Data sheet at page with back-up battery switchover states: Vout = VDD if VDD <= Vbat and VDD > Vit. So if Vit =1,1V Vout could be 1,2V with VDD is 1,2V and Vbat=3V. Most SRAM's are cleared at Vcc=1,5V. At page 2 is stated Vout = VDD if VDD <= Vbat and Vsense > Vit Which voltage determines the back-up battery switchover


The switchover voltage depends on whether the voltage on VDD is rising or falling.  When rising, VOUT will switch to VDD if VDD>VBATT OR VDD>VIT. When falling, VOUT will switch to VBATT when VDD<VIT and VDD<VBATT. This is true if the SENSE pin is tied to VDD.  It is possible to tie the SENSE pin to VDD through a resistor divider.  In this case the voltage on the SENSE pin must be above or below VIT.