Maxim MAX6655 Dual remote/local temperature sensors and four-channel voltage monitor Datasheet

19-2117; Rev 1; 5/06
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Features
The MAX6655/MAX6656 are precise voltage and temperature monitors. The digital thermometer reports the
temperature of two remote sensors and its own die temperature. The remote sensors are diode-connected
transistors—typically a low-cost, easily mounted
2N3906 PNP type—that replace conventional thermistors or thermocouples. Remote accuracy is ±1°C for
multiple transistor manufacturers with no calibration
necessary. The remote channels can also measure the
die temperature of other ICs, such as microprocessors,
that contain a substrate-connected PNP with its collector grounded and its base and emitter available for temperature-sensing purposes. The temperature is
digitized with 11-bit resolution.
The MAX6655/MAX6656 also measure their own supply
voltage and three external voltages with 8-bit resolution.
Each voltage input’s sensitivity is set to give approximately 3/4-scale output code when the input voltage is
at its nominal value. The MAX6655 operates at +5V
supply and its second voltage monitor is 3.3V. The
MAX6656 operates on a +3.3V supply and its second
voltage monitor is 5V.
The 2-wire serial interface accepts standard SMBus™
Write Byte, Read Byte, Send Byte, and Receive Byte
commands to program the alarm thresholds and to read
data. The MAX6655/MAX6656 also provide SMBus alert
response and timeout functions. The MAX6655/MAX6656
measure automatically and autonomously, with the conversion rate programmable. The adjustable rate allows
the user to control the supply current.
♦ Three Temperature Channels
Two Remote PN Junctions
One Local Sensor
In addition to the SMBus ALERT output, the MAX6655/
MAX6656 feature an OVERT output, which is used as a
temperature reset that remains active only while the
temperature is above the maximum temperature limit.
The OVERT output is optimal for fan control or for system shutdown.
Typical Application Circuit appears at end of data sheet.
Applications
♦ Four Voltage Channels
+12V, +5V, +3.3V, +2.5V
Three External Monitors
One Internal Supply Monitor
♦ 11-Bit, 0.125°C Resolution
♦ High Accuracy: ±1°C Over +60°C to +100°C
Temperature Range
♦ Programmable Under/Over-Threshold Alarms
♦ Programmable Power-Saving Mode
♦ No Calibration Required
♦ SMBus/I2C-Compatible Interface
♦ OVERT Output for Fan Control and System
Shutdown
Ordering Information
Workstations
Thin Clients
Communication
Equipment
Servers
Desktop PC
S.
*P,
Is
ae
cSMBus is a trademark of Intel Corp.
PKG
CODE
TEMP RANGE
MAX6655MEE
-55°C to +125°C
16 QSOP
E16-5
MAX6656MEE
-55°C to +125°C
16 QSOP
E16-5
Pin Configuration
TOP VIEW
16 STBY
VCC 1
Notebooks
PINPACKAGE
PART
15 SMBCLK
DXP1 2
14 OVERT
DXN1 3
ADD0 4
ADD1 5
MAX6655
MAX6656
13 SMBDATA
12 ALERT
DXP2 6
11 VIN2
DXN2 7
10 VIN1
9
GND 8
VIN3
QSOP
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX6655/MAX6656
General Description
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V
DXN_ to GND ........................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, STBY,
OVERT to GND .....................................................-0.3V to +6V
VIN1 to GND............................................................-0.3V to +16V
VIN2 to GND..............................................................-0.3V to +6V
VIN3 to GND..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (VCC + 0.3V)
SMBDATA, ALERT, OVERT Current....................-1mA to +50mA
DXN_ Current......................................................................±1mA
ESD Protection (all pins, Human Body Model) ..................2000V
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.30mW/°C above +70°C)........667mW
Operating Temperature Range .........................-55°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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 +3.6V for MAX6656, VCC = +4.5V to +5.5V for MAX6655, TA = -55°C to +125°C, unless otherwise noted. Typical values
are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25°C.)
PARAMETER
Supply Range
SYMBOL
CONDITIONS
VCC
MIN
+60°C ≤ TA ≤ +100°C
Accuracy (Local Sensor)
Accuracy (Remote Sensor)
ZIN
+60°C ≤ TRJ ≤ +100°C
±1
0°C ≤ TRJ ≤ +120°C
±3
VIN1, VIN2, VIN3 input resistance
VCC input, disables A/D conversion,
falling edge
°C
Bits
kΩ
±1
2.50
±1.5
2.70
VCC, falling edge
1
POR Threshold Hysteresis
1.7
2.90
SMBus static, STBY = GND
DXP and DXN Leakage Current
In standby mode
Average Operating Current
Continuous temperature mode
Conversion Time for Single
Temperature Measurement
tCON
From stop bit to conversion completed
Monitoring Cycle Time
tMONI
Total of 3 temperature plus 4 voltage
measurements
3
95
V
mV
2.5
90
Standby Current
%
Bits
90
Power-On Reset (POR)
Threshold
°C
11
8
UVLO
°C
0.125
100
Undervoltage Lockout
Hysteresis
2
V
±3
VIN ADC Resolution
Undervoltage Lockout Threshold
UNITS
5.5
0°C ≤ TA ≤ +125°C
VIN1, VIN2, VIN3 between 30% and 120% of
nominal
ADC Total Error
MAX
±1.5
Temperature Measurement
Resolution
ADC Input Impedance
TYP
3.0
V
mV
10
µA
2
µA
550
1000
µA
125
155
ms
625
_______________________________________________________________________________________
ms
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
(VCC = +3.0V to +3.6V for MAX6656, VCC = +4.5V to +5.5V for MAX6655, TA = -55°C to +125°C, unless otherwise noted. Typical values
are at VCC = +3.3V for MAX6656, VCC = +5.0V for MAX6655, TA = +25°C.)
