LTC1840 Datasheet, PDF (1/12 Pages) Linear Technology – Dual Fan Controller with 2-Wire Interface

FEATURES
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 _{2-Wire Serial Interface Compatible with I}²_C^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}
U
APPLICATIO S
s _Servers
s _{Desktop Computers}
s _{Power Supplies}
s _{Cooling Systems}
, LTC and LT are registered trademarks of Linear Technology Corporation.
I²C is a trademark of Philips Electronics N.V.
LTC1840
Dual Fan Controller
with 2-Wire Interface
DESCRIPTIO
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 compat-
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.
TYPICAL APPLICATIO
Low Parts Count, High Efficiency Dual Fan Control
3.3V
3.3V
+
10µF
10k
V_CC
FAULT
GPI04
TO
MASTER
SDA
BLAST
SYSTEM
RESET
SCL IDACOUTA
0.1µF
R_C1
10k
C_C1
220pF
C_FB1
100pF
12V
V_IN
RUN/SS SENSE
LTC1771
I_TH
PGATE
R_SENSE1
0.05Ω
V_FB
MODE
GND
+
C_VIN1
22µF
Si6447DQ
L1 47µH
UPS5817
R_FB1A
75k ₊
R_FB1B
28k
DC
FAN
C_OUT1
150µF
3.3V
10k
TACH
OUT
LTC1840
3.3V
3.3V
130Ω
NC
A0
GPI03
130Ω
LED2
LED1 ^{NC A1}
IDACOUTB
GPI01
TACHB
GPI02
TACHA
GND
ADDRESS = 1110010
(8 OTHERS POSSIBLE)
R_C2
10k
C_C2
220pF
C_FB2
100pF
12V
V_IN
RUN/SS SENSE
LTC1771
I_TH
PGATE
R_SENSE2
0.05Ω
V_FB
MODE
GND
+
C_VIN2
22µF
Si6447DQ
L2 47µH
UPS5817
2-NMB 6820PL-04W-B29-D50 FANS
1.1A NOM AT 12V
3.3V
R_FB2A
75k ₊
R_FB2B
28k
DC
FAN
C_OUT2
150µF
10k
TACH
OUT
1840 TA01
1840f
1