NTC

B

2T

R18 = R

(T)

B + 2T

-

´

(28)

NTC

NTC||R18

NTC

R18

R

(T)

R

=

R18 + R

(T)

´

(29)

0kW

50kW

100kW

150kW

200kW

250kW

-20ºC

0ºC

20ºC

40ºC

60ºC

80ºC

0kW

5kW

10kW

15kW

20kW

25kW

30kW

-20ºC

0ºC

20ºC

40ºC

60ºC

80ºC

TS

logic

NTC||R18

NTC||R18

R19

R19

V

= V

= 3.3 V

R

+ R19

R

+ R19

´

´

(30)

OFFE

TS

logic

TS

TS

TS

R21

R21

V

= 2V

(V

2V

)

= 2V

(3.3V 2V

)

R20

R20

-

-

´

-

-

´

(31)

TPS65166

The NTC termistor manufacturer provides the above parameters. Typically a 22k

Ω NTC is used. Table 9

provides a suggestion for NTCs.

Table 9. Negative Termistor Selection

RESISTANCE (25°C)

B CONSTANT

COMPONENT SUPPLIER

COMMENT

22k

Ω

3950 K

Murata, NCP18XW223E

±3%

22k

Ω

3800 K

Vishay, NTCS0805E3223FHT

±1%

22k

Ω

4554 K

TDK, NTCG164LH223HT

±3%

To linearize the resistance-temperature characteristic of the NTC termistor, a parallel resistor R18 is added. T is

the temperature at which the NTC characteristic curve is linearized. Typically T is located in the middle of the set

should start at 0°C and stop at 25°C T = 12.5°C + 273.15 K/°C = 285.65 K.

Figure 29. Resistance-Temperature Characteristics NTC (22 k

Ω) and Linearized NTC Network at 12.5°C

To achieve different slopes, different R18 values are required. To obtain the most linear slope, the calculated

value has to be used. To achieve steeper slopes, higher values for R18 are necessary, smaller values produce

shallower slopes. By adjusting the resistor R19, the start and end point of the compensation can be set. The

the temperature compensation. For further compensation characteristics, refer to the available TPS65166

support excel sheet.

Copyright © 2009, Texas Instruments Incorporated

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