PARAMETER
SYMBOL
Remote Junction Current
(DXP, DXN)
CONDITIONS
MIN
TYP
MAX
High level
80
100
140
Low level
8
10
14
UNITS
µA
SMBus INTERFACE (SMBCLK, SMBDATA, STBY)
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
VIL
VIH
ILEAK
Output Low Sink Current
IOL
Input Capacitance
CIN
SMBus Timeout
VCC = +3.0V to +5.5V
0.8
VCC = +3.0V
2.1
VCC = +5.5V
2.6
V
V
VIN = GND or VCC
±1
µA
VOL = +0.6V
6
mA
5
SMBCLK or SMBDATA time low for reset
30
35
pF
60
ms
ALERT, OVERT
Output Low Sink Current
VOL = +0.6V
6
mA
Output High Leakage Current
VOH = +5.5V
1
µA
400
kHz
SMBus TIMING
Serial Clock Frequency
fSCL
Bus Free Time Between STOP
and START Condition
tBUF
START Condition Setup Time
4.7
µs
4.7
µs
Repeat START Condition Setup
Time
tSU:STA
90% to 90%
50
ns
START Condition Hold Time
tHD:STA
10% of SMBDATA to 90% of SMBCLK
4
µs
STOP Condition Setup Time
tSU:STO
90% of SMBCLK to 10% of SMBDATA
4
Clock Low Period
Clock High Period
tLOW
10% to 10%
tHIGH
90% to 90%
Data Setup Time
tSU:DAT
90% of SMBDATA to 10% of SMBCLK
Data Hold Time
tHD:DAT
(Note 1)
µs
4.7
µs
4
µs
250
ns
0
µs
Receive SMBCLK/SMBDATA
Rise Time
tR
1
µs
Receive SMBCLK/SMBDATA
Fall Time
tF
300
ns
Pulse Width of Spike
Suppressed
tSP
50
ns
0
_______________________________________________________________________________________
3
MAX6655/MAX6656
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
PATH = DXP TO VCC (5V)
-10
3
2
1
0
-1
-2
20
MAX6655/MAX6656 toc03
RANDOM SAMPLE
2N3906
4
TEMPERATURE ERROR (°C)
PATH = DXP TO GND
0
MAX6655/MAX6656 toc02
10
5
REMOTE TEMPERATURE ERROR (°C)
MAX6655/MAX6656 toc01
REMOTE TEMPERATURE ERROR (°C)
20
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
REMOTE TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
VIN = SQUARE WAVE
APPLIED TO VCC WITH
NO VCC BYPASS CAPACITOR
15
VIN = 250mVp-p
REMOTE DIODE
10
5
-3
-4
0
-5
-55
100
-5
VIN = SQUARE WAVE
AC-COUPLED TO DXN
10
8
VIN = 200mVp-p
6
4
VIN = 100mVp-p
2
10
20
30
40
40
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
VCC = +5V
12
10
8
6
4
SMBCLK IS DRIVEN
RAIL-TO-RAIL
45
40
35
30
25
20
15
10
5
0
0
50
100
150
200
1
10
100
1000
DXP-DXN CAPACITANCE (nF)
SMBCLK FREQUENCY (kHz)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
RESPONSE TO THERMAL SHOCK
VOLTAGE ACCURACY
vs. TEMPERATURE
100
80
60
40
ADD0, ADD1 = HIGH-Z
100
80
60
40
20
20
0
0
REMOTE DIODE IMMERSED
IN +115°C FLUORINERT BATH
12
OUTPUT VOLTAGE (V)
ADD0, ADD1 = GND
120
TEMPERATURE (°C)
120
MAX6655/MAX6656 toc08
FREQUENCY (MHz)
140
50
50
2
50
MAX6655/MAX6656 toc07
0
30
REMOTE TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
0
0
20
MAX6655/MAX6656 toc09
12
10
FREQUENCY (MHz)
14
REMOTE TEMPERATURE ERROR (°C)
MAX6655/MAX6656 toc04
REMOTE TEMPERATURE ERROR (°C)
14
0
95
TEMPERATURE (°C)
LEAKAGE RESISTANCE (MΩ)
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
45
MAX6655/MAX6656 toc06
10
SUPPLY CURRENT (µA)
1
MAX6655/MAX6656 toc05
-20
SUPPLY CURRENT (µA)
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
VIN1
10
8
6
VCC
4
VIN2
2
VIN3
INPUT VOLTAGES ARE NOMINAL
0
1
2
3
SUPPLY VOLTAGE (V)
4
4
5
0
-1
0
1
2
TIME (s)
3
4
5
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
100
120
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
PIN
NAME
1
VCC
Supply Voltage. +5V for MAX6655; +3.3V for MAX6656. Bypass VCC to GND with a 0.1µF capacitor.
