Rainbow Electronics MAX6649 - Manual (Page 5)

MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
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Detailed Description
The MAX6646/MAX6647/MAX6649 are temperature sen-
sors designed to work in conjunction with a microproces-
sor or other intelligence in thermostatic, process-control,
or monitoring applications. Communication with the
MAX6646/MAX6647/MAX6649 occurs through the
SMBus-compatible serial interface and dedicated alert
and overtemperature outputs. ALERT asserts if the mea-
sured local or remote temperature is greater than the
software-programmed ALERT high limit or less than the
ALERT low limit in the MAX6649. ALERT also asserts, in
the MAX6649, if the remote-sensing diode pins are short-
ed or unconnected. The overtemperature alarm, OVERT,
asserts if the software-programmed OVERT limit is
exceeded. OVERT can be connected to fans, a system
shutdown, a clock throttle control, or other thermal-man-
agement circuitry.
The MAX6646/MAX6647/MAX6649 convert temperatures
to digital data either at a programmed rate or in single
conversions. Temperature data is represented as 11 bits,
with the LSB equal to 0.125°C. The “main” temperature
data registers (at addresses 00h and 01h) are 8-bit regis-
ters that represent the data as 8 bits with the full-scale
reading indicating the diode fault status (Table 1). The
remaining 3 bits of temperature data are available in the
“extended” registers at addresses 11h and 10h (Table 2).
ADC and Multiplexer
The averaging ADC integrates over a 60ms period
(each channel, typically), with excellent noise rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward volt-
age and compute the temperature based on this volt-
age. Both channels are automatically converted once
the conversion process has started, either in free-run-
ning or single-shot mode. If one of the two channels is
not used, the device still performs both measurements,
and the results of the unused channel can be ignored.
If the remote-diode channel is unused, connect DXP to
DXN rather than leaving the inputs open.
Pin Description
PIN NAME FUNCTION
1 V CC
Supply Voltage Input, 3V to 5.5V. Bypass V CC to GND with a 0.1µF capacitor. A 200 Ω series
resistor is recommended but not required for additional noise filtering.
2 DXP
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. DO
NOT LEAVE DXP FLOATING; connect DXP to DXN if no remote diode is used. Place a 2200pF
capacitor between DXP and DXN for noise filtering.
3 DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to
ground.
4 OVERT
Overtemperature Alert/Interrupt Output, Open Drain. OVERT is logic low when the temperature is
above the software-programmed threshold.
5 GND Ground
6 ALERT
SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds limits
(high or low temperature). ALERT stays asserted until acknowledged by either reading the status
register or by successfully responding to an alert response address, provided that the fault
condition no longer exists. See the
ALERT Interrupts section.
7 SDA SMBus Serial-Data Input/Output, Open Drain
8 SCLK SMBus Serial-Clock Input
TEMP ( °C) DIGITAL OUTPUT
+145 1001 0001
+130 1000 0010
+128 1000 0000
+25 0001 1001
0 0000 0000
<0 0000 0000
Diode fault
(short or open)
1111 1111
Table 1. Main Temperature Data Register
Format (00h, 01h)