Definitions for technical terms and acronyms related to HSS & controllers.
|
Term |
Definition |
|
/FLT, /ST |
Active-low fault-flag output pins that signal a fault condition (open load, short circuit, thermal shutdown, etc.) to the MCU. |
|
ADC |
Analog-to-Digital Converter; converts an analog voltage (e.g., a current-sense or temperature signal) into a digital value an MCU can read. |
|
AEC-Q100 |
Automotive Electronics Council qualification standard for integrated circuits used in automotive applications; defines temperature grades (Grade 0–4) and stress-test requirements. |
|
BCM |
Body Control Module; the automotive ECU that typically manages body electronics such as lighting, door, and comfort loads. |
|
BJT |
Bipolar Junction Transistor; sometimes used as a discrete temperature-sensing element placed near an external FET. |
|
Charge pump |
An internal circuit that generates a gate-drive voltage above the supply rail without needing an external bootstrap capacitor, enabling continuous (100% duty cycle) operation. |
|
Cold crank |
An automotive event where battery voltage sags to as low as 3V while starting the engine in cold conditions. |
|
CRC |
Cyclic Redundancy Check; a checksum appended to SPI frames to detect communication errors. |
|
Deglitch |
A filtering delay added to a fault-detection comparator to prevent false trips from brief, expected transients (e.g., PWM edges). |
|
eFuse (smart eFuse HSS) |
A high-side switch or controller with digital I²T-based overcurrent protection that emulates a traditional melting fuse in software. |
|
GPIO |
General-Purpose Input/Output; a simple digital pin used to enable/disable a device or read a fault flag, as opposed to a serial bus like SPI. |
|
HSS |
High-Side Switch; an integrated-FET device that switches power to a load from the supply (high) side rather than the ground (low) side. |
|
HSSC |
High-Side Switch Controller; drives one or more external FETs rather than integrating the FET, enabling higher current and custom current scaling. |
|
ICL, ILIM |
Current-limit trip threshold, typically set via an external resistor (RILIM) or SPI register. |
|
I²T |
Current-squared multiplied by time; a programmable time-current characteristic used by smart eFuse devices to replicate the thermal trip behavior of a melting fuse. |
|
K_SNS |
The sense ratio (e.g., 1µA per 1mA of load current) that relates a device's SNS pin output current to the actual load current. |
|
MCU |
Microcontroller; the system controller that reads sense/fault signals and commands the HSS via GPIO or SPI. |
|
MOSFET |
Metal-Oxide-Semiconductor Field-Effect Transistor; the power switching element, either integrated (HSS) or external (HSSC). |
|
NTC |
Negative Temperature Coefficient (thermistor); used by some HSS controllers to remotely sense external FET temperature. |
|
OTA |
Over-the-Air (update); used here to describe remotely reconfiguring current limits or I²T curves via SPI/software rather than physical rework. |
|
PWM |
Pulse-Width Modulation; a switching technique used to control average power delivered to a load. |
|
Rds(on) |
The FET's on-state drain-to-source resistance; increases substantially (~2×) from 25°C to 125°C and must be accounted for in thermal budget calculations. |
|
RILIM |
The external resistor that programs a device's current-limit threshold. |
|
RSNS |
The external resistor that converts a device's internal sense current into a readable voltage at the SNS/CS pin. |
|
RθJA / RθJB |
Junction-to-ambient / junction-to-board thermal resistance parameters used to estimate junction temperature from power dissipation. |
|
SNS / CS pin |
The analog current- or voltage-sense output pin on a high-side switch. |
|
SPI |
Serial Peripheral Interface; a digital communication bus used for configuration, telemetry, and fault reporting on smart HSS/eFuse devices. |
|
Tj |
Junction temperature; the peak temperature of the semiconductor die. |
|
TSD |
Thermal Shutdown; a protection feature that disables the FET when junction temperature exceeds a safe threshold. |
|
UVLO |
Undervoltage Lockout; disables the device below a minimum supply voltage to avoid operating in an undefined state. |
|
VBB / VDD / VS |
Common HSS/HSSC supply-pin names (VBB and VS refer to the switched battery/supply rail; VDD is a logic/bias supply). |
|
VCL / KCL |
Datasheet constants relating RILIM to the actual current-limit threshold (ICL = RILIM × VCL / KCL, or the equivalent per-datasheet formula). |
|
VSNS |
The voltage measured at the SNS pin, proportional to load current via K_SNS and RSNS. |
|
ΨJT (Psi-JT) |
Junction-to-top characterization parameter; the most accurate way to estimate junction temperature from a measured package-top temperature. |