This guide describes the package thermal model and discusses design considerations for the MAX5860 and the MAX5862, high-density downstream cable QAM modulator, digital upconverter (DUC), and RF digital-to-analog converter (RF-DAC) devices.
Table of Contents
and the MAX5862
are high-performance, highly integrated devices housed in compact 12mm x 17mm packages. It is very important that the thermal system is designed properly to maintain junction temperature in the safe operating range. There are two circuits in the package: the digital upconverter (DUC) and the digital-to-analog converter (DAC). This guide describes a method to measure the internal junction temperatures of both circuits.
The thermal system design must meet both of the following conditions for safe operation:
- The junction temperature of the DUC (TJDUC) must be kept below 110°C.
- The junction temperature of the DAC (TJDAC) must be kept below 110°C.
Depending on the system application, meeting these two conditions may require heatsinks and/or cooling fans. The power for both the DUC and the DAC are specified in the MAX5860 data sheet
and the MAX5862 data sheet
Package Thermal Model
In order to do a thorough thermal analysis, one needs to understand the package construction and its material composition. See Table 1 for the package construction and material composition and Table 2 for the substrate construction and material composition.
|Table 1. Package Construction and Materials
||17 x 12 x 1.4 mm3
|Die size of DUC
||8.201 x 7.261 x 0.356 mm3
|Die size of DAC
||5.700 x 5.500 x 0.356 mm3
|Bump counts of DUC
|Bump counts of DAC
|Table 2. Substrate (PCB) Construction and Materials
|Custom 3s3p PCB (6-layer)
||101.5 x 114.3 x 1.6 mm3
|Inner plane thickness
|Solder mask thickness
|Diameter of PCB vias
|Number of PCB vias
|Top Cu coverage ratio
|L2/L5 Cu coverage ratio
|L3/L4 Cu coverage ratio
|Bottom Cu coverage ratio
The thermal properties of the package and substrate component materials are listed in Table 3.
|Table 3. Thermal Properties of the Component Materials
||Material or Material Name
||Thermal Conductivity (W/mK)
||148 at 25°C
|98.9 at 125°C
|Substrate and PCB planes
This data can be used to create a package thermal model for thermal simulations. Upon request, Maxim Integrated will provide the FloTHERM® thermal model for users that have access to the FloTHERM simulator tool. Contact your Maxim Integrated representative.
DUC Junction Temperature Measurement
The DUC junction temperature (TJDUC
) is measured via a thermal diode and is described in the MAX5860 data sheet
and the MAX5862 data sheet
. The DUC temperature can be measured continuously in system operation. See Figure 1
for the recommended method of measuring the DUC temperature, which uses the MAX6642
Figure 1. The MAX5860/MAX5862 junction temperature measurement.
DAC Junction Temperature Measurement
The DAC junction temperature (TJDAC) is measured via a ESD diode using the SE pin circuit shown in Figure 1. The DAC temperature measurement should only be made during the thermal system design phase. The measurement should not be made during normal system operation.
The temperature of the DAC is measured pulling a 1mA current out of the SE pin while measuring the voltage of the SE pin. If the voltage at the SE pin is < -0.6V (relative to GND), the temperature of the DAC is < 110°C and the DAC is operating in the safe TJDAC range. To maintain a temperature within the allowable range of 0°C to 110°C, the voltage at the SE pin should be in the following range: -0.78V < SE < -0.6V.