MAXIM MAX6655, MAX6656 Technical data
19-2117; Rev 1; 5/06
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
General Description
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.
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 sys-
tem shutdown.
Features
♦ Three Temperature Channels
Two Remote PN Junctions
One Local Sensor
♦ 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/I
2
C-Compatible Interface
♦ OVERT Output for Fan Control and System
Shutdown
Ordering Information
PART TEMP RANGE
MAX6655MEE -55°C to +125°C
MAX6656MEE -55°C to +125°C
Typical Application Circuit appears at end of data sheet.
PINPACKAGE
16 QSOP
16 QSOP
Pin Configuration
MAX6655/MAX6656
PKG
CODE
E16-5
E16-5
TOP VIEW
V
DXP1
DXN1
ADD0
ADD1
DXP2
DXN2
GND
16
15
14
13
12
11
10
9
STBY
SMBCLK
OVERT
SMBDATA
ALERT
V
IN2
V
IN1
V
IN3
1
CC
2
3
MAX6655
4
MAX6656
5
6
7
8
QSOP
Notebooks
Thin Clients
Servers
S.
*P,
Is
ae
c-
SMBus is a trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products 1
Applications
Workstations
Communication
Equipment
Desktop PC
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.
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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 V
CC
= +3.3V for MAX6656, VCC= +5.0V for MAX6655, TA= +25°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.
VCCto GND..............................................................-0.3V to +6V
DXN_ to GND ........................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, STBY,
OVERT to GND .....................................................-0.3V to +6V
V
IN1
to GND............................................................-0.3V to +16V
V
IN2
to GND..............................................................-0.3V to +6V
V
IN3
to GND..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (V
CC
+ 0.3V)
SMBDATA, ALERT, OVERT Current....................-1mA to +50mA
DXN_ Current......................................................................±1mA
ESD Protection (all pins, Human Body Model) ..................2000V
Continuous Power Dissipation (T
A
= +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
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Range V
CC
3.0 5.5 V
+60°C ≤ TA ≤ +100°C
Accuracy (Local Sensor)
0°C ≤ T
A
≤ +125°C ±3
°C
+60°C ≤ T
RJ
≤ +100°C ±1
Accuracy (Remote Sensor)
0°C ≤ T
RJ
≤ +120°C ±3
°C
°C
Temperature Measurement
Resolution
11
Bits
ADC Input Impedance Z
IN
V
IN1
, V
IN2
, V
IN3
input resistance
kΩ
ADC Total Error
V
IN1
, V
IN2
, V
IN3
between 30% and 120% of
nominal
±1
%
VIN ADC Resolution 8
Bits
Undervoltage Lockout Threshold
VCC input, disables A/D conversion,
falling edge
V
Undervoltage Lockout
Hysteresis
90 mV
Power-On Reset (POR)
Threshold
V
CC
, falling edge 1 1.7 2.5 V
POR Threshold Hysteresis 90 mV
Standby Current SMBus static, STBY = GND 3 10 µA
DXP and DXN Leakage Current In standby mode 2 µA
Average Operating Current Continuous temperature mode
µA
Conversion Time for Single
Temperature Measurement
t
CON
From stop bit to conversion completed 95
ms
Monitoring Cycle Time t
MONI
Total of 3 temperature plus 4 voltage
measurements
ms
±1.5
0.125
UVLO
100
2.50 2.70 2.90
550 1000
125 155
625
±1.5
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(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 V
CC
= +3.3V for MAX6656, VCC= +5.0V for MAX6655, TA= +25°C.)
PARAMETER
CONDITIONS
UNITS
High level 80
Remote Junction Current
(DXP, DXN)
Low level 8 10 14
µA
SMBus INTERFACE (SMBCLK, SMBDATA, STBY)
Logic Input Low Voltage V
IL
V
CC
= +3.0V to +5.5V 0.8 V
V
CC
= +3.0V 2.1
Logic Input High Voltage V
IH
V
CC
= +5.5V 2.6
V
Input Leakage Current I
LEAK
V
IN
= GND or V
CC
±1µA
Output Low Sink Current I
OL
V
OL
= +0.6V 6 mA
Input Capacitance C
IN
5pF
SMBus Timeout SMBCLK or SMBDATA time low for reset 30 35 60 ms
ALERT, OVERT
Output Low Sink Current V
OL
= +0.6V 6 mA
Output High Leakage Current V
OH
= +5.5V 1 µA
SMBus TIMING
Serial Clock Frequency f
SCL
kHz
Bus Free Time Between STOP
and START Condition
t
BUF
4.7 µs
START Condition Setup Time 4.7 µs
Repeat START Condition Setup
Time
90% to 90% 50 ns
START Condition Hold Time
10% of SMBDATA to 90% of SMBCLK 4 µs
STOP Condition Setup Time
90% of SMBCLK to 10% of SMBDATA 4 µs
Clock Low Period t
LOW
10% to 10% 4.7 µs
Clock High Period t
HIGH
90% to 90% 4 µs
Data Setup Time
90% of SMBDATA to 10% of SMBCLK
ns
Data Hold Time
(Note 1) 0 µs
Receive SMBCLK/SMBDATA
Rise Time
t
R
1µs
