MIC502YN Micrel Inc, MIC502YN Datasheet - Page 12

• Manufacturer Part Number: MIC502YN
• Description: IC MANAGEMENT FAN/THERMAL 8DIP
• Manufacturer: Micrel Inc

Specifications of MIC502YN

• Applications: Fan Controller
• Number Of Outputs: 1
• Current - Output: 10mA
• Voltage - Supply: 4 V ~ 13.2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Operating Current: 1.5mA
• Operating Temperature Classification: Industrial
• Package Type: PDIP
• Operating Supply Voltage (min): 4V
• Operating Supply Voltage (max): 13.2V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Load: -
• Lead Free Status / Rohs Status: Compliant
• Other names: 576-1242

Design Example
The thermistor-resistor interface network is shown in the
Typical Application drawing. The following example
describes the design process: A thermistor datasheet
specifies a thermistor that is a candidate for this design
as having an R25 resistance of 100kΩ. The datasheet
also supports calculation of resistance at arbitrary tem-
peratures, and it was discovered the candidate
thermistor has a resistance of 13.6k at 70°C (R70).
Accuracy is more important at the higher temperature
end of the operating range (70°C) than the lower end
because we wish the overtemperature fault output
(/OTF) to be reasonably accurate — it may be critical to
operating a power supply crowbar or other shutdown
mechanism, for example. The lower temperature end of
the range is less important because it simply establishes
minimum fan speed, which is when less cooling is
required.
Referring to the “Typical Application,” the following
approach can be used to design the required thermistor
interface network:
let
and
since
and
Let’s continue by determining what the temperature-
proportional voltage is at 25°C.
let
and
from
Micrel, Inc.
November 2006
R1 = ∞
R
V
0.7R
0.7R
R2 = 2.33R
R1 = ∞
R
V
0.7
V
V
V
T
T
T1
T1
T
T
T
= 0.7V
= 0.248V
= 13.6k
= 100k
=
=
=
=
T1
T1
(
(
(
(
R
R
100k
V
R
+ 0.7R2 = R2
= 0.3R2
V
DD
T1
T1
T1
DD
V
DD
R2
DD
||
+
+
×
T1
×
DD
+
R1
R2
R2
R2
33k
×
= 2.33 × 13.6k = 31.7k ≈ 33k
33k
R2
)
+
)
(at 70°C)
(70% of VDD)
(at 25°C).
R2
)
)
12
Recalling from above discussion that the desired V
25°C should be about 40% of V
24.8% is far too low. This would produce a voltage that
would stop the fan (recall from the above that this occurs
when V
value for R1 we need to learn what the parallel
combination of R
again
and
since
and
let
While that solves the low temperature end of the range,
there is a small effect on the other end of the scale. The
new value of V
This represents only a 3% shift from the design goal of
70% of V
candidate thermistor used in this design example is the
RL2010-54.1K-138-D1,
Thermometrics.
The R25 resistance (100kΩ) of the chosen thermistor is
probably on the high side of the range of potential
thermistor resistances. The result is a moderately high-
impedance network for connecting to the V
input(s). Because these inputs can have up to 1µA of
leakage current, care must be taken if the input network
impedance becomes higher than the example. Leakage
current and resistor accuracy could require consideration
in such designs. Note that the V
leakage current specification.
Secondary Fan-Control Input
The above discussions also apply to the secondary fan-
control input, V
thermistor, mounted at another temperature-critical
location outside the power supply, may be appropriate.
There is also the possibility of accommodating the NLX
“FanC” signal via this input. If a second thermistor is the
desired solution, the V
like the V
directly. If, however, the NLX FanC signal is to be
T
0.4(R
0.4(R
R
R
R
R1 = 100k
0.4
V
is about 30% of V
DD
T1
T1
T1
T
T1
. In summary, R1 = 100k, and R2 = 33k. The
=
|| R1 = 1.5R2 = 1.5 × 33k = 49.5k
= 100k
|| R1 = 49.5k ≈ 50k
=
input. The above discussions then apply
T1
T1
(
(
R
R
T
|| R1) + 0.4R2 = R2
|| R1) = 0.6R2
T2
T1
T1
for 70°C is 0.734, or about 73% of V
T1
V
, pin 5. It is possible that a second
DD
and R1 should beat 25°C:
||
||
R2
R1
R1
×
R2
T2
+
+
R2
R2
manufactured
input may be treated exactly
DD
)
)
. To choose an appropriate
SLP
DD
, the above value of
input has this same
M9999-112206
by
T1
and/or V
Keystone
MIC502
T
DD
for
T2
.