FUNCTION
2
DXP1
External Diode 1 Positive Connection. DXP1 is the combined current source and ADC positive input
for remote-diode 1. If a remote-sensing junction is not used, connect DXP1 to DXN1.
3
DXN1
External Diode 1 Negative Connection. DXN1 is the combined current sink and ADC negative input
for remote-diode 1. DXN1 is normally biased to a diode voltage above ground.
4
ADD0
SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. Table 5 is the
truth table.
5
ADD1
SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up.
6
DXP2
External Diode 2 Positive Connection. DXP2 is the combined current source and ADC positive input
for remote-diode 2. If a remote-sensing junction is not used, connect DXP2 to DXN2.
7
DXN2
External Diode 2 Negative Connection. DXN2 is the combined current sink and ADC negative input
for remote-diode 2. DXN2 is normally biased to a diode voltage above ground.
8
GND
Ground
9
VIN3
External Voltage Monitor 3. VIN3 is typically used to monitor +2.5V supplies.
10
VIN1
External Voltage Monitor 1. VIN1 is typically used to monitor +12V supplies.
11
VIN2
External Voltage Monitor 2. VIN2 is typically used to monitor voltage supplies of +3.3V for MAX6655
and +5.0V for MAX6656.
12
ALERT
13
SMBDATA
14
OVERT
15
SMBCLK
16
STBY
SMBus Alert (Interrupt) Output, Open-Drain
SMBus Serial-Data Input/Output, Open-Drain
Overtemperature Alarm Output, Open-Drain. OVERT is an unlatched alarm output that responds to
the programmed maximum temperature limit for all temperature channels.
SMBus Serial-Clock Input
Hardware Standby Input. Drive STBY low for low-power standby mode. Drive STBY high for normal
operating mode. Temperature and comparison threshold data are retained in standby mode.
Detailed Description
The MAX6655/MAX6656 are voltage and temperature
monitors that communicate through an SMBus-compatible interface with a microprocessor or microcontroller
in thermal management applications.
Essentially an 11-bit serial ADC with a sophisticated front
end, the MAX6655/MAX6656 contain a switched-current
source, a multiplexer, an ADC, an SMBus interface, and
the associated control logic. Temperature data from the
ADC is loaded into a data register, where it is automatically compared with data previously stored in over/undertemperature alarm threshold registers. Temperature data
can be read at any time with 11 bits of resolution.
The MAX6655/MAX6656 can monitor external supply voltages of typically 12V, 2.5V, and 3.3V for the MAX6655
and 5.0V for the MAX6656, as well as their own supply
voltage. All voltage inputs are converted to an 8-bit code
using an ADC. Each input voltage is scaled down by an
on-chip resistive-divider so that its output, at the nominal
input voltage, is approximately 3/4 of the ADC’s full-scale
range, or a decimal count of 198.
ADC
The averaging ADC integrates over a 40ms period (typ)
with excellent noise rejection. The ADC converts a temperature measurement in 125ms (typ) and a voltage
measurement in 62.5ms (typ). For temperature measurements, the multiplexer automatically steers bias
currents through the remote diode, then the forward
voltage is measured and the temperature is computed.
The DXN input is biased at one diode drop above
ground by an internal diode to set up the ADC inputs for
a differential measurement. The worst-case DXP-DXN
differential input voltage range is +0.25V to +0.95V.
Excess resistance in series with the remote diode causes about +1/2°C error/Ω. A 200µV offset voltage at
DXP-DXN causes about -1°C error.
_______________________________________________________________________________________
5
MAX6655/MAX6656
Pin Description
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
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 which
register you are writing to
Data Byte: data goes into the register
set by the co mma nd byte ( to se t
thresholds, configuration masks, and
sampling rate)
Read Byte Format
S
WR
ADDRESS
ACK
7 bits
COMMAND
ACK
Slave Address: equivalent to chip-select line
ADDRESS
WR
7 bits
Command Byte: selects
which register you are
reading from
RD
ACK
DATA
A
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
ACK
COMMAND
ACK
P
8 bits
Data Byte: writes data to the
register commanded by the
last read byte or write byte
transmission
S = Start condition
P = Stop condition
ADDRESS
7 bits
Send Byte Format
S
S
8 bits
Shaded = Slave transmission
A = Not acknowledged
S
ADDRESS
7 bits
RD
ACK
DATA
A
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
Figure 1. SMBus/I2C Protocols
ADC Conversion Sequence
Each time a conversion begins, all channels are converted, and the results of the measurements are available after the end of conversion. A BUSY status bit in
the Status Byte shows that the device is actually performing a new conversion; however, even if the ADC is
busy, the results of the previous conversion are always
available. The conversion sequence for the MAX6655
(MAX6656) is External Diode 1, External Diode 2,
Internal Diode, VIN3, VIN2 (VCC), VIN1, VCC (VIN2).
