May 2005
rev 0.3
ASM2I99448
TJ, MAX should be selected according to the MTBF
system requirements and Table 9. Rthja can be derived
from Table 10. The Rthja represent data based on 1S2P
boards, using 2S2P boards will result in 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 eight derating charts
describe the safe frequency operation range for the
ASM2I99448. 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 3.3V 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 10. Thermal package impedance of the
32LQFP
Convection,
LFPM
Rthja (1P2S
Rthja (2P2S
board), °C/W
board), °C/W
Still air
86
76
71
68
66
60
61
56
54
53
52
49
100 lfpm
200 lfpm
300 lfpm
400 lfpm
500 lfpm
fMAX (AC)
fMAX (AC)
350
300
250
200
350
300
250
200
°
TA = 75 C
°
TA = 85 C
°
TA = 85 C
150
100
50
150
100
50
Safe operation
Safe operation
0
0
400
200
500
300
100
0
400
200
500
300
100
0
Convection Ifpm
Convection Ifpm
Figure 6. Maximum ASM2I99448 frequency
VCC= 3.3V, MRBF 9.1 years, 4pF load per line,
2s2p board
Figure 5. Maximum ASM2I99448 frequency VCC
=
3.3V, MTBF 9.1 years, driving series terminated
transmission lines, 2s2p board
fMAX (AC)
fMAX (AC)
350
350
300
250
200
300
250
200
150
°
TA = 85 C
150
100
50
Safe operation
Safe operation
100
50
0
0
400
200
500
300
100
0
400
200
500
300
100
0
Convection Ifpm
Convection Ifpm
Figure 8. Maximum ASM2I99448
Figure 7. No maximum frequency limitation for
CC = 3.3V, MTBF 4 years, driving series terminated
transmission lines, 2s2p board
frequency VCC = 3.3V, MRBF 4 years, 4pF
load per line, 2s2p board
V
3.3V/2.5V LVCMOS 1:12 Clock Fanout Buffer
9 of 15
Notice: The information in this document is subject to change without notice.
PULSECORE [ PulseCore Semiconductor ]
