Rainbow-electronics DS2715 Manual do Utilizador descarregar pdf (Página 11)

DS2715: NiMH Cell Pack Charge Controller

11 of 12

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 10kW NTC thermistor between THM and V

, and a 10kW 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 10kW

thermistors are shown in Table 2.

Min, Max Temperature Compare

The voltage thresholds of the THM input (V

THM-MIN

, V

THM-MAX

) are set to allow charging to start if 0°C < T

CELL

< 45°C

when using the recommended 10kW bias and 10kW thermistor. If pre-charging is in progress, and the voltage on

THM reaches V

THM-STOP

, pre-charging stops and a fault condition is generated. If the voltage on THM reaches V

THM-

STOP

during fast charge or top-off, charging stops and the DS2715 enters the DONE state. Fast charging will

complete normally and top-off will begin if the voltage change on THM exceeds T

TERM

ºC per minute (dT/dt charge

termination).

Table 2. THM1, THM2 THRESHOLDS

TEMPERATURE (°C)

THM

THRESHOLD

RATIO

OF V

CBIAS

THERMISTOR

RESISTANCE

(W)

Semitec

103AT-2

Fenwal

197-103LAG-A01

173-103LAF-301

MIN 0.73 27.04k

0°C 4°C

MAX 0.33 4.925k

45°C 42°C

STOP 0.29 4.085k

50°C 47°C

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 (V

Cbias

Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE

Divider Output

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0 1020304050

Degrees Centigrade

Voltage Ratio

1 2 ... 6 7 8 9 10 11 12

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