The ADC always converts at maximum speed, but the
time between a sequence of conversions is adjustable.
The Conversion Rate Control Byte (Table 1) shows the
possible delays between conversions. Disabling voltage
or temperature measurements with the Configuration
Byte makes the ADC complete the conversion
sequence faster.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply current drain to 3µA (typ). Enter standby mode by
forcing STBY low or through the RUN/STOP bit in the
6
Configuration Byte register. Hardware and software
standby modes behave identically; all data is retained
in memory, and the SMBus interface is alive and listening for reads and writes. Standby mode is not a shutdown mode. Activity on the SMBus draws extra supply
current (see Typical Operating Characteristics).
Enter hardware standby mode by forcing STBY low. In
a notebook computer, this line may be connected to
the system SUSTAT# suspend-state signal. The STBY
low state overrides any software conversion command.
If a hardware or software standby command is
received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into the Temperature Reading
register. The previous data is not changed and remains
available.
Supply current during the 125ms conversion is typically
550µA. Between conversions, the instantaneous supply
current is about 25µA, due to the current consumed by
the conversion-rate timer. With very low supply voltages
(under the POR threshold), the supply current is higher
due to the address input bias currents.
_______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
tLOW
B
C
tHIGH
D
E
F
G
I
H
J
K
L
MAX6655/MAX6656
A
M
SMBCLK
SMBDATA
tHD:STA
tSU:STA
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
tHD:DAT
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
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
Figure 2. SMBus/I2C Write Timing Diagram
A
tLOW
B
C
tHIGH
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
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
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 3. SMBus/I2C Read Timing Diagram
SMBus Digital Interface
From a software perspective, the MAX6655/MAX6656
appear as a set of byte-wide registers that contain temperature data, voltage data, alarm threshold values,
and control bits. Use a standard SMBus 2-wire serial
interface to read temperature data and write control
bits and alarm threshold data.
The MAX6655/MAX6656 employ four standard SMBus
protocols: Write Byte, Read Byte, Send Byte, and
Receive Byte (Figures 1, 2, and 3). The two shorter protocols (Receive and Send) allow quicker transfers, provided that the correct data register was previously
selected by a Write or 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.
_______________________________________________________________________________________
7
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
the T HIGH or T LOW alarms at their POR settings.
Similarly, if DXP_ is short circuited to V CC, the ADC
reads -1°C for both remote channels, and the ALERT
outputs are activated.
+3V TO +5.5V
Alert Interrupts
VCC
MAX6655
MAX6656
SMBCLK
SMBus
SERIAL
INTERFACE
(TO HOST)
SMBDATA
TO SYSTEM
SHUTDOWN
ALERT
OVERT
DXP2
ADD0
ADD1
DXN2
2N3906
GND
2200pF
Figure 4. System Shutdown Application
The temperature data is stored in internal registers
RRTE, RRT2, and RLTS as 7 bits + sign in two’s complement form with each LSB representing 1°C.
Additionally, the 3MSBs of the Extended Temperature
register contain fractional temperature data with
+0.125°C resolution (Tables 2 and 3). The voltage data
is stored in RV0, RV1, RV2, and RV3 as 8 bits in binary
form (Table 4).
OVERT Output
OVERT output is an unlatched open-drain output that
behaves as a thermostat for fan control or system shutdown (Figure 4). This output responds to the current
temperature. If the current temperature is above THIGH,
OVERT activates and does not go inactive until the temperature drops below THIGH.
Diode Fault Alarm
A continuity fault detector at DXP detects whether the
remote diode has an open-circuit condition, short-circuit to GND, or short-circuit DXP-to-DXN condition. At
the beginning of each conversion, the diode fault is
checked, and the Status Byte is updated. This fault
detector is a simple voltage detector; if DXP rises
above VCC - 1V (typ) or below VDXN + 50mV (typ), a
fault is detected. Note that the diode fault isn’t checked
until a conversion is initiated, so immediately after POR,
the status byte indicates no fault is present, even if the
diode path is broken.
If the remote channel is shorted (DXP to DXN or DXP to
GND), the ADC reads 1111 1111 so as not to trip either
8
Normally, the ALERT interrupt output signal is latched
and can be cleared either by responding to the Alert
Response Address or by reading the Status register.
Interrupts are generated in response to T HIGH and
TLOW, VHIGH and VLOW comparisons, and when the
remote diode is faulted. The interrupt does not halt automatic conversions; new temperature data continues to
be available over the SMBus interface after ALERT is
asserted. The interrupt output pin is open-drain so multiple devices can share a common interrupt line.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see the Alert Response Address section). Before taking corrective action, always check to ensure that an
interrupt is valid by reading the current temperature.
