MIC502_06 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – Fan Management IC

Micrel, Inc.
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
Reset?
V_T1 < V_IL
?
NO
YES
POWER ON
V_T1 and V_T2
< V_{S L E E P}
?
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 essentially 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
immediate, 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.
MIC502
• 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).
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
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_{S L P}+V_{H Y S T}
?
YES
POWER ON
Figure 5. Sleep-Mode Behavior
November 2006
10
M9999-112206