MC100H641FNR2 データシートの表示（PDF） - ON Semiconductor

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MC100H641FNR2

Single Supply PECL to TTL 1:9 Clock Distribution Chip

ON Semiconductor 

MC10H641, MC100H641

propagation delay for the device in question. A more

common use would be to establish an ambient temperature

range for the H641’s in the system and utilize the above

methodology to determine the potential increased skew of

the distribution network. Note that for this information if the

TPD versus Temperature curve were linear the calculations

would not be required. If the curve were linear over all

temperatures a simple temperature coefficient could be

provided.

6.4

6.2

TPHL

6.0

5.8

5.6

TPLH

5.4

5.2

−30 −10 10 30 50 70 90 110 130

JUNCTION TEMPERATURE (°C)

Figure 3. TPD versus Junction Temperature

VCC Dependence

TTL and CMOS devices show a significant propagation

delay dependence with VCC. Therefore the VCC variation in

a system will have a direct impact on the total skew of the

clock distribution network. When calculating the skew

between two devices on a single board it is very likely an

assumption of identical VCC’s can be made. In this case the

number provided in the data sheet for part−to−part skew

would be overly conservative. By using Figure 4 the skew

given in the data sheet can be reduced to represent a smaller

or zero variation in VCC. The delay variation due to the

specified VCC variation is ≈ 270 ps. Therefore, the 1 ns

window on the data sheet can be reduced by 270 ps if the

devices in question will always experience the same VCC.

The distribution of the propagation delay ranges given in the

data sheet is actually a composite of three distributions

whose means are separated by the fixed difference in

propagation delay at the typical, minimum and maximum

VCC.

140

100

60

20

−20

−60

TPHL

TPLH

−100

−140

4.75

4.85

4.95

5.05

5.15

5.25

VCC (V)

Figure 4. DTPD versus VCC

Capacitive Load Dependence

As with VCC the propagation delay of a TTL output is

intimately tied to variation in the load capacitance. The skew

specifications given in the data sheet, of course, assume

equal loading on all of the outputs. However situations could

arise where this is an impossibility and it may be necessary

to estimate the skew added by asymmetric loading. In

addition the propagation delay numbers are provided only

for 50 pF loads, thus necessitating a method of determining

the propagation delay for alternative loads.

Figure 5 shows the relationship between the two

propagation delays with respect to the capacitive load on the

output. Utilizing this graph and the 50 pF limits the

specification of the H641 can be mapped into a spec for

either a different value load or asymmetric loads.

1.15

1.10

1.05

TPLH

1.00

0.95 MEASURED

0.90

TPHL

0.85

0.80

THEORETICAL

0.75

0

10 20 30 40 50 60 70 80

CAPACITIVE LOAD (pF)

Figure 5. TPD versus Load

90 100

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