12. External resistors

• R4 and R5

R4 and R5 are used to apply the high-level input to the F/R pin. Since the F/R pin has a built-in pull-down resistor

which is about 50 k

Ω, it will be at the low level when left open. A voltage of between 4.0 and 6.3 V must be

applied to input a high level to the F/R pin.

• R15

R15 is used to apply the high-level input to the S/S pin. Since the S/S pin has a built-in pull-down resistor which is

about 50 k

Ω, it will be at the low level when left open. (A voltage of between 4.0 and 6.3 V must be applied to

input a start-state high level to the S/S pin.) As is the case with the F/R input, using a two-resistor voltage divider

to apply a voltage to the S/S pin provides better noise immunity since a lower input impedance can be set up.

However, in applications where noise is not a problem, the high level may be applied with a single resistor, as is

done with R15 in this circuit.

even though the circuit is in stop mode. This is because the S/S pin input voltage is provided through a two-

is the start mode input level. If it is impossible to increase the speed with which the power voltage is brought up

13. Through currents due to the direct PWM technique

In the direct PWM technique, through currents may flow in the output due to the switching. (This occurs in both

discrete component implementations as well as with the LB1822.) This is due to the delay and parasitic capacitors in

the output transistors. Earlier application used capacitors to deal with this problem if it occurred. However, since this

IC includes circuits designed to deal with this phenomenon, there is no need for external components to deal with

these currents. During switching, whiskers of up to about 10 ns may appear in the RF waveform, but they will not

cause problems in applications.

14. Oscillators

Normally, applications using this IC will use a crystal oscillator. However, it may be possible to use a ceramic

oscillator in applications in which the requirements on the speed control characteristics are not demanding. To avoid

problems, always consult the manufacturer of the oscillator element concerning the values of the external capacitors

and resistors used.

Stop mode:

Start mode:

• Power dissipation when a –10-mA load current is drawn from the 7-V fixed voltage output.

• Power dissipation due to the output drive current (when the output duty is 100%)

Therefore, the IC overall power dissipation will be:

Start mode:

P = P2 = 0.08 W

Stop mode:

P = P1 + P3 + P4 + P5 = 5.95 W

(For an output duty of 100%)

No. 5679-7/10

LB1922