Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
______________________________________________________________Pin Description
PIN
1, 5, 9,
13, 16
2
NAME
N.C.
V
CC
FUNCTION
No Connection. Not internally connected. May be used for PC board trace routing.
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.
Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave DXP floating; tie
DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filter-
ing.
Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above
ground.
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.
Ground
SMBus Slave Address Select pin
SMBus Alert (interrupt) Output, open drain
SMBus Serial-Data Input/Output, open drain
SMBus Serial-Clock Input
Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
3
DXP
4
6
7, 8
10
11
12
14
15
DXN
ADD1
GND
ADD0
ALERT
SMBDATA
SMBCLK
STBY
_______________Detailed Description
The MAX1617 (patents pending) is a temperature sen-
sor designed to work in conjunction with an external
microcontroller (µC) or other intelligence in thermostat-
ic, process-control, or monitoring applications. The µC
is typically a power-management or keyboard con-
troller, generating SMBus serial commands by “bit-
banging” general-purpose input-output (GPIO) pins or
via a dedicated SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1617
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, where it is automatically com-
pared with data previously stored in four over/under-
temperature alarm registers.
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. If the remote diode channel is unused, tie DXP
to DXN rather than leaving the pins open.
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.
6
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