Datasheet

(POR) state. See Tables 3–7 for all other register functions
and the Register Descriptions section.
Temperature Measurements
The averaging ADC integrates over a 120ms period
(each channel, typically), with excellent noise rejection.
For internal temperature measurements, the ADC and
associated circuitry measure the forward voltage of the
internal sensing diode at low- and high-current levels
and compute the temperature based on this voltage.
For thermistor measurements, the reference voltage
and the thermistor voltage are measured and offset is
applied to yield a value that correlates well to thermistor
temperature within a wide temperature range. Both
channels are automatically converted once the conver-
sion process has started. If one of the two channels is
not used, the circuit still performs both measurements,
and the data from the unused channel may be ignored.
If either of the measured temperature values is below
0°, the value in the corresponding temperature register
is clipped to zero when a negative offset is pro-
grammed into the thermistor offset register (17h).
Local (internal) temperature data is expressed directly
in degrees Celsius. Two registers contain the tempera-
ture data for the local channel. The high-byte register
has an MSB of 128°C and an LSB of 1°C. The low- byte
register contains 3 bits, with an MSB of 0.5°C and an
LSB of 0.125°C. The data format is shown in Table 1.
Thermistors allow measurements of external tempera-
tures. Connect a thermistor in series with a resistor,
R
EXT
. The thermistor should be connected between the
TH_ input and ground, and R
EXT
should be connected
between the reference output, REF, and the TH_ input,
as shown in the Typical Application Circuit .
The voltage across R
EXT
is measured by the ADC,
resulting in a value that is directly related to tempera-
MAX6615/MAX6616
Dual-Channel Temperature Monitors and
Fan-Speed Controllers with Thermistor Inputs
_______________________________________________________________________________________ 7
SMBCLK
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
SMBDATA
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
SMBCLK
AB CD
E
FG H
I
J
K
SMBDATA
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