Datasheet TC55 (Microchip) - 10

TC55 5.0 THERMAL CONSIDERATIONS EQUATION
P
5.1 Power Dissipation
D = (VINMAX – VOUTMIN) x IOUTMAX The amount of power dissipated internal to the low Given: dropout linear regulator is the sum of the power dissi- VIN = 3.3V to 4.1V pation within the linear pass device (P-Channel MOS- V FET) and the quiescent current required to bias the OUT = 3.0 V ± 2% internal reference and error amplifier. The internal lin- IOUT = 1 mA to 100 mA ear pass device power dissipation is calculated by mul- TAMAX = 55°C tiplying the voltage across the linear device by the P current through the device. MAX = (4.1V – (3.0V x 0.98)) x 100 mA PMAX = 116.0 milliwatts
EQUATION
To determine the junction temperature of the device, the thermal resistance from junction-to-ambient must be PD (Pass Device) = (VIN – VOUT) x IOUT known. The 3-pin SOT-23 thermal resistance from junc- The internal power dissipation, as a result of the bias tion-to-air (RθJA) is estimated to be approximately current for the LDO internal reference and error 359°C/W. The SOT-89 RθJA is estimated to be approxi- amplifier, is calculated by multiplying the ground or mately 110°C/W when mounted on 1 square inch of quiescent current by the input voltage. copper. The TO-92 RθJA is estimated to be 131.9°C/W. The RθJA will vary with physical layout, airflow and other application-specific conditions.
EQUATION
The device junction temperature is determined by PD (Bias) = VIN x IGND calculating the junction temperature rise above ambient, then adding the rise to the ambient The total internal power dissipation is the sum of PD temperature. (Pass Device) and PD (Bias).
EQUATION EQUATION Junction Temperature
PTOTAL = PD (Pass Device) + PD (Bias)
SOT-23 Example:
T For the TC55, the internal quiescent bias current is so J = PDMAX x RθJA + TA low (1 µA typical) that the P T D (Bias) term of the power J = 116.0 milliwatts x 359°C/W + 55°C dissipation equation can be ignored. The maximum TJ = 96.6°C power dissipation can be estimated by using the
SOT-89 Example:
maximum input voltage and the minimum output T voltage to obtain a maximum voltage differential J = 116.0 milliwatts x 110°C/W + 55°C between input and output. The next step would be to TJ = 67.8°C multiply the maximum voltage differential by the
TO-92 Example:
maximum output current. TJ = 116.0 milliwatts x 131.9°C/W + 55°C TJ = 70.3°C DS21435F-page 10 © 2005 Microchip Technology Inc. Document Outline 1.0 Electrical Characteristics 2.0 Typical Performance Curves FIGURE 2-1: Output Voltage vs. Output Current (TC55RP3002). FIGURE 2-2: Output Voltage vs. Input Voltage (TC55RP3002). FIGURE 2-3: Output Voltage vs. Input Voltage (TC55RP3002). FIGURE 2-4: Dropout Voltage vs. Output Current (TC55RP3002). FIGURE 2-5: Output Voltage vs. Operating Temperature (TC55RP3002). FIGURE 2-6: Supply Current vs. Input Voltage (TC55RP3002). FIGURE 2-7: Supply Current vs. Operating Temperature (TC55RP3002). FIGURE 2-8: Load Transient Response (TC55RP3002). FIGURE 2-9: Output Voltage vs. Output Current (TC55RP5002). FIGURE 2-10: Output Voltage vs. Input Voltage (TC55RP5002). FIGURE 2-11: Output Voltage vs. Input Voltage (TC55RP5002). FIGURE 2-12: Dropout Voltage vs. Output Current (TC55RP5002). FIGURE 2-13: Output Voltage vs. Operating Temperature (TC55RP5002). FIGURE 2-14: Supply Current vs. Input Voltage (TC55RP5002). FIGURE 2-15: Supply Current vs. Operating Temperature (TC55RP5002). FIGURE 2-16: Input Transient Response, 1mA (TC55RP5002). FIGURE 2-17: Input Transient Response, 10mA (TC55RP5002). FIGURE 2-18: Load Transient Response (TC55RP5002). 3.0 Pin Descriptions TABLE 3-1: Pin Function Table 3.1 Ground Terminal (GND) 3.2 Regulated Voltage Output (VOUT) 3.3 Unregulated Supply Input (VIN) 4.0 Detailed Description 4.1 Output Capacitor 4.2 Input Capacitor 5.0 Thermal Considerations 5.1 Power Dissipation 6.0 Packaging Information 6.1 Package Marking Information Worldwide Sales and Service Trademarks Worldwide Sales