I came across the TPS51225RUKR IC while learning how to repair my dell inspiron laptop. I did not know what this IC was and so I am writing this note.
The TPS51225RUKR is a synchronous buck controller IC designed by Texas Instruments (TI), commonly used in laptops (including Dell systems like the Inspiron 14z) to generate low-voltage power rails for critical components like the CPU, RAM, and chipset.
Below are its key details:
1. Key Features
Function: Dual-output step-down (buck) DC-DC controller.
Rail 1: Produces 5V rail.
Rail 2: Produces 3.3V rail
Input Voltage: 5.5V–28V (supports laptop battery/adapter voltage ranges).
Output Current: 100mA per phase.
Efficiency: >90% (optimized for battery life).
Control Method: Voltage-mode PWM with adaptive transient response.
2. Role in the Laptop Power Sequence
The TPS51225RUKR is a critical power management IC that:
Receives input power from the BQ24727 charger IC (after AC/battery power is validated).
Generates stable voltages for:
CPU VCore (via Rail 1).
PCH (Platform Controller Hub) and RAM VCCSA/VCCIO (via Rail 2).
Synchronizes with the PCH/KBC to enable/disable rails during sleep/wake cycles.
3. Failure Symptoms
No boot: If Rail 1 fails, the CPU won’t power on.
Random crashes: Unstable VCCSA can cause chipset/RAM errors.
Overheating: Faulty MOSFETs driven by the TPS51225 may overheat.
4. Schematic Context (Dell Inspiron 14z)
The schematic diagram below shows the TPS51123:
It outputs are:
- VREG3, pin no. 3, 3D3V_PWR_2 output
- VREG5, pin no. 13, 5V_PWR_2 output
5. Replacement/Equivalent
TPS51225C: Similar specs, different package.
RT8120D: Alternative from Richtek (requires circuit tweaks).
To to this note I liked to mention that I wrote number of diary notes on voltage regulators, buck converter and boost converters. But those are made by discrete components unlike this TPS51225 Buck converter IC.
