What this part is and where it fits
The Maxim Integrated MAX6639ATE+ is a two-channel temperature monitor with integrated fan control, packing an ADC, PWM generator, and tachometer counter into a single 16-TQFN package. It reads its own die temperature and one external diode-connected transistor over a 0°C to 150°C sensing range, reporting ±2°C local and ±1°C remote accuracy. The I²C/SMBus interface lets a host controller read temperatures and set fan speed without extra glue logic. This is the kind of part you drop onto a server motherboard, a telecom line card, or an industrial controller where you need closed-loop thermal management and don't want to route analog signals across the board.
Accuracy and sensor choice — what the numbers mean for your BOM
The ±1°C remote accuracy is the headline number: it means you can trust the external diode reading to within a degree, which matters when you're setting a fan speed threshold or a thermal shutdown limit. The local sensor is ±2°C, fine for board-level monitoring. The external sensor must be a diode-connected transistor (not a thermistor) — the part expects the -2mV/°C slope of a silicon junction. A common diode-connected transistor with base and collector tied works; Maxim also sells dedicated sensor transistors. The 0°C to 150°C external range covers most hot spots, but the part itself runs from -40°C to 125°C, so it survives the ambient around a hot chassis.
Package and mounting — field-swappable?
It comes in a 16-TQFN (5x5 mm) with an exposed pad — that means you need a reflow station or a hot-air tool to swap it. Not a field-swap part unless you carry a hot-air pencil in your kit. The exposed pad must be soldered to a thermal land on the PCB for the local sensor to read board temperature accurately.
Lifecycle and sourcing — active, no LTB worry
The MAX6639ATE+ is listed as Active with ROHS3 compliance. No last-time-buy risk for ongoing production. If you're freezing a BOM, this part won't trigger a PCN-driven respin anytime soon.