Receive SMBCLK/SMBDATA
Fall Time
t
F
ns
Pulse Width of Spike
Suppressed
t
SP
050ns
SYMBOL
t
SU:STA
t
HD:STA
t
SU:STO
t
SU:DAT
t
HD:DAT
MIN TYP MAX
100 140
250
400
300
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
4 _______________________________________________________________________________________
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
20
10
0
-10
-20
1 10 100
REMOTE TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX6655/MAX6656 toc01
LEAKAGE RESISTANCE (MΩ)
REMOTE TEMPERATURE ERROR (°C)
PATH = DXP TO GND
PATH = DXP TO VCC (5V)
-5
-2
-3
-4
-1
0
1
2
3
4
5
-55 -5 45 95
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6655/MAX6656 toc02
TEMPERATURE (°C)
REMOTE TEMPERATURE ERROR (°C)
RANDOM SAMPLE
2N3906
20
15
10
5
0
02010 30 40 50
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6655/MAX6656 toc03
FREQUENCY (MHz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
APPLIED TO V
CC
WITH
NO V
CC
BYPASS CAPACITOR
V
IN
= 250mVp-p
REMOTE DIODE
0
2
4
6
8
10
12
14
0 1020304050
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6655/MAX6656 toc04
FREQUENCY (MHz)
REMOTE TEMPERATURE ERROR (°C)
VIN = 200mVp-p
VIN = 100mVp-p
VIN = SQUARE WAVE
AC-COUPLED TO DXN
0
2
4
6
8
10
12
14
0 50 100 150 200
REMOTE TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6655/MAX6656 toc05
DXP-DXN CAPACITANCE (nF)
REMOTE TEMPERATURE ERROR (°C)
VCC = +5V
0
15
10
5
20
25
30
35
40
45
50
1 10 100 1000
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
MAX6655/MAX6656 toc06
SMBCLK FREQUENCY (kHz)
SUPPLY CURRENT (µA)
SMBCLK IS DRIVEN
RAIL-TO-RAIL
0
20
40
60
80
100
120
140
012345
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6655/MAX6656 toc07
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
ADD0, ADD1 = GND
ADD0, ADD1 = HIGH-Z
0
40
20
80
60
120
100
-1 1 20 345
RESPONSE TO THERMAL SHOCK
MAX6655/MAX6656 toc08
TIME (s)
TEMPERATURE (°C)
REMOTE DIODE IMMERSED
IN +115°C FLUORINERT BATH
0
4
2
8
6
12
10
0406020 80 100 120
VOLTAGE ACCURACY
vs. TEMPERATURE
MAX6655/MAX6656 toc09
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
V
IN1
V
CC
V
IN2
V
IN3
INPUT VOLTAGES ARE NOMINAL
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.
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
_______________________________________________________________________________________ 5
Pin Description
PIN NAME FUNCTION
1VCCSupply Voltage. +5V for MAX6655; +3.3V for MAX6656. Bypass VCC to GND with a 0.1µF capacitor.
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
9V
IN3
External Voltage Monitor 3. V
IN3
is typically used to monitor +2.5V supplies.
10 V
IN1
External Voltage Monitor 1. V
IN1
is typically used to monitor +12V supplies.
11 V
IN2
External Voltage Monitor 2. V
IN2
is typically used to monitor voltage supplies of +3.3V for MAX6655
and +5.0V for MAX6656.
12 ALERT SMBus Alert (Interrupt) Output, Open-Drain
13
SMBus Serial-Data Input/Output, Open-Drain
14 OVERT
Overtemperature Alarm Output, Open-Drain. OVERT is an unlatched alarm output that responds to
the programmed maximum temperature limit for all temperature channels.
15 SMBCLK SMBus Serial-Clock Input
16 STBY
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.
SMBDATA
MAX6655/MAX6656
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, V
IN3
, V
IN2 (VCC
), V
IN1
, V
CC (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
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
6 _______________________________________________________________________________________
Write Byte Format
Read Byte Format
Send Byte Format Receive Byte Format
Slave Address: equivalent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave Address: equivalent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in dataflow direction
Data Byte: reads from
the register set by the
command byte
Data Byte: writes data to the
register commanded by the
last read byte or write byte
transmission
Data Byte: reads data from
the register commanded
by the last read byte or
write byte transmission;
also used for SMBus alert
response return address
S = Start condition
P = Stop condition
Shaded = Slave transmission
A = Not acknowledged
ACK
7 bits
ADDRESS ACK
8 bits
DATA ACK P
8 bits
S COMMANDWR
ACK
7 bits
ADDRESS ACK S ACK
8 bits
DATA
7 bits
ADDRESS RD
8 bits
PS COMMAND A
WR
ACK
7 bits
ADDRESS
8 bits
COMMAND ACK PS
WR
ACK
7 bits
ADDRESS RD
8 bits
DATA PS
A
Figure 1. SMBus/I2C Protocols
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