LTC1695 Datasheet, PDF (1/20 Pages) Linear Technology – SMBus/I2C Fan Speed Controller in SOT-23

LTC1695
SMBus/I²C Fan Speed
Controller in SOT-23
FEATURES
s _{Complete SMBus/I}²_C^TM _{Brushless DC Fan Speed}
Control System in a 5-Pin SOT-23 package
s _{0.75Ω PMOS Linear Regulator with 180mA}
Output Current Rating
s _{0V to 4.922V Output Voltage Range Controlled by a}
6-Bit DAC
s _{Simple 2-Wire SMBus/I}²_{C Interface}
s _{250ms Internal Timer Ensures Fan Start-Up}
s _{Current Limit and Thermal Shutdown}
s _{Fault Status Indication via SMBus Host Readback}
U
APPLICATIO S
s _{Notebook Computers}
s _{Spot Cooling}
s _{Portable Instruments}
s _{Battery-Powered Systems}
s _{DC Motor Control}
s _{White LED Power Supplies}
s _{Programmable Low Dropout Regulator}
, LTC and LT are registered trademarks of Linear Technology Corporation.
I²C is a trademark of Philips Electronics N.V.
DESCRIPTIO
The LTC^®1695 fan speed controller provides all the func-
tions necessary for a power management microprocessor
to regulate the speed of a 5V brushless DC fan via a 2-wire
SMBus/I²C interface. Fan speed is controlled according to
the system’s required temperature profile and permits
lower fan power consumption, longer battery run time and
lower acoustical generated noise versus systems that
only provide simple on-off control for the fan.
The LTC1695 incorporates a 180mA low dropout linear
regulator, a 2-wire SMBus/I²C interface and a 6-bit DAC.
Fan speed is controlled by varying the fan’s terminal
voltage through the output voltage of the LTC1695’s linear
regulator. The LTC1695’s output voltage is programmed
by sending a 6-bit digital code to the LTC1695 DAC via the
SMBus. To eliminate fan start-up problems at lower fan
voltages, users can enable the LTC1695’s boost start
feature that provides the DAC’s full-scale output voltage
for 250ms before decreasing to the programmed output
voltage.
The LTC1695 includes output current limiting and thermal
shutdown as well as status monitors that can be read back
by the microprocessor during fault conditions. The
LTC1695 is available in a 5-lead SOT-23 package.
TYPICAL APPLICATION
5V
+
10µF
SYSTEM
CONTROLLER
1
V_CC
5
V_OUT
LTC1695
2 _GND
+
4.7µF
3
SCL
SDA ⁴
5V DC FAN
SUNON
KDE0502PFB2-8
0.6W, 1.7 CFM
(25 • 25 • 10)mm³
1695 • TA01
Fan Voltage and Current vs DAC Code
120
6
V_CC = 5V
T_A = 25°C
100
5
80
4
I_LOAD
V_OUT
60
3
40
2
20
1
0
0
0 10 20 30 40 50 60 70
DAC CODE
1695 • TA02
1