Eight low-side channels, SPI-controlled, rated for the harsh edge
The STMicroelectronics L9825TR is an 8-output low-side power driver in a PowerSO-20 package with exposed pad for thermal management. Each N-channel output switches up to 1A into loads referenced to ground, with a maximum load voltage of 45V — covering 12V and 24V automotive solenoid, relay, and lamp banks. Control is over SPI, which keeps the host MCU pin count low; a single chip-select line addresses all eight channels through the 1:8 input-to-output ratio. A status flag output reports fault conditions back to the controller over a dedicated line.
With a maximum on-resistance of 750 mOhm per channel, each output conducting 1A dissipates up to 750 mW. The PowerSO-20 exposed pad conducts heat to the PCB copper plane.
SPI control — how it changes the BOM
The SPI interface replaces the parallel data lines and latch strobes typical of older octal latched drivers. The host MCU needs four wires (SCK, MOSI, CS, and the status-flag readback).