Heat Sinking Requirements
for GaN & GaAs SSPAs
1. Units can operate at CASE temperature between -30°C to +70°C. For wider temperature range requirements contact the factory.
2. Proper heat sinking is ABSOLUTELY required, otherwise, permanent damage or degradation may occur. Heat sinks should be selected based on the dissipated power within the PA (ie: DC power into the unit in Watts, minus the RF output that is delivered to the load).
3. Thermal grease or some alternate highly-conductive thermal interface material should be applied between the mounting surface of the amplifier and the heat sink.
4. Good mechanical pressure is imperative to guarantee effective thermal transfer to the heat sink for reliable operation. Customers should use all mounting features provided on the amplifier units to apply this mechanical pressure.
Heat Sink Selection Example
ie: CTT GaN Amplifier Model AGW105-4855
• Pdiss = Dissipated Power within the SSPA (AKA Heat)
• Pdiss = PDC (Watts) – Pout (Watts) + Pin (Watts)
• PDC = +30 VDC @ 13.0 Amps = 390 Watts
• Pout = RF Output Power = 63 Watts
• Pin ≈ 0 dBm = 1 Milliwatt – 0.001 Watt is negligible
• Pdiss = 390 Watts – 63 Watts = 327 Watts
In this example a heat sink is selected for a temperature rise of +20°C, or less, due to ambient temperature and maximum allowable case temperature boundary conditions. Thermal resistance of the heat sink must therefore be: 20°C/327 Watts = 0.06°C/W or lower. Conclusion: A thermal resistant 0.06°C/W heat sink is needed for this amplifier. Based on this number, forced air cooling is necessary.
Optional Gating or Blanking Function
For CTT’s CW amplifiers the blanking function can be built-in. In this case there is a TTL pin on the amplifier. When +5V (TTL high) or no voltage (floating) is applied, the amplifier is ON all the time. If the TTL is 0V (shorted to ground), the amplifier is turned OFF (the majority of DC current will be cut off while the bias, delay and protection circuits remain on). This turn ON/OFF time can vary from 250ns to 10ms. If faster speed is required consult the factory.