The alert activates only once per crossing of a given
temperature threshold to prevent any reentrant interrupts. To enable a new interrupt, rewrite the value of the
violated temperature threshold.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that lack
the complex, expensive logic needed to be a bus master.
Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the
Alert Response slave address (0001100). Any slave
device that generated an interrupt then attempts to identify itself by putting its own address on the bus (Table 5).
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 serviced (implies that the host interrupt input is
level sensitive). The alert is cleared after the slave
address is returned to the host.
Command Byte Functions
The 8-bit Command Byte register (Table 6) is the master index that points to the other registers within the
MAX6655/MAX6656. The register’s POR state is 0000
0000, so a Receive Byte transmission (a protocol that
lacks the Command Byte) that occurs immediately after
POR returns the current internal temperature data.
_______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Configuration Byte Functions
Configuration Bytes 1 and 2 (Tables 7 and 8) are used
to mask (disable) interrupts, disable temperature and
voltage measurements, and put the device in software
standby mode. The serial interface can read back the
contents of these registers.
Status Byte Functions
The two Status Byte registers (Tables 9 and 10) indicate which (if any) temperature or voltage thresholds
have been exceeded. Status Byte 1 also indicates
whether the ADC is converting and whether there is a
fault in the remote-diode DXP-DXN path. After POR, the
normal state of all the flag bits is zero, except the MSB,
assuming none of the alarm conditions are present. The
MSB toggles between 1 and 0 indicating whether the
ADC is converting or not. A Status Byte is cleared by
any successful read of that Status Byte. Note that the
ALERT interrupt latch clears when the status flag bit is
read, but immediately asserts after the next conversion
if the fault condition persists.
High and low alarm conditions can exist at the same time
in the Status Byte because the MAX6655/MAX6656 are
correctly reporting environmental changes.
Applications Information
Remote-Diode Selection
Remote temperature accuracy depends on having a
good-quality, diode-connected transistor. See Table 11
for appropriate discrete transistors. The MAX6655/
MAX6656 can directly measure the die temperature of
CPUs and other ICs with on-board temperature-sensing
transistors.
The transistor must be a small-signal type with a relatively high forward voltage. This ensures that the input
voltage is within the ADC input voltage range. The forward voltage must be greater than 0.25V at 10µA at the
highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expect-
ed temperature. The base resistance has to be less
than 100Ω. Tight specification of forward-current gain
(+50 to +150, for example) indicates that the manufacturer has good process controls and that the devices
have consistent VBE characteristics. Do not use power
transistors.
Self-Heating
Thermal mass can significantly affect the time required
for a temperature sensor to respond to a sudden
change in temperature. The thermal time constant of
the 16-pin QSOP package is about 140s in still air.
When measuring local temperature, it senses the temperature of the PC board to which it is soldered. The
leads provide a good thermal path between the PC
board traces and the MAX6655/MAX6656 die. Thermal
conductivity between the MAX6655/MAX6656 die and
the ambient air is poor by comparison. Because the
thermal mass of the PC board is far greater than that of
the MAX6655/MAX6656, the device follows temperature
changes on the PC board with little or no perceivable
delay.
When measuring temperature with discrete remote sensors, the use of smaller packages, such as a SOT23,
yields the best thermal response time. 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. 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.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
worst-case error occurs when autoconverting at the
fastest rate and simultaneously sinking maximum current at the ALERT output. For example, at the minimum
delay between conversions, and with ALERT sinking
1mA, the typical power dissipation is VCC x 550µA +
0.4V x 1mA. Package θJA is about 150°C/W, so with
VCC = +5V and no copper PC board heat sinking, the
resulting temperature rise is:
∆T = 3.1mW x 150°C/W = +0.46°C
Even with these contrived circumstances, it is difficult
to introduce significant self-heating errors.
ADC Noise Filtering
The integrating ADC has inherently good noise rejection, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
_______________________________________________________________________________________
9
MAX6655/MAX6656
Alarm Threshold Registers
Seventeen registers store ALARM and OVERT threshold data. The MAX6655/MAX6656 contain three registers for high-temperature (T HIGH ), three for lowtemperature (TLOW), four for high-voltage (VHIGH), four
for low-voltage (VLOW) thresholds, and three more registers store OVERT data. If a measured temperature or
voltage exceeds the corresponding alarm threshold
value, an ALARM interrupt is asserted. OVERT asserts
when temperature exceeds the corresponding alarm
threshold value. The POR state of the THIGH register is
full scale (0111 1111 or +127°C). The POR state of the
TLOW register is 1100 1001 or -55°C.
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
places constraints on high-frequency noise rejection.
Lay out the PC board carefully with proper external
noise filtering for high-accuracy remote measurements
in electrically noisy environments. Filter high-frequency
electromagnetic interference (EMI) at DXP and DXN
with an external 2200pF capacitor connected between
the two inputs. This capacitor can be increased to
about 3300pF (max), including cable capacitance. A
capacitance higher than 3300pF introduces errors due
to the rise time of the switched-current source.
