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RFHA3942D Datasheet(PDF) 9 Page - RF Micro Devices |
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RFHA3942D Datasheet(HTML) 9 Page - RF Micro Devices |
9 / 9 page RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421 DS131024 For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com. The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended application circuitry and specifications at any time without prior notice. 9 of 9 RFHA3942D Mounting and Thermal Considerations The thermal resistance provided as RTH (junction to case) represents only the packaged device thermal characteristics. This is measured using IR microscopy capturing the device under test temperature at the hottest spot of the die. At the same time, the package temperature is measured using a thermocouple touching the backside of the die embedded in the device heatsink but sized to prevent the measurement system from impacting the results. Knowing the dissipated power at the time of the measurement, the thermal resistance is calculated. In order to achieve the advertised MTTF, proper heat removal must be considered to maintain the junction at or below the maximum of 200°C. Proper thermal design includes consideration of ambient temperature and the thermal resistance from ambient to the back of the package including heatsinking systems and air flow mechanisms. Incorporating the dissipated DC power, it is possible to calculate the junction temperature of the device. DC Bias The GaN HEMT device is a depletion mode high electron mobility transistor (HEMT). At zero volts VGS the drain of the device is saturated and uncontrolled drain current will destroy the transistor. The gate voltage must be taken to a potential lower than the source voltage to pinch off the device prior to applying the drain voltage, taking care not to exceed the gate voltage maximum limits. RFMD recommends applying VGS = -5V before applying any VDS. RF Power transistor performance capabilities are determined by the applied quiescent drain current. This drain current can be adjusted to trade off power, linearity, and efficiency characteristics of the device. The recommended quiescent drain current (IDQ) shown in the RF typical performance table is chosen to best represent the operational characteristics for this device, considering manufacturing variations and expected performance. The user may choose alternate conditions for biasing this device based on performance trade-offs. GaN HEMT Capacitances The physical structure of the GaN HEMT results in three terminal capacitors similar to other FET technologies. These capacitances exist across all three terminals of the device. The physical manufactured characteristics of the device determine the value of the CDS (drain to source), CGS (gate to source) and CGD (gate to drain). These capacitances change value as the terminal voltages are varied. RFMD presents the three terminal capacitances measured with the gate pinched off (VGS = -8V) and zero volts applied to the drain. During the measurement process, the parasitic capacitances of the package that holds the amplifier is removed through a calibration step. Any internal matching is included in the terminal capacitance measurements. The capacitance values presented in the typical characteristics table of the device represent the measured input (CISS), output (COSS), and reverse (CRSS) capacitance at the stated bias voltages. The relationship to three terminal capacitances is as follows: CISS = CGD + CGS COSS = CGD + CDS CRSS = CGD |
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