JAJSDS0 September 2017 TLV742P
Place input and output capacitors as close to the device pins as possible. To improve ac performance (such as PSRR, output noise, and transient response), TI recommends that the board be designed with separate ground planes for VIN and VOUT, with the ground plane connected only at the GND pin of the device, as shown in Figure 53. Connect the ground connection for the output capacitor directly to the GND pin of the device. High ESR capacitors can degrade PSRR performance.
Thermal protection disables the output when the junction temperature rises to approximately 160°C, allowing the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry is enables again. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may cycle on and off. This cycling limits the dissipation of the regulator, which protects the regulator from damage as a result of overheating.
Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, limit junction temperature to 125°C (maximum). To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection is triggered; use worst-case loads and signal conditions.
For good reliability, thermal protection triggers at least 35°C above the maximum expected ambient condition of the particular application. This configuration produces a worst-case junction temperature of 125°C at the highest expected ambient temperature and worst-case load.
The internal protection circuitry of the LDO is designed to protect against overload conditions. This circuitry is not intended to replace proper heat sinking. Continuously running the LDO into thermal shutdown degrades device reliability.
The ability to remove heat from the die is different for each package type, presenting different considerations in the printed-circuit-board (PCB) layout. The PCB area around the device that is free of other components moves the heat from the device to the ambient air.
Performance data for JEDEC low- and high-K boards are shown in Thermal Information. Using heavier copper increases the effectiveness in removing heat from the device. The addition of plated through-holes to heat-dissipating layers improves heat sink effectiveness.
Power dissipation depends on input voltage and load conditions. Power dissipation (PD) is equal to the product of the output current and the voltage drop across the output pass element, as shown in Equation 2.