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參數(shù)資料
| 型號(hào)： | MPC941FAR2 |
| 廠商： | FREESCALE SEMICONDUCTOR INC |
| 元件分類： | 時(shí)鐘及定時(shí) |
| 英文描述： | 941 SERIES, LOW SKEW CLOCK DRIVER, 27 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PQFP48 |
| 封裝： | 7 X 7 MM, LQFP-48 |
| 文件頁(yè)數(shù)： | 6/9頁(yè) |
| 文件大?。?/td> | 326K |
| 代理商： | MPC941FAR2 |
6
MPC941
MOTOROLA ADVANCED CLOCK DRIVERS DEVICE DATA
544
Power Consumption of the MPC941 and Thermal Man-
agement
The MPC941 AC specification is guaranteed for the entire
operating frequency range up to 250 MHz. The MPC941 pow-
er consumption and the associated long-term reliability may
decrease the maximum frequency limit, depending on operat-
ing conditions such as clock frequency, supply voltage, output
loading, ambient temperture, vertical convection and thermal
conductivity of package and board. This section describes the
impact of these parameters on the junction temperature and
gives a guideline to estimate the MPC941 die junction temper-
ature and the associated device reliability. For a complete
analysis of power consumption as a function of operating con-
ditions and associated long term device reliability please refer
to the application note AN1545. According the AN1545, the
long-term device reliability is a function of the die junction tem-
perature:
Table 7: Die junction temperature and MTBF
Junction temperature (
°C)
MTBF (Years)
100
20.4
110
9.1
120
4.2
130
2.0
Increased power consumption will increase the die junction
temperature and impact the device reliability (MTBF). Accord-
ing to the system-defined tolerable MTBF, the die junction tem-
perature of the MPC941 needs to be controlled and the ther-
mal impedance of the board/package should be optimized.
The power dissipated in the MPC941 is represented in equa-
tion 1.
Where ICCQ is the static current consumption of the
MPC941, CPD is the power dissipation capacitance per output,
(Μ)ΣCL represents the external capacitive output load, N is
the number of active outputs (N is always 27 in case of the
MPC941). The MPC941 supports driving transmission lines to
maintain high signal integrity and tight timing parameters. Any
transmission line will hide the lumped capacitive load at the
end of the board trace, therefore,
ΣCL is zero for controlled
transmission line systems and can be eliminated from equa-
tion 1. Using parallel termination output termination results in
equation 2 for power dissipation.
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 and DCQ is the
clock signal duty cyle. 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 de-
scribes the die junction temperature TJ as a function of the
power consumption.
Where Rthja is the thermal impedance of the package (junc-
tion to ambient) and TA is the ambient temperature. According
to Table 7, 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 MPC941 in a series terminated transmission line system.
TJ,MAX should be selected according to the MTBF system
requirements and Table 7. Rthja can be derived from Table 8.
The Rthja represent data based on 1S2P boards, using 2S2P
boards will result in a lower thermal impedance than indicated
below.
Table 8: Thermal package impedance of the 48ld LQFP
Convection, LFPM
Rthja (1P2S board), K/W
Still air
78
100 lfpm
68
200 lfpm
59
300 lfpm
56
400 lfpm
54
500 lfpm
53
If the calculated maximum frequency is below 250 MHz, it
becomes the upper clock speed limit for the given application
conditions. The following eight derating charts describe the
safe frequency operation range for the MPC941. The charts
were calculated for a maximum tolerable die junction tempera-
ture of 110
°C (120°C), corresponding to a estimated MTBF of
9.1 years (4 years), a supply voltage of either 3.3V or 2.5V and
series terminated transmission line or capacitive loading. De-
pending on a given set of these operating conditions and the
available device convection a decision on the maximum oper-
ating frequency can be made.
P
TOT +
I
CCQ ) VCC @ fCLOCK @
N
@ C
PD )
M
CL
@ V
CC
Equation 1
P
TOT + VCC @
I
CCQ ) VCC @ fCLOCK @
N
@ C
PD )
M
CL
)
P
DC
Q @ IOH @ VCC * VOH ) 1 * DCQ @ IOL @ VOL Equation 2
TJ + TA ) PTOT @ Rthja
Equation 3
f
CLOCK,MAX +
1
CPD @ N @ V2
CC
@
T
J,MAX * TA
R
thja
* I
CCQ @ VCC
Equation 4
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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