PCK9448 datasheet(13/20 Pages) PHILIPS

13 / 20 page

9397 750 12534

Product data sheet

Rev. 01 — 29 November 2005

13 of 20

Philips Semiconductors

PCK9448

3.3 V/2.5 V LVCMOS 1 : 12 clock fan-out buffer

(2)

In Equation 2, P stands for the number of outputs with a parallel or Thevenin termination;

VOL, IOL, VOH and IOH are a function of the output termination technique; δo is the clock

signal duty cycle. If transmission lines are used,

ΣCL is zero in Equation 2 and can be

eliminated. In general, the use of controlled transmission line techniques eliminates the

impact of the lumped capacitive loads at the end lines and greatly reduces the power

dissipation of the device. Equation 3 describes the die junction temperature Tj as a

function of the power consumption.

(3)

Where Rth(j-a) is the thermal impedance of the package (junction-to-ambient) and Tamb is

the ambient temperature. According to Table 10, the junction temperature can be used to

estimate the long-term device reliability. Further, combining Equation 1 and Equation 2

results in a maximum operating frequency for the PCK9448 in a series terminated

transmission line system, Equation 4.

(4)

Tj(max) should be selected according to the MTBF system requirements and Table 10.

Rth(j-a) can be derived from Table 11. The Rth(j-a) represent data based on 1S2P boards;

using 2S2P boards will result in a lower thermal impedance than indicated below.

If the calculated maximum frequency is below 350 MHz, it becomes the upper clock speed

limit for the given application conditions. The following four derating charts describe the

safe frequency operation range for the PCK9448. The charts were calculated for a

maximum tolerable die junction temperature of 110

°C (120 °C), corresponding to an

estimated MTBF of 9.1 years (4 years), a supply voltage of 3.3 V and series terminated

transmission line or capacitive loading. Depending on a given set of these operating

conditions and the available device convection, a decision on the maximum operating

frequency can be made.

Table 11:

Thermal package impedance of the LQFP32

Convection (LFPM)

Rth(j-a) (°C/W) (1P2S board)

Rth(j-a) (°C/W) (2P2S board)

still air

100

200

300

400

500

tot

qmax

()

clk

∑





–

()

1DC

–

() I

[]

∑

amb

tot

th j-a

()

clk max

()

-----------------------------------------

jmax

()

amb

–

th j-a

()

------------------------------------

qmax

()

–

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