Regulator ICs System power supply for CD radio cassette players BA3940A With built-in 9V, 7V, and 5V outputs, the BA3940A system power supply IC is best suited for use in CD radio cassette players. Applications CD radio cassette players Features 1) One 9V output, two 7V outputs (switched by MODE SW, only one output is available at the same time) and one 5V output are built in. 2) Output current limit circuit protects the IC against short-circuiting damage. Absolute maximum ratings (Ta = 25C) Recommended operating conditions (Ta = 25C) 192 3) Thermal protection circuit prevents heat damage to the IC. 4) Compact SIP-M12 package allows a large power dissipation. Regulator ICs BA3940A Block diagram Pin descriptions 193 Regulator ICs Input / output circuits 194 BA3940A Regulator ICs BA3940A Electrical characteristics (unless otherwise noted, Ta = 25C and VCC = 15V) 195 Regulator ICs Circuit operation Vo1, Vo2 and Vo4 rise when ST pin is 1.8V. With voltage applied on ST, the Vo2 output turns OFF when MODE is 1.6V (typical), and Vo3 turns ON when MODE is 3.2V (typical). Application example 196 BA3940A Regulator ICs Operation notes (1) Operating power supply 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 thermal derating curve (Fig. 4) and the rough estimation of IC power dissipation given on a separate page. If power dissipation exceeds the allowable limit, the functionality of IC will be degraded (such as reduction of current capacity by increased chip temperature). Make sure to use the IC within the allowable range of power dissipation with a sufficient margin. (3) Preventing oscillation at each output To stop oscillation of output, make sure to connect a capacitor having a capacitance of 1µF or greater between GND and each output pin. (To avoid the noise effect, lay out the grounding close to the IC) Oscillation can occur if capacitance is susceptible to temperature. We recommend using a tantalum electrolytic capacitor with minimal changes in capacitance. (4) Overcurrent protection circuit An overcurrent protection circuit is installed in each output system, 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, when output is clamped at 1VF or higher). Note that the circuit ability is negatively correlated with temperature. BA3940A (5) Thermal protection circuit A built-in thermal protection circuit prevents thermal damage to the IC. All outputs are switched OFF when the circuit operates, and revert to the original state when temperature drops to a certain level. (6) Improving ripple rejection by capacitors Ripple rejection of the 9V and 7V (current capacity = 1A) outputs can be improved by installing a capacitor that reduces the AC gain. (7) Malfunction in intense electric fields Note that bringing the IC into an intense electric field (such as a radio relay station) may result in malfunction. 197 Regulator ICs BA3940A FThermal derating curve Estimate of allowable power dissipation (PMAX.) S Power consumed by OUT 7V P1 = (VCC 7V) maximum load current of OUT 7V S Power consumed by OUT 5V P2 = (VCC 5V) maximum load current of OUT 5V S Power consumed by OUT 9V P3 = (VCC 9V) maximum load current of OUT 9V S Power consumed internally by each circuit P4 = VCC supply current PMAX. = P1 P2 P3 P4 FExternal dimensions (Units: mm) 198