Dynamic Shift Registers - Bitsavers - Trailing-Edge

UM....oo::I:~.......M....oo::I:~fan-out calculationThe drive capability of the MH0013 is a functionof system requirements, i.e., speed, ambient tem·perature, voltage swing, drive circuitry, and straywiring capacity .The following equations cover the necessary calculationsto enable the fan·out to be calculated forany system condition. Some typical fan-outs forconditions are given in Table 1.Transient CurrentThe maximum peak output current of the MH0013is given as 600 mAo Average transient current requiredfrom the driver can be calculated from:C L (V+ - V-,I =TR(1)This can give a maximum limit to the load.Figure 1 shows maximum voltage swing andcapacitive load for various rise times.1. Transient Output PowerThe average transient power (P A cI dissipated isequal to the energy needed to charge and dischargethe output capacitive load (C L) multiplied by thefrequency of operation (F).PAC = C L x (V+ - V-)2 xF (2)Figures 2 and 3 show transient power for two dif·ferent values of (V+ - V-, versus output load andfrequency.2. Internal Power"0" StateNegligible «3 mW)"1" State(V+ - v-)2PINT = R2 X Duty Cycle. (3)Figure 4 gives various values of internal powerversus ouptut voltage and duty cycle.3. Input PowerThe average input power is a (unction of the inputcurrent and duty cycle. Due to input voltageclamping, this power contribution is small and cantherefore be neglected. At maximum duty cycle of50%, at 25° C, the average input power is less than10 mW per phase for R IN CI N controlled pulsewidths. For pulse widths much shorter thanRINC IN , and maximum duty cycle of 50%, inputpower could be as high as 30 mW, since II N peak ismaintained for the full duration of the pulsewidth.4. Package Power DissipationTotal Average Power = Transient Output Power +Internal Power + InputPowerTypical Example Calculation for One HalfMH0013CHow many MM506 shift registers can be driven byan MH0013C driver at 1 MHz using a clock pulsewidth of 400 ns, rise time 30-50 ns and 16 voltsamplitude over the temperature range 0-70°C?Power DissipationFrom the graph of power dissipation versus temperature,Figure 7, it can be seen that anMH0013C at 70°C can dissipate lW without a heatsink; therefore, each half can dissipate 500 mW.Transient Peak Current LimitationFrom Figure 1 (equation 1), it can be seen thatat 16V and 30 ns, the maximum load that can bedriven is limited to 1140 pF.Average I nternal PowerFigure 4 (equation 3) gives an average power of102 mW at 16V 40% duty cycle.Input power will be a maximum of 8 mW.Transient Output PowerFor one half of the MH0013C500 mW = 102 mW + 8 mW+ transient output power390 mW = transient output powerUsing Figure 2 (equation 2) at 16V, 1 MHz and390 mW, each ha'lf of the MH0013C can drive a1520 pF load. This is, however, in excess of theload derived from the transient current limitation(Figure 1, equation 1), and so a maximum loadof 1140 pF would prevail.From the data sheet for the MM506, the averageclock pulse load is 80 pF. Therefore the numbero f d eVlces· d'riven.IS 801140or 14registers..For nonsymmetrical clock widths, drive capabilityis improved.126