MIC502 datasheet(10/15 Pages) MICREL

10 / 15 page

Micrel, Inc.

MIC502

November 2006

M9999-112206

Normal Operation

Normal operation consists of the PWM operating to

control the speed of the fan according to VT1 and VT2.

Exceptions to this otherwise indefinite behavior can be

caused by any of three conditions: VT1 exceeding VOT,

an overtemperature condition; VT1 being pulled below VIL

initiating a device shutdown and reset; or both VT1 and

VT2 falling below VSLP, activating sleep mode. Each of

these exceptions is treated as follows:

Overtemp?

VT1 >VOT

NORMAL

OPERATION

VT1 and VT2

<VSLEE P

OUT Duty Cycl

Proportional to

Greater of VT1, VT2

YES

Assert /OTF while

VT1 >VOT

Reset?

VT1 <VIL

POWER ON

SL EEP

YES

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. (VT1 > VOT) Overtemperature

detection is essentially independent of other

operations — the PWM continues its normal

behavior; with VT1 > VPWM(max), the output duty-cycle

will be 100%. If VT1 falls below VOT, 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 VT1 is driven below VIL an

immediate, asynchronous shutdown occurs. While in

shutdown mode, OUT is off (low), and /OTF is

unconditionally

inactive

(high/floating).

VT1

subsequently rises above VIH, 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 VT1 and VT2 fall below VSLP, the device

enters sleep mode. All internal functions cease

unless VT1 or VT2 rise above VWAKE. (VWAKE = VSLP +

VHYST). The /OTF output is unconditionally inactive

(high/floating) and the PWM is disabled during sleep

(OUT will float).

Sleep Mode

During normal operation, if VT1 and VT2 fall below VSLP,

the device will go into sleep mode and fan operation will

stop. The MIC502 will exit sleep mode when VT1 or VT2

rise above VSLP by the hysteresis voltage, VHYST. 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.)

Disable PWM

Reset Released

VT1 >VIH

SL EEP

Reset Initiate

VT1 <VIL

YES

Wake Up?

VT1 or VT2 >

VSLP+VHYST

POW E R ON

YES

Figure 5. Sleep-Mode Behavior

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