Rainbow Electronics MAX6656 User Manual

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 system shutdown.

Applications

Notebooks

Thin Clients

Servers

Workstations

Communication Equipment

Desktop PC

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

C™-Compatible Interface

♦ OVERT Output for Fan Control and System

Shutdown

MAX6655/MAX6656

Dual Remote/Local Temperature Sensors and

Four-Channel Voltage Monitors

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Ordering Information

19-2117; Rev 0; 7/01

SMBus is a trademark of Intel Corp.

C is a trademark of Philips Corp.

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.

Typical Application Circuit appears at end of data sheet.

PART TEMP. RANGE PIN-PACKAGE

MAX6655MEE -55°C to +125°C 16 QSOP

MAX6656MEE -55°C to +125°C 16 QSOP

TOP VIEW

DXP1

DXN1

ADD0

ADD1

DXP2

DXN2

GND

MAX6655

MAX6656

QSOP

STBY

SMBCLK

OVERT

SMBDATA

ALERT

IN2

IN1

IN3

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

= +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

IN1

to GND............................................................-0.3V to +16V

IN2

to GND..............................................................-0.3V to +6V

IN3

to GND..............................................................-0.3V to +6V

All Other Pins to GND.................................-0.3V to (V

+ 0.3V)

SMBDATA, ALERT, OVERT Current....................-1mA to +50mA

DXN_ Current......................................................................±1mA

ESD Protection (all pins, Human Body Model) ..................2000V

Continuous Power Dissipation (T

= +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

Supply Range V

Accuracy (Local Sensor)

Accuracy (Remote Sensor)

Temperature Measurement Resolution

ADC Input Impedance Z

ADC Total Error

VIN ADC Resolution 8 Bits

Undervoltage Lockout Threshold UVLO

Undervoltage Lockout Hysteresis

Power-On Reset (POR) Threshold

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 550 1000 µA

Conversion Time for Single Temperature Measurement

Monitoring Cycle Time t

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

+60°C ≤ TA≤ +100°C ±1.5

CON

MONI

0°C ≤ T

+60°C ≤ TRJ≤ +100°C ±1

0°C ≤ T

V nominal

V falling edge

From stop bit to conversion completed 95 125 155 ms

Total of 3 temperature plus 4 voltage measurements

≤ +125°C ±3

≤ +120°C ±3

, V

IN1

, V

IN2

, V

IN2

input, disables A/D conversion,

, falling edge 1 1.7 2.5 V

input resistance 100 kΩ

IN3

between 30% and 120% of

IN3

3.0 5.5 V

0.125 °C

11 Bits

±1 ±1.5 %

2.50 2.70 2.90 V

90 mV

625 ms

°C

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

= +3.3V for MAX6656, VCC= +5.0V for MAX6655, TA= +25°C.)

Remote Junction Current (DXP, DXN)

SMBus INTERFACE (SMBCLK, SMBDATA, STBY)

Logic Input Low Voltage V

Logic Input High Voltage V

Input Leakage Current I

Output Low Sink Current I

Input Capacitance C

SMBus Timeout SMBCLK or SMBDATA time low for reset 30 35 60 ms

ALERT, OVERT

Output Low Sink Current VOL= +0.6V 6 mA

Output High Leakage Current VOH= +5.5V 1 µA

SMBus TIMING

Serial Clock Frequency f

Bus Free Time Between STOP and START Condition

START Condition Setup Time 4.7 µs

Repeat START Condition Setup Time

START Condition Hold Time t

STOP Condition Setup Time t

Clock Low Period t

Clock High Period t

Data Setup Time t

Data Hold Time t

Receive SMBCLK/SMBDATA Rise Time

Receive SMBCLK/SMBDATA Fall Time

Pulse Width of Spike Suppressed

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

High level 80 100 140

Low level 8 10 14

VCC= +3.0V to +5.5V 0.8 V

VCC= +3.0V 2.1

LEAK

SCL

BUF

SU:STA

HD:STA

SU:STO

LOW

HIGH

SU:DAT

HD:DAT

= +5.5V 2.6

VIN= GND or V

VOL= +0.6V 6 mA

90% to 90% 50 ns

10% of SMBDATA to 90% of SMBCLK 4 µs

90% of SMBCLK to 10% of SMBDATA 4 µs

10% to 10% 4.7 µs

90% to 90% 4 µs

90% of SMBDATA to 10% of SMBCLK 250 ns

(Note 1) 0 µs

5pF

4.7 µs

050ns

±1µA

400 kHz

1µs

300 ns

µA

MAX6655/MAX6656

Dual Remote/Local Temperature Sensors and Four-Channel Voltage Monitors

4 _______________________________________________________________________________________

Typical Operating Characteristics

(TA= +25°C, unless otherwise noted.)

-10

-20 110100

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

-55 -5 45 95

REMOTE TEMPERATURE ERROR

vs. REMOTE-DIODE TEMPERATURE

MAX6655/MAX6656 toc02

TEMPERATURE (°C)

REMOTE TEMPERATURE ERROR (°C)

RANDOM SAMPLE 2N3906

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

WITH

NO V

BYPASS CAPACITOR

= 250mVp-p

REMOTE DIODE

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 50 100 150 200

REMOTE TEMPERATURE ERROR

vs. DXP-DXN CAPACITANCE

MAX6655/MAX6656 toc05

DXP-DXN CAPACITANCE (nF)

REMOTE TEMPERATURE ERROR (°C)

VCC = +5V

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

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

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

0406020 80 100 120

VOLTAGE ACCURACY

vs. TEMPERATURE

MAX6655/MAX6656 toc09

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

IN1

IN2

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

3 DXN1

4 ADD0

5 ADD1 SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up.

6 DXP2

7 DXN2

8 GND Ground

10 V

11 V

12 ALERT SMBus Alert (Interrupt) Output, Open-Drain

13 SMBDATA SMBus Serial-Data Input/Output, Open-Drain

14 OVERT

15 SMBCLK SMBus Serial-Clock Input

16 STBY

IN3

IN1

IN2

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.

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.

SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. Table 5 is the truth table.

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.

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.

External Voltage Monitor 3. V

External Voltage Monitor 1. V

External Voltage Monitor 2. V and +5.0V for MAX6656.

Overtemperature Alarm Output, Open-Drain. OVERT is an unlatched alarm output that responds to the programmed maximum temperature limit for all temperature channels.

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.

is typically used to monitor +2.5V supplies.

IN3

is typically used to monitor +12V supplies.

IN1

is typically used to monitor voltage supplies of +3.3V for MAX6655

IN2

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

, VCC(V

IN2

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 _______________________________________________________________________________________

Figure 1. SMBus/I2C Protocols

Write Byte Format

S COMMANDWR

Read Byte Format

Send Byte Format Receive Byte Format

S = Start condition P = Stop condition

ADDRESS ACK

7 bits

Slave Address: equivalent to chip-select line of a 3-wire interface

ADDRESS ACK S ACK

7 bits

Slave Address: equivalent to chip-select line

ADDRESS

7 bits

Shaded = Slave transmission

A = Not acknowledged

ACK

COMMAND ACK PS

Data Byte: writes data to the register commanded by the last read byte or write byte transmission

ACK

Command Byte: selects which register you are writing to

8 bits

Command Byte: selects which register you are reading from

8 bits

DATA ACK P

8 bits

Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate)

ADDRESS RD

7 bits

Slave Address: repeated due to change in dataflow direction

ADDRESS RD

7 bits

DATA

8 bits

Data Byte: reads from the register set by the command byte

ACK

DATA PS

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

PS COMMAND A

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