Raspberry Pi 4 X735 V2.5 Expansion Board for Raspberry PiSKU: SBC2048
Raspberry Pi 4B/3B+/3B X735 V2.5 Safe Shutdown Power Management & PWM Cooling Expansion Board
The X735 is a multifunctional expansion board for all current models of the Raspberry Pi using a 40-pin header. It provides intelligent and safe power management, safe shutdown and full poweroff through software, an automatic temperature controlled fan which enables the use of the Raspberry Pi in extreme conditions including very high temperature environments. The X735 also reserves the 40-pin header that can be stacked with other Raspberry Pi accessory boards for enhanced applications.
WIKI for reference: wiki.geekworm.com/X735