Texas Instruments recommends a 4-layer PCB with a solid ground plane, and to keep the analog and digital signals separate. Additionally, use short traces, and avoid routing signals under the device. Refer to the TI application note 'PCB Layout Guidelines for Switching Regulators' for more information.
The output voltage ripple can be calculated using the formula: ΔVout = (Iout * ESL) / (Cout * fsw), where ESL is the equivalent series inductance of the output capacitor, Cout is the output capacitance, and fsw is the switching frequency. TI provides a calculator tool to help with this calculation.
Although the datasheet specifies a maximum input voltage of 18V, TI recommends limiting the input voltage to 15V to ensure reliable operation and to prevent damage to the device.
To ensure stability, TI recommends using a minimum output capacitance of 10uF, and a maximum ESR of 1 ohm. Additionally, use a compensation network as described in the datasheet, and avoid using ceramic capacitors with high ESL values.
The thermal derating of the 78ST133HC is 12.5mW/°C. To calculate the junction temperature, use the formula: Tj = Ta + (Pd * Rθja), where Ta is the ambient temperature, Pd is the power dissipation, and Rθja is the thermal resistance from junction to ambient.
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