HD74AC Datasheet, PDF (34/52 Pages) Hitachi Semiconductor – HD74AC Series Common Information

Design Considerations
ECL devices cannot directly drive FACT devices. Interfacing FACT-to-ECL can be accomplished by
using TTL-to-ECL translators and 10125 ECL-to-TTL translators in addition to following the same rules
on the TTL outputs to CMOS inputs (i.e., a resistor pull-up to V_CC of approximately 4.7 kΩ). The
translation can also be accomplished by a resistive network. A three-resistor interface between FACT and
ECL logic is illustrated in figure 4. Figures 5 and 6 show the translation from ECL-to-FACT, which is
somewhat more complicated. These two examples offer some possible interfaces between ECL and FACT
logic.
+5V
AC/ACT
560Ω
510Ω
470Ω
–5.2V
Figure 4 Resistive FACT-to-ECL Translation
T1,T2 - 2SC641 (K)
D1,D2 - HP5082 - 2811
510
D1
5.0V
AC
D2
ECL
T1 T2
Vbb
510
270
–5.2V
Figure 5 Single-Ended ECL-to-HD74AC Circuit
33