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M
TC670
Tiny Predictive Fan Failure Detector
Features
General Description
• Fan Wear-Out Detection for 2-Wire
Linear-Controlled Fans
• Replacement System for 3-Wire Fans
• Fan Alert Signal when Fan Speed is below
Programmed Threshold
• CLEAR Capability for Eliminating False Alarm
• Low Operating Current, 90 µA (typ.)
• VDD Range 3.0V to 5.5V
• Available in a 6-Pin SOT-23 Package
The TC670 is an integrated fan speed sensor that
predicts and/or detects fan failure, preventing thermal
damage to systems with cooling fans. When the fan
speed falls below a user-specified level, the TC670
asserts an ALERT signal. With this design, a critical
minimum fan speed is determined by the user. The fan
alert level is then set with a resistor divider on the
THRESHOLD pin (Pin 1) of the TC670. When the
minimum fan speed is reached, the ALERT pin (Pin 5)
changes from a digital high to low. This failure detection
works with all linear-controlled 2-wire fans. The TC670
eliminates the need for 3-wire fan solutions.
Applications
•
•
•
•
•
•
•
A CLEAR option can be used to reset the ALERT signal, allowing the flexibility of connecting the ALERT
output of the TC670 with other ALERT/FAULT interrupts in the system. This feature can be implemented
so that false fan fault conditions do not initiate system
shutdown.
Protection for Linear-Controlled Fans
Power Supplies
Industrial Equipment
PCs and Notebooks
Data Storage
Data Communications Equipment
Instrumentation
The TC670 is specified to operate over the full
industrial temperature range of -40°C to +85°C. The
TC670 is offered in a 6-pin SOT-23 pin package and
consumes 90 µA (typ.) during operation. The spacesaving package and low power consumption make this
device an ideal choice for systems requiring fan speed
monitoring.
Package Type
THRESHOLD
1
GND
2
CLEAR
3
TC670
SOT-23A-6
6
SENSE
5
ALERT
4
VDD
Typical Application Circuit
+5V
ALERT
LED
4 V
DD
R4
0.1 µF
3
CLEAR
From
R3
Microcontroller
1
R2
C
THRESHOLD
6 SENSE
SENSE
GND
2
 2003 Microchip Technology Inc.
+12V
ALERT 5
DC
DC
FAN
FAN
RSENSE
DS21688C-page 1
TC670
1.0
ELECTRICAL
CHARACTERISTICS
TABLE 1-1:
PIN FUNCTION TABLE
Symbol
THRESHOLD
Absolute Maximum Ratings†
GND
VDD...................................................................................6.0V
CLEAR
All Inputs and Outputs. ............ (GND − 0.3V) to (VDD + 0.3V)
VDD
Output Short-Circuit Current .................................continuous
Description
Analog Input
Ground Terminal
Digital Input
Bias Supply Input
Current at Input Pin ................................................... +/-2 mA
ALERT
Digital (Open-Drain) Output
Current at Output Pin .............................................. +/-25 mA
SENSE
Analog Input
Junction Temperature, TJ ............................................. 150°C
ESD protection on all pins ..................................................≥ 4 kV
Operating Temperature Range........................-40°C to +85°C
Storage Temperature Range.........................-55°C to +150°C
† Notice: Stresses above those listed under "Maximum
Ratings" may cause permanent damage to the device. This is
a stress rating only and functional operation of the device at
those or any other conditions above those indicated in the
operation listings of this specification is not implied. Exposure
to maximum rating conditions for extended periods may affect
device reliability.
