DS2712 Maxim Integrated Products, Inc., DS2712 Datasheet - Page 11

• Manufacturer Part Number: DS2712
• Description: Loose Cell Nimh Chargers
• Manufacturer: Maxim Integrated Products, Inc.

Charge Timer
The charge timer monitors the duration of charge in fast and top-off charge phases, and is reset at the beginning of
each phase. The time-out period is set with an external resistor connected from the TMR pin to V
be selected to support fast-charge time-out periods of 0.5 to 10 hours and top-off charge time-out periods of 0.25 to
5 hours. If the timer expires in fast-charge, the timer count is reset and charging proceeds to the top-off charge
phase. The top-off time-out period is half of the fast charge time-out period. If the timer expires in top-off, charging
proceeds to the maintenance phase. The programmed charge time approximately follows the equation:
Suspend
Suspension of charge activity is possible by floating the TMR pin. The CC1 and CC2 outputs become high-Z and
the charge timer stops. The state machine and all timers are reset to their presence test conditions.
Temperature Sense
Connecting an external 10kW NTC thermistor between THM1 or THM2 (THMx) and V
between V
locate the thermistor close to the body of the battery cell so THM1 monitors the temperature of cell-1 and THM2
monitors the temperature of cell-2. Alternatively, the thermistor can sense ambient temperature by locating it away
from the cells. THM1 and THM2 can be connected together to sense temperature using a single thermistor and
bias resistor. The temperature qualification function can be defeated by connecting THM1 and THM2 to a single
resistor-divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold voltages. Several
recommended 10kW thermistors are shown in Table 2.
Min, Max Temperature Compare
The voltage thresholds of the THMx inputs (VTHM-MIN, VTHM-MAX) are set to allow fast charging to start if 0°C <
T
voltage on THMx reaches VTHM-STOP, fast charging stops and the maintenance phase begins.
Table 2. THM1, THM2 THRESHOLDS
Figure 7. CELL VOLTAGE SENSE POINTS
A
< 45°C when using the recommended 10kW bias and 10kW thermistor. If fast charging is in progress, and the
THRESHOLD
STOP
THM
MAX
MIN
DD
and THMx allows the DS2711 to sense temperature. To sense the temperature of the battery cells,
OF V
RATIO
0.73
0.33
0.29
Series Configuration
Charge Source
Vcell2
Vcell1
DD
t = 1.5 x R / 1000
CC1
THERMISTOR
RESISTANCE
VP2
VP1
VN1
VN0
27.04k
4.925k
4.085k
(W)
11 of 14
Charge Source
(time in minutes)
103AT-2
Semitec
45°C
50°C
0°C
Parallel Configuration
Vcell1
CC2
CC1
TEMPERATURE (°C)
VP1
VN1
VN0
197-103LAG-A01
173-103LAF-301
Fenwal
42°C
47°C
SS
4°C
VP2
, and a 10kW bias resistor
Vcell2
SS
. Resistors can