MIC502 Micrel Semiconductor, MIC502 Datasheet - Page 11

• Manufacturer Part Number: MIC502
• Description: Fan Management IC Advance Information
• Manufacturer: Micrel Semiconductor

The design consists soley of choosing the value R
Figures 7 and 8. To minimize on-chip power dissipation in the
MIC502, the value of R
power supply voltage. The Electrical Characteristics table
specifies a minimum output current of 10mA. However,
different output voltage drops (V
12V operation. The value R
possible for a given required transistor base-drive current in
order to reduce on-chip power dissipation.
Referring to the “Typical Application” and to the “Electrical
Characteristics” table, the value for R
follows. For V
guaranteed to be a minimum of 10mA with a V
R
For V
Overtemperature Fault Output
The /OTF output, pin 6, is an open-collector NPN output. It is
compatible with CMOS and TTL logic and is intended for
May 1999
MIC502
RL2010-54.1K-138-D1
Keystone Thermonics
Signal Input
NLX FanC
BASE
or similar
DD
Figure 7. Typical 5V V
R3
56k
R4
56k
then equals (2.4V – V
= 12V systems, R
33k
T1
R2
0.1µF
C
R1
100k
F
DD
= 5V systems, I
1
2
3
4
VT1
CF
VSLP
GND
BASE
MIC502
BASE
VDD
OUT
OTF
BE
VT2
should be determined by the
DD
BASE
120k
)
= (3.4 – 0.7)
DD
8
7
6
5
Application Circuit
5V
10mA = 170 .
– V
should be as high as
OH
100k
BASE
47k
OUT
R
180
of OUT (pin 7) is
BASE
Overtemperature
Fault Output
) exist for 5V vs.
is calculated as
12V
0.01 = 250 .
Q1
OH
Yate Loon
YD80SM-12
or similar fan
of 2.4V.
BASE
in
173
alerting a system about an overtemperature condition or
triggering a power supply crowbar circuit. If V
MIC502 is 5V the output should not be pulled to a higher
voltage. This output can sink up to 2mA and remain compat-
ible with the TTL logic-low level.
Timing Capacitors vs. PWM Frequency
The recommended C
at a PWM frequency of 30Hz. This frequency is factory
trimmed within 3Hz using a 0.1% accurate capacitor. If it is
desired to operate at a different frequency, the new value for
C
The composition, voltage rating, ESR, etc., parameters of the
capacitor are not critical. However, if tight control of frequency
vs. temperature is an issue, the temperature coefficient may
become a consideration.
RL2010-54.1K-138-D1
Keystone Thermonics
Signal Input
NLX FanC
F
is calculated as follows:
or similar
Figure 8. Typical 12V V
C =
R3
56k
R4
56k
33k
3
T1
R2
0.1µF
f
, where C is in F and f is in Hz.
C
R1
100k
F
F
1
2
3
4
(see first page) is 0.1 F for opertaion
VT1
CF
VSLP
GND
MIC502
VDD
OUT
OTF
VT2
DD
8
7
6
5
12V
Application Circuit
4.7k
5V
47k
R
280
BASE
Overtemperature
Fault Output
Q1
DD
Yate Loon
YD80SM-12
or similar fan
MIC502
for the
Micrel