Features

• Two 8-Bit Current DACs
• DACs Guaranteed Monotonic
• Known IC State on Power-Up
• Serial Interface Watchdog Timer with Disable
• 2-Wire Serial Interface Compatible with I²C™ and SMBus
• 2 Programmable Fan Tachometer Interfaces
• 4 Programmable General Purpose I/Os
• Small 16-Pin SSOP Package
• Single 2.7V to 5.75V Supply Operation
• Fault Output Signal
• Status Register
• Fan Blasting Function
• Nine Addresses Using Two Programming Lines

Typical Application

Description

The LTC®1840 is a fan controller with two 8-bit current output DACs, two tachometer interfaces, and four general purpose I/O (GPIO) pins. It operates from a single supply with a range of 2.7V to 5.75V. A current output DAC is used to control an external switching regulator, which controls the fan speed. A current output DAC and tachometer allow a controller to form a closed control loop on fan velocity. The GPIO pins can be used as digital inputs or open drain pull-down outputs.

The part features a simple 2-wire I²C and SMBus compatible serial interface that allows communication between many devices. The interface includes a fault status register that reflects the state of the part and which can be polled to find the cause of a fault condition. Other operational characteristics of the part, such as DAC output currents, GPIO modes, and tachometer frequency, are also programmed through the serial interface. Two address pins provide nine possible device addresses.

The BLAST pin is provided to force the DAC output currents to program the maximum regulator output voltages through a single pin and gate the operation of the serial access timer.