LM3488MM datasheet(14/24 Pages) NSC

14 / 24 page

Functional Description (Continued)

TABLE 1. (Continued)

OFF(SYNC) (µsec)

SYNC range (k

Ω)

55to90

70to110

85to140

100 to 160

120 to 190

135 to 215

150 to 240

It is also necessary to have the width of the synchronization

pulse narrower than the duty cycle of the converter. It is also

necessary to have the synchronization pulse width

≥

300nsecs.

The FA/SYNC/SD pin also functions as a shutdown pin. If a

high signal (refer to the electrical characteristics for definition

of high signal) appears on the FA/SYNC/SD pin, the LM3488

stops switching and goes into a low current mode. The total

supply current of the IC reduces to less than 10µA under

these conditions.

Figure 8 and Figure 9 show implementation of shutdown

function when operating in Frequency adjust mode and syn-

chronization mode respectively. In frequency adjust mode,

connecting the FA/SYNC/SD pin to ground forces the clock

to run at a certain frequency. Pulling this pin high shuts down

the IC. In frequency adjust or synchronization mode, a high

signal for more than 30ms shuts down the IC.

10138816

FIGURE 6. Frequency Adjust

10138815

FIGURE 7. Frequency Synchronization

10138816

FIGURE 8. Shutdown Operation in Frequency Adjust Mode

LM3488MM Datasheet(PDF) 14 Page - National Semiconductor (TI)