DRIVEN GATE萨 IIH DRIVI DRIVEN GATE HIGH GATE萨2 curre 工H GATE F1 L DRIVEN GATE GATE F2 current ng DRIVEN GATE F FIGURE 79.5 Current loading of driving gates. TABLE 79.4 Worst Case Current Parameters for Selected Logic Subfamilies ubfamil 16 mA AA叭 8 mA 201 8 mA 20uA-100μ 201 0.6mA 74HCxx 4 mA 4AHCXX 74AHCTxX -50 mA -265μA500 10Hxxx 50 mA OH(min)vIH(min) (79.1) (79.2) Using the logic voltage values given in Table 79.3 for the selected subfamilies reveals that highest noise immunity is obtained with logic devices in the CMOS family, while lowest noise immunity is endemic to the ECL family. Switching circuit outputs are loaded by the inputs of the devices that they are driving, as illustrated in Fig. 79.5. Worst case input loading current levels and output driving current capabilities are listed in Table 79.4 for various logic subfamilies. The fan-out of a driving device is the ratio between its output current capabilities at each logic level and the corresponding gate input current loading value. Switching circuits based on bipolar transistors have fan-out limited primarily by the current-sinking and current-sourcing capabilities of the driving c2000 by CRC Press LLC© 2000 by CRC Press LLC VNH = VOH(min) – VIH(min) (79.1) VNL = VIL(max) – VOL(max) (79.2) Using the logic voltage values given in Table 79.3 for the selected subfamilies reveals that highest noise immunity is obtained with logic devices in the CMOS family, while lowest noise immunity is endemic to the ECL family. Switching circuit outputs are loaded by the inputs of the devices that they are driving, as illustrated in Fig. 79.5. Worst case input loading current levels and output driving current capabilities are listed in Table 79.4 for various logic subfamilies. The fan-out of a driving device is the ratio between its output current capabilities at each logic level and the corresponding gate input current loading value. Switching circuits based on bipolar transistors have fan-out limited primarily by the current-sinking and current-sourcing capabilities of the driving device. FIGURE 79.5 Current loading of driving gates. TABLE 79.4 Worst Case Current Parameters for Selected Logic Subfamilies Subfamily IOH(max) IOL(max) IIH(max) IIL(max) 74xx –400 mA 16 mA 40 mA –1.6 mA 74LSxx –400 mA 8 mA 20 mA –400 mA 74ASxx –2 mA 20 mA 200 mA –2 mA 74ALSxx –400 mA 8 mA 20 mA –100 mA 74Fxx –1 mA 20 mA 20 mA –0.6 mA 74HCxx –4 mA 4 mA 1 mA –1 mA 74HCTxx –4 mA 4 mA 1 mA –1 mA 74ACxx –24 mA 24 mA 1 mA –1 mA 74ACTxx –24 mA 24 mA 1 mA –1 mA 74AHCxx –8 mA 8 mA 1 mA –1 mA 74AHCTxx –8 mA 8 mA 1 mA –1 mA 10xxx 50 mA –50 mA –265 mA 500 nA 10Hxxx 50 mA –50 mA –265 mA 500 nA