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PDF MAX6670 Data sheet ( Hoja de datos )
| Número de pieza | MAX6670 | |
| Descripción | (MAX6668 / MAX6670) Remote Temperature Switches | |
| Fabricantes | Maxim Integrated Products | |
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19-2133; Rev 2; 11/02
Remote Temperature Switches with Integrated
Fan Controller/Driver
General Description
The MAX6668/MAX6670 remote-junction thermal
switches with an internal power transistor drive a cool-
ing fan rated for supply voltages up to +12V and
250mA. These devices measure the temperature of an
external P-N junction (typically a diode-connected tran-
sistor) and turn on the fan power switch when the
remote temperature rises above a factory-programmed
threshold. Self-contained and requiring no software
development, the MAX6668/MAX6670 are simple
“drop-in” fan-control solutions for a variety of systems.
The MAX6670 features an open-drain WARN output
that goes active when the remote temperature exceeds
the factory-programmed fan activation threshold by
+15°C. The MAX6670 features an open-drain OT output
that goes active when the remote temperature exceeds
the factory-programmed threshold by +30°C. The
MAX6668/MAX6670 provide a fan-control input,
FORCEON, that allows the fan to be driven externally,
regardless of temperature.
Available temperature thresholds range from +40°C to
+75°C in 5°C increments. Hysteresis is preset to 8°C on
the MAX6668 or pin selectable to 4°C, 8°C, or 12°C
using a three-level logic input on the MAX6670.
Temperature threshold accuracy is ±1°C (typ) and
±2.2°C (max) for remote-junction temperatures from
+40°C to +75°C.
The MAX6668/MAX6670 operate from a +3V to +3.6V
power supply, and are specified over the automotive
temperature range (-40°C to +125°C). The MAX6668 is
www.DoaftfaeSrehedeti4nUa.cnom8-pin µMAX package and the MAX6670 is
available in a space-saving 10-pin µMAX package.
Applications
Notebook and Desktop Computers
Network Switches
PC Power Supplies
Laboratory Instruments
Card Racks
Temperature Alarms
Fan Controls
Features
o +12V, 250mA Integrated Fan Driver
o No Calibration Required
o Pin-Selectable 4°C, 8°C, or 12°C Hysteresis
(MAX6670)
o Factory-Programmed Temperature Thresholds
from +40°C to +75°C
o Overtemperature Warning Signals
o 110µA (typ) Supply Current
o Space-Saving 8-Pin and 10-Pin µMAX Packages
Ordering Information
PART
TEMP
RANGE
PIN-
PACKAGE
THRESH-
OLD
(°C)
MAX6668AUA40 -40°C to +125°C
MAX6668AUA45 -40°C to +125°C
MAX6668AUA50 -40°C to +125°C
MAX6668AUA60 -40°C to +125°C
MAX6668AUA70 -40°C to +125°C
MAX6668AUA75 -40°C to +125°C
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
40
45
50
60
70
75
Ordering Information continued at end of data sheet.
Typical Application Circuit
CS
2200pF
2N3904
+3.3V
VDD
DXP FANOUT
MAX6670
DXN WARN
+12V
250mA
FAN
VDD
10kΩ
VDD
10kΩ
Pin Configuration appears at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
HYST
OT
GND PGND FORCEON
VDD
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
Remote Temperature Switches with Integrated
Fan Controller/Driver
trip temperature. As the cooling fan operates, the cir-
cuit board temperature should decrease, which causes
the external P-N junction’s temperature to decrease.
When the P-N junction’s temperature is equal to the trip
threshold minus the hysteresis, the FANOUT pin turns
the fan off, removing power from the fan. For the
MAX6670, HYST is a three-level logic input for control-
ling the fan-drive comparator’s hysteresis. Connect
HYST to GND to select 4°C hysteresis, to VDD to select
12°C hysteresis, or leave floating to select 8°C hystere-
sis. The MAX6668 has a built-in hysteresis of 8°C. This
allows the amount of hysteresis to be matched to the
cooling and noise requirements of the system. Figure 1
shows the temperature trip threshold hysteresis.
Applications Information
Remote-Diode Selection
The MAX6668/MAX6670 directly measure the die tem-
perature of CPUs and other ICs that have on-board tem-
perature-sensing diodes (see Typical Operating Circuit)
or they can measure the temperature of a discrete
diode-connected transistor. For best accuracy, the dis-
crete transistor should be a small-signal device with its
collector and base connected together. Several satisfac-
tory discrete sensing transistors are shown in Table 1.
The sensing transistor must be a small-signal type with
a relatively high forward voltage. Otherwise, the DXP
input voltage range may be violated. The forward volt-
age at the highest expected temperature must be
greater than 0.25V at 10µA, and at the lowest expected
temperature, forward voltage must be less than 0.95V
www.Daatta1S0he0eµt4AU..cDomo not use large power transistors. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < BF < 150,
for example) indicate that the manufacturer has good
process controls and that the transistors have consis-
tent VBE characteristics.
Noise-Filtering Capacitor
In noisy environments, high-frequency noise can be
attenuated using an external 2200pF capacitor located
at the DXP and DXN pins. Larger capacitor values may
be used for additional filtering, but do not exceed
3300pF; excessive capacitance increases error. Figure
2 shows the recommended DXP/DXN PC traces.
Bypassing and Layout
The location of the remote-sensing junction in the sys-
tem affects the MAX6668/MAX6670s’ operation. When
using a discrete temperature-sensing transistor, place
the sensing junction close to major heat-generating
components, such as a high-speed CPU or a power
device.
Table 1. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
Central Semiconductor (USA)
ON Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
Zetex (England)
MODEL NO.
CMPT3904
2N3904, 2N3906
SST3904
KST3904-TF
SMBT3904
FMMT3904CT-ND
To minimize noise and other errors, follow the guide-
lines below:
1) Place the MAX6668/MAX6670 as close as possible to
the remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 10cm to
20cm (typ) or more as long as the worst noise
sources (such as CRTs, clock generators, memory
buses, and ISA/PCI buses) are avoided. In general,
minimize the distance to the remote-sensing junction.
2) Do not route the DXP/DXN traces next to the deflec-
tion coils of a CRT. Also, do not route the traces
across a fast memory bus, which can introduce
+30°C error or more, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any high-
voltage traces, such as +12VDC. Avoid leakage cur-
rents from PC board contamination, since a 20MΩ
leakage path from DXP to GND causes about +1°C
error.
4) Connect guard traces to GND on either side of the
DXP/DXN traces (Figure 2). With guard traces in
place, routing near high-voltage traces is no longer
an issue.
5) Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects.
6) Use wide traces where possible. Narrow traces are
more inductive and tend to pick up radiated noise.
7) Do not use copper as an EMI shield. Only ferrous
materials such as steel work well. Placing a copper
ground plane between the DXP/DXN traces and
other traces carrying high-frequency noise signals
does not help reduce EMI.
The MAX6668/MAX6670s’ PGND is the ground return
for the fan driver. Bypass VDD to GND with a 1µF
capacitor located as close to VDD as possible. Add
additional bypass capacitors for long VDD and GND
lines.
_______________________________________________________________________________________ 5
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MAX6670.PDF ] | |
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