If necessary, bypass VIN_ pins with any appropriatevalue capacitor for greater noise performance. Do not
put resistance in series with the inputs. Series resistance degrades voltage measurements.
GND
10MILS
10MILS
DXP
10MILS
DXN
MINIMUM
10MILS
GND
PC Board Layout
1) Place the MAX6655/MAX6656 as close as practical
to the remote diode. In a noisy environment, such as
a computer motherboard, this distance can be 4in to
8in (typ) or more, as long as the worst noise sources
(such as CRTs, clock generators, memory buses,
and ISA/PCI buses) are avoided.
2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces
across a fast memory bus, which can easily introduce +30°C error, even with good filtering.
Otherwise, most noise sources are fairly benign.
3) Route the DXP and DXN traces parallel and close to
each other, away from any high-voltage traces such
as +12VDC. Avoid leakage currents from PC board
contamination. A 20mΩ leakage path from DXP to
ground causes approximately +1°C error.
4) Connect guard traces to GND on either side of the
DXP-DXN traces when possible (Figure 5). With
guard traces in place, routing near high-voltage
traces is no longer an issue.
5) Route as few vias and crossunders as possible to
minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. In general, PC board-induced thermocouples are not a serious problem. A copper-solder thermocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP-DXN to
cause a 1°C measurement error, so most parasitic
thermocouple errors are swamped out.
7) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10-mil
widths and spacings recommended in Figure 5 are
not absolutely necessary (as they offer only a minor
10
Figure 5. Recommended DXP/DXN PC Traces
improvement in leakage and noise), but use them
where practical.
8) Note that copper cannot be used as an EMI shield.
Placing a copper ground plane between the DXPDXN traces and traces carrying high-frequency
noise signals does not help reduce EMI.
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8in, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6ft to 12ft (typ) before
noise becomes a problem, as tested in a noisy electronics laboratory. 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.
Connect the twisted pair to DXP and DXN and the
shield to GND, and leave the shield’s remote end unterminated. Excess capacitance at DX_ limits practical
remote-sensor distances (see Typical Operating
Characteristics).
For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the recommended 2200pF capacitor can often be removed or reduced
in value.
Cable resistance also affects remote-sensor accuracy.
A 1Ω series resistance introduces about +1/2°C error.
Chip Information
TRANSISTOR COUNT: 26,783
PROCESS: BiCMOS
______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Table 3. Extended Resolution Register
DATA
(RCRA, 04H)
WAIT TIME
BETWEEN CONVERSION
SEQUENCES (s)
FRACTIONAL TEMPERATURE (°C)
DIGITAL OUTPUT
0
0000 0000
0.125
0010 0000
00h
0
0.250
0100 0000
01h
0.125
0.375
0110 0000
02h
0.250
0.500
1000 0000
03h
0.500
0.625
1010 0000
04h
1.000
0.750
1100 0000
05h
2.000
0.875
1110 0000
06h
4.000
07h
4.000
Table 2. Temperature Data Format
TEMP (°C)
ROUNDED
TEMP (°C)
DIGITAL
OUTPUT
130.00
+127
0 111 1111
127.00
+127
0 111 1111
126.00
+126
0 111 1111
25.25
+25
0 001 1001
0.50
+1
0 000 0001
0
0
0 000 0000
-0.625
-1
1 111 1111
-65
-65
1 011 1111
Diode Fault (Short or Open)
—
1111 1111
______________________________________________________________________________________
11
MAX6655/MAX6656
Table 1. Conversion Rate Control Byte
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Table 4. Voltage Data Format
ADC OUTPUT CODE
INPUT
VOLTAGE AT VIN1
(+12V)
INPUT
VOLTAGE AT VIN2
(+5V) OR VCC
INPUT
VOLTAGE AT VIN2
(+3.3V) OR VCC
INPUT
VOLTAGE AT VIN3
(+2.5V)
LSB weight
57.1mV
23.8mV
15.7mV
11.9mV
64 (≈ 1/4 scale)
4.343V to 4.400V
1.810V to 1.833V
1.194V to 1.210V
0.905V to 0.917V
65
4.400V to 4.457V
1.833V to 1.857V
1.210V to 1.226V
0.917V to 0.929V
66
4.457V to 4.514V
1.857V to 1.881V
1.226V to 1.242V
0.929V to 0.941V
—
—
—
—
—
128 (≈ 1/2 scale)
