197

Regulator ICs

BA3940A

FOperation 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, char-

acteristic 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 ca-

pacitor having a capacitance of 1

µF 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 recom-

mend using a tantalum electrolytic capacitor with minimal

changes in capacitance.

(4)

Overcurrent protection circuit

An overcurrent protection circuit is installed in each out-

put 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 capaci-

tor. 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 oper-

ate continuously under transitional conditions (for

that the circuit ability is negatively correlated with temper-

ature.

(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 re-

duces 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.