MIC502 Micrel Semiconductor, MIC502 Datasheet - Page 7

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

Functional Description
Oscillator
A capacitor connected to CF determines the frequency of the
internal time base which drives the state-machine logic and
determines the PWM frequency. This operating frequency
will be typically 30Hz to 60Hz. (C
Pulse-Width Modulator
A triangle-wave generator and threshold detector comprise
the internal pulse-width modulator (PWM). The PWM’s out-
put duty-cycle is determined by the higher of V
typical voltage range of 30% to 70% of V
and VT2 pins corresponds to 0% to 100% duty-cycle. Since
at least one of the control voltage inputs is generally from a
thermistor-resistor divider connected to V
put duty cycle will not be affected by changes in the supply
voltage.
Driver Output
OUT is a complementary push-pull digital output with asym-
metric drive (approximately 10mA source, 1mA sink—see
“Electrical Characteristics”). It is optimized for directly driving
an NPN transistor switch in the fan’s ground-return. See
“Applications Information” for circuit details.
Shutdown/Reset
Internal circuitry automatically performs a reset of the MIC502
when power is applied. The MIC502 may be shut down at any
time by forcing V
accomplished by connecting the VT1 pin to open-drain or
open-collector logic and results in an immediate and asyn-
chronous shutdown of the MIC502. The OUT and /OTF pins
will float while V
If V
equivalent to a power-up condition: the state of /OTF is
cleared, a startup interval is triggered, and normal fan opera-
tion begins.
Startup Interval
Any time the fan is started from the off state (power-on or
coming out of sleep mode or shutdown mode), the PWM
output is automatically forced high for a startup interval of 64
will commence and the duty-cycle of the output will be
determined by the higher of V
Overtemperature Fault Output
/OTF is an active-low, open-collector logic output. An over-
temperature condition will cause /OTF to be asserted. An
overtemperature condition is determined by V
the normal operating range of 30% to 70% of V
V
higher than V
Sleep Mode
When V
capable of operating without fan cooling and the MIC502
enters sleep mode and discontinues fan operation. The
threshold where the MIC502 enters sleep mode is deter-
mined by V
sleep mode.
May 1999
MIC502
t
DD
PWM
T1
. Note that V
then rises above V
. Once the startup interval is complete, PWM operation
T1
and V
SLP
PWM(max)
. Connecting the VSLP pin to ground disables
T1
T1
T2
OT
is below V
below its V
fall below V
is guaranteed by design to always be
.
IH
, a device reset occurs. Reset is
IL
T1
.
IL
SLP
or V
F
threshold. This is typically
= 0.1 F for 30Hz.)
, the system is deemed
T2
DD
.
DD
applied to the VT1
, the PWM out-
DD
T1
T1
exceeding
by > 7% of
or V
T2
. A
169
Once in sleep mode, all device functions cease (/OTF in-
active, PWM output off) unless V
(V
esis added to the sleep comparator which prevents erratic
operation around the V
stable and predictable thermostatic action: whenever pos-
sible the fan is shut down to reduce energy consumption and
acoustic noise, but will always be activated if the system
temperature rises.
If the device powers-up or exits its reset state, the fan will not
start unless V
System Operation
Power Up
•
•
•
•
•
WAKE
A complete reset occurs when power is applied.
OUT is off (low) and /OTF is inactive (high/floating).
If V
The startup interval begins. OUT will be on (high) for 64
clock cycles (64
Following the startup interval, normal operation begins.
T1
NO
= V
< V
SLP
Reset Startup Timer;
OUT Held On (High)
T1
IL
Figure 3. Power-Up Behavior
Deassert OUT
Deassert /OTF;
OUT Off (Low).
Startup Interval
, the MIC502 remains in shutdown.
During Startup
(OUT = Low)
+ V
POWER ON
or V
V
V
Finished
Interval.
T1
T1
YES
HYST
NO
NO
> V
?
?
?
< V
T2
OT
t
IL
PWM
rises above V
.) V
SLP
HYST
).
operating point. The result is
YES
YES
T1
is a fixed amount of hyster-
or V
OPERATION
Assert /OTF While
WAKE
NORMAL
T2
V
T1
rise above V
> V
.
OT
MIC502
WAKE
Micrel
.