DC CHARACTERISTICS
Electrical Specifications: Unless otherwise specified, all limits are specified at +25°C, VDD = 3.0V to 5.5V,
CLEAR = Low. Boldface type specifications apply for temperature range of -40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
Conditions
Supply Voltage
VDD
3.0
—
5.5
V
Supply Current
IDD
—
90
150
µA
Logic Input High Level
VIH
0.8VDD
—
—
V
Logic Input Low Level
VIL
—
—
0.2VDD
V
VTH(SENSE)
—
124
—
mV
RSENSE
—
50
—
kΩ
Input Voltage Minimum
—
0.0
—
V
Input Voltage Maximum
—
2.4
—
V
Input Resistance
—
100
—
MΩ
ALERTACC
-10
—
+10
%
VDD = 3.0V
Output Low Voltage
VLOW
—
—
0.3
V
ISINK = 2.5 mA
Output Delay Time
tDELAY
—
176
—
ms
Specified Temperature Range
TA
-40
—
+85
°C
Operating Temperature Range
TA
-40
—
+125
°C
θJA
—
230
—
°C/W
Power Supply
CLEAR Input
SENSE Input
Input Level Threshold Voltage
Input Resistance
THRESHOLD Input
Programmed Fan Speed Alert Accuracy
(Note 1)
ALERT Output
Temperature Ranges
Thermal Package Resistances
Thermal Resistance, 6L-SOT-23
Note 1: The TC670 will operate properly over the entire power supply range of 3.0V to 5.5V. As VDD varies from
3.0V, accuracy will degrade based on the percentage of VDD, as shown in Section 2.0, “Typical
Performance Curves”.
DS21688C-page 2
 2003 Microchip Technology Inc.
TC670
2.0
TYPICAL PERFORMANCE CURVES
Note:
The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
Note: Unless otherwise indicated, all limits are specified at +25°C, VDD = 3.0V to 5.5V, CLEAR = Low.
115
110
160
+90°C
100
+25°C
95
90
-45°C
85
140
ALERT VOUT LOW (mV)
Supply Current (µA)
105
80
75
100
80
60
40
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
5.7
VDD = 5.5V
20
0
0.5
70
2.7
VDD = 3.0V
120
1
1.5
Supply Current vs. Supply
VDD = 3.0V
VDD = 2.7V
VDD = 3.3V
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
177
VDD = 5.5V
VDD = 5.0V
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
THRESHOLD Voltage (V)
FIGURE 2-3:
Voltage.
Fan Speed vs. Threshold
 2003 Microchip Technology Inc.
Fan Speed vs. ALERTACC.
FIGURE 2-5:
VDD = 3.6V
0.25
4.5
ALERTACC (%)
ALERT Output Delay Time (ms)
Fan Speed (RPM)
0.00
4
2.50
Fan Speed vs. Threshold
15000
14000
13000
12000
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
3.5
13000
12000
TA = -40˚C
11000
TA = +25˚C
10000
9000
8000
TA = +90˚C
7000
6000
5000
VDD = 3.0V
4000
3000
-10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0
THRESHOLD Voltage (V)
FIGURE 2-2:
Voltage.
3
ALERT VLOW vs. ALERT
FIGURE 2-4:
ISINK.
FAN SPEED (RPM)
Fan Speed (RPM)
15000
14000
13000
12000
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
2.5
ALERT ISINK (mA)
Supply Voltage (V)
FIGURE 2-1:
Voltage.
2
6.0
176
175
174
173
172
171
170
169
168
2.5
3.0
3.5
4.0
4.5
5.0
Power Supply Voltage (VDD)
FIGURE 2-6:
ALERT Output Delay vs.
Power Supply Voltage.
DS21688C-page 3
TC670
Note: Unless otherwise indicated, all limits are specified at +25°C, VDD = 3.0V to 5.5V, CLEAR = Low.
FIGURE 2-7:
CLEAR pin high to ALERT
pin high Timing Diagram.
DS21688C-page 4
 2003 Microchip Technology Inc.
TC670
3.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1:
PIN FUNCTION TABLE
Pin
No.
Symbol
1
THRESHOLD
2
GND
3
CLEAR
4
VDD
5
ALERT
Digital (Open-Drain) Output
6
SENSE
Analog Input
Description
Analog Input
Ground Terminal
Digital Input
Bias Supply Input
3.3
Digital Input (CLEAR)
The CLEAR input is used to reset or blank the ALERT
output. When the CLEAR input is driven high, the
ALERT output will be high-impedance (the ALERT
output requires a pull-up resistor).
