11.2 V_DD, BYP, and Powering Options

The separate V_DD pin provides flexibility for operational power and controlled rail voltage. While the internal UVLO has been set to 2.5 V, the TPS2412/13 requires at least 3 V to generate the specified GATE drive voltage. Sufficient BYP voltage to run internal circuits occurs at V_DD voltages from 2.5 V to 3 V. There are three choices for power, A, C, or a separate supply, two of which are demonstrated in Figure 14. One choice for voltage rails over 3.3 V is to power from C, because it is typically the source of reliable power. Voltage rails below 3.3 V nominal, for example, 2.5 V and below, should use a separate supply such as 5 V. A separate V_DD supply can be used to control voltages above it, for example 5 V powering V_DD to control a 12-V bus.

V_DD is the main source of power for the internal control circuits. The charge pump that powers BYP draws most of its power from V_DD. The input should be low impedance, making a bypass capacitor a preferred solution. A 10-Ω series resistor may be used to limit inrush current into the bypass capacitor, and to provide noise filtering for the supply.

BYP is the interconnection point between a charge pump, V_(AC) monitor amplifiers and comparators, and the gate driver. C_(BYP) must be used to filter the charge pump. A 2200 pF is recommended, but the value is not critical.