TX4939XBG-400 Toshiba, TX4939XBG-400 Datasheet - Page 740

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TX4939XBG-400

Manufacturer Part Number
TX4939XBG-400
Description
Manufacturer
Toshiba
Datasheet

Specifications of TX4939XBG-400

Cpu Core
TX49/H4 90nm
Clock Mhz/max Mips
400/520
Inst./data Cache
32KB (4 Way)/32KB (4 Way)
Tlb
x
1cycle Mac
x
Volts (v)
1.25/2.5/3.3
Peripherals
DDR, NAND, ATA, ETHERNET, SECURITY, FPU, MMU, SPI, I2S, I2C, PCI, VIDEO, UART, TIMER, RTC
Companion Chip
TC86C001FG
Package
PGBA456

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Package
29.2. Recommended Motherboard Footprint
Since this package, i.e. PBGA-2727-100P has thermal balls in the center of package, motherboard need to have lower
thermal resistance from the footprint of these balls to ambient. Figure 29-1 shows recommended footprint for this processor.
There are 36 thermal balls in this package. The Via around these thermal balls are considered as thermal via. In this
condition, 49 Via around thermal balls are considered default. Each thermal Via's thermal resistance can be calculated by
following formula:
Since the heat dissipates not only center ball but also balls around peripheral, these thermal via acts additional heat
dissipation path. Therefore it is recommended to build more via at the area of "Additional Via" in Figure 29-1.
Also it is recommended to increase copper coverage of the internal planes both thermal ball area and additional area.
Table 29-1 is the result of calculation for thermal resistance of each Via and 49 Via.
Rev. 3.1 November 1, 2005
Thermal Resistance =
where
L = length of pipe (=PCB thickness), K
R = semidiameter of through-hole, T = Copper plating thickness, π = 3.1415926
Plating thickness = 0.015 mm
PCB thickness = 1.6 mm
Diameter of Via = 0.25
Diameter of Via = 0.30
Diameter of Via = 0.35
Diameter of Via = 0.40
Diameter of Via = 0.45
Diameter of Via = 0.50
Figure 29-1 Recommended Footprint for heat disspation
Table 29-1 Thermal Resistance of Via and Vias
Solder RAND
K
copper
x ( R – (R-T)
copper
= thermal conductance of Copper (=395 W/mK)
2
Default Via
L
29-2
2
) x π
Additional Via if possible
365.8 DegC/W
301.6 DegC/W
256.6 DegC/W
223.3 DegC/W
197.6 DegC/W
177.2 DegC/W
Per Via
Thermal Resistance
7.5 DegC/W
6.2 DegC/W
5.2 DegC/W
4.6 DegC/W
4.0 DegC/W
3.6 DegC/W
With 49 Via
Toshiba RISC Processor
TX4939
29
29

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