Single-Cell NiMH Charger
DS2710
TOP-OFF complete normally if the cell temperature
remains below this threshold.
the STATUS output and LED operation for each charge
condition.
Used with a 10kΩ 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
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-
voltage (V ).
DD
age drop of V
- 0.5 x V
across the sense
resistor during FAST-CHARGE:
= V - 0.5 x V = 0.113V (typ)
HYS-COMP
IREF
HYS-COMP
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
V
SENSE
IREF
The sense resistor can therefore be selected by:
= 0.113V/Desired FAST-CHARGE Current
R
SENSE
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 (0.200Ω sense) current source and
a 1130mA (0.100Ω sense) current source.
Table 2. LED Display Patterns Based on Charge State
CHARGE STATE
FAST-CHARGE/
TOP-OFF
NO BATTERY
PRECHARGE
MAINTENANCE
FAULT
Oscillates at 1Hz,
50% duty cycle
Oscillates at 4Hz,
50% duty cycle
STATUS PIN
Logic-low
Off
Logic-high
On
Logic-low
Off
STATUS PIN LED
1Hz toggle
4Hz toggle
Table 3. Charge-Rate Examples
565mA CHARGE RATE (0.200ꢀ)
1130mA CHARGE RATE (0.100ꢀ)
AT CELL CAPACITY
AT CELL CAPACITY
STATE
900mAH
C/1.64
C/6.37
C/102
1700mAH
C/3.10
2200mAH
C/4.00
900mAH
1700mAH
C/1.55
C/6.0
2200mAH
FAST-CHARGE
C/0.82
C/3.19
C/51
C/2.0
C/7.75
C/125
PRECHARGE/TOP-OFF
MAINTENANCE
C/12.0
C/15.5
C/193
C/249
C/96
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9
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
