July 17, 2002
103
System Design Considerations
6.7 Thermal Design
TM5500/TM5800 processors use a new 474-pin CBGA package. The solder footprint and pinout is identical
to the TM5400/TM5600 474-pin CBGA package. The location and dimensions of the exposed silicon die and
bypass capacitors on the top of the package have changed on this new TM5500/TM5800 package compared
to the previous TM5400/TM5600 package. Note that the exposed silicon die contact area available for the
thermal solution has decreased on the TM5500/TM5800 processor (compared to TM5400/TM5600) due to
the smaller device die produced by the 0.13µ
process technology used to manufacture TM5500/TM5800
processors.
Transmeta strongly recommends die-referenced thermal solutions over PCB-referenced thermal solutions for
new systems designed for TM5500/TM5800 processors. Die-referenced thermal solutions allow for possible
improved packages with slightly different Z-axis dimensions in the future.
6.8 Thermal Diode and Thermal Sensor
The external thermal sensor device connects to the DIODE_CATHODE and DIODE_ANODE pins of the
processor. The ALERT# signal from the temperature sensor is connected to the dedicated THRM# input on
the southbridge. This device is powered from V3_3.
Careful layout is required to ensure the lowest noise and greatest accuracy of the thermal sensor/diode.
6.8.1 Thermal Sensor Circuit
The thermal sensing circuit on a TM5500/TM5800 processor-based system has three components: a diode
on the processor die, a thermal sensor chip (in a separate package), and the interconnecting circuitry.
The on-chip diode is operated in forward-bias mode with a carefully-controlled (and very small) bias current.
In this mode the voltage-temperature curve is essentially linear within the processor operating temperature
range.
The thermal sensor chip provides the bias current to the diode, measures the resulting voltage, and sends the
information via the SMBUS to the system (usually the southbridge). This chip is available from Maxim (the
MAX1617) or from Analog Devices (AD1021). The two chips generate slightly different bias currents, but
otherwise operate in the same fashion.
Note
Refer to the
Thermal Design Guide
for detailed thermal design information. Thermal design power (TDP)
specifications can be found in the
Data Book
Note
The signals from the thermal diode operate at very low voltage and current levels and are susceptible to
induced noise. Transmeta recommends following each manufacturer’s design guidelines when
incorporating their thermal sensors.
Summary of Contents for Crusoe TM5500
Page 1: ...TM5500 TM5800 System Design Guide July 17 2002...
Page 6: ...July 17 2002 6 List of Tables...
Page 8: ...July 17 2002 8 List of Figures...
Page 50: ...July 17 2002 50 Processor Power Supplies and Power Management...
Page 110: ...July 17 2002 110 System Design Considerations...
Page 122: ...July 17 2002 122 System Design Checklists...
Page 128: ...July 17 2002 128 Serial Write protection PLD Data...
Page 130: ...July 17 2002 130 Index...
