Maxim MAX6622 5-channel precision temperature monitor Datasheet

19-3003; Rev 0; 12/07
5-Channel Precision Temperature Monitor
The MAX6622 precision multichannel temperature sensor monitors its own temperature and the temperatures
of up to four external diode-connected transistors. All
temperature channels have programmable alert thresholds. Channels 1 and 4 also have programmable
overtemperature thresholds. When the measured temperature of a channel exceeds the respective threshold, a status bit is set in one of the status registers. Two
open-drain outputs, OVERT and ALERT, assert corresponding to these bits in the status register.
The 2-wire serial interface supports the standard system
management bus (SMBus™) protocols: write byte, read
byte, send byte, and receive byte for reading the temperature data and programming the alarm thresholds.
The MAX6622 is specified for a -40°C to +125°C operating temperature range and is available in a 16-pin
TSSOP package.
Features
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Four Thermal-Diode Inputs
Local Temperature Sensor
1°C Remote Temperature Accuracy (+60°C to +100°C)
Temperature Monitoring Begins at POR for FailSafe System Protection
ALERT and OVERT Outputs for Interrupts,
Throttling, and Shutdown
STBY Input for Hardware Standby Mode
Small, 16-Pin TSSOP Package
2-Wire SMBus Interface
Penryn CPU-Compatible
Pin- and Register-Compatible with MAX6602
Ordering Information
Notebook Computers
PINSLAVE
PKG
PACKAGE
ADDRESS
CODE
MAX6622UE9A+ 16 TSSOP
1001 101
U16-1
Note: This device is specified over the -40°C to +125°C
temperature range.
Workstations
+Denotes lead-free package.
Applications
Desktop Computers
PART
Servers
SMBus is a trademark of Intel Corp.
Pin Configuration appears at end of data sheet.
Typical Application Circuit
+3.3V
CPU
1
DXP1
GND 16
4.7kΩ
EACH
2
DXN1
SMBCLK 15
CLK
3
DXP2
MAX6622 SMBDATA 14
4
DXN2
ALERT 13
5
DXP3
VCC 12
6
DXN3
OVERT 11
7
DXP4
N.C. 10
8
DXN4
2200pF
DATA
2200pF
INTERRUPT
TO μP
0.1μF
2200pF
TO SYSTEM
SHUTDOWN
2200pF
STBY
9
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
MAX6622
General Description
MAX6622
5-Channel Precision Temperature Monitor
ABSOLUTE MAXIMUM RATINGS
VCC, SMBCLK, SMBDATA, ALERT, OVERT,
STBY to GND .......................................................-0.3V to +6V
DXP_ to GND..............................................-0.3V to (VCC + 0.3V)
DXN2, DXN3, DXN4 to GND .................................-0.3V to +0.8V
SMBDATA, ALERT, OVERT Current....................-1mA to +50mA
DXN Current .......................................................................±1mA
Continuous Power Dissipation (TA = +70°C)
16-Pin TSSOP
(derate 11.1mW/°C above +70°C)..............................888.9mW
Junction-to-Case Thermal Resistance (θJC) (Note A)
16-Pin TSSOP ..............................................................27°C/W
Junction-to-Ambient Thermal Resistance (θJA) (Note A)
16-Pin TSSOP...............................................................90°C/W
ESD Protection (all pins, Human Body Model) ................±2000V
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note A: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a
4-layer board. For detailed information on package thermal considerations, refer to Application Note 4083 available
at www.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, VSTBY = VCC, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and
TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
Supply Voltage
VCC
Software Standby Supply Current
ISS
SMBus static
30
Operating Current
ICC
During conversion
500
Channel 1 only
11
Other diode channels
8
Temperature Resolution
3.0
Remote Temperature Accuracy
VCC = 3.3V
Local Temperature Accuracy
VCC = 3.3V
tCONV1
Remote Channels 2 Through 4
Conversion Time
tCONV_
Remote-Diode Source Current
IRJ
UVLO
1000
+1.0
TA = TRJ = 0°C to +125°C
-3.0
+3.0
TA = +60°C to +100°C
-4.4
-0.4
TA = 0°C to +125°C
-6.1
-0.1
Resistance cancellation off
95
125
156
Resistance cancellation on
190
250
312
95
125
156
High level
80
100
120
Low level
8
10
12
Falling edge of VCC disables ADC
2.30
2.80
2.95
VCC falling edge
1.2
2.0
POR Threshold Hysteresis
o
C
o
o
90
Power-On-Reset (POR) Threshold
µA
Bits
-1.0
Undervoltage-Lockout Hysteresis
