SLVSDN4 June 2017 TPS82150
The SS/TR pin is externally driven by another voltage source to achieve output voltage tracking. The application circuit is shown in Figure 4.
When the SS/TR pin voltage is between 50 mV and 1.2 V, the VOUT2 tracks the VOUT1 as described in Equation 5.
When the SS/TR pin voltage is above 1.2 V, the voltage tracking is disabled and the FB pin voltage is regulated at 0.8 V. For decreasing SS/TR pin voltage, the device doesn't sink current from the output. So the resulting decreases of the output voltage may be slower than the SS/TR pin voltage if the load is light. When driving the SS/TR pin with an external voltage, do not exceed the voltage rating of the SS/TR pin which is VIN+0.3V.
Details about tracking and sequencing circuits are found in SLVA470.