I described earlier the laptop power up sequence, that which part and IC receives the power supply first. Continuing my notes on laptop repair I found out that NPCE885PA0DX - I/O controller chip also known as KBC(Keyboard Controller) is the first IC connected to the DC power input supply circuit which receives the power input in dell Laptop. The NPCE885PA0DX keyword controller is connected to the following parts as shown in the circuit diagram:
- NCT7718W(Thermal Fan Controller IC)
- PCH(Platform Controller Hub)
- BQ24727(Battery Controller IC)
- Touchpad
Here I wanted to write some note on the NCT7718W(Thermal Fan Controller IC), how it works and how it connected to the rest of the circuit.
The NCT7718W is a hardware monitoring and fan control IC from Nuvoton, used in the Dell Inspiron 14z (BMW Z4 DIS) schematic.
.png "Thermal IC (NCT7718W)")
Below is a breakdown of its functionality and connections based on the schematic:
1. Functionality of NCT7718W
The NCT7718W is a system hardware monitor with the following key features:
Temperature Sensing: Monitors multiple thermal zones (e.g., CPU, GPU, system).
Fan Control: Adjusts fan speed via PWM or voltage based on temperature inputs.
SMBus/I²C Interface: Communicates with the PCH (Platform Controller Hub) or EC (Embedded Controller) for configuration and reporting.
GPIO Pins: Can be used for additional system control (e.g., alarms, interrupts).
2. Connections in the Schematic
The following shows the circuit diagram which shows connection of the NCT7717W thermal sensor IC that monitors CPU/GPU temperatures via a remote diode (connected to D+ and D- pins). The PMBS3904-1-GP is used here for diode fault protection and signal conditioning.
Thermal Diode Inputs:
Connected to CPU/GPU thermal diodes (e.g.,
D+/D-pins) to measure temperature.Uses remote diode sensing for accurate CPU/GPU temp monitoring.
Fan Control
PWM/Voltage Output:
Drives the system fan(s) via PWM or voltage modulation.
Feedback from fan tachometer (TACH) may be connected to monitor RPM.
SMBus/I²C Interface
SMBDATA/SMBCLK:
Connected to the PCH's SMBus (e.g.,
PCH_SMBDATAandPCH_SMBCLK).Allows the PCH or EC to read temperature data and configure fan curves.
Interrupts/Alerts
ALERT# Pin:
May be connected to the PCH or EC to trigger interrupts for critical temperature events.
Example: Over-temperature shutdown.
GPIO/Other Pins
GPIO Pins:
Can be configured for additional functions (e.g., system alerts, fan fail detection).
May connect to the PCH's GPIO or other system components.
3. Integration with I/O Controller
The NCT7718W interfaces with the PCH (Panther Point HM77) via:
SMBus: For communication (data read/write).
Thermal Signals: Directly monitors CPU/GPU diodes.
Interrupts: Alerts the PCH/EC if temperatures exceed thresholds.
Fan Control: Adjusts fan speed based on PCH/EC commands or autonomous operation.
4. Key Schematic References
Page 2 (Block Diagram): Shows the NCT7718W under the "Thermal/KBC" section.
Page 18 (PCH PCI/USB/NVRAM): Confirms SMBus connections (
SMBDATA/SMBCLK).Page 19 (PCH DMI/FDI/PM): Mentions thermal management signals.
Conclusion
The NCT7718W acts as a hardware monitor and fan controller, interfacing with the PCH via SMBus and directly controlling cooling components. Its connections ensure real-time thermal management and system stability.
