MAX1619
Remote/Local Temperature Sensor with Dual-
Alarm Outputs and SMBus Serial Interface
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Pin Description
Detailed Description
The MAX1619 is a temperature sensor designed to work
in conjunction with an external microcontroller (µC) or
other intelligence in thermostatic, process-control, or
monitoring applications. The µC is typically a power-
management or keyboard controller, generating SMBus
serial commands either by “bit-banging” general-pur-
pose input/output (GPIO) pins or through a dedicated
SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1619
contains a switched current source, a multiplexer, an
ADC, an SMBus interface, and associated control logic
(Figure 1). Temperature data from the ADC is loaded
into two data registers (local and remote). The remote
temperature data is automatically compared with data
previously stored in four temperature-alarm threshold
registers. One pair of alarm-threshold registers is used
to provide hysteretic fan control; the other pair is used
for alarm interrupt. The local temperature data is avail-
able for monitoring.
ADC and Multiplexer
The ADC is an averaging type that integrates over a
60ms period (each channel, typical) with excellent
noise rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes, measures their
forward voltages, and computes their temperatures.
Both channels are automatically converted once the
conversion process has started, either in free-running
or single-shot mode. If one of the two channels is not
used, the device still performs both measurements, and
the user can simply ignore the results of the unused
channel.
The DXN input is biased at 0.65V above ground by an
internal diode to set up the analog-to-digital (A/D)
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 per ohm. Likewise, 200µV of off-
set voltage forced on DXP–DXN causes about 1°C error.
SMBus Serial-Data Input/Output, Open DrainSMBDATA12
SMBus Serial-Clock InputSMBCLK14
Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
STBY
15
SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance
(>50pF) at the address pins when floating may cause address-recognition problems.
ADD16
GroundGND7, 8
SMBus Slave Address Select PinADD010
SMBus Alert (interrupt) Output, Open Drain
ALERT
11
Combined Current Sink and A/D Negative Input. DXN is normally internally biased to a diode voltage
above ground.
DXN4
Combined 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.
DXP3
PIN
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recom-
mended but not required for additional noise filtering.
V
CC
1
FUNCTIONNAME
Overtemperature Alarm Output, Open Drain. This is an unlatched alarm output that responds only to the
remote diode temperature.
OVERT
9
Not internally connected. Connect to GND to act against leakage paths from V
CC
to DXP.GND2
No Connection. Not internally connected. May be used for PC board trace routing.N.C.
5, 13,
16
