# Thermal Characteristics for SMPTE HOTLink - CY7B9235/CY7B9335

Version 1

Thermal Characteristics for SMPTE HOTLink - CY7B9235/CY7B9335

Questions:

- How do I calculate case temperature?

- How do I calculate board temperature?

- What is the maximum ambient temperature for HOTlink?

- What are the Theta-JA and Theta-JC values?

- What is the maximum junction temperature, Tj?

Response:

Because the thermal characteristics are dependent on the ambient temperature and power used by the system, both the equations and values are provided below.

Tj = Junction temperature

Tb = Board temperature

Ta = Ambient temperature

Tc = Case temperature

Theta-Ja = Junction to ambient thermal resistance

Theta-Jb = Junction to board thermal resistance

Theta-Jc = Junction to case thermal resistance

Pd = Power used by the device.

TEMPERATURE RANGES:

Commercial: Ta = 0 to 70 °C

Industrial: Ta= -40 to 85 °C

KNOWN VALUES

These are gotten from the table below.

JUNCTION TEMPERATURE

Tj = Theta-Ja*Power   Ta (1)

BOARD TEMPERATURE

Tj = Theta-Jb*Power   Tb (2)

so Tb = Tj - Theta-Jb*Power (3)

>From Eq(1) and (3) we get

Tb = (Theta-Ja - Theta-Jb)*Power   Ta (4)

CASE TEMPERATURE

Tc = Tj - Theta-Jc*Pd (5)

so Tc = (Theta-JA - Theta-JC)*Power   Ta (6)

 CY7B9235 CY7B9335 Part Number - Theta-JA (°C/W) Theta-JC (°C/W) Tj (°C) Theta-JA (°C/W) Theta-JC (°C/)W Tj (°C) 270JC 27 15 91.6 24 5 104.8 400JC 27 15 91.6 24 5 104.8