8.000V to 8.057V
3.333V to 3.357V
2.200V to 2.216V
1.250V to 1.262V
—
—
—
—
—
198 (≈ 3/4 scale)
12.000V to 12.057V
5.000V to 5.024V
3.300V to 3.3157V
2.500V to 2.512V
—
—
—
—
—
210
12.686V to 12.743V
5.286V to 5.310V
3.486V to 3.504V
2.643V to 2.655V
211
12.743V to 12.800V
5.310V to 5.333V
3.504V to 3.521V
2.655V to 2.667V
—
—
—
—
—
237 (≈ 5/4 scale)
14.228V to 14.285V
5.929V to 5.952V
3.913V to 3.929V
2.964V to 2.976V
Table 5. Address Map (ADD[1:0])
12
ADD0
ADD1
ADDRESS
0
0
0011 0000
0
High-Z
0011 0010
0
1
0011 0100
High-Z
0
0101 0010
High-Z
High-Z
0101 0100
High-Z
1
0101 0110
1
0
1001 1000
1
High-Z
1001 1010
1
1
1001 1100
______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
REGISTER
RLTS
ADDRESS
00h
POR STATE
0000 0000
RRTE
01h
0000 0000
MAX6655/MAX6656
Table 6. Command Byte Register Map
FUNCTION
Read Internal Temperature
Read External Temperature 1
RSL
02h
0000 0000
Read Status Byte; Note 1
RCL
03h
0000 0000
Read Configuration Byte
RCRA
04h
0000 0010
Read Conversion Rate Byte
RLHN
05h
0111 1111
Read Internal ALERT High Limit
RLLI
06h
1100 1001
Read Internal ALERT Low Limit
RRHI
07h
0111 1111
Read External Temperature 1 ALERT High Limit
RRLS
08h
1100 1001
WCA
09h
N/A
Write Configuration Byte
WCRW
0Ah
N/A
Write Conversion Rate Control Byte
Read External Temperature 1 ALERT Low Limit
WLHO
0Bh
N/A
Write Internal ALERT High Limit
WLLM
0Ch
N/A
Write Internal ALERT Low Limit
WRHA
0Dh
N/A
Write External Temperature 1 ALERT High Limit
Write External Temperature 1 ALERT Low Limit
WRLN
0Eh
N/A
RRET1
10h
0000 0000
Read External 1 Extended Temperature
RRET2
11h
0000 0000
Read External 2 Extended Temperature
RLET
12h
0000 0000
Read Internal Extended Temperature
RRT2
13h
0000 0000
Read External Temperature 2
RRHL2
14h
0111 1111
Read External Temperature 2 ALERT High Limit
RRLL2
15h
1100 1001
Read External Temperature 2 ALERT Low Limit
RLOL
16h
0111 1111
Read Internal OVERT Limit
RLOL1
17h
0111 1111
Read External 1 OVERT Limit
RLOL2
18h
0111 1111
WLOL
19h
N/A
Write Internal OVERT Limit
WROL1
1Ah
N/A
Write External 1 OVERT Limit
WROL2
1Bh
N/A
Write External 2 OVERT Limit
WRH2
1Ch
N/A
Write External Temperature 2 ALERT High Limit
Read External 2 OVERT Limit
WRL2
1Dh
N/A
Write External Temperature 2 ALERT Low Limit
WV0HL
1Eh
N/A
Write VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656)
WV0LL
1Fh
N/A
Write VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656)
WV1HL
20h
N/A
Write VIN1 ALERT High Limit
WV1LL
21h
N/A
Write VIN1 ALERT Low Limit
WV2HL
22h
N/A
Write VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656)
Write VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656)
WV2LL
23h
N/A
WV3HL
24h
N/A
Write VIN3 ALERT High Limit
WV3LL
25h
N/A
Write VIN3 ALERT Low Limit
RV0HL
26h
1101 0011
Read VCC (VIN2) ALERT High Limit for MAX6655 (MAX6656)
RV0LL
27h
1010 1101
Read VCC (VIN2) ALERT Low Limit for MAX6655 (MAX6656)
______________________________________________________________________________________
13
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Table 6. Command Byte Register Map (continued)
REGISTER
ADDRESS
POR STATE
RV1HL
28h
1101 0011
Read VIN1 ALERT High Limit
FUNCTION
RV1LL
29h
1010 1101
Read VIN1 ALERT Low Limit
RV2HL
2Ah
1101 0011
Read VIN2 (VCC) ALERT High Limit for MAX6655 (MAX6656)
RV2LL
2Bh
1010 1101
Read VIN2 (VCC) ALERT Low Limit for MAX6655 (MAX6656)
RV3HL
2Ch
1101 0011
Read VIN3 ALERT High Limit
RV3LL
2Dh
1010 1101
Read VIN3 ALERT Low Limit
RV0
2Eh
0000 0000
Read VCC (VIN2) for MAX6655 (MAX6656)
RV1
2Fh
0000 0000
Read VIN1
RV2
30h
0000 0000
Read VIN2 (VCC) for MAX6655 (MAX6656)
RV3
31h
0000 0000
Read VIN3
RSL2
32h
0000 0000
Read Status Byte 2
Read Configuration Byte 2
RCL2
33h
0000 0000
WCA2
34h
N/A
RDID
FEh
0000 1010
Read Device ID
RDRV
FFh
0100 1101
Read Manufacture ID
Write Configuration Byte 2
Note 1: Upon application of power, the ADC begins converting. The MSB of the Status Byte register indicates a conversion in
progress. The Status Byte has a value of 80h during conversions and a value of 00h between conversions. Therefore, at power-on,
the Status Byte alternates between 00h and 80h.
