11.1 Layout Guidelines

• Place the filter and bypass capacitor between IN and GND as close as possible ensuring a low-impedance trace for IN and a low-impedance trace and via path from GND to ground plane.
• Place the output filter capacitor as close as possible to OUT between OUT and GND. Place the higher-value electrolytic bypass capacitor between OUT and GND. The bypass capacitor is recommended when large transient currents are expected on the output. The OUT trace must be low-impedance to the load.
• Place the pullup resistor for OCx between the pullup voltage source and OCx.

11.2 Layout Examples

Figure 33. Layout Example for TPS2062-Q1

Figure 34. Layout Example for TPS2065-Q1

11.3 Thermal Considerations

Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for extended periods of time. The TPS2065-Q1 and TPS2062-Q1 implement a thermal sensing to monitor the operating junction temperature of the power distribution switch. In an overcurrent or short-circuit condition, the junction temperature rises due to excessive power dissipation. Once the die temperature rises above a minimum of 135°C due to overcurrent conditions, the internal thermal-sense circuitry turns the power switch off, thus preventing the power switch from damage. Hysteresis is built into the thermal-sense circuit, and after the device has cooled approximately 10°C, the switch turns back ON. The switch continues to cycle in this manner until the load fault or input power is removed. The OCx open-drain output is asserted (active low, with a 10-ms deglitch) when an overtemperature shutdown or overcurrent occurs.

11.4 Power Dissipation and Junction Temperature

The low ON-resistance on the N-channel MOSFET allows the small surface-mount packages to pass large currents. The thermal resistances of these packages are high compared to those of power packages; it is good design practice to check power dissipation and junction temperature. Begin by determining the r_DS(ON) of the N-channel MOSFET relative to the input voltage and operating temperature. As an initial estimate, use the highest operating ambient temperature of interest and read r_DS(ON) from Figure 9. Using this value, the power dissipation per switch can be calculated using Equation 1:

Multiply this number by the number of switches being used. This step renders the total power dissipation from the N-channel MOSFETs.

The thermal resistance, R_θJA = 1 / (DERATING FACTOR), where DERATING FACTOR is obtained from Dissipation Ratings. Thermal resistance is a strong function of the printed-circuit board construction, and the copper trace area connecting the integrated circuit.

Finally, calculate the junction temperature with Equation 2:

Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees, repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally sufficient to get a reasonable answer.