Calculating Pulse Widths High (Twh Twl) Products INTRODUCTION Thi

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Calculating Pulse Widths High (Twh Twl) Products INTRODUCTION Thi

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Pulse Application Note
Calculating Pulse Widths High (Twh Twl) Products
INTRODUCTION This application note address pulse widths high (Twh Twl) clock outputs, calculate them. Several components have pulse width requirements clock signal. pulse widths high calculated from period, duty cycle slope rise fall times, (Tr, respectively). PARAMETERS THAT AFFECT related following parameters: Frequency accuracy Duty cycle point (DC) where, Tw50% duty cycle pulse width. voltage which pulse width high calculated
Example with duty cycle defined 50%.
example that, lets consider calculating 24.576 frequency ICS9120-08. 24.576 clock 24.54545 MHz, with period 40.74 From data sheet duty cycle range minimum, typical, maximum. Therefore, Tw50% period Tw50%min 40.74 18.33 Tw50%typ 40.74 20.37 Tw50%max 40.74 22.4 rise fall times defined data sheet. rise time, goes from Trtyp Trmax 3.25 fall time goes from Tftyp Tfmax
CALCULATING PULSE WIDTH Since model clock waveform trapezoid pattern, duty cycle extrapolate pulse width high pulse width low. calculating pulse width, take duty cycle pulse width specification calculation subtract portion from point pulse width level. Twhx Tw50% (portion from (portion from -(1) Twlx Tw50% (portion from (portion from -(2)
Pulse 4/17/00
Pulse Application Note
ICS9120-08, duty cycle point defined 2.5V 2.5V Figure below shows wave form frequency with full period 40.74 that equal both Tw+50% plus Tw50% (100%).
Twhx Duty Cycle point 1.0V +50% 0.8V -50% 0.8V
Figure
TwIx
calculate Twhx using equation Twhx will calculated this example. From equation get, Twhx Tw50% (portion from (portion from -(1) Twh(4V) Tw50% (4V-2.5V)/(4V1V))) (4V-2.5V)/(4V-1V))) With typical value Tw50% 18.33 (minimum), 20.37 (typical), 22.4 (maximum). Substituting these values equation gives Twh(4V) 16.7 Twh(4V) 18.8 Twh(4V) 20.8 worst case (maximum) value 3.25 Tw50% 18.33 (minimum), 20.37 (typical), 22.4 (maximum).
Substituting these values equation gives Twh(4V) 15.46 Twh(4V) 17.50 Twh(4V) 19.53 pulse width low, Twlx logic level, With 0.8, from equation get, Twlx Tw50% (portion from (portion from -(2) Twl(0.8V) Tw50% (2.5V-0.8V)/(4V1V))) (2.5V-0.8V)/(4V-1V))) With typical value Tw50% 18.33 (minimum), 20.37 (typical), 22.4 (maximum). Substituting these values equation gives Twl(0.8V) 15.08 Twl(0.8V) 17.12 Twl(0.8V) 19.15
Pulse Application Note
worst case (maximum) value 3.25 Tw50% 18.33 (minimum), 20.37 (typical), 22.4 (maximum). Substituting these values equation gives Twl(0.8V) 16.50 Twl(0.8V) 18.60 Twl(0.8V) 20.60
Example with duty cycle defined 1.4V.
Again calculate Twhx using same equations, with equation becomes follows. Twh(4V) Tw1.4 (4V-1.4V)/(4V1V))) (4V-1.4V)/(4V-1V))) With typical values nsec, nsec. Tw1.4 6.75 (minimum), (typical), 8.25 (maximum). Substituting these values equation gives Twh(4V) 4.757 Twh(4V) 5.507 Twh(4V) 6.257 worst case (maximum) value nsec, nsec, Tw1.4 6.75 (minimum), (typical), 8.25 (maximum).
some data sheets will notice that duty cycle threshold defined 1.4V shown figure This newer clocks which drive compatible inputs, check data sheet test conditions. example that, consider ICS9169-01 66.6 MHz. period before
Twhx Duty Cycle 1.4V point 1.0V +50% 0.8V -50% 0.8V
Figure
TwIx
Tw1.4 period Tw1.4min 6.75 Tw1.4typ Tw1.4max 8.25
Substituting these values equation gives Twh(4V) 3.197 Twh(4V) 3.947 Twh(4V) 4.697
Pulse Application Note
calculating Twlx, with 0.8, equation becomes follows Twl(0.8V) Tw1.4 (1.4V-0.8V)/(4V1V))) (1.4V-0.8V)/(4V-1V))) With same typical values 1.2nsec, 1.1nsec. Tw1.4 6.75 (minimum), (typical), 8.25 (maximum). Substituting these values equation gives Twl(0.8V) 6.29 Twl(0.8V) 7.04 Twl(0.8V) 7.79 worst case (maximum) value nsec, nsec, Tw1.4 6.75 (minimum), (typical), 8.25 (maximum). Substituting these values equation gives Twl(0.8V) 5.93 Twl(0.8V) 6.68 Twl(0.8V) 7.43
Example with 3.3V part duty cycle defined 1.4V.
Tw1.4 period Tw1.4min Tw1.4typ Tw1.4max Again calculate Twhx using same equations, with equation becomes follows. Twh(2.4V) Tw1.4 (2.4V-1.4V)/(2.4V0.4V))) (2.4V-1.4V)/(2.4V-0.4V))) With typical values nsec, nsec. Tw1.4 (minimum), (typical), (maximum). Substituting these values equation gives Twh(2.4V) 3.25 Twh(2.4V) 3.65 Twh(2.4V) 4.25 worst case (maximum) value nsec, nsec, Tw1.4 (minimum), (typical), (maximum).
Since have good number parts that 3.3V, figure shows duty cycle threshold definition 1.4V part. These newest parts. example that ICS9250-16. consider SDRAM frequency MHz. period nsec, before
Twhx 2.4V Duty Cycle 1.4V point 0.4V +50%
Substituting these values equation gives Twh(2.4V) Twh(2.4V) Twh(2.4V)
-50% 0.4V 0.4V
Figure
TwIx
Pulse Application Note
calculating Twlx, with 0.4, equation becomes follows Twl(0.4V) Tw1.4 (1.4V-0.4V)/(2.4V0.4V))) (1.4V-0.4V)/(2.4V-0.4V))) With same typical values 1.0nsec, 1.5nsec. Tw1.4 (minimum), (typical), (maximum). Substituting these values equation gives Twl(0.4V) 3.25 Twl(0.4V) 3.65 Twl(0.4V) 4.25 worst case (maximum) value nsec, nsec, Tw1.4 (minimum), (typical), (maximum). Substituting these values equation gives Twl(0.4V) Twl(0.4V) Twl(0.4V)

Calculating Pulse Widths High (Twh Twl) Products INTRODUCTION Thi

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