3.4
Bias Supply Input (VDD)
Bias Supply Input, 3.0V to 5.5V. The bias supply input
should be bypassed to ground with a 0.1 µF ceramic
capacitor.
3.5
Digital (Open-Drain) Output
(ALERT)
The voltage set at the THRESHOLD input represents
the fan speed at which the TC670 will signal a fan
speed warning by pulling the ALERT output low. The
threshold voltage to fan speed correlation can be seen
in Figures 2-2 and 2-3.
The ALERT output is an open-drain output that
requires an external pull-up resistor. The ALERT output
is pulled low when the sensed fan speed (detected by
the pulses occurring at the SENSE input) falls below
the speed that is represented by the voltage at the
THRESHOLD pin. The ALERT output is latched in this
state until power is cycled or the CLEAR input is
toggled.
3.2
3.6
3.1
Analog Input (THRESHOLD)
Ground (GND)
The GND pin (Pin 2) of the TC670 should be connected
directly to the analog ground plane of the circuit board.
Care should be taken to keep this pin away from
switching signals, such as the fan excitation signals in
order to avoid false signals on the SENSE pin.
 2003 Microchip Technology Inc.
Analog Input (SENSE)
Voltage pulses, which are generated by the fan current
flowing through a sense resistor, are detected at the
SENSE pin and used to calculate the fan speed.
DS21688C-page 5
TC670
4.0
DETAILED DESCRIPTION
+5V
The TC670 is an integrated fan speed sensor that
predicts/detects fan failure, consequently preventing
thermal damage to systems with cooling fans. When
the fan speed falls below a user-programmed threshold
level, the TC670 asserts an ALERT signal. This
threshold is set with an external resistor divider
network.
1
ALERT
Logic
R2
Frequency-toVoltage
GND
Bandgap
Oscillator
50 kΩ
C
THRESHOLD
6 SENSE
SENSE
DC
FAN
FAN
RSENSE
SENSE
124 mV
TC670 Block Diagram.
As shown in Figure 4-1, the TC670 senses the fan
pulses and internally converts those pulses from a
frequency into an analog voltage. This voltage is then
compared with the DC voltage at the THRESHOLD pin.
If the converted frequency-to-voltage value from the
fan's pulses falls below the threshold voltage, the
ALERT output is pulled low.
In a 3.0V system, the external fan alert level on the
THRESHOLD pin can be designed from 0.0V (stalled
fan) to 2.4V (for 13,000 RPM) to cover most of the common fan speeds. This failure detection system works
with linear-controlled 2-wire fans and eliminates the
need for 3-wire fans. The TC670 can also work with
3-wire fans either by using the SENSE circuit or by
directly sensing the RPM output from the 3rd wire.
A CLEAR pin is provided to allow the user to reset the
ALERT pin status back to a high state. This clear option
also allows the flexibility of connecting the ALERT output of the TC670 with other alert/fault interrupts in the
system without having a risk of a system shutdown due
to false fan fault condition.
DS21688C-page 6
+12V
ALERT 5
GND
2
Note: This typical application circuit uses a LED to
indicate that a fan failure has occurred.
FIGURE 4-2:
FIGURE 4-1:
CLEAR
R3
CLEAR
THRESHOLD
R4
0.1 µF
3
VDD
ALERT
LED
4 V
DD
4.1
Typical Application Circuit.
SENSE Input
As shown in Figure 4-2, the SENSE input (Pin 6) is
connected to the sense resistor (RSENSE) through a
capacitor (CSENSE). The low value current sensing
resistor (R SENSE) is connected between the ground
return leg of the fan and the fan bias ground. During
normal fan operation, commutation occurs as each
pole of the fan is energized. This causes the fan current
to be an AC waveform with fast falling edges.
