Datasheet

MAX6653/MAX6663/MAX6664
Temperature Monitors and
PWM Fan Controllers
6 _______________________________________________________________________________________
Detailed Description
The MAX6653/MAX6663/MAX6664 are local/remote
temperature monitors and fan controllers for micro-
processor-based systems. These devices communi-
cate with the system through a serial SMBus interface.
The serial bus controller features a hard-wired address
pin for device selection, an input line for a serial clock,
and a serial line for reading and writing addresses and
data (see Functional Diagram).
The MAX6653/MAX6663/MAX6664 fan control section
can operate in three modes. In the automatic fan-control
mode, the fan’s power-supply voltage is automatically
adjusted based on temperature. The control algorithm
parameters are programmable to allow optimization to
the characteristics of the fan and the system. RPM select
mode forces the fan speed to a programmed tachome-
ter value. PWM duty cycle select mode allows user
selection of the PWM duty cycle. PWM rise and fall times
are limited to maximize fan reliability.
To ensure overall system reliability, the MAX6653/
MAX6663/MAX6664 feature an SMBus timeout so that
the MAX6653/MAX6663/MAX6664 can never “lock” the
SMBus. Furthermore, the availability of hard-wired
default values for critical temperature set points
ensures the MAX6653 controls critical temperature
events properly even if the SMBus is “locked” by some
other device on the bus.
SMBus Digital Interface
From a software perspective, the MAX6653/MAX6663/
MAX6664 appear as a set of byte-wide registers. These
devices use a standard SMBus 2-wire/I
2
C-compatible
serial interface to access the internal registers. The
MAX6653/MAX6663/MAX6664 slave address can be
set to three different values by the input pin ADD
(Table 2) and, therefore, a maximum of three MAX6653/
MAX6663/MAX6664 devices can share the same bus.
The MAX6653/MAX6663/MAX6664 employ four stan-
dard SMBus protocols: Write Byte, Read Byte, Send
Byte, and Receive Byte (Figures 1, 2, and 3). The short-
er Receive Byte protocol allows quicker transfers, pro-
vided that the correct data register was previously
selected by a Read Byte instruction. Use caution with
the shorter protocols in multimaster systems, since a
second master could overwrite the command byte with-
out informing the first master.
Alert Response Address
The MAX6653/MAX6663/MAX6664 respond to the
SMBus alert response address, an event which typical-
ly occurs after an SMBus host master detects an INT
interrupt signal going active (referred to as ALERT in
SMBus nomenclature). When the host master puts the
alert response address (0001 1001) on the bus, all
devices with an active INT output respond by putting
their own address onto the bus. The alert response can
activate several different slave devices simultaneously,
similar to the I
2
C general call. If more than one slave
attempts to respond, bus arbitration rules apply, and
the device with the lowest address code wins. The
master then services the devices from the lowest
address up.
THERM SET POINT (°C) SHUTDOWN SET POINT (°C)
CRIT1 CRIT0
REMOTE LOCAL REMOTE LOCAL
GND Open 85 55 110 80
GND GND 90 60 115 85
GND V
CC
95 65 120 90
Open Open 100 70 125 95
Open GND 105 75 125 95
Open V
CC
110 80 125 95
V
CC
Open 115 85 125 95
V
CC
GND 120 90 125 95
V
CC
V
CC
125 95 125 95
Table 1. MAX6653 Power-Up Set-Point Decoding
Table 2. MAX6653/MAX6663/MAX6664
Slave Address Decoding
ADD PIN ADDRESS
GND 0101 100
No connect 0101 110
V
CC
0101 101