LTC4015 datasheet(21/76 Pages) LINER

21 / 76 page

LTC4015

4015fb

For more information www.linear.com/LTC4015

Figure 1. NTC Bias Configuration

4015 F01

RNTCBIAS

NTCBIAS

NTC

RNTC

THERMISTOR

OPERATION

Wheninputpowerisabsent,themeasurementsystemcan

be sampled periodically at reduced battery load using the

following procedure as an example:

a. Write en_meas_sys_valid_alert = 1

b. Write force_meas_sys_on = 1

c. Wait for SMBALERT to go low (typically 20ms from

force_meas_sys_on = 1)

d. UponSMBALERTgoinglow,performARAcommand.If

therearemultipleslavedevices,verifythattheLTC4015

is asserting the alert.

e. Verify meas_sys_valid_alert = 1

f. Write en_meas_sys_valid_alert = 0

g. Write force_meas_sys_on = 0

h. Read updated measurement system data from the

LTC4015

This procedure can be repeated at desired intervals (for

example, once per second) in order to periodically moni-

tor the system.

Thermistor/NTC Measurement

chosen thermistor at 25°C (r25). NTC_RATIO (0x40) is

available via the serial port, except when the ship mode

feature has been activated.

TheLTC4015measurementsystemisconfiguredtodirectly

calculate NTC_RATIO, where:

NTC_RATIO= 21845 •

RNTC

RNTCBIAS+RNTC

RNTC=RNTCBIAS •

NTC_RATIO

21845–NTC_RATIO

NTC_RATIO has a bit weight of 1/21845 = 4.5777–5/LSB.

For a NTC_RATIO of 0.5, where RNTC = RNTCBIAS, the

value of NTC_RATIO reported by the serial port would be

approximately 10922.

The data in the first two columns in the following table

are from a Vishay NTC thermistor with a R25 of 10k

and

β value of 3490k, such as provided by a Vishay

NTCS0402E3103FLT or NTHS0402N02N1002JE. The

NTC_RATIO value is 21845 • [RNTC/( RNTC + RNTCBIAS )],

where RNTCBIAS = R25 = 10k.

TEMPERATURE

RNTC

NTC_RATIO

10.0

18290

14122

15.0

14867

13059

20.0

12157

11985

25.0

10000

10922

30.0

8272

9889

35.0

6879

8902

40.0

5751

7975

Steps to find NTC resistor temperature given a NTC_RATIO value;

1. Retrieve value for the NTC_RATIO from the LTC4015 via the I2C port

2. Calculate RNTC;

3. Using the calculated RNTC, use NTC resistor manufacturers data to

determine temperature.

Battery temperature is sensed by using an external NTC

(negative temperature coefficient) thermistor, RNTC. RNTC

is normally located in the battery pack. Connect RNTC

betweentheNTCpinandground.Abiasresistor,RNTCBIAS,

is connected between NTCBIAS and NTC. RNTCBIASshould

be a 1% resistor with a value equal to the value of the

RNTC=RNTCBIAS

NTC_RATIO

21845–NTC_RATIO

LTC4015 Datasheet(PDF) 21 Page - Linear Technology

LTC4015 Datasheet(HTML) 21 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

Datasheet Download

Link URL