DS2715 Ver la hoja de datos (PDF) - Maxim Integrated
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DS2715 Datasheet PDF : 17 Pages
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DS2715: NiMH Battery Pack Charge Controller
TEMPERATURE SENSE
Accurate temperature sensing is needed to determine end of charge by dT/dt and to detect over temperature fault
conditions. Connecting an external 10k NTC thermistor between THM and VSS, and a 10k bias resistor between
Div and THM allows the DS2715 to sense temperature. To sense the temperature of the cell pack, locate the
thermistor close to the body of a cell, preferably in the middle of the cell pack. Several recommended 10k
thermistors are shown in Table 3.
Min, Max Temperature Compare
The voltage thresholds of the THM input (VTHM-MIN, VTHM-MAX) are set to allow charging to start if the thermistor
temperature is between 0C and 45C when using the recommended 10k bias resistor and 10k thermistor
circuit. If pre-charging is in progress, and the voltage on THM reaches VTHM-STOP, pre-charging stops and a fault
condition is generated. If the voltage on THM reaches VTHM-STOP during FAST-CHARGE or TOPOFF, charging
stops and the DS2715 enters the DONE state. FAST_CHARGE will complete normally and TOPOFF will begin if
the voltage change on THM exceeds the equivalent TTERM ºC per minute (dT/dt Detect specification).
Table 3. THM THRESHOLDS
THM
THRESHOLD
MIN
MAX
STOP
RATIO
OF VCBIAS
0.73
0.33
0.29
THERMISTOR
RESISTANCE
()
27.04k
4.925k
4.085k
Semitec
103AT-2
0C
45C
50C
TEMPERATURE (C)
Fenwal
197-103LAG-A01
173-103LAF-301
4C
42C
47C
Used with a 10k resistor, the Semitec 103AT-2 provides about 0.9% full scale per degree sensitivity. This linearity
is shown in the curve in Figure 4. The left axis is the ratio of the sensed voltage to the divider’s input voltage
(VCbias).
Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0
Divider Output
10
20
30
40
50
Degrees Centigrade
12 of 17
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