Rainbow Electronics DS2710 - Manual (Page 9)

TOP-OFF complete normally if the cell temperature
remains below this threshold.
Used with a 10k
Ω resistor, the Semitec 103AT-2 pro-
vides approximately 0.9% full scale-per-degree sensi-
tivity. Figure 4 shows this linearity curve. The left axis is
the ratio of the sensed voltage to the divider’s input
voltage (V
DD ).
Charge-Status Output
The DS2710 indicates the state of charge and the
charge results on the STATUS output pin. When no cell
is present, the output is driven to a logic-low. Any LED
attached to the STATUS pin is off. When a cell is insert-
ed, STATUS oscillates in a 1Hz, 50% duty-cycle pattern
to indicate the cell is precharging. Once the DS2710
transitions to FAST-CHARGE, the STATUS output goes
to logic-high and stays high until the end of TOP-OFF.
STATUS returns to logic-low for MAINTENANCE charge
and remains at logic-low until the cell is removed or the
DS2710 is power cycled. If a FAULT occurs during
charging, STATUS toggles at a fast 4Hz, 50% duty-
cycle rate until the cell is removed. Table 2 summarizes
the STATUS output and LED operation for each charge
condition.
Charge-Rate Selection
The charge rate is determined by an external sense
resistor connected between the VN1 and VN0 pins. The
DS2710 regulates the charge current to maintain a volt-
age drop of V
IREF
- 0.5 x V
HYS-COMP
across the sense
resistor during FAST-CHARGE:
V SENSE = V IREF - 0.5 x V HYS-COMP = 0.113V (typ)
The sense resistor can therefore be selected by:
R SENSE = 0.113V/Desired FAST-CHARGE Current
The effective FAST-CHARGE rate is equal to 0.969 times
the regulated current limit, TOP-OFF rate is 0.25 times
the regulated current, and MAINTENANCE charge rate
is 0.0156 times the regulated current. Table 3 shows
the charge rates for charging three different cell capac-
ities using a 565mA (0.200
Ω sense) current source and
a 1130mA (0.100
Ω sense) current source.
DS2710
Single-Cell NiMH Charger
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Table 2. LED Display Patterns Based on Charge State
CHARGE STATE
NO BATTERY PRECHARGE
FAST-CHARGE/
TOP-OFF
MAINTENANCE FAULT
STATUS PIN Logic-low
Oscillates at 1Hz,
50% duty cycle
Logic-high Logic-low
Oscillates at 4Hz,
50% duty cycle
STATUS PIN LED Off 1Hz toggle On Off 4Hz toggle
Table 3. Charge-Rate Examples
565mA CHARGE RATE (0.200 )
AT CELL CAPACITY
1130mA CHARGE RATE (0.100 )
AT CELL CAPACITY STATE
900mAH 1700mAH 2200mAH 900mAH 1700mAH 2200mAH
FAST-CHARGE C/1.64 C/3.10 C/4.00 C/0.82 C/1.55 C/2.0
PRECHARGE/TOP-OFF C/6.37 C/12.0 C/15.5 C/3.19 C/6.0 C/7.75
MAINTENANCE C/102 C/193 C/249 C/51 C/96 C/125