Datasheet

SMBus Digital Interface
From a software perspective, the MAX6639 appears as
a set of byte-wide registers. This device uses a stan-
dard SMBus 2-wire/I
2
C-compatible serial interface to
access the internal registers.
The MAX6639 features an address select input (ADD)
that allows the MAX6639 to have three unique addresses
(see Table 1).
The MAX6639 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figures 1, 2, and 3). The shorter receive byte protocol
allows quicker transfers, provided that the correct data
register was previously selected by a read byte instruc-
tion. Use caution with the shorter protocols in multimas-
ter systems, since a second master could overwrite the
command byte without informing the first master.
Table 4 details the register addresses and functions,
whether they can be read or written to, and the power-
on reset (POR) state. See Tables 5–9 for all other regis-
ter functions and the
Register Descriptions section.
Temperature Reading
Temperature data can be read from registers 00h and
01h. The temperature data format for these registers is
8 bits, with the LSB representing 1°C (Table 2) and the
MSB representing +128°C. The MSB is transmitted first.
Three additional temperature bits provide resolution
down to 0.125°C and are in the channel 1 extended
temperature (05h) and channel 2 extended temperature
(06h) registers. All values below 0°C clip to 00h.
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Maxim Integrated 7
MAX6639/MAX6639F
SCL
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
AB CD
E
FG
HIJ
SDA
t
SU:STA
t
HD:STA
t
LOW
t
HIGH
t
SU:DAT
t
SU:STO
t
BUF
LMK
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram
SCL
AB CD
E
FG H
I
J
K
SDA
t
SU:STA
t
HD:STA
t
LOW
t
HIGH
t
SU:DAT
t
HD:DAT
t
SU:STO
t
BUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
L
M
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 3. SMBus Read Timing Diagram
ADD INPUT STATE I
2
C SLAVE ADDRESS
BINARY
EQUIVALENT
V
CC
5Eh 0101 111
Floating 5Ch 0101 110
GND 58h 0101 100
Table 1. I
2
C Slave Address