CDH2D09 datasheet(40/44 Pages) MAXIM

40 / 44 page

PMIC with Integrated Charger and

Smart Power Selector for Handheld Devices

______________________________________________________________________________________

Since the thermistor monitoring circuit employs an

external bias resistor from THM to VL (RTB in Figure

14), any resistance thermistor can be used as long as

the value of RTB is equivalent to the thermistor’s +25°C

resistance. For example, with a 10k

Ω at +25°C thermis-

tor, use 10k

Ω at RTB, and with a 100kΩ at +25°C ther-

mistor, use 100k

Ω at RTB. The general relation of

thermistor resistance to temperature is defined by the

following equation:

where:

RT = The resistance in ohms of the thermistor at tem-

perature T in Celsius

R25 = The resistance in ohms of the thermistor at

+25°C

β = The material constant of the thermistor that typically

ranges from 3000K to 5000K

T = The temperature of the thermistor in °C that corre-

sponds to RT

T =×

−

⎛

⎝⎜

⎞

⎠⎟

⎧

⎨

⎩

⎫

⎬

⎭

273

298

THERMISTOR BETA (ß [K])

3000

3250

3500

3750

4250

RTB (k

Ω)

101010101010

RTP (k

Ω)

Open

120

RTS (k

Ω)

Short

Resistance at +25°C [k

Ω]

101010101010

Resistance at +50°C [k

Ω]

4.59

4.30

4.03

3.78

3.32

Resistance at 0°C [k

Ω]

25.14

27.15

29.32

31.66

36.91

Nominal Hot Trip

Temperature [°C]

Nominal Cold Trip

Temperature [°C]

-3

-1

0250

Table 8. Trip Temperatures for Different Thermistors

THM

AGND

ESD

DIODE

0.74 x VL

0.284 x VL

HOT

COLD

TEMPERATURE

SUSPEND

CEN

RTB

BOTH COMPARATORS

HAVE 65mV HYSTERESIS

RTP

RTS

ALTERNATE THERMISTOR

CONFIGURATION

MAX8671X

Figure 14. Thermistor Input

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