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.
3) Thermal protection circuit prevents heat damage to
the IC.
4) Compact SIP-M12 package allows a large power dissipation.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions (Ta = 25C)
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Regulator ICs BA3940A
Block diagram
Pin descriptions
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Regulator ICs BA3940A
Input / output circuits
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Regulator ICs BA3940A
Electrical characteristics (unless otherwise noted, Ta = 25C and VCC = 15V)
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Regulator ICs BA3940A
Circuit operation
Vo1, Vo2 and V o4 rise when ST pin is 1.8V . With voltage applied on ST , the V
(typical), and V
o2 output turns OFF when MODE is 1.6V
o3 turns ON when MODE is 3.2V (typical).
Application example
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Regulator ICs BA3940A
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. (T o avoid the noise ef fect, 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 1V
that the circuit ability is negatively correlated with temperature.
F or higher). Note
(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.
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Regulator ICs BA3940A
FThermal derating curve
Estimate of allowable power dissipation (P
MAX.)
S Power consumed by OUT 7V P
S Power consumed by OUT 5V P
S Power consumed by OUT 9V P
S Power consumed internally by each circuit P
P
MAX. = P1 P2 P3 P4
FExternal dimensions (Units: mm)
1 = (VCC 7V) maximum load current of OUT 7V
2 = (VCC 5V) maximum load current of OUT 5V
3 = (VCC 9V) maximum load current of OUT 9V
4 = VCC supply current
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