Datasheet for the Texas Instruments TPS51285B, supplied as a 1.37 MB PDF. The TPS51285 family are dual synchronous step-down controllers with 5 V and 3.3 V LDOs, commonly used to generate the always-on and system 3V/5V rails on laptop boards. The document details pin functions, enable sequencing and power-good behaviour, which is essential when a board shows no standby voltage. Check the VIN supply, EN pins and LDO outputs against its tables, and confirm the suffix letter matches the chip fitted.
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