V
µA
±0.2
Remote Channel 1 Conversion
Time
UNITS
5.5
TA = TRJ = +60°C to +100°C
Supply Sensitivity of Temperature
Accuracy
Undervoltage-Lockout Threshold
MAX
C
C/V
ms
ms
µA
V
mV
2.5
90
V
mV
ALERT, OVERT
Output Low Voltage
VOL
ISINK = 1mA
0.3
ISINK = 6mA
0.5
Output Leakage Current
2
_______________________________________________________________________________________
1
V
µA
5-Channel Precision Temperature Monitor
(VCC = +3.0V to +5.5V, VSTBY = VCC, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and
TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.8
V
SMBus INTERFACE (SCL, SDA), STBY
Logic Input Low Voltage
Logic Input High Voltage
VIL
VIH
VCC = 3.0V
2.2
VCC = 5.0V
2.4
Input Leakage Current
V
-1
Output Low Voltage
VOL
Input Capacitance
CIN
+1
ISINK = 6mA
0.3
5
µA
V
pF
SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 2)
Serial-Clock Frequency
Bus Free Time Between STOP
and START Condition
fSCL
tBUF
START Condition Setup Time
Repeat START Condition Setup
Time
START Condition Hold Time
STOP Condition Setup Time
tSU:STA
tHD:STA
tSU:STO
Clock Low Period
tLOW
Clock High Period
tHIGH
Data Hold Time
tHD:DAT
Data Setup Time
tSU:DAT
Receive SCL/SDA Rise Time
tR
Receive SCL/SDA Fall Time
tF
Pulse Width of Spike Suppressed
tSP
SMBus Timeout
Note 1:
Note 2:
Note 3:
Note 4:
tTIMEOUT
(Note 3)
400
fSCL = 100kHz
4.7
fSCL = 400kHz
1.6
fSCL = 100kHz
4.7
fSCL = 400kHz
0.6
90% of SCL to 90% of SDA,
fSCL = 100kHz
0.6
90% of SCL to 90% of SDA,
fSCL = 400kHz
0.6
10% of SDA to 90% of SCL
0.6
90% of SCL to 90% of SDA,
fSCL = 100kHz
4
90% of SCL to 90% of SDA,
fSCL = 400kHz
0.6
10% to 10%, fSCL = 100kHz
1.3
10% to 10%, fSCL = 400kHz
1.3
µs
µs
µs
µs
µs
90% to 90%
0.6
fSCL = 100kHz
300
µs
µs
fSCL = 400kHz (Note 4)
900
fSCL = 100kHz
250
fSCL = 400kHz
100
1
fSCL = 400kHz
0.3
0
25
ns
ns
fSCL = 100kHz
SDA low period for interface reset
kHz
37
µs
300
ns
50
ns
45
ms
All parameters are tested at TA = +85°C. Specifications over temperature are guaranteed by design.
Timing specifications are guaranteed by design.
The serial interface resets when SCL is low for more than tTIMEOUT.
A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCL’s falling edge.
_______________________________________________________________________________________
3
MAX6622
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VCC = 3.3V, VSTBY = VCC, TA = +25°C, unless otherwise noted.)
SOFTWARE STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
6
5
4
3
2
1
0
350
345
340
335
330
4.8
5.3
3.8
3.3
SUPPLY VOLTAGE (V)
4.3
4.8
5.3
-2
0
SUPPLY VOLTAGE (V)
25
50
75
REMOTE-DIODE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
5
MAX6622 toc04
4
2
1
0
-1
-2
100mVP-P
4
TEMPERATURE ERROR (°C)
3
3
2
1
0
-1
-2
-3
-3
-4
-4
-5
0
75
100
0.1
1
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
100mVP-P
5
3
4
2
1
0
-1
-2
2
1
0
-1
-2
-3
-4
-4
0.1
FREQUENCY (MHz)
1
100mVP-P
3
-3
0.01
MAX6622 toc07
FREQUENCY (MHz)
-5
0.001
4
125
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
4
50
DIE TEMPERATURE (°C)
MAX6622 toc06
5
25
100
REMOTE-DIODE TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
TEMPERATURE ERROR (°C)
-1
MAX6622 toc05
4.3
0
-4
320
3.8
1
-3
325
3.3
MAX6622 toc03
2
TEMPERATURE ERROR (°C)
355
8
7
3
MAX6622 toc02
360
SUPPLY CURRENT (μA)
10
9
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6622 toc01
12
11
STANDBY SUPPLY CURRENT (μA)
MAX6622
5-Channel Precision Temperature Monitor
-5
0.001
0.01
0.1
1
FREQUENCY (MHz)
_______________________________________________________________________________________
10
125
5-Channel Precision Temperature Monitor
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
0
3
2
1
0
-1
-2
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-3
-4.0
-4
-4.5
-5
0.001
MAX6622 toc09
100mVP-P
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
4
MAX6622 toc08
5
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
-5.0
0.01
0.1
1
10
1
FREQUENCY (MHz)
100
10
DXP-DXN CAPACITANCE (nF)
Pin Description
PIN
NAME
FUNCTION
1
DXP1
Combined Current Source and A/D Positive Input for Channel 1 Remote Diode. Connect to the anode
of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if
no remote diode is used. Place a 2200pF capacitor between DXP1 and DXN1 for noise filtering.
