MAX1253 Datasheet, PDF(23/29 Page) Maxim Integrated Products – Stand-Alone, 10-Channel, 12-Bit System Monitors with Internal Temperature Sensor and VDD Monitor

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MAX1253 Datasheet, PDF (23/29 Pages) Maxim Integrated Products – Stand-Alone, 10-Channel, 12-Bit System Monitors with Internal Temperature Sensor and VDD Monitor

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Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and VDD Monitor

ential, or unipolar/bipolar), carry out the following steps

to execute a manual conversion. See Figure 9 for man-

ual conversion timing:

1) Disable autoscan (set up register scan mode bit to

zero), if necessary.

2) Pull CS low.

3) Initiate a conversion by issuing a Manually Triggered

Conversion command (0000, followed by the

address bits of the channel to be converted).

4) Pull CS high to start the conversion.

5) Maintain a logic high on CS to allow for reference

power-up (if the reference mode requires it) and

conversion time.

6) Pull CS low.

7) Issue a Read Current Data Register for Selected-

Channel command (0010, followed by the same

address of the channel in the Manually Triggered

Conversion command).

Voltage Measurements

Every voltage measurement (internal VDD or external

input channel) requires 10.6Âµs to complete. If the inter-

nal reference needs to power up (reference mode =

01), an additional 40Âµs is required every time the

MAX1253/MAX1254 come out of automatic shutdown

mode after a sample wait period greater than 80Âµs.

Monitoring VDD

This internal acquisition channel samples and converts

the supply voltage, VDD.

VDD value can be calculated from the digitized data

with the following equation:

VDD

(current

data

content)

ï£«

ï£ï£¬

VREF

4096

ï£¶

ï£¸ï£·

The reference voltage must be larger than 1/2VDD for

the operation to work properly. VDD monitoring requires

10.6Âµs (typ) per measurement.

Temperature Measurement

The MAX1253/MAX1254 perform temperature measure-

ment by measuring the voltage across a diode-con-

nected transistor at two different current levels. The

following equation illustrates the algorithm used for

temperature calculations:

temperature

(VHIGH -

VLOW)

x ln

ï£® IHigh ï£¹

ï£°ï£¯ILOW ï£»ï£º

where:

VHIGH = sensor-diode voltage with high current flowing

(IHIGH)

VLOW = sensor-diode voltage with low current flowing

(ILOW)

q = charge of electron = 1.602 â 10-19 coulombs

k = Boltzman constant = 1.38 â 10-23 J/K

n = ideality factor (slightly greater than 1)

tPU+CONV

SCLK

DIN

C3 C2 C1 C0 A3 A2 A1 A0

DOUT

Figure 9. Manual Conversion Timing Without Reading Data

______________________________________________________________________________________ 23

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