuit must be adequately short regarding the GND (pin 12) pin. Make sure to arrange the ground lines, the AUDIO system, and other outputs in a pattern that prevents electric interference. FThermal derating curve FExternal dimensions (Units: mm) BA3936 183 |
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