2
DXN1
Cathode Input for Channel 1 Remote Diode. Connect the cathode of the channel 1 remote-diodeconnected transistor to DXN1. Internally connected to GND.
3
DXP2
Combined Current Source and A/D Positive Input for Channel 2 Remote Diode. Connect to the anode
of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if
no remote diode is used. Place a 2200pF capacitor between DXP2 and DXN2 for noise filtering.
4
DXN2
Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diodeconnected transistor to DXN2.
5
DXP3
Combined Current Source and A/D Positive Input for Channel 3 Remote Diode. Connect to the anode
of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if
no remote diode is used. Place a 2200pF capacitor between DXP3 and DXN3 for noise filtering.
6
DXN3
Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 3 remote-diodeconnected transistor to DXN3.
_______________________________________________________________________________________
5
MAX6622
Typical Operating Characteristics (continued)
(VCC = 3.3V, VSTBY = VCC, TA = +25°C, unless otherwise noted.)
5-Channel Precision Temperature Monitor
MAX6622
Pin Description (continued)
PIN
NAME
FUNCTION
7
DXP4
Combined Current Source and A/D Positive Input for Channel 4 Remote Diode. Connect to the anode
of a remote-diode-connected temperature-sensing transistor. Leave unconnected or connect to VCC if
no remote diode is used. Place a 2200pF capacitor between DXP4 and DXN4 for noise filtering.
8
DXN4
Cathode Input for Channel 4 Remote Diode. Connect the cathode of the channel 4 remote-diodeconnected transistor to DXN4.
9
STBY
Standby Input. Drive STBY logic-low to place the MAX6622 in hardware standby mode, or logic-high
for normal operation. Temperature and threshold data are retained in standby mode.
10
N.C.
No Connection. Must be connected to ground.
11
OVERT
12
VCC
13
ALERT
14
SMBDATA
15
SMBCLK
16
GND
Overtemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature of
channels 1 and 4 exceed the programmed threshold limit.
Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.
SMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature of
any channel exceeds the programmed ALERT threshold.
SMBus Serial-Data Input/Output. Connect to a pullup resistor.
SMBus Serial-Clock Input. Connect to a pullup resistor.
Ground
Detailed Description
The MAX6622 is a precision multichannel temperature
monitor that features one local and four remote temperature-sensing channels with a programmable alert
threshold for each temperature channel and a programmable overtemperature threshold for channels 1 and 4
(see Figure 1). Communication with the MAX6622 is
achieved through the SMBus serial interface and a
dedicated alert output. The alarm outputs, OVERT and
ALERT, assert if the software-programmed temperature
thresholds are exceeded. ALERT typically serves as an
interrupt, while OVERT can be connected to a fan, system shutdown, or other thermal-management circuitry.
ADC Conversion Sequence
In the default conversion mode, the MAX6622 starts the
conversion sequence by measuring the temperature on
channel 1, followed by 2, 3, local channel, and 4. The
conversion result for each active channel is stored in
the corresponding temperature data register.
In some systems, one of the remote thermal diodes may
be monitoring a location that experiences temperature
changes that occur much more rapidly than in the other
channels. If faster temperature changes must be monitored in one of the temperature channels, the MAX6622
6
allows channel 1 to be monitored at a faster rate than
the other channels. In this mode (set by writing a 1 to
bit 4 of the configuration 1 register), measurements of
channel 1 alternate with measurements of the other
channels. The sequence becomes channel 1, channel
2, channel 1, channel 3, channel 1, etc. Note that the
time required to measure all five channels is considerably greater in this mode than in the default mode.
Low-Power Standby Mode
Enter software standby mode by setting the STOP bit to
1 in the configuration 1 register. Enter hardware standby
by pulling STBY low. Software standby mode disables
the ADC and reduces the supply current to approximately 30µA. Hardware standby mode halts the ADC clock,
but the supply current is approximately 350µA. During
either software or hardware standby, data is retained in
memory, and the SMBus interface is active and listening
for SMBus commands. The timeout is enabled if a start
condition is recognized on SMBus. Activity on the
SMBus causes the supply current to increase. If a standby command is received while a conversion is in
progress, the conversion cycle is interrupted, and the
temperature registers are not updated. The previous
data is not changed and remains available.
_______________________________________________________________________________________
5-Channel Precision Temperature Monitor
MAX6622
VCC
MAX6622
DXP1
10/100μA
ADC
ALARM
ALU
DXN1
OVERT
AVERT
DXP2
DXN2
COUNT
INPUT
BUFFER
DXP3
REGISTER BANK
COMMAND BYTE
COUNTER
REMOTE TEMPERATURES
DXN3
LOCAL TEMPERATURES
REF
DXP4
ALERT THRESHOLD
OVERT THRESHOLD
DXN4
ALERT RESPONSE ADDRESS
SMBus
INTERFACE
STBY
SMBCLK
SMBDATA
Figure 1. Internal Block Diagram
SMBus Digital Interface
From a software perspective, the MAX6622 appears as
a series of 8-bit registers that contain temperature measurement data, alarm threshold values, and control bits.
