There are two ways to set the output voltage of the TPS61379-Q1: adjustable or fixed. If the resistance between FB and GND is higher than 14.4kΩ and less than 100kΩ during start-up, the TPS61379-Q1 works as an adjustable output version. The FB pin is connected to the negative input of the internal error amplifier directly. The output voltage can be programmed by adjusting the external resistor divider R_Upper and R_Lower according to Equation 2. When the output voltage is in well regulation, the typical voltage at the FB pin is V_REF of 0.8 V.

Equation 2.

For some applications where the resistor needs to be as low as possible, the low-side divider can be 20 kΩ. The reference voltage is 0.8 V, the high-side divider is 205 kΩ for 9-V output voltage.

For other applications without specific requirements on divider resistance, the user can choose R_Lower to be approximately 80.6 kΩ. Slightly increasing or decreasing R_Lower can result in closer output voltage matching when using standard values resistors.

For the best accuracy, R_Lower is recommended to be smaller than 100 kΩ to ensure that the current following through R_Lower is at least 100 times larger than FB pin leakage current. Changing R_Lower towards the lower value increases the robustness against noise injection. Changing the R_Lower to higher values reduces the quiescent current for achieving higher efficiency at light load.

If the resistance between FB and GND is less than 9.6kΩ during start-up, the TPS61379-Q1 works as a fixed output voltage version. The TPS61379-Q1 uses the internal resistor divider.

For 5-V fixed output voltage, R_Lower is between 0Ω and 2.4kΩ and R_Upper should be removed.

For 5.25-V fixed output voltage, R_Lower is between 3.6kΩ and 4.8 kΩ and R_Upper should be removed.

For 5.5-V fixed output voltage, R_Lower is between 7.2kΩ and 9.6kΩ and R_Upper should be removed.