The TC648 is a switch mode, fan speed controller for use with brushless DC fans. Temperature proportional speed control is accomplished using pulse width modulation (PWM). A thermistor (or other voltage output temperature sensor) connected to the VIN input furnishes the required control voltage of 1.25V to 2.65V (typical) for 0% to 100% PWM duty cycle. The TC648 can be configured to operate in either auto-shutdown or minimum speed mode.
The TC648 is a switch‑mode fan speed controller that provides temperature‑proportional PWM control for brushless DC fans. It supports 3.0 V to 5.5 V supply, auto‑shutdown, over‑temperature fault detection and a start‑up timer to ensure reliable fan start‑up.
The document includes detailed electrical characteristics, pin descriptions, functional block diagrams, system behavior flowcharts and full specifications such as PWM frequency, supply currents, temperature ranges and timing parameters.
| Supply Voltage | 3.0 V to 5.5 V |
|---|---|
| Operating Supply Current | 0.5 mA to 1.0 mA |
| Shutdown Supply Current | 25 µA (typical) |
| PWM Frequency | 30 Hz (typical) |
| Start‑up Timer Duration | 32 PWM cycles (~1 s) |
| Specified Temperature Range | -40 °C to +125 °C |
The TC648 operates from a supply voltage of 3.0 V to 5.5 V.
The typical PWM frequency is 30 Hz.
When the analog input voltage (Vix) falls below the programmed threshold (Vag), the fan is automatically shut off; it restarts when Vix rises above Vag plus hysteresis.
The OTF (over‑temperature fault) output goes low when the PWM reaches 100 % duty cycle, signaling a possible thermal runaway condition.