MIC502 Micrel Semiconductor, MIC502 Datasheet - Page 8

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

MIC502
Normal Operation
Normal operation consists of the PWM operating to control
the speed of the fan according to V
this otherwise indefinite behavior can be caused by any of
three conditions: V
condition; V
shutdown and reset; or both V
activating sleep mode. Each of these exceptions is treated as
follows:
• Overtemperature: If the system temperature rises
• Shutdown/Reset: If V
• Sleep: If V
MIC502
typically 7% above the 100% duty-cycle operating point,
/OTF will be activated to indicate an overtemperature
fault. (V
tially independent of other operations—the PWM
continues its normal behavior; with V
output duty-cycle will be 100%. If V
the overtemperature condition is cleared and /OTF is no
longer asserted. It is assumed that in most systems, the
/OTF output will initiate power supply shutdown.
ate, asynchronous shutdown occurs. While in shutdown
mode, OUT is off (low), and /OTF is unconditionally
inactive (high/floating). If V
V
from a power-up condition. The state of /OTF is cleared,
a startup interval is triggered, and normal fan operation
begins.
sleep mode. All internal functions cease unless V
V
/OTF output is unconditionally inactive (high/floating)
and the PWM is disabled during sleep. (OUT will float.)
IH
T2
, a device reset will occur. Reset is indistinguishable
rise above V
T1
Figure 4. Normal System Behavior
T1
> V
Greater of V
T1
OUT Duty Cycle
Proportional to
OPERATION
being pulled below V
V
Overtemp?
and V
OT
NORMAL
V
V
T1
< V
Reset?
T1
T1
and V
NO
NO
NO
) Overtemperature detection is essen-
T1
WAKE
> V
?
SLEEP
?
?
< V
OT
T1
IL
T2
exceeding V
T2
, V
T1
. (V
fall below V
T2
is driven below V
WAKE
YES
YES
YES
T1
T1
subsequently rises above
and V
T1
= V
OT
Assert /OTF while
POWER ON
SLP
and V
, an overtemperature
T1
SLP
IL
T2
SLEEP
V
T1
T1
, the device enters
falls below V
initiating a device
falling below V
> V
+ V
> V
T2
OT
IL
. Exceptions to
HYST
PWM(max)
an immedi-
.) The
T1
OT
or
, the
SLP
,
,
170
Sleep Mode
During normal operation, if V
device will go into sleep mode and fan operation will stop. The
MIC502 will exit sleep mode when V
by the hysteresis voltage, V
operation will resume. The resumption of normal operation
upon exiting sleep is indistinguishable from a power-on reset.
(See “Sleep: Normal Operation,” above.)
Figure 5. Sleep-Mode Behavior
Reset Released
Reset Initiated
Disable PWM
POWER ON
V
V
Wake Up?
V
V
T1
SLP
SLEEP
T1
T1
YES
YES
YES
or V
+V
?
> V
?
?
< V
HYST
HYST
T2
IH
IL
T1
>
and V
. When this occurs, normal
NO
T1
NO
NO
T2
or V
fall below V
T2
rise above V
May 1999
SLP
Micrel
, the
SLP