MAX1668_00 Datasheet, PDF (6/16 Pages) Maxim Integrated Products – Multichannel Remote/Local Temperature Sensor

Multichannel Remote/Local
Temperature Sensor
Pin Description
PIN
MAX1668 MAX1805
NAME
FUNCTION
—
5–8
N.C.
No Connection. Not internally connected. May be used for PC board trace routing.
9
1, 3, 5, 7
2, 4, 6, 8
10
11
16
12
13
14
15
9
V_CC
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series
resistor is recommended but not required for additional noise filtering.
Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave
1, 3
DXP_
DXP floating; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor
between DXP and DXN for noise filtering.
2, 4
DXN_
Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode volt-
age above ground.
SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up.
10
ADD1
Excess capacitance (>50pF) at the address pins when floating may cause address-
recognition problems.
16
GND
Ground
11
ADD0
SMBus Slave Address Select Pin
12
ALERT SMBus Alert (Interrupt) Output, Open Drain
13
SMBDATA SMBus Serial-Data Input/Output, Open Drain
14
SMBCLK SMBus Serial-Clock Input
15
STBY
Hardware Standby Input. Temperature and comparison threshold data are retained in
standby mode. Low = standby mode, high = operate mode.
_______________Detailed Description
The MAX1668/MAX1805 are temperature sensors
designed to work in conjunction with an external micro-
controller (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 by “bit-banging”
general-purpose input-output (GPIO) pins or via a dedi-
cated SMBus interface block.
These devices are essentially 8-bit serial analog-to-dig-
ital converters (ADCs) with sophisticated front ends.
However, the MAX1668/MAX1805 also contain a
switched current source, a multiplexer, an ADC, an
SMBus interface, and associated control logic (Figure
1). In the MAX1668, temperature data from the ADC is
loaded into five data registers, where it is automatically
compared with data previously stored in 10 over/under-
temperature alarm registers. In the MAX1805, tempera-
ture data from the ADC is loaded into three data
registers, where it is automatically compared with data
previously stored in six over/undertemperature alarm
registers.
ADC and Multiplexer
The ADC is an averaging type that integrates over a
64ms 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.
Each channel is automatically converted once the con-
version process has started. If any one of the channels
is not used, the device still performs measurements on
these channels, and the user can ignore the results of
the unused channel. If any 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_ to
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 offset
voltage forced on DXP_ to DXN causes about 1°C error.
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