These short, rapid changes in fan current cause a
corresponding dV/dt voltage across the sense resistor,
as well as a corresponding dI/dt current through the
sense capacitor. The current through CSENSE is terminated with the internal 50 kΩ input resistance at the
SENSE pin of the TC670. When positive-going fan
pulses at the SENSE input are greater than 124 mV
(typ.), the TC670 latches-in those voltage spikes. This
124 mV (typ.) SENSE input built-in threshold reduces
false triggering errors caused by extraneous noise
pulses associated with a running fan. The presence
and frequency of these pulses is a direct indication of
fan operation and fan speed.
 2003 Microchip Technology Inc.
TC670
The design of the proper input SENSE circuitry is a
matter of scaling RSENSE to provide the necessary
amount of gain and proper selection of the sensing
capacitor. The following table (Table 4-1) lists some
recommended values for RSENSE according to the
nominal operating current of the fan. Please note that
the current draw specified by the fan manufacturer may
be a worst-case rating and not the fan’s nominal operating current. If the fan current falls between two of the
values listed, it is recommended that the higher value
resistor is used.
TABLE 4-1:
RECOMMENDED VALUES
FOR RSENSE PER FIGURE 4-2
Nominal Fan Current
(mA)
RSENSE (Ω)
100
4.7
200
2.4
300
1.8
400
1.3
500
1.0
600
0.8
4.2.1
THRESHOLD CALIBRATION USING
FAN’S FULL SCALE SPEED
The fan should first be run at full speed. At full speed,
the threshold voltage level should be adjusted until the
ALERT output is asserted. With this full-scale value of
the threshold voltage, the value can be scaled down to
the fan fault speed as a percentage of the full speed.
For example, if the fan full speed threshold voltage is
1.5V, then the fan fault threshold voltage at 30% of full
speed would be 30% x 1.5V = 0.45V.
4.2.2
THRESHOLD CALIBRATION USING
FAN’S MINIMUM ALLOWABLE
SPEED ESTIMATE
For a more exact fan fault trip point, the user can run
the fan at its minimum allowed speed. At this speed,
the threshold voltage can be adjusted until the ALERT
output is asserted.
4.3
CLEAR Input
A 0.1 µF ceramic capacitor is recommended for
CSENSE. Smaller capacitor values will require larger
sense resistors, whereas larger capacitors are more
expensive and occupy more board space.
The CLEAR input allows the user to reset the ALERT
pin to a high status. This is an active-high input.
Consequently, as long as CLEAR is high, ALERT will
always be high as well. To allow ALERT to operate correctly, CLEAR must be held low. This feature can be
implemented so that false fan fault conditions do not
initiate system shutdown.
4.2
4.4
THRESHOLD Input
The voltage at the THRESHOLD input sets the
equivalent minimum allowable fan speed for the application. As shown in Section 2.0, “Typical Performance
Curves”, the relationship between the threshold voltage and minimum fan speed is also power supply and
temperature dependant.
All the values for the threshold voltage that are shown
in these graphs represent typical numbers and might
not be optimized for all fans in all applications. To
ensure accurate fan speed monitoring of a specific fan
in a specific application, the user must perform a onetime correlation check with the prototype.
There are two techniques that can be used to calibrate
the system. One approach is to find the fan’s full-scale
capability and mathematically estimate the minimum
acceptable speed of the fan. A second technique is to
identify the fan’s minimum speed and calibrate the
threshold voltage accordingly.
ALERT Output
The ALERT output is an open-drain output capable of
sinking 2.5 mA (typ). The ALERT output is asserted
whenever the detected fan speed equals or falls below
the equivalent voltage set at the threshold pin. The
ALERT output is only deactivated once the CLEAR pin
is brought to a high state. Although the absolute
maximum sink current of this pin is 25 mA, it is
recommended that the current sinking into the ALERT
output does not exceed 20 mA.
