LTC1840

1

1840f

APPLICATIO S

DESCRIPTIO

FEATURES

TYPICAL APPLICATIO

The LTC

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.

ible 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 pro-

grammed 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.

s

Servers

s

Desktop Computers

s

Power Supplies

s

Cooling Systems

s

Two 8-Bit Current DACs

s

DACs Guaranteed Monotonic

s

Known IC State on Power-Up

s

Serial Interface Watchdog Timer with Disable

s

TM

and SMBus

s

2 Programmable Fan Tachometer Interfaces

s

4 Programmable General Purpose I/Os

s

Small 16-Pin SSOP Package

s

Single 2.7V to 5.75V Supply Operation

s

Fault Output Signal

s

Status Register

s

Fan Blasting Function

s

Nine Addresses Using Two Programming Lines

Dual Fan Controller

with 2-Wire Interface

1840 TA01

+

100pF

220pF

0.05

Ω

0.05

Ω

75k

28k

150

µF

+

DC

FAN

22

µF

L1 47

µH

Si6447DQ

UPS5817

TACH

OUT

3.3V

3.3V

3.3V

3.3V

3.3V

GND

+

100pF

220pF

75k

28k

150

µF

+

DC

FAN

22

µF

L2 47

µH

Si6447DQ

UPS5817

TACH

OUT

3.3V

12V

12V

SYSTEM

RESET

GPI04

BLAST

IDACOUTA

GPI03

IDACOUTB

TACHB

TACHA

FAULT

SDA

SCL

A0

A1

GPI01

GPI02

LTC1840

10k

10k

TO

MASTER

NC

NC

130

Ω

LED1

130

Ω

LED2

ADDRESS = 1110010

(8 OTHERS POSSIBLE)

2-NMB 6820PL-04W-B29-D50 FANS

1.1A NOM AT 12V

10k

10k

10k

+

10

µF

0.1

µF

RUN/SS

GND

SENSE

PGATE

MODE

LTC1771

RUN/SS

GND

SENSE

PGATE

MODE

LTC1771

Low Parts Count, High Efficiency Dual Fan Control

, LTC and LT are registered trademarks of Linear Technology Corporation.