MIC502 Datasheet, PDF(5/11 Page) Micrel Semiconductor – Fan Management IC Advance Information

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MIC502 Datasheet, PDF (5/11 Pages) Micrel Semiconductor – Fan Management IC Advance Information

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MIC502

Micrel

VOT

0.7VDD

VT1

VT2

VSLP

0.3VDD

VIH

VIL

40%

60%

30%

100%

PWM

Range

20%

VOTF

VOH

VOL

VOUT

VOH

VOL

tSTARTUP

tPWM

100%

40%

60%

100%

30%

Output

Duty Cycle

VDD

Figure 2. MIC502 Typical Power-Up System Behavior

Note H. At power-on, the startup timer forces OUT on for 64 PWM cycles of the internal timebase (tPWM). This insures that the fan will start from a

dead stop.

Note I.

Note J.

Note K.

Note L.

Note M.

Note N.

Note O.

The PWM duty-cycle follows the higher of VT1 and VT2, in the case, VT1.

The PWM duty-cycle follows VT1 as it increases.

PWM duty-cycle is 100% (OUT constantly on) anytime VT1 > VPWM(max).

/OTF is asserted anytime VT1 > VOT. (The fan continues to run at 100% duty-cycle.)

/OTF is deasserted when VT1 falls below VOT; duty-cycle once again follows VT1.

Duty-cycle follows VT1 until VT1 < VT2, at which time VT2 becomes the controlling input signal. Note that VT1 is below VSLP but above VIH; so

normal operation continues. (Both VT1 and VT2 must be below VSLP to active sleep mode.)

All functions cease when VT1 < VIL; this occurs regardless of the state of VT2.

May 1999

167

MIC502

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