max2003cse Maxim Integrated Products, Inc., max2003cse Datasheet - Page 6

• Manufacturer Part Number: max2003cse
• Description: Nicd/nimh Battery Fast-charge Controllers Integrated Products
• Manufacturer: Maxim Integrated Products, Inc.

NiCd/NiMH Battery
Fast-Charge Controllers
The MAX2003/MAX2003A is a fast-charge battery charg-
er that uses several methods of charge termination. The
device constantly monitors your choice of the following
conditions to determine termination of fast-charge:
Figure 2 shows the block diagram for the MAX2003/
MAX2003A.
The first step in creating a fast-charge battery-charger
circuit is to determine what type of battery will be used
and what conditions the battery manufacturer recom-
mends for termination of fast-charge. The type of bat-
tery (NiCd or NiMH) and charge rate determine which
method(s) of termination should be used.
The charging characteristics of NiMH batteries are simi-
lar to those of NiCd batteries, but there are some key dif-
ferences that affect the choice of charge-termination
method. Since the type of charge termination can be dif-
ferent for NiCd and NiMH batteries, it may not always be
possible to use the same circuit for both battery types.
A comparison of the voltage profiles for NiCd and NiMH
batteries (shown in Figure 3) reveals that NiCd batteries
display a larger negative drop in voltage at the end of
charge than do NiMH batteries. Therefore, the negative
delta voltage detection (- V) method of terminating
fast-charge should only be used for NiCd batteries.
This termination method can cause errors in NiMH bat-
teries, since the drop in voltage at full capacity is not as
great, and may lead to an overcharged battery.
Figure 4 shows the temperature profiles of the two
types of batteries. During the first 80% of the charge
cycle, the NiCd battery temperature slowly rises. The
NiMH battery temperature rises more rapidly during this
period. As the cells approach 90% of capacity, the
temperature of the NiCd cells rises more rapidly. When
the cells approach full capacity, the rates-of-rise of
temperature are comparable for both battery types. The
rate of temperature change ( T/ t) can therefore be
used to terminate fast-charge for both NiCd and NiMH
batteries; fast-charge is terminated when the rate of
temperature rise exceeds a preset rate.
Table 1 provides some guidelines to help in the selec-
tion of the proper fast-charge termination method, but
the manufacturer’s recommendations take priority in
case of conflict.
6
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• Negative Delta Voltage (- V)
• Rate-of-Change of Temperature ( T/ t)
• Maximum Voltage
• Maximum Time
• Maximum Temperature
Detailed Description
Table 1a. Fast-Charge Termination
Methods for NiMH Batteries
Table 1b. Fast-Charge Termination
Methods for NiCd Batteries
* Use one or both of these termination methods.
Figure 1 shows a standard application circuit for a
switched-mode battery charger that charges NiMH bat-
teries at a rate of C. Though this circuit is shown for
NiMH batteries, it can be used for NiCd batteries (see
Table 1b). The description below will use this standard
application to explain, in detail, the functionality of the
MAX2003/MAX2003A.
The BAT pin measures the per-cell voltage of the bat-
tery pack; this voltage is used to determine fast-charge
initiation and termination. The voltage is determined by
the resistor-divider combination R
Figure 1, where:
Since BAT has extremely high input impedance (50M
minimum), reasonable values can be selected for resis-
tors R
low enough to drain the battery or high enough to
unduly lengthen the time constant of the signal going to
the BAT pin. The total resistance value from the positive
to negative terminal of the battery (R
be between 100k
lems.
A simple RC lowpass filter (R
give a more accurate reading by removing any noise
that may be present. Remember that the RC time delay
from the cell to BAT must not exceed 200ms or the bat-
tery detection logic might not function properly (R
C
Charge
Charge
B
2C to
Rate
>C/2
Rate
>2C
C/2
< 200ms).
B1
Total Number of Cells = (R
and R
Yes
Yes
T/ t
T/ t
*
