DS2715 Dallas Semiconducotr, DS2715 Datasheet - Page 11

• Manufacturer Part Number: DS2715
• Description: NiMH Battery Pack Charge Controller
• Manufacturer: Dallas Semiconducotr

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
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
when using the recommended 10kW bias and 10kW thermistor. If pre-charging is in progress, and the voltage on
THM reaches V
STOP
complete normally and top-off will begin if the voltage change on THM exceeds T
termination).
Table 2. THM1, THM2 THRESHOLDS
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
Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE
during fast charge or top-off, charging stops and the DS2715 enters the DONE state. Fast charging will
THRESHOLD
STOP
THM
MAX
MIN
THM-STOP
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
, pre-charging stops and a fault condition is generated. If the voltage on THM reaches V
0
OF V
RATIO
0.73
0.33
0.29
CBIAS
THERMISTOR
RESISTANCE
10
27.04k
4.925k
4.085k
(W)
THM-MIN
Divider Output
, V
Degrees Centigrade
THM-MAX
20
11 of 12
103AT-2
Semitec
45°C
50°C
) are set to allow charging to start if 0°C < T
0°C
30
TEMPERATURE (°C)
SS
, and a 10kW bias resistor between
197-103LAG-A01
173-103LAF-301
TERM
40
Fenwal
42°C
47°C
ºC per minute (dT/dt charge
4°C
50
CELL
< 45°C
Cbias
THM-
).