MAX77650CEWVT datasheet(60/82 Pages) MAXIM

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Thermistor Bias

An external ADC can optionally perform conversions on

the THM and TBIAS pins to measure the battery's tem-

perature. An on-chip analog multiplexer is used to route

these nodes to the AMUX pin. The operation of the analog

multiplexer does not interfere with the charger's tempera-

ture monitoring comparators or the charger's automatic

JEITA response. See the Analog Multiplexer & Power

Monitor AFEs section for more information.

The NTC thermistor's bias source (TBIAS) follows the

simple operation outlined below:

● If CHGIN is valid and the thermistor is enabled

(THM_EN = 1), then the thermistor is biased so the

charger can automatically respond to battery tem-

perature changes.

● If the analog multiplexer is connecting THM or

TBIAS to AMUX, then the thermistor is biased so an

external ADC can perform a meaningful temperature

conversion.

The AMUX pin is a buffered output. The operation of the

analog multiplexer and external ADC does not collide with

the function of the on-chip temperature monitors. Both

functions may be used simultaneously with no ill effect.

Configurable Temperature Thresholds

Temperature thresholds for different NTC thermistor beta

values are listed in Table 4. The largest possible program-

mable temperature range can be realized by using an NTC

with a beta of 3380K. Using a larger beta compresses the

temperature range. The trip voltage thresholds are pro-

grammable with the THM_HOT[1:0], THM_WARM[1:0],

THM_COOL[1:0], and THM_COLD[1:0] bitfields. All pos-

sible programmable trip voltages are listed in Table 4.

These are theoretical values computed by a formula.

Refer to the particular NTC's data sheet for more accurate

measured data. In all cases, select the value of RBIAS to

be equal to the NTC's effective resistance at +25°C.

TRIPVOLTAGE

(V)

TRIP TEMPERATURES (°C)

3380K

3435K

3940K

4050K

4100K

4250K

1.024

-10.0

-9.5

-5.6

-4.8

-4.5

-3.5

0.976

-5.0

-4.6

-1.1

-0.5

-0.2

0.6

0.923

0.0

0.3

3.3

3.8

4.1

4.8

0.867

5.0

5.3

7.7

8.1

8.3

8.9

0.807

10.0

10.2

12.0

12.4

12.5

12.9

0.747

15.0

15.1

16.4

16.6

16.7

17.0

0.511

35.0

34.8

33.5

33.3

33.2

32.9

0.459

40.0

39.8

37.8

37.4

37.3

36.8

0.411

45.0

44.7

42.0

41.5

41.3

40.7

0.367

50.0

49.6

46.2

45.6

45.3

44.6

0.327

55.0

54.5

50.4

49.7

49.3

48.4

0.291

60.0

59.4

54.6

53.7

53.3

52.2

Table 4. Trip Temperatures vs. Trip Voltages for Different NTC β

Figure 16. Thermistor Bias State Diagram

THERMISTOR BIASED

TBIAS = 1.25V

MUX_SEL = 0b0111 or 0b1000

(THM_EN = 1 AND CHGIN VALID)

MUX_SEL ≠ 0b0111 or 0b1000

AND

(THM_EN = 0 OR CHGIN INVALID)

THERMISTOR OFF

TBIAS = GND

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Maxim Integrated │ 60

MAX77650/MAX77651

Ultra-Low Power PMIC with 3-Output SIMO

and Power Path Charger for Small Li+

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