The TPS25948xx provides a digital output (SPLYGD/SPLYGD) which is asserted to indicate when the priority input supply is in a valid range (above UVP/UVLO and below OVLO thresholds) and the device has successfully completed its inrush sequence. The SPLYGD/SPLYGD pin is an open-drain signal which needs to be pulled up to an external supply. For the TPS259480x/2x variants, SPLYGD is an active high output. For the TPS259481x variant, SPLYGD is an active low output.

After power up, SPLYGD/SPLYGD pin is de-asserted initially. The device initiates a inrush sequence in which the HFET is turned on in a controlled manner. When the FET gate voltage has reached the full overdrive indicating that the inrush sequence is complete and device is capable of delivering full power, the SPLYGD/SPLYGD pin is asserted. Thereafter, the SPLYGD/SPLYGD pin is de-asserted only if the input supply becomes invalid (below UVP/UVLO or above OVLO thresholds). No load side events/faults have any control over the SPLYGD/SPLYGD de-assertion.

This pin is used to control the auxiliary channel when 2 TPS25948xx devices are connected in a priority power MUX configuration. It can also be used as a supply valid status indication to the downstream load or system supervisor.

Figure 8-15 TPS25948xx SPLYGD Behavior

When there is no supply to the device, the SPLYGD pin is expected to stay low. However, there is no active pull-down in this condition to drive this pin all the way down to 0 V. If the SPLYGD pin is pulled up to an independent supply which is present even if the device is unpowered, there can be a small voltage seen on this pin depending on the pin sink current, which is a function of the pull-up supply voltage and resistor. Minimize the sink current to keep this pin voltage low enough not to be detected as a logic HIGH by associated external circuits in this condition. This also ensures that the auxiliary channel is not turned off inadvertently in a priority power MUX configuration.