4.5
Power Supply Input (VDD)
To assure proper operation of the TC670 in a noisy
environment where the fans are running, the VDD pin
(Pin 4) must be decoupled with a 0.1 µF capacitor, as
shown in Figure 4-1. This capacitor should be located
as close to the TC670 VDD pin as possible, as well as
being promptly terminated to the ground plane. A
ceramic capacitor is recommended.
4.6
Ground Terminal (GND)
The GND pin (Pin 2) of the TC670 should be connected
directly to the analog ground plane of the circuit board.
Care should be taken to keep this pin away from
switching signals, such as the fan excitation signals in
order to avoid false signals on the SENSE pin.
 2003 Microchip Technology Inc.
DS21688C-page 7
TC670
5.0
PACKAGE INFORMATION
5.1
Package Marking Information
6-Pin SOT-23A (EIAJ SC-74) Device
6
5
4
cdef
1
2
3
1 & 2 = part number code
Part Number
Code
TC670ECH
DA
3 = year and quarter code
4 = lot ID number
5.2
Taping Form
Component Taping Orientation for 6-Pin SOT-23A (EIAJ SC-74) Devices
User Direction of Feed
Device
Marking
W
P
PIN 1
Carrier Tape, Number of Components Per Reel and Reel Size:
Package
6-Pin SOT-23A
DS21688C-page 8
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
8 mm
4 mm
3000
7 in.
 2003 Microchip Technology Inc.
TC670
5.3
Package Dimensions (6-Pin SOT-23)
E
E1
B
p1
n
D
1
α
c
A
φ
L
β
Units
Dimension Limits
n
p
MIN
A2
A1
INCHES*
NOM
MAX
MILLIMETERS
NOM
6
0.95
1.90
0.90
1.18
0.90
1.10
0.00
0.08
2.60
2.80
1.50
1.63
2.80
2.95
0.35
0.45
0
5
0.09
0.15
0.35
0.43
0
5
0
5
MIN
Number of Pins
6
Pitch
.038
p1
Outside lead pitch (basic)
.075
Overall Height
A
.035
.046
.057
Molded Package Thickness
.035
.043
.051
A2
Standoff
.000
.003
.006
A1
Overall Width
E
.102
.110
.118
Molded Package Width
.059
.064
.069
E1
Overall Length
D
.110
.116
.122
Foot Length
L
.014
.018
.022
φ
Foot Angle
0
5
10
c
Lead Thickness
.004
.006
.008
Lead Width
B
.014
.017
.020
Mold Draft Angle Top
0
5
10
α
Mold Draft Angle Bottom
0
5
10
β
*Controlling Parameter
Notes:
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not
exceed .005" (0.127mm) per side.
MAX
1.45
1.30
0.15
3.00
1.75
3.10
0.55
10
0.20
0.50
10
10
JEITA (formerly EIAJ) equivalent: SC-74A
Drawing No. C04-120
 2003 Microchip Technology Inc.
DS21688C-page 9
TC670
NOTES:
DS21688C-page 10
 2003 Microchip Technology Inc.
TC670
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
PART NO.
X
XXXX
Device
Temperature
Range
Package
Device:
TC670:
Temperature Range:
E
Package:
CHTR: = SOT-23, Small Outline Transistor, 6-lead
(Tape and Reel only)
=
Examples:
a)
TC670ECHTR: Predictive Fan Failure
Detector, SOT-23 package.
Predictive Fan Failure Detector
-40°C to +85°C
Sales and Support
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1.
2.
3.
Your local Microchip sales office
The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
 2003 Microchip Technology Inc.
DS21688C-page11
TC670
NOTES:
DS21688C-page 12
 2003 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip's Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such
acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications. No
representation or warranty is given and no liability is assumed
by Microchip Technology Incorporated with respect to the
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PowerSmart are registered trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.
FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL
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All other trademarks mentioned herein are property of their
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© 2003, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
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The Company’s quality system processes and
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 2003 Microchip Technology Inc.
DS21688C - page 13
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