Rainbow Electronics BA3938 User Manual

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 V
Features
1) One 11V output (external transistor required) and in­terlocked outputs of 8.5V , 5V , 9V , and V
2) Output current limit circuit protects the IC against short-circuiting damage.
CC, the IC is best suited for CD radio cassette players.
3) Compact HSIP-B12 package allows a large power
CC are built in.
dissipation.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions (Ta = 25C)
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Regulator ICs BA3938
Block diagram
Pin descriptions
185
Regulator ICs BA3938
Input / output circuits
186
Regulator ICs BA3938
Electrical characteristics (unless otherwise noted, Ta = 25C and VCC = 15.0V)
187
Regulator ICs BA3938
Circuit operation All outputs rise when voltage is applied on the STANDBY pin.
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Regulator ICs BA3938
Application example
Operation 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 10µF 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 V 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 V
CC 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 1V
F or lower). Note that the circuit ability is negatively
at 1V
F or higher, short mode circuit operates
correlated with temperature.
CC
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Regulator ICs BA3938
(5) Thermal protection circuit A built-in thermal protection circuit prevents thermal damage to the IC. All outputs except V
CC + 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 1 1, for small current) pins are sep­arately provided. Make sure to connect circuits to correct pins.
FThermal derating cueve
(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
Estimate of allowable power dissipation (P
S Power consumed by V
CC + B P1 = (VCC * VCC + B) maximum output current of VCC + B
MAX.)
S Power consumed by OUT 5V P S Power consumed by CD 8.5V P S Power consumed by OUT 9V P S Power consumed internally by each circuit P
MAX. = P1 ) P2 ) P3 ) P4 ) P5
P
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2 = (VCC * 5V) maximum output current of OUT 5V 3 = (VCC * 8.5V) maximum output current of OUT 8.5V 4 = (VCC * 9V) maximum output current of OUT 9V 5 = VCC supply current
Regulator ICs BA3938
External dimensions (Units: mm)
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