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| Regulator ICs System power supply for CD radio cassette players BA3938 The BA3938 is a system power supply IC for use in CD radio cassette players. With one 11V output and interlocked outputs of 8.5V, 5V, 9V, and VCC, the IC is best suited for CD radio cassette players. FApplications CD radio cassette players FFeatures 1) One 11V output (external transistor required) and interlocked outputs of 8.5V, 5V, 9V, and VCC are built in. 2) Output current limit circuit protects the IC against short-circuiting damage. 3) Compact HSIP-B12 package allows a large power dissipation. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 184 Regulator ICs FBlock diagram BA3938 FPin descriptions 185 Regulator ICs FInput / output circuits BA3938 186 Regulator ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 15.0V) BA3938 187 Regulator ICs BA3938 FCircuit operation All outputs rise when voltage is applied on the STANDBY pin. 188 Regulator ICs FApplication example BA3938 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. 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 10F or greater between GND and each output pin. Oscillation can occur if capacitance is susceptible to temperature. We recommend using a tantalum electrolytic capacitor with minimal changes in capacitance. Also, output can be further sta- bilized by connecting a bypass capacitor between VCC and GND. (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 (a curve shape of "inverted -L" for VCC ) B). 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). Note that the circuit ability is negatively correlated with temperature. 189 Regulator ICs (5) Thermal protection circuit A built-in thermal protection circuit prevents thermal damage to the IC. All outputs except VCC + B are switched OFF when the circuit operates, and revert to the original state when temperature drops to a certain level. (6) Grounding To minimize the variation of output voltage due to variations in load current, the GND (pin 12, for large current) and the PRE GND (pin 11, for small current) pins are separately provided. Make sure to connect circuits to correct pins. BA3938 (7) STANDBY voltage Note that ON-state voltage and HIGH-state input current of each output change when the external resistors of the STANDBY pin are changed. These values are roughly estimated as : STB voltage when ON = 0.7 (R1 ) R2) / R2 STB current when HIGH = (5*0.7) / R1 FThermal derating cueve Estimate of allowable power dissipation (PMAX.) S Power consumed by VCC + B S Power consumed by OUT 5V S Power consumed by CD 8.5V S Power consumed by OUT 9V S Power consumed internally by each circuit P1 = (VCC * VCC + B) maximum output current of VCC + B maximum output current of OUT 5V P2 = (VCC * 5V) P3 = (VCC * 8.5V) maximum output current of OUT 8.5V maximum output current of OUT 9V P4 = (VCC * 9V) supply current P5 = VCC PMAX. = P1 ) P2 ) P3 ) P4 ) P5 190 Regulator ICs FExternal dimensions (Units: mm) BA3938 191 |
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