A standard SMBus-compatible, 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. The same SMBus slave
address also provides access to all functions.
The MAX6622 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figure 2). The shorter receive byte protocol allows
quicker transfers, provided 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 without informing the first master. Figure
3 is the SMBus write timing diagram and Figure 4 is the
SMBus read timing diagram.
The remote diode 1 measurement channel provides 11
bits of data (1 LSB = +0.125°C). All other temperaturemeasurement channels provide 8 bits of temperature
data (1 LSB = +1°C). The 8 most significant bits (MSBs)
can be read from the local temperature and remote
temperature registers. The remaining 3 bits for remote
diode 1 can be read from the extended temperature
register. If extended resolution is desired, the extended
resolution register should be read first. This prevents
the most significant bits from being overwritten by new
_______________________________________________________________________________________
7
MAX6622
5-Channel Precision Temperature Monitor
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
DATA
8 bits
SLAVE ADDRESS: EQUIVALENT
TO CHIP-SELECT LINE OF A
3-WIRE INTERFACE
ACK
P
8 bits
COMMAND BYTE: SELECTS TO
WHICH REGISTER YOU ARE
WRITING
1
DATA BYTE: DATA GOES INTO THE REGISTER
SET BY THE COMMAND BYTE (TO SET
THRESHOLDS, CONFIGURATION MASKS, AND
SAMPLING RATE)
Read Byte Format
S
ADDRESS
WR
ACK
7 bits
COMMAND
ACK
RD
DATA
///
P
8 bits
SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATAFLOW DIRECTION
DATA BYTE: READS FROM
THE REGISTER SET BY THE
COMMAND BYTE
Receive Byte Format
WR
7 bits
ACK
COMMAND
ACK
P
8 bits
S
ADDRESS
7 bits
RD
ACK
DATA
///
P
8 bits
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
COMMAND BYTE: SENDS COMMAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
S = Start condition
P = Stop condition
ACK
7 bits
COMMAND BYTE: SELECTS
FROM WHICH REGISTER YOU
ARE READING
Send Byte Format
ADDRESS
ADDRESS
8 bits
SLAVE ADDRESS: EQUIVALENT
TO CHIP-SELECT LINE
S
S
Shaded = Slave transmission
/// = Not acknowledged
Figure 2. SMBus Protocols
Table 1. Main Temperature Register
(High Byte) Data Format
TEMP (°C)
DIGITAL OUTPUT
> +127
+127
+126
TEMP (°C)
DIGITAL OUTPUT
0111 1111
0
000X XXXX
0111 1111
+0.125
001X XXXX
0111 1110
+0.250
010X XXXX
+25
0001 1001
+0.375
011X XXXX
0
0000 0000
+0.500
100X XXXX
<0
0000 0000
+0.625
101X XXXX
Diode fault (open)
1111 1111
+0.725
110X XXXX
Diode fault (short)
1111 1111 or 1110 1110
+0.875
111X XXXX
conversion results until they have been read. If the
most significant bits have not been read within an
SMBus timeout period (nominally 37ms), normal updating continues. Table 1 shows the main temperature
register (high byte) data format, and Table 2 shows the
extended resolution register (low byte) data format.
Diode Fault Detection
If a channel’s input DXP_ and DXN_ are left open, the
MAX6622 detects a diode fault. An open diode fault
8
Table 2. Extended Resolution Temperature
Register (Low Byte) Data Format
does not cause either ALERT or OVERT to assert. A bit in
the status register for the corresponding channel is set to
1 and the temperature data for the channel is stored as
all 1s (FFh). It takes approximately 4ms for the MAX6622
to detect a diode fault. Once a diode fault is detected,
the MAX6622 goes to the next channel in the conversion
sequence. Depending on operating conditions, a shorted diode may or may not cause ALERT or OVERT to
assert, so if a channel will not be used, its DXN and DXP
inputs should be left unconnected.
_______________________________________________________________________________________
5-Channel Precision Temperature Monitor
B
tLOW
C
D
E
F
G
H
tHIGH
I
J
K
L
MAX6622
A
M
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:STO
tSU:DAT
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
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
tBUF
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 Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
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
tSU:DAT
tHD:DAT
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
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 4. SMBus Read Timing Diagram
Alarm Threshold Registers
ALERT Interrupt Mode
There are seven alarm threshold registers that store
overtemperature ALERT and OVERT threshold values.
