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2002 Microchip Technology Inc.
DS21688B-page 1
TC670
Features
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
A (typ.)
V
DD
Range 3.0V to 5.5V
Available in a 6-Pin SOT-23 Package
Applications
Protection for Linear Controlled Fans
Power Supplies
Industrial Equipment
PCs and Notebooks
Data Storage
Data Communications Equipment
Instrumentation
Device Selection Table
Package Type
General Description
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.
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.
The TC670 is specified to operate over the full
industrial temperature range of -40C to +85C. The
TC670 is offered in a SOT23-6 pin package and
consumes 90
A (typ) during operation. The space
saving package and low power consumption make this
device an ideal choice for systems requiring fan speed
monitoring.
Typical Application Circuit
Part Number
Package
Temp. Range
TC670ECH
6-Pin SOT-23
-40C to +85C
2
5
SOT-23A-6
THRESHOLD
GND
CLEAR
SENSE
ALERT
V
DD
1
3
6
4
T
C
6
70E
CH
From
5
6
C
SENSE
R
4
R
SENSE
+12V
ALERT
LED
DC
FAN
DC
FAN
SENSE
ALERT
2
4
3
1
+5V
R
3
R
2
0.1 F
V
DD
CLEAR
THRESHOLD
GND
Microcontroller
Tiny Predictive Fan Failure Detector
TC670
DS21688B-page 2
2002 Microchip Technology Inc.
1.0
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
V
DD
...................................................................................6.0V
All inputs and outputs w.r.t. ..... (GND
-
0.3V) to (V
DD
+ 0.3V)
Difference Input voltage ...................................... IV
DD
- GND
Output Short Circuit Current ..................................continuous
Current at Input Pin ................................................... +/-2 mA
Current at Output Pin .............................................. +/-25 mA
Junction Temperature, T
J
............................................. 150C
ESD protection on all pins
..................................................
4 kV
Operating Temperature Range........................-40C to +85C
Storage Temperature Range .........................-55C to +150C
Stresses above those listed under "Absolute Maximum Rat-
ings" may cause permanent damage to the device. These are
stress ratings only and functional operation of the device at
these or any other conditions above those indicated in the
operation sections of the specifications is not implied. Expo-
sure to Absolute Maximum Rating conditions for extended
periods may affect device reliability.
TC670 ELECTRICAL SPECIFICATIONS
TEMPERATURE SPECIFICATIONS
Electrical Characteristics: Unless otherwise specified, all limits are specified at +25C, V
DD
= 3.0V to 5.5V, CLEAR = Low.
Boldface type specifications apply for temperature range of -40C to +85C
Symbol
Parameters
Min
Typ
Max
Unit
Conditions
Power Supply:
V
DD
Supply Voltage
3.0
--
5.5
V
I
DD
Supply Current
--
90
150
A
CLEAR Input:
V
IH
CLEAR Logic Input High Level
0.8V
DD
--
--
V
V
IL
CLEAR Logic Input Low Level
--
--
0.2V
DD
V
SENSE Input:
V
TH(SENSE)
SENSE Input Level Threshold Voltage
--
124
--
mV
R
SENSE
SENSE Input Resistance
--
50
--
k
THRESHOLD Input:
THRESHOLD Input Voltage Minimum
--
0.0
--
V
THRESHOLD Input Voltage Maximum
--
2.4
--
V
THRESHOLD Input Resistance
--
100
--
M
ALERT
ACC
Programmed Fan Speed Alert Accuracy
(1)
-10
--
+10
%
V
DD
= 3.0V
ALERT Output:
V
LOW
ALERT Output Low Voltage
--
--
0.3
V
I
SINK
= 2.5 mA
t
DELAY
ALERT Output Delay Time
--
176
--
ms
Note 1:
The TC670 will operate properly over the entire power supply range of 3.0V to 5.5V. As V
DD
varies from 3.0V, accuracy will degrade
based on the percentage of V
DD
as shown in Section 3.0.
Electrical Characteristics: Unless otherwise specified, all limits are specified for -40C to +85C and V
DD
= 3.0V to 5.5V
Symbol
Parameters
Min
Typ
Max
Unit
Conditions
Temperature Ranges:
T
A
Specified Temperature Range
-40
--
+85
C
T
A
Operating Temperature Range
-40
--
+85
C
Thermal Package Resistances:
JA
Thermal Resistance, 6L-SOT-23
--
230
--
C/W
2002 Microchip Technology Inc.
DS21688B-page 3
TC670
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
Pin No.
(6-Pin SOT-23)
Symbol
Description
1
THRESHOLD
Analog Input used to set Fan ALERT Threshold Voltage. Input range = 0.0V to
2.4V.