Table 7. Configuration Byte 1 Bit Assignments
14
BIT
NAME
POR
STATE
7 (MSB)
Mask All
0
Masks out all ALERT interrupts if high.
6
RUN/STOP
0
Standby mode control bit; if high, the device immediately stops converting and
enters standby mode. If low, the device enters normal conversion mode.
5
Mask Remote
Temperature 1
0
High masks out OVERT and ALERT interrupts due to remote-diode 1.
4
Mask Remote
Temperature 2
0
High masks out OVERT and ALERT interrupts due to remote-diode 2.
3
Mask VIN3
0
High masks ALERT interrupts due to VIN3.
2
Mask VIN2
0
High masks ALERT interrupts due to VIN2 (VCC) for MAX6655 (MAX6656).
1
Mask VIN1
0
High masks ALERT interrupts due to VIN1.
0
Mask VCC
0
High masks ALERT interrupts due to VCC (VIN2) for MAX6655 (MAX6656).
FUNCTION
______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
MAX6655/MAX6656
Table 8. Configuration Byte 2-Bit Assignments
BIT
NAME
POR
STATE
7 (MSB)
Disable Remote
Temperature 1
Measurement
0
If high, the remote temperature 1 measurement is disabled.
6
Disable Remote
Temperature 2
Measurement
0
If high, the remote temperature 2 measurement is disabled.
5
Disable Internal
Temperature
Measurement
0
If high, the internal temperature measurement is disabled.
4
Disable VIN3
Measurement
0
If high, the input voltage VIN3 measurement is disabled.
3
Disable VIN2
Measurement
0
If high, the input voltage VIN2 (VCC) measurement is disabled for MAX6655
(MAX6656).
2
Disable VIN1
Measurement
0
If high, the input voltage VIN1 measurement is disabled.
1
Disable VCC
Measurement
0
If high, the input voltage VCC (VIN2) measurement is disabled for MAX6655
(MAX6656).
0
Reserved
0
Reserved for future use.
FUNCTION
Table 9. Status Byte 1-Bit Assignments
BIT
NAME
POR STATE
FUNCTION
7 (MSB)
BUSY
0
ADC is busy converting when high.
6
LHIGH
0
Internal high-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
5
LLOW
0
Internal low-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
4
RHIGH
0
External 1 high-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
3
RLOW
0
External 1 low-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
2
DODS1
0
A high indicates external diode 1 open/short.
1
R2HIGH
0
External 2 high-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
0
R2LOW
0
External 2 low-temperature ALERT has tripped when high; cleared by POR or
readout of the entire Status Byte.
______________________________________________________________________________________
15
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
Table 10. Status Byte 2-Bit Assignments
BIT
NAME
POR STATE
FUNCTION
7(MSB)
LO
0
Internal temperature has exceeded OVERT limit. Clear by falling below limit.
6
R1O
0
External temperature 1 has exceeded OVERT limit. Clear by falling below limit.
5
R2O
0
External temperature 2 has exceeded OVERT limit. Clear by falling below limit.
4
DODS2
0
A high indicates external diode 2 open or short.
3
VA3
0
VIN3 out of window ALERT has tripped when high; cleared by POR or reading
the Status Byte.
2
VA2
0
VIN2 out of window ALERT has tripped when high; cleared by POR or reading
the Status Byte.
1
VA1
0
VIN1 out of window ALERT has tripped when high; cleared by POR or reading
the Status Byte.
0
VCCA
0
VCC out of window ALERT has tripped when high; cleared by POR or reading
the Status Byte.
Table 11. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
MODEL NUMBER
Central Semiconductor (USA)
CMPT3906
Fairchild Semiconductor (USA)
MMBT3906
Infineon (Germany)
SMBT3906
ON Semiconductor (USA)
MMBT3906
Rohm Semiconductor (Japan)
Zetex (England)
16
SST3906
FMMT3906CT-ND
______________________________________________________________________________________
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
2.5V
VCC
CPU
VCC
DXP1
TO 12V
TO 3.3V OR 5V
TO 2.5V
0.1µF
10kΩ
MAX6655
MAX6656
DXN1
SMBCLK
VIN1
SMBDATA
VIN2
ALERT
VIN3
OVERT
DXP2
ADD0
SMBus/I2C
CONTROLLER
TO SYSTEM SHUTDOWN
ADD1
DXN2
2N3906
GND
2200pF
Functional Diagram
VCC
MAX6655/MAX6656
VIN1
VIN2
VIN3
DXP1
DXN1
INPUT VOLTAGE
SCALING AND
MULTIPLEXER
ADC
TEMPERATURE
SENSOR
VOLTAGE
REFERENCE
DXP2 DXN2
DATA AND
CONTROL
LOGIC
SMBus/I2CCOMPATIBLE
INTERFACE
SMBDATA
SMBCLK
ALERT
OVERT
ADD0 ADD1
______________________________________________________________________________________
17
MAX6655/MAX6656
Typical Application Circuit
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.)
QSOP.EPS
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
21-0055
F
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
© 2006 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.