Five of these registers are dedicated to store one local
alert temperature threshold limit and four remote alert
temperature threshold limits (see the ALERT Interrupt
Mode section). The remaining two registers are dedicated to remote channels 1 and 4 to store overtemperature threshold limits (see the OVERT Overtemperature
Alarm section). Access to these registers is provided
through the SMBus interface.
An ALERT interrupt occurs when the internal or external
temperature reading exceeds a high-temperature limit
(user programmable). The ALERT interrupt output signal
can be cleared by reading the status register(s) associated with the fault(s) or by successfully responding to an
alert response address transmission by the master. In
both cases, the alert is cleared but is reasserted at the
end of the next conversion if the fault condition still
exists. The interrupt does not halt automatic conversions.
The ALERT output is open drain so that multiple devices
can share a common interrupt line. All ALERT interrupts
can be masked using the configuration 3 register. The
POR state of these registers is shown in Table 1.
_______________________________________________________________________________________
9
MAX6622
5-Channel Precision Temperature Monitor
ALERT Response Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex logic needed to be a bus master.
Upon receiving an interrupt signal, the host master can
broadcast a receive byte transmission to the alert
response slave address (see the Slave Address section). Then, any slave device that generated an interrupt attempts to identify itself by putting its own
address on the bus.
The alert response can activate several different slave
devices simultaneously, similar to the I2C General Call.
If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledgment and continues to hold the ALERT line
low until cleared. (The conditions for clearing an alert
vary depending on the type of slave device.)
Successful completion of the alert response protocol
clears the output latch. If the condition that caused the
alert still exists, the MAX6622 reasserts the ALERT
interrupt at the end of the next conversion.
OVERT Overtemperature Alarms
The MAX6622 has two overtemperature registers that
store remote alarm threshold data for the OVERT output.
OVERT is asserted when a channel’s measured temperature is greater than the value stored in the corresponding threshold register. OVERT remains asserted until the
temperature drops below the programmed threshold
minus 4°C hysteresis. An overtemperature output can
be used to activate a cooling fan, send a warning, initiate clock throttling, or trigger a system shutdown to prevent component damage. See Table 3 for the POR state
of the overtemperature threshold registers.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the various other registers within the
MAX6622. This register’s POR state is 0000 0000.
Configuration Byte Functions
There are three read-write configuration registers
(Tables 4, 5, and 6) that can be used to control the
MAX6622’s operation.
10
Configuration 1 Register
The configuration 1 register (Table 4) has several functions. Bit 7 (MSB) is used to put the MAX6622 either in
software standby mode (STOP) or continuous conversion mode. Bit 6 resets all registers to their power-onreset conditions and then clears itself. Bit 5 disables
the SMBus timeout. Bit 4 enables more frequent conversions on channel 1, as described in the ADC
Conversion Sequence section. Bit 3 enables resistance
cancellation on channel 1. See the Series Resistance
Cancellation section for more details. The remaining
bits of the configuration 1 register are not used. The
POR state of this register is 0000 0000 (00h).
Configuration 2 Register
The configuration 2 register functions are described in
Table 5. Bits [6:0] are used to mask the ALERT interrupt
output. Bit 6 masks the local alert interrupt and bit 5
through bit 2 mask the remote alert interrupts. The
power-up state of this register is 0000 0000 (00h).
Configuration 3 Register
Table 6 describes the configuration 3 register. Bits 5, 4,
3, and 0 mask the OVERT interrupt output for channels
4 and 1. The remaining bits, 7, 6, 5, 4, 2, and 1, are
reserved. The power-up state of this register is 0000
0000 (00h).
Status Register Functions
Status registers 1, 2, and 3 (Tables 7, 8, and 9) indicate
which (if any) temperature thresholds have been
exceeded and if there is an open-circuit or short-circuit
fault detected with the external sense junctions. Status
register 1 indicates if the measured temperature has
exceeded the threshold limit set in the ALERT registers
for the local or remote-sensing diodes. Status register 2
indicates if the measured temperature has exceeded
the threshold limit set in the OVERT registers. Status
register 3 indicates if there is a diode fault (open or
short) in any of the remote-sensing channels.
Bits in the alert status register clear by a successful
read, but set again after the next conversion unless the
fault is corrected, either by a drop in the measured temperature or an increase in the threshold temperature.
The ALERT interrupt output follows the status flag bit.
Once the ALERT output is asserted, it can be
deasserted by either reading status register 1 or by
successfully responding to an alert response address.
