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LTC3554

3554f

NTC thermistors have temperature characteristics which

are indicated on resistance-temperature conversion ta-

bles. The Vishay-Dale thermistor NTHS0603N011-N1003F,

used in the following examples, has a nominal value of

100k and follows the Vishay curve 1 resistance-tempera-

ture characteristic.

In the explanation below, the following notation is used.

R25 = Value of the thermistor at 25°C

RNTC|COLD = Value of thermistor at the cold trip point

RNTC|HOT = Value of the thermistor at the hot trip point

rCOLD = Ratio of RNTC|COLD to R25

rHOT = Ratio of RNTC|HOT to R25

RNOM = Primary thermistor bias resistor (see Figure 2)

R1 = Optional temperature range adjustment resistor (see

Figure 2)

The trip points for the LTC3554’s temperature qualiﬁca-

tion are internally programmed at 0.35 • VBUS for the hot

threshold and 0.76 • VBUS for the cold threshold.

OPERATION

Figure 1. Typical NTC Thermistor Circuit

Figure 2. NTC Thermistor Circuit with Additional Bias Resistor

–

RNOM

100k

RNTC

100k

NTC

VBUS

NTC_ENABLE

3554 F01

NTC BLOCK

TOO_COLD

TOO_HOT

0.76 • VBUS

(NTC RISING)

0.35 • VBUS

(NTC FALLING)

0.017 • VBUS

(NTC FALLING)

–

RNOM

105k

RNTC

100k

12.7k

NTC

VBUS

NTC_ENABLE

3554 F02

TOO_COLD

TOO_HOT

0.76 • VBUS

(NTC RISING)

0.35 • VBUS

(NTC FALLING)

0.017 • VBUS

(NTC FALLING)

–

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