The TPS544C26 device offers write protection feature through Section 7.6.51 register. After power-on, the user accessible registers with write access are by default under "write protected" state, meaning the response to a write is NACK. The device always acknowledges a read command and responds the data byte accordantly. Only after writing the correct passcodes (multiple writes in the right order) into this REG_LOCK register, the user accessible registers are "unlocked" and the device acknowledges the next write commands. Section 7.6.51 shows more details.