MAX31790 datasheet(4/46 Pages) MAXIM

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(VCC = +3.0V to +5.5V, TA = -40°C to +125°C, timing referenced to VIL(MAX) and VIH(MIN), unless otherwise noted.) (Notes 3, 8)

(Figure 1)

(Notes 3)

Note 2: All voltages referenced to ground. Currents entering the IC are specified as positive.

Note 3: Limits are 100% production tested at TA = +25°C and/or TA = +85°C. Limits over the operating temperature range and rel-

evant supply voltage range are guaranteed by design and characterization. Typical values are not guaranteed.

Note 4: SDA = SCL = VCC, PWM active with PWM_FREQUENCY = 25kHz.

Note 5: The watchdog timer is derived from fTOSC and the watchdog timer accuracy specifications do not include the oscillator’s

associated error fERR:TOSC.

Note 6: Applies to pins SDA, SCL, PWM_STARTn, WD_START, FREQ_START, SPIN_START, ADDn, TACHn, PWMOUTn, FULL_

SPEED

Note 7: fTOSC is used to measure fan speed by counting the number of 8192Hz (fTOSC/4) clock cycles that take place during a

selectable number of tachometer periods. For internal oscillator only, typical frequency shift due to aging is within ±0.5%.

Aging stressing includes level 1 moisture reflow preconditioning (24hr +125°C bake, 168hr +85°C/85%RH moisture soak,

and three solder reflow passes +260°C +0°C/-5°C peak) followed by 192hr (max) VCC biased.

Note 8: All timing specifications are guaranteed by design.

Note 9: A master device must provide a hold time of at least 300ns for the SDA signal to bridge the undefined region of SCL’s falling

edge.

Note 10:CB—total capacitance of one bus line in pF.

Note 11:Holding the SDA line low for a time greater than tTIMEOUT causes the device to reset SDA to the idle state of the serial bus

communication (SDA set high).

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Maximum Receive SCL/SDA Fall

Time

(Note 10)

300

Minimum Receive SCL/SDA Fall

Time

(Note 10)

20 + 0.1 x CB

Transmit SDA Fall Time

10pF P CB P 400pF (Note 10)

20 +

0.1 x

250

Pulse Width of Suppressed Spike

tSP

SDA Time Low for Reset of Serial

Interface

tTIMEOUT

(Note 11)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Crystal Oscillator Startup Time

Nominal Frequency

32.768

kHz

Series Resistance

ESR

Load Capacitance

I2C AC Electrical Characteristics (continued)

External Crystal Parameters

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MAX31790

6-Channel PWM-Output Fan RPM Controller

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