______________________________________________________________________________________
5-Channel Precision Temperature Monitor
MAX6622
Table 3. Command Byte Register Bit Assignment
ADDRESS
(hex)
POR STATE
(hex)
READ/
WRITE
Local
07
00
R
Read local temperature register
Remote 1
01
00
R
Read channel 1 remote temperature register
Remote 2
02
00
R
Read channel 2 remote temperature register
Remote 3
03
00
R
Read channel 3 remote temperature register
REGISTER
DESCRIPTION
Remote 4
04
00
R
Configuration 1
41
00
R/W
Read/write configuration register 1
Read channel 4 remote temperature register
Configuration 2
42
00
R/W
Read/write configuration register 2
Configuration 3
43
00
R/W
Status1
44
00
R
Read status register 1
Status2
45
00
R
Read status register 2
Read status register 3
Read/write configuration register 3
Status3
46
00
R
Local ALERT High Limit
17
5A
R/W
Read/write local alert high-temperature threshold limit register
Remote 1 ALERT High Limit
11
6E
R/W
Read/write channel 1 remote-diode alert high-temperature
threshold limit register
Remote 2 ALERT High Limit
12
7F
R/W
Read/write channel 2 remote-diode alert high-temperature
threshold limit register
Remote 3 ALERT High Limit
13
64
R/W
Read/write channel 3 remote-diode alert high-temperature
threshold limit register
Remote 4 ALERT High Limit
14
64
R/W
Read/write channel 4 remote-diode alert high-temperature
threshold limit register
Remote 1 OVERT High Limit
21
6E
R/W
Read/write channel 1 remote-diode overtemperature threshold
limit register
Remote 4 OVERT High Limit
24
7F
R/W
Read/write channel 4 remote-diode overtemperature threshold
limit register
Remote 1 Extended
Temperature
09
00
R
Read channel 1 remote-diode extended temperature register
Manufacturer ID
0A
4D
R
Read manufacturer ID
In both cases, the alert is cleared even if the fault condition exists, but the ALERT output reasserts at the end of
the next conversion. The bits indicating the fault for the
OVERT interrupt output clear only on reading the status 2
register even if the fault conditions still exist. Reading the
status 2 register does not clear the OVERT interrupt output. To eliminate the fault condition, either the measured
temperature must drop below the temperature threshold
minus the hysteresis value (4°C), or the trip temperature
must be set at least 4°C above the current temperature.
______________________________________________________________________________________
11
MAX6622
5-Channel Precision Temperature Monitor
Table 4. Configuration 1 Register
BIT
NAME
POR
STATE
7 (MSB)
STOP
0
Standby Mode Control Bit. If STOP is set to logic 1, the MAX6622 stops
converting and enters standby mode.
6
POR
0
Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is selfclearing.
5
TIMEOUT
0
Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.
4
Fast remote 1
0
Channel 1 Fast Conversion Bit. Set to logic 1 to enable fast conversion of
channel 1.
3
Resistance
cancellation
0
Resistance Cancellation Bit. When set to logic 1, the MAX6622 cancels series
resistance in the channel 1 thermal diode.
2
Reserved
0
—
1
Reserved
0
—
0
Reserved
0
—
FUNCTION
Table 5. Configuration 2 Register
BIT
NAME
POR
STATE
FUNCTION
7 (MSB)
Reserved
0
—
6
Mask Local ALERT
0
Local Alert Mask. Set to logic 1 to mask local channel ALERT.
5
Reserved
0
—
4
Reserved
0
—
3
Mask ALERT 4
0
Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT.
2
Mask ALERT 3
0
Channel 3 Alert Interrupt Mask. Set to logic 1 to mask channel 3 ALERT.
1
Mask ALERT 2
0
Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT.
0
Mask ALERT 1
0
Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.
Table 6. Configuration 3 Register
12
BIT
NAME
POR
STATE
7 (MSB)
Reserved
0
—
6
Reserved
0
—
5
Reserved
0
—
4
Reserved
0
—
3
Mask OVERT 4
0
Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4
OVERT.
2
Reserved
0
—
1
Reserved
0
—
0
Mask OVERT 1
0
Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1
OVERT.
FUNCTION
______________________________________________________________________________________
5-Channel Precision Temperature Monitor
BIT
NAME
POR
STATE
7 (MSB)
Reserved
0
—
6
Local ALERT
0
Local Channel High-Alert Bit. This bit is set to logic 1 when the local
temperature exceeds the temperature threshold limit in the local ALERT highlimit register.
5
Reserved
0
—
4
Reserved
0
—
3
Remote 4 ALERT
0
Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 4 remote-diode temperature exceeds the temperature threshold limit
in the remote 4 ALERT high-limit register.
2
Remote 3 ALERT
0
Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 3 remote-diode temperature exceeds the programmed temperature
threshold limit in the remote 3 ALERT high-limit register.
1
Remote 2 ALERT
0
Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 2 remote-diode temperature exceeds the temperature threshold limit
in the remote 2 ALERT high-limit register.
0
Remote 1 ALERT
0
Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the
channel 1 remote-diode temperature exceeds the temperature threshold limit
in the remote 1 ALERT high-limit register.
FUNCTION
Table 8. Status 2 Register
NAME
POR
STATE
7 (MSB)
Reserved
0
—
6
Reserved
0
—
5
Reserved
0
—
4
Reserved
0
—
3
Remote 4 OVERT
0
Channel 4 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1
when the channel 4 remote-diode temperature exceeds the temperature
threshold limit in the remote 4 OVERT high-limit register.
