
DS2714: Quad Loose Cell NiMH Charger 
9 of 12 
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
SS
. 
Resistors can 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. When the timer 
expires in Top-Off, charging proceeds to the Maintenance phase. The programmed charge time approximately 
follows the equation: 
t = 1.5 * R / 1000          (time in minutes) 
SUSPEND 
Suspension of charge activity is possible by floating the TMR pin. All  CCx 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 10k
 NTC thermistor between THM1 or THM2 (THMx) and VSS, and a 10k
 bias resistor 
between V
DD
 and THMx allows the DS2714 to sense temperature. In order to sense the temperature of the battery 
cells, locate the thermistor close to the body of the battery cell. The THM1 thermistor should be placed between 
cells 1 and 2, and THM2 thermistor between cells 3 and 4. Alternatively, the thermistors can sense ambient 
temperature by locating them away from the cells. THM1 and THM2 can be tied together to sense temperature 
using a single thermistor and bias resistor. The temperature qualification function can be defeated by tying THMx 
pins to a single resistor divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold 
voltages. 
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
A
 < 45 C when using the recommended 10k
 bias and 10k
 thermistor. If Fast charging is in progress, and the 
voltage on THMx reaches VTHM-STOP (T
A
 > 50 C), Fast charging stops and the maintenance phase begins. In 
Pre-charge the device will transition to the Fault state if the voltage on THMx reaches VTHM-STOP.  
Table 1. THM1, THM2 Thresholds 
TEMPERATURE 
THM 
THRESHOLD 
RATIO 
OF VDD 
THERMISTOR 
RESISTANCE 
Semitec 
103AT-2 
Fenwal 
197-103LAG-A01 
173-103LAF-301 
4C 
42C 
47C 
MIN 
MAX 
STOP 
0.73 
0.33 
0.29 
27.04k 
4.925k 
4.085k 
0C 
45C 
50C 
CELL VOLTAGE MONITORING 
Individual cell voltages are monitored for minimum and maximum values, using the V
BAT-LOW
 , V
BAT-MAX1
 and V
BAT-
MAX2 
threshold limits. Upon inserting a cell or power-up with cells inserted, cell voltages must be less than the V
BAT-
MAX1 
threshold before charging begins. The V
BAT-LOW 
threshold determines whether a Pre-charge cycle should 
precede the Fast charge cycle, and when to transition from Pre-charge to Fast charge. Once Fast charging 
commences, cell voltages are compared to the V
BAT-MAX2 
threshold once every 2 seconds. The comparison occurs 
while the charge control pin (CC1-4) controlling current to the cell is active (low). When the charge control pin is 
active such that charge is applied to the cell, the cell voltage is referred to as the V
ON
 voltage. When the charge 
control pin is inactive, the cell voltage is referred to as the V
OFF
 voltage. Charging is halted and a Fault condition is 
displayed if V
ON
 is greater than V
BAT-MAX2
. Charging is also halted and a fault condition is entered if V
OFF
 is greater 
than V
BAT-MAX1
. While Fast charge is in progress, cell voltage measurements are stored and compared to future 
measurements for charge termination and cell test purposes.