11.1 Layout Guidelines

Input and output capacitors should be placed as close to the device pins as possible. To improve ac performance such as PSRR, output noise, and transient response, it is recommended that the board be designed with separate ground planes for IN and OUT, with the ground planes connected only at the GND pin of the device. In addition, the ground connection for the output capacitor should be connected directly to the GND pin of the device. High-ESR capacitors may degrade PSRR performance.

11.2 Layout Example

Figure 25. TPS768xx-Q1 Layout Example

11.3 Power Dissipation and Junction Temperature

Specified regulator operation is assured to a junction temperature of 125°C; the maximum junction temperature should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation the regulator can handle in any given application. To ensure the junction temperature is within acceptable limits, calculate the maximum allowable dissipation, P_Dmax, and the actual dissipation, P_D, which must be less than or equal to P_Dmax.

The maximum power dissipation limit is determined using Equation 3:

Equation 3.

where:

T_Jmax = maximum allowable junction temperature

R_θJA = junction-to-ambient thermal resistance for the package; that is, 32.6°C/W for the 20-pin TSSOP (PWP) with no airflow

T_A = ambient temperature

The regulator dissipation is calculated using Equation 4:

Equation 4.

Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal protection circuit.