2
Reserved
0
—
1
Reserved
0
—
0
Remote 1 OVERT
0
Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1
when the channel 1 remote-diode temperature exceeds the temperature
threshold limit in the remote 1 OVERT high-limit register.
BIT
FUNCTION
______________________________________________________________________________________
13
MAX6622
Table 7. Status 1 Register
MAX6622
5-Channel Precision Temperature Monitor
Table 9. Status 3 Register
BIT
NAME
POR
STATE
FUNCTION
7 (MSB)
Reserved
0
—
6
Reserved
0
Not Used. 0 at POR, then 1.
5
Reserved
0
Not Used. 0 at POR, then 1.
4
Diode fault 4
0
Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4
are open circuit or when DXP4 is connected to VCC.
3
Diode fault 3
0
Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3
are open circuit or when DXP3 is connected to VCC.
2
Diode fault 2
0
Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2
are open circuit or when DXP2 is connected to VCC.
1
Diode fault 1
0
Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1
are open circuit or when DXP1 is connected to VCC.
0
Reserved
0
—
Applications Information
Remote-Diode Selection
The MAX6622 directly measures the die temperature of
CPUs and other ICs that have on-chip temperaturesensing diodes (see the Typical Application Circuit) or
it can measure the temperature of a discrete diodeconnected transistor.
Effect of Ideality Factor
The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote
“diode” (actually a transistor). The MAX6622 is optimized for n = 1.015. A thermal diode on the substrate
of an IC is normally a pnp with the base and emitter
brought out the collector (diode connection) grounded.
DXP_ must be connected to the anode (emitter) and
DXN_ must be connected to the cathode (base) of this
pnp. If a sense transistor with an ideality factor other
than 1.015 is used, the output data is different from the
data obtained with the optimum ideality factor.
Fortunately, the difference is predictable. Assume a
remote-diode sensor designed for a nominal ideality
factor nNOMINAL is used to measure the temperature of
a diode with a different ideality factor n1. The measured
temperature TM can be corrected using:
⎛
⎞
n1
TM = TACTUAL ⎜
⎟
⎝ nNOMINAL ⎠
14
where temperature is measured in Kelvin and
nNOMIMAL for the MAX6622 is 1.015. As an example,
assume you want to use the MAX6622 with a CPU that
has an ideality factor of 1.002. If the diode has no
series resistance, the measured data is related to the
real temperature as follows:
⎛n
⎞
⎛ 1.015 ⎞
TACTUAL = TM × ⎜ NOMINAL ⎟ = TM × ⎜
⎟ = T (1.01297)
⎝ 1.002 ⎠ M
n1
⎝
⎠
For a real temperature of +85°C (358.15K), the measured temperature is +80.41°C (353.56K), an error of
-4.587°C.
Series Resistance Cancellation
Some thermal diodes on high-power ICs can have
excessive series resistance, which can cause temperature measurement errors with conventional remote temperature sensors. Channel 1 of the MAX6622 has a
series resistance cancellation feature (enabled by bit 3
of the configuration 1 register) that eliminates the effect
of diode series resistance. Set bit 3 to 1 if the series
resistance is large enough to affect the accuracy of
channel 1. The series resistance cancellation function
increases the conversion time for channel 1 by 125ms.
This feature cancels the bulk resistance of the sensor
and any other resistance in series (wire, contact resistance, etc.). The cancellation range is from 0 to 100Ω.
______________________________________________________________________________________
5-Channel Precision Temperature Monitor
Unused Diode Channels
If one or more of the remote diode channels is not
needed, the DXP and DXN inputs for that channel
should either be unconnected, or the DXP input should
be connected to VCC. The status register indicates a
diode "fault" for this channel and the channel is ignored
during the temperature-measurement sequence. It is
also good practice to mask any unused channels
immediately upon power-up by setting the appropriate
bits in the configuration 2 and configuration 3 registers.
This will prevent unused channels from causing ALERT
or OVERT to assert.
Table 10. Remote-Sensors Transistor
Manufacturers
MANUFACTURER
MODEL NO.
Central Semiconductor (USA)
CMPT3904
Rohm Semiconductor (USA)
SST3904
Samsung (Korea)
KST3904-TF
Siemens (Germany)
SMBT3904
Zetex (England)
FMMT3904CT-ND
Note: Discrete transistors must be diode connected (base
shorted to collector).
Thermal Mass and Self-Heating
When sensing local temperature, the MAX6622 measures the temperature of the printed-circuit board (PCB)
to which it is soldered. The leads provide a good thermal path between the PCB traces and the die. As with
all IC temperature sensors, thermal conductivity
between the die and the ambient air is poor by comparison, making air temperature measurements impractical.
