BA3918 データシートの表示（PDF） - ROHM Semiconductor

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BA3918

System power supply for car stereo

ROHM Semiconductor 

Regulator ICs

FOperation notes

(1) Example of application

The application circuit of Fig. 3 is recommended for use.

Make sure to confirm the adequacy of parts characteris-

tics. When using the circuit with changes to external cir-

cuit constants, make sure to leave sufficient margins in

consideration of fluctuations in the IC and external com-

ponents including static and transitional characteristics.

Note that ROHM has not carried out extensive survey re-

garding the patent right of this application.

(2) Operating power supply voltage

When operating within the 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, char-

acteristic values do not change drastically within the

proper ranges.

(3) Power dissipation (Pd)

Refer to the power dissipation curves (Fig. 4) and the

rough estimation of IC power dissipation given on a sepa-

rate page. Make sure your design allows a maximum

power within the operating temperature range.

(4) Overvoltage protection circuit

The overvoltage protection circuit turns OFF all outputs

when the potential difference between VCC (pin 7) and

GND (pin 12) is more than about 26V at normal tempera-

ture. Make sure to use the IC within this voltage limit.

(5) Preventing oscillation at each output

To stop output oscillation, make sure to connect a capaci-

tor having a capacitance of 10µF or greater between

GND and each of the VDD (pin 5), COM (pin 9), AM (pin

10), and FM (pin 11) output pins. We recommend using

a tantalum electrolytic capacitor whose capacitance is

unsusceptible to temperature.

(6) Overcurrent protection circuit

An overcurrent protection circuit is installed on the VDD

(pin 5), AMP (pin 6), ANT (pin 8), COM (pin 9), AM (pin

10), and FM (pin 11) outputs, based on the respective

output current. This prevents IC destruction due to over-

current, 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. The circuit should be carefully

set because output current is further restricted when out-

put voltage is less than 1VF (considered as short mode).

BA3918

(7) Thermal protection circuit

A built-in thermal protection circuit prevents thermal

damage to the IC. All outputs except VDD are switched

OFF when the circuit operates, and revert to the original

state when temperature drops to a certain level.

(8) Grounding

Each ground trace in the application circuit of Fig. 3 must

be adequately short from GND (pin 12). Make sure to ar-

range the ground traces in a pattern that prevents mutual

interference.

(9) Although the quality of this IC is rigorously con-

trolled, the IC may be destroyed when the supply voltage

or the operating temperature exceeds their absolute

maximum ratings. Because short mode or open mode

cannot be specified when the IC is destroyed, be sure to

take physical safety measures, such as fusing, if any of

the absolute maximum ratings might be exceeded.

(10) We recommend installing a bypass line in your ap-

plication if there is a mode where potential difference be-

tween each output and input (VCC) or GND is reversed

from the normal state.

FThermal derating characteristic curve

249

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