Detailed Description

The MAX6655/MAX6656 are voltage and temperature

monitors that communicate through an SMBus-compat-

ible 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 automati-

cally compared with data previously stored in over/under-

temperature alarm threshold registers. Temperature data

can be read at any time with 11 bits of resolution.

The MAX6655/MAX6656 can monitor external supply volt-

ages 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 tem-

perature measurement in 125ms (typ) and a voltage

measurement in 62.5ms (typ). For temperature mea-

surements, 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 caus-

es about +1/2°C error/

Ω. A 200µV offset voltage at

DXP-DXN causes about -1°C error.

Dual Remote/Local Temperature Sensors and

Four-Channel Voltage Monitors

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5

Pin Description

PIN

NAME

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

10

11

and +5.0V for MAX6656.

12

ALERT

SMBus Alert (Interrupt) Output, Open-Drain

13

SMBDATA

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.