Rainbow Electronics MAX6640 - Manual (Page 6)

MAX6640
Detailed Description
The MAX6640 monitors its own temperature and a
remote diode-connected transistor or the temperatures
of two external diode-connected transistors, which typi-
cally reside on the die of a CPU or other integrated cir-
cuit. The 2-wire serial interface accepts standard
SMBus write byte, read byte, send byte, and receive
byte commands to read the temperature data and pro-
gram the alarm thresholds. Temperature data can be
read at any time over the SMBus, and a programmable
alarm output can be used to generate interrupts, throt-
tle signals, or overtemperature shutdown signals.
The temperature data is also used by the internal dual
PWM fan-speed controller to adjust the speed of up to
two cooling fans, thereby minimizing noise when the
system is running cool, but providing maximum cooling
when power dissipation increases. RPM feedback
allows the MAX6640 to control the fan’s actual speed.
2-Channel Temperature Monitor with Dual
Automatic PWM Fan-Speed Controller
6 _______________________________________________________________________________________
GND
SMBus
INTERFACE AND
REGISTERS
LOGIC
PWM
GENERATOR
BLOCK
V CC
TEMPERATURE
PROCESSING
BLOCK
SDA
SCL
DXP1
DXN
PWM1
PWM2
TACH1
TACH2
DXP2
OT
THERM
FANFAIL
ALERT
MAX6640
Block Diagram
Write Byte Format
Read Byte Format
Send Byte Format Receive Byte Format
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface Command Byte: selects which
register you are writing to Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave Address: equiva-
lent to chip-select line Command Byte: selects
which register you are
reading from Slave Address: repeated
due to change in data-
flow direction Data Byte: reads from
the register set by the
command byte
Command Byte: sends com-
mand with no data, usually
used for one-shot command
Data Byte: reads data from
the register commanded
by the last Read Byte or
Write Byte transmission;
also used for SMBus Alert
Response return address
S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged
Figure 1. SMBus Protocols
S ADDRESS RD ACK DATA /// P
7 bits 8 bits
WR S ACK COMMAND ACK P
8 bits
ADDRESS
7 bits
P
1
ACK DATA
8 bits
ACK COMMAND
8 bits
ACK WR ADDRESS
7 bits
S
S ADDRESS WR ACK COMMAND ACK S ADDRESS
7 bits 8 bits 7 bits
RD ACK DATA
8 bits
/// P