Because the thermal mass of the PCB is far greater than
that of the MAX6622, the device follows temperature
changes on the PCB with little or no perceivable delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote
transistors, the best thermal response times are
obtained with transistors in small packages (i.e., SOT23
or SC70). Take care to account for thermal gradients
between the heat source and the sensor, and ensure
that stray air currents across the sensor package do
not interfere with measurement accuracy. Self-heating
does not significantly affect measurement accuracy.
Remote-sensor self-heating due to the diode current
source is negligible.
ADC Noise Filtering
The integrating ADC has good noise rejection for lowfrequency signals, such as power-supply hum. In environments with significant high-frequency EMI, connect
an external 2200pF capacitor between DXP_ and
DXN_. Larger capacitor values can be used for added
filtering, but do not exceed 3300pF because it can
introduce errors due to the rise time of the switched
current source. High-frequency noise reduction is
needed for high-accuracy remote measurements.
Noise can be reduced with careful PCB layout as discussed in the PCB Layout section.
______________________________________________________________________________________
15
MAX6622
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor,
its collector and base must be connected together.
Table 10 lists examples of discrete transistors that are
appropriate for use with the MAX6622. The transistor
must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range
can be violated. The forward voltage at the highest
expected temperature must be greater than 0.25V at
10µA, and at the lowest expected temperature, the forward voltage must be less than 0.95V at 100µA. Large
power transistors must not be used. Also, ensure that
the base resistance is less than 100Ω. Tight specifications for forward current gain (50 < ß < 150, for example) indicate that the manufacturer has good process
controls and that the devices have consistent VBE characteristics. Manufacturers of discrete transistors do not
normally specify or guarantee ideality factor. This is
normally not a problem since good-quality discrete
transistors tend to have ideality factors that fall within a
relatively narrow range. We have observed variations in
remote temperature readings of less than ±2°C with a
variety of discrete transistors. Still, it is good design
practice to verify good consistency of temperature
readings with several discrete transistors from any
manufacturer under consideration.
MAX6622
5-Channel Precision Temperature Monitor
Slave Address
The slave address of the MAX6622 is 9Ah or 1001 101.
PCB Layout
Follow these guidelines to reduce the measurement
error when measuring remote temperature:
1) Place the MAX6622 as close as is practical to the
remote diode. In noisy environments, such as a computer motherboard, this distance can be 4in to 8in
(typ). This length can be increased if the worst noise
sources are avoided. Noise sources include CRTs,
clock generators, memory buses, and PCI buses.
2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily introduce +30°C error, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other. Each parallel pair of
traces should go to a remote diode. Route these
traces away from any higher voltage traces, such as
+12VDC. Leakage currents from PCB contamination
must be dealt with carefully since a 20MΩ leakage
path from DXP to ground causes about +1°C error.
If high-voltage traces are unavoidable, connect
guard traces to GND on either side of the DXP-DXN
traces (Figure 5).
4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.
5) Use wide traces when practical. 5-mil to 10-mil
traces are typical. Be aware of the effect of trace
resistance on temperature readings when using
long, narrow traces.
6) When the power supply is noisy, add a resistor (up
to 47Ω) in series with VCC.
16
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor
for remote-sensor distances longer than 8in or in very
noisy environments. Twisted-pair cable lengths can be
between 6ft and 12ft before noise introduces excessive
errors. For longer distances, the best solution is a
shielded twisted pair like that used for audio microphones. For example, Belden 8451 works well for distances up to 100ft in a noisy environment. At the
device, connect the twisted pair to DXP and DXN and
the shield to GND. Leave the shield unconnected at the
remote sensor. For very long cable runs, the cable’s
parasitic capacitance often provides noise filtering, so
the 2200pF capacitor can often be removed or reduced
in value. Cable resistance also affects remote-sensor
accuracy. For every 1Ω of series resistance, the error is
approximately +1/2°C.
GND
5 MILS TO
10 MILS
5 MILS TO
10 MILS
DXP
MINIMUM
5 MILS TO
10 MILS
DXN
5 MILS TO
10 MILS
GND
Figure 5. Recommended DXP-DXN PCB Traces. The two outer
guard traces are recommended if high-voltage traces will be
near the DXN and DXP traces.
______________________________________________________________________________________
5-Channel Precision Temperature Monitor
Chip Information
PROCESS: BiCMOS
TOP VIEW
+
DXP1 1
16 GND
DXN1 2
15 SMBCLK
DXP2 3
MAX6622
14 SMBDATA
DXN2 4
13 ALERT
DXP3 5
12 VCC
DXN3 6
11 OVERT
DXP4 7
10 N.C.
DXN4 8
9
STBY
TSSOP
______________________________________________________________________________________
17
MAX6622
Pin Configuration
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
TSSOP4.40mm.EPS
MAX6622
5-Channel Precision Temperature Monitor
PACKAGE OUTLINE, TSSOP 4.40mm BODY
21-0066
I
1
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products
Heaney
is a registered trademark of Maxim Integrated Products, Inc.