3.3V fixed LDO with 500mA ceiling
The KF33BD-TR is a 3.3V fixed-output positive LDO from STMicroelectronics, delivering up to 500 mA continuous current. The 20V input maximum gives headroom for unregulated rails like a 12V or 15V supply bus without needing a pre-regulator. The 1 mA quiescent current (Iq) is moderate; for always-on circuits drawing microamps, a lower-Iq LDO would waste less standby power.
PSRR and noise rejection across frequency
PSRR is 80 dB at 120 Hz, dropping to 60 dB at 10 kHz. That 20 dB roll-off means the regulator attenuates 100/120 Hz ripple from a rectifier stage well, but switching noise above 10 kHz (from a buck converter upstream) passes through with only 60 dB of rejection — budget a post-filter if the load is sensitive above that corner. The -40°C to 125°C operating range covers automotive under-hood and industrial enclosure environments. The SO-8 package (0.154-inch body width) dissipates heat through the leads — the junction-to-ambient thermal resistance is set by the copper area on the PCB, not the package itself.
Protection features include over-current and over-temperature shutdown — the regulator folds back or latches off under fault, protecting the load and the pass element. The Enable pin allows external on/off control; pulling it low drops the output and reduces Iq to near zero.