LTC2949 datasheet(69/80 Pages) AD

69 / 80 page

LTC2949

Rev A

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APPLICATION INFORMATION

The following linear equation system has to be solved to

calculateA,B,Cusingthreevalues,R1(T1),R2(T2),R3(T3)

from a R versus T (in K) resistor table:

T1−

T2−

T3−

⎛

⎝

⎜

⎞

⎠

⎟

1 ln R1 ln

3 R1

1 ln R2 ln

3 R2

1 ln R3 ln3 R3

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

After solving the linear equation system, A, B, C can be

expressed as:

l1=lnR1

l2 =lnR2

l3 =lnR3

m2 =

T2−

1−T1−1

l2 −l1

m3 =

T3−

1−T1−1

l3 −l1

C =

m3 −m2

l3 −l2

l3 +l2 +l1

B=m2 −C•(l1

2 +l1•l2+l22)

A = T1−

1−(B+l12•C)•l1

SENSE RESISTOR TEMPERATURE COMPENSATION

The LTC2949 can be configured to compensate the tem-

perature dependency of the used current sense resistors

up to 2nd order based on temperature measurements with

external NTCs. The compensation is enabled by writing

thetemperaturecoefficients(TC,TC2)ofthesenseresistor

and the reference temperature (T0) in the NTC configura-

tion register. The LTC2949 will then compensate for the

temperature induced deviation of the sense resistor from

its nominal value R0 according to:

RSENSE =RO •[1+TC •(T−TO)+TC2• T−T0

(

)

2 ]

The temperature coefficient and reference temperature

can be set for each sense resistor individually in the NTC

configuration register. Table 76 shows the programmed

coefficients for a copper sense resistor with a temperature

coefficient of 3900ppm/K whose nominal value R0 was

measured at 20°C.

If temperature compensation is enabled for one or both

channels, the sense resistor connected to CH1 is compen-

sated with the temperature of NTC1 measured during the

first slot of CHAUX, while the sense resistor connected to

CH2 is compensated with the temperature of NTC2 mea-

sured during the second slot of CHAUX. The multiplexer

settings must be set such that the input pin connected

to the corresponding NTC is selected during the respec-

tive slot. If CHAUX is changed to fast mode, the last NTC

temperature measurements taken in Round Robin mode

are used for temperature compensation.

LTC2949 Datasheet(PDF) 69 Page - Analog Devices

LTC2949 Datasheet(HTML) 69 Page - Analog Devices

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