2
GND
Ground Terminal.
3
CLEAR
Digital Input. Active High. The ALERT Output is cleared when a high level signal is
applied to this input.
4
V
DD
Power Supply Input, 3.0V to 5.5V.
5
ALERT
Digital (Open Drain) Output, active low. This pin goes low to indicate an alert
condition when the fan speed at the SENSE pin reaches the alert threshold
applied on the THRESHOLD pin.
6
SENSE
Analog Input. Current spikes are detected at this pin as the fan excitation signal
transitions from high to low and low to high.
TC670
DS21688B-page 4
2002 Microchip Technology Inc.
3.0
TYPICAL PERFORMANCE CHARACTERISTICS
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.
SUPPLY VOLTAGE (V)
SUPPL
Y CURRENT (
A)
110
105
100
95
90
85
80
75
115
70
2.7
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
5.7
6.0
Supply Current I
DD
vs. Supply Voltage (V
DD
)
vs. Temperature (T
A
)
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
THRESHOLD VOLTAGE (V)
FAN SPEED (
R
P
M
)
THRESHOLD Voltage vs. Fan Speed vs. Supply Voltage (V
DD
)
V
DD
= 3.6V
V
DD
= 3.0V
V
DD
= 3.3V
V
DD
= 5.5V
V
DD
= 5.0V
V
DD
= 2.7V
0
20
40
60
80
100
120
140
160
0.5
1
1.5
2
2.5
3
3.5
4
4.5
ALERT V
LOW
vs. ALERT I
SINK
ALERT V
OUT
LOW (mV)
ALERT I
SINK
(mA)
V
DD
= 2.7V
V
DD
= 3.0V
V
DD
= 3.6V
V
DD
= 5.0V
V
DD
= 5.5V
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
-10.0 -8.0 -6.0 -4.0 -2.0 0.0
2.0
4.0
6.0
8.0 10.0
FA
N
SPEED
(
R
PM
)
ALERT
ACC
(%)
ALERT
ACC
vs. Fan Speed vs. Temperature
V
DD
= 3.0V
T
A
= -40C
T
A
= +25C
T
A
= +90C
168
169
170
171
172
173
174
175
176
177
2.5
3.0
3.5
4.0
4.5
5.0
POWER SUPPLY VOLTAGE (V
DD
)
A
L
E
R
T O
U
TP
U
T
D
E
LA
Y
TI
ME
(m
s)
Alert Output Delay (T
DELAY
) vs.
Power Supply Voltage (V
DD
)
CLEAR Pin HIGH to ALERT pin HIGH
Timing Diagram
2002 Microchip Technology Inc.
DS21688B-page 5
TC670
4.0
DETAILED DESCRIPTION
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.
FIGURE 4-1:
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 a DC voltage present on the THRESH-
OLD pin. If the converted frequency-to-voltage value
from the fan's pulses falls below the THRESHOLD
voltage, a FAULT signal is asserted through the ALERT
pin (active LOW).
In a 3.0V system, the external fan alert level on the
THRESHOLD pin can be designed from 0.0V (stalled
fan) and up 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 work with 3-
wire fans as well 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.
FIGURE 4-2:
TYPICAL APPLICATION
CIRCUIT
4.1
SENSE Input
As shown in Figure 4-2, the SENSE input (Pin 6) is
connected through a sensing capacitor (C
SENSE
). A
low value current sensing resistor (R
SENSE
) is also
connected to the low side of the fan to the ground return
leg of the fan. During normal fan operation, commuta-
tion occurs as each pole of the fan is energized. This
causes brief interruptions in the fan current, seen as
pulses across the sense resistor.
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 across the
sense capacitor. The current across C
SENSE
is termi-
nated with the internal 50k
input resistance at the
SENSE pin of the TC670. When positive going fan
pulses at the SENSE input are greater than 124mV
(typ) the TC670 latches in those voltage spikes. This
124mV (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.
THRESHOLD
124mV
50k
SENSE
ALERT
CLEAR
Logic
Frequency to
Voltage
GND
V
DD
Bandgap
Oscillator
From
Microcontroller
5
6
C
SENSE
R
4
R
SENSE
+12V
ALERT
LED
DC
FAN
DC
FAN
SENSE
ALERT
2
4
3
1
V
DD
= +5V
R
3
R
2
0.1 F
V
DD
CLEAR
THRESHOLD
GND
V
threshold
V
TH RESHO LD
V
D D
R
2
R
2
R
3
+
----------------------
=
Note: This typical application circuit uses an LED to indicate that a
fan failure has occurred.
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