MIC502 Datasheet, PDF (8/11 Pages) Micrel Semiconductor – Fan Management IC Advance Information

MIC502
Normal Operation
Normal operation consists of the PWM operating to control
the speed of the fan according to V_T1 and V_T2. Exceptions to
this otherwise indefinite behavior can be caused by any of
three conditions: V_T1 exceeding V_OT, an overtemperature
condition; V_T1 being pulled below V_IL initiating a device
shutdown and reset; or both V_T1 and V_T2 falling below V_SLP,
activating sleep mode. Each of these exceptions is treated as
follows:
NORMAL
OPERATION
Micrel
Sleep Mode
During normal operation, if V_T1 and V_T2 fall below V_SLP, the
device will go into sleep mode and fan operation will stop. The
MIC502 will exit sleep mode when V_T1 or V_T2 rise above V_SLP
by the hysteresis voltage, V_HYST. When this occurs, normal
operation will resume. The resumption of normal operation
upon exiting sleep is indistinguishable from a power-on reset.
(See “Sleep: Normal Operation,” above.)
SLEEP
Reset?
V_T1 < V_IL
?
NO
YES
POWER ON
V_T1 and V_T2
< V_SLEEP
?
NO
YES
SLEEP
Overtemp?
V_T1 > V_OT
?
NO
YES
Assert /OTF while
V_T1 > V_OT
OUT Duty Cycle
Proportional to
Greater of V_T1, V_T2
Figure 4. Normal System Behavior
• Overtemperature: If the system temperature rises
typically 7% above the 100% duty-cycle operating point,
/OTF will be activated to indicate an overtemperature
fault. (V_T1 > V_OT) Overtemperature detection is essen-
tially independent of other operations—the PWM
continues its normal behavior; with V_T1 > V_PWM(max), the
output duty-cycle will be 100%. If V_T1 falls below V_OT,
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.
• Shutdown/Reset: If V_T1 is driven below V_IL an immedi-
ate, asynchronous shutdown occurs. While in shutdown
mode, OUT is off (low), and /OTF is unconditionally
inactive (high/floating). If V_T1 subsequently rises above
V_IH, a device reset will occur. Reset is indistinguishable
from a power-up condition. The state of /OTF is cleared,
a startup interval is triggered, and normal fan operation
begins.
• Sleep: If V_T1 and V_T2 fall below V_SLP, the device enters
sleep mode. All internal functions cease unless V_T1 or
V_T2 rise above V_WAKE. (V_WAKE = V_SLP + V_HYST.) The
/OTF output is unconditionally inactive (high/floating)
and the PWM is disabled during sleep. (OUT will float.)
Disable PWM
Reset Initiated
V_T1 < V_IL
NO
?
YES
NO
Reset Released
V_T1 > V_IH
?
YES
Wake Up?
V_T1 or V_T2 >
NO
V_SLP+V_HYST
?
YES
POWER ON
Figure 5. Sleep-Mode Behavior
MIC502
170
May 1999