Rainbow Electronics MAX6656 - Manual (Page 5)

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.
MAX6655/MAX6656
Dual Remote/Local Temperature Sensors and
Four-Channel Voltage Monitors
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Pin Description
PIN NAME FUNCTION
1 V CC Supply Voltage. +5V for MAX6655; +3.3V for MAX6656. Bypass V CC 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
9 V 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 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.