2.1V fixed rail, 200 mA — what the dropout and PSRR mean for the supply
The BU21TD3WG-TR is a positive fixed-output LDO from ROHM, delivering 2.1 V at up to 200 mA from a 6 V max input rail. PSRR is 70 dB at 1 kHz, which attenuates 100 mVpp of 1 kHz ripple on the input down to roughly 32 µVpp at the output. For an analog front-end or a sensor bias rail, this keeps switching-regulator noise from coupling into the signal chain — the rejection drops at higher frequencies, so upstream filtering ahead of the LDO still matters above 100 kHz.
Package footprint and board integration — SC-74A / SOT-753 / 5-SSOP
This is a 5-pin surface-mount footprint with 0.95 mm pitch — the same land pattern serves all three package descriptors. The enable pin allows the regulator to be gated by a logic signal; unused, the pin should be tied to the input to keep the output active.
Active lifecycle and compliance — sourcing posture
ROHM lists the BU21TD3WG-TR as active and ROHS3 compliant.