MAX2003 Maxim Integrated Products, MAX2003 Datasheet - Page 11

• Manufacturer Part Number: MAX2003
• Description: Nicd/nimh Battery Fast-charge Controllers
• Manufacturer: Maxim Integrated Products

The Negative Delta Voltage Termination (-∆V) method
measures a negative delta voltage to determine termi-
nation of fast-charge. After maximum charge is
reached, the terminal voltage of NiCd batteries
declines significantly, whereas the terminal voltage of
NiMH batteries does not. Hence, the -∆V method of
fast-charge termination is suitable for NiCd batteries,
but not for NiMH batteries.
The MAX2003/MAX2003A sample the BAT pin every 34
seconds and compare it with all previous values. If the
new value is less than any of the previous values by
more than 12mV, a negative delta voltage has been
detected and fast-charge is terminated.
Note: This method of charge termination is valid only
when the voltage at BAT is between V
0.2V
The -∆V method is inhibited during the hold-off time to
prevent false termination of fast-charge. The hold-off
time depends on the charge rate used, and is selected
by the inputs TM1 and TM2 (as shown in Table 4). After
the hold-off time has expired, the device begins to
monitor BAT for a voltage drop.
The Maximum Temperature Termination method is used
as a safety net to prevent problems, and should never
be needed under normal operation of the charger. The
maximum temperature that the battery can reach during
fast-charge has a corresponding voltage—the tempera-
ture cutoff voltage (V
age is set externally at the TCO pin using a resistor
divider from V
excessively low temperature will also terminate fast-
charge. The minimum temperature is the low tempera-
ture fault (V
When the thermistor exceeds these temperature limits,
fast-charge is terminated. The thermistor configuration
shown in Figure 5 is used to measure the battery’s tem-
perature and scale it to operate from V
Resistors R
required cutoff at V
for a detailed design example.
The Maximum Voltage Termination method is another
safety feature designed to work if something is drastically
wrong. Under normal operation of the charger, this condi-
tion should only be reached when the battery is removed.
The maximum cell voltage expected is applied at the
MCV pin using a resistor-divider network. If the cell volt-
CC
.
LTF
T1
). This value is internally set at 0.4V
and R
CC
Maximum Temperature Termination
Negative Delta Voltage Termination
______________________________________________________________________________________
. Although rarely experienced, an
TCO
TCO
T2
Maximum Voltage Termination
. See the Design Guide section
), as seen in Figure 5. This volt-
are calculated to provide the
MCV
LTF
and V
to V
CC
MCV
TCO
.
-
.
Fast-Charge Controllers
age measured at BAT exceeds that at MCV, fast-
charge is terminated. For most applications using both
NiCd and NiMH batteries, this voltage (V
set to 1.9V.
The MAX2003/MAX2003A do not terminate fast-charge
if the maximum voltage is reached before the hold-off
time has expired. If the cell voltage is greater than the
MCV during the hold-off time, the device will continue
fast-charge until the hold-off time has expired, and then
it will terminate fast-charge. The hold-off time is deter-
mined by the inputs TM1 and TM2, as shown in Table 4.
The final method is Maximum Timeout Termination,
which (like the maximum voltage and maximum tem-
perature methods) is another backup safety feature.
The timeout time depends on the charge rate selected
and is set by the control signals TM1 and TM2. Table 4
shows a list of different timeout periods available for dif-
ferent control-signal inputs. If the timeout is reached
before any other termination method is seen, fast-
charge is terminated to protect the charger and battery.
Top-off charge is used to provide the last bit of charge
needed to reach full capacity after fast-charge is termi-
nated. Top-off charging puts slightly more energy into
the battery than simple trickle charging, and can be
used for both NiCd and NiMH batteries. Select it by
choosing the appropriate control signals on TM1 and
TM2 (Table 4).
Table 4. Programmable Inputs for
Timeout/Hold-Off/Fast-Charge/Top-Off/
Pulse Trickle (V
* MAX2003 is on for 4sec and off for 30sec.
Open
Open
Open
GND
GND
GND
TM1
V
V
V
MAX2003A is on for 0.5sec and off for 3.5sec.
CC
CC
CC
Open
Open
Open
GND
GND
GND
TM2
V
V
V
CC
CC
CC
NiCd/NiMH Battery
Charge
Fast-
Rate
C/4
C/2
C/2
2C
4C
2C
4C
C
C
Timeout
Charge
Fast-
(min)
360
180
180
90
45
23
90
45
23
CC
Maximum Timeout Termination
Hold-Off
∆V/MCV
= 5V)
Time
(sec)
140
820
410
200
100
820
410
200
100
Top-Off
Charge
Disable
Disable
Disable
Disable
Disable
*Enable
*Enable
*Enable
*Enable
Top-Off Charge
MAX2003A
Charge (s)
0.5
0.5
0.5
0.5
Disable
1
1
1
1
Trickle
On/Off
MCV
128
128
16
32
64
16
32
64
) can be
MAX2003A
Sampling
Interval
(sec)
544
544
136
544
136
68
68
68
68
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