MF8 datasheet(8/24 Pages) NSC

8 / 24 page

10 Application Information (Continued)

TLH8694 – 6

FIGURE 2c Multiple Feedback Loop Connection

12 CLOCKS

The MF8 has two clock input pins one for CMOS logic lev-

els and the other for TTL levels The TTL (pin 7) input auto-

matically adjusts its switching threshold to enable operation

on either single or split power supplies When this input is

used the CMOS logic input should be connected to pin

11(Vb) The CMOS Schmitt trigger input at pin 8 accepts

CMOS logic levels When it is used the TTL input should be

connected to either pin 11 (Vb) or pin 12 (Va) The basic

clock hookups for single and split supply operation are

shown in

Figures 3 and 4

Clock signals derived from a crystal-controlled oscillator are

recommended when maximum center frequency accuracy

is desired but in less critical applications the MF8 can gen-

erate its own clock signal as in

Figures 3c and 4c An exter-

nal resistor and capacitor determine the oscillation frequen-

cy Tolerance of these components and part-to-part varia-

tions in Schmitt-trigger logic thresholds limit the accuracy of

the RC clock frequency In the self-clocked mode the TTL

Clock input should be connected to either pin 11 or pin 12

TLH8694 – 7

(a) MF8 Driven with CMOS Logic Level Clock

TLH8694 – 8

(b) MF8 Driven with TTL Logic Level Clock

fCLK e

RC ln

VS b VT

Typically for VS e 10V

fCLK e

169 RC

VS e Va b Vb

TLH8694 – 9

FIGURE 3 Dual Supply Operation

MF8 Datasheet(PDF) 8 Page - National Semiconductor (TI)