MIC502YN Micrel Inc, MIC502YN Datasheet - Page 11

• 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

Application Information
The Typical Application drawing on page 1 illustrates a
typical application circuit for the MIC502. Interfacing the
MIC502 with a system consists of the following steps:
Temperature Sensor Selection
Temperature sensor T1 is a negative temperature
coefficient (NTC) thermistor. The MIC502 can be
interfaced with either a negative or positive tempco
thermistor; however, a negative temperature coefficient
thermistor typically costs less than its equivalent positive
tempco counterpart. While a variety of thermistors can
be used in this application, the following paragraphs
reveal that those with an R25 rating (resistance at 25°C)
of from about 50kΩ to 100kΩ lend themselves nicely to
an interface network that requires only a modest current
drain. Keeping the thermistor bias current low not only
indicates prudent design; it also prevents self-heating of
the sensor from becoming an additional design
consideration. It is assumed that the thermistor will be
located within the system power supply, which most
likely also houses the speed-controlled fan.
Temperature Sensor Interface
As shown by the Electrical Characteristics table, the
working voltage for input V
percentage of V
from having to be concerned with interactions resulting
from variations in the supply voltage. By design, the
operating range of V
70% of V
When V
motor-drive signal is generated. Conversely, when V
V
cycle. Resistor voltage divider R1 || T1, R2 in the Typical
Application diagram is designed to preset V
of V
speed when the resistance of thermistor T1 is at its
highest (cold) value. As temperature rises the resistance
of T1 decreases and V
parallel connection of R1 and T1.
Since V
cycle drive), and since it is foreseen that at least some
cooling will almost always be required, the lowest
voltage applied to the V
Micrel, Inc.
November 2006
PWM(min)
1. Selecting a temperature sensor
2. Interfacing the temperature sensor to the V
3. Selecting a fan-drive transistor, and base-drive
4. Deciding what to do with the Secondary Fan-
5. Making use of the Overtemperature Fault Output
PWM
current limit resistor
Control Input
T1
V
T1
DD
≈ 0.3V
PWM(min)
that corresponds to the slowest desired fan
= V
.
= V
PWM(min)
DD
DD
PWM(max)
= V
, the motor-drive signal has a 0% duty
. This conveniently frees the designer
T1
PWM(min)
represents a stopped fan (0% duty-
is from about 30%of V
≈ 0.7V
T1
– V
T1
increases because of the
PWM(span)
input will normally be
T1
DD
, a 100% duty-cycle
is specified as a
T1
DD
to a value
to about
T1
input
T1
=
11
somewhat higher than 0.3V
assumed that the system will be in sleep mode rather
than operate the fan at a very low duty cycle (<25%).
Operation at very low duty cycle results in relatively little
airflow. Sleep mode should be used to reduce acoustic
noise when the system is cool. For a given minimum
desired fan speed, a corresponding V
determined via the following observation:
since
and
then
Figure 6 shows the following linear relationship between
the voltage applied to the V
cycle, and approximate motor speed.
since
then
and
and
In addition to the R25 thermistor rating, sometimes a
datasheet will provide the ratio of R25/R50 (resistance at
25°C divided by resistance at 50°C) is given. Sometimes
this is given as an R0/R50 ratio. Other datasheet
contents either specify or help the user determine device
resistance at arbitrary temperatures. The thermistor
interface to the MIC502 usually consists of the thermistor
and two resistors.
V
V
V
V
V
V
V
Figure 6. Control Voltage vs. Fan Speed
PWM(max)
PWM(min)
PWM(span)
T1
T1
T1
T1
= 0.7V
= 0.6V
= 0.5V
= 0.4V
100
80
60
40
20
0
0
= 30% of V
= 70% of V
= 40% of V
DD
DD
DD
DD
V
T1
2 0
∝ 100% PWM
∝ 75% PWM
∝ 50% PWM
∝ 25% PWM
/SUPPLY VOLTAGE (%)
40
DD
DD
DD
T1
DD
∝ 0% RPM
∝ 100% RPM
∝ 100% RPM range.
60
input, motor drive duty
(or >V
80
M9999-112206
PWM(min)
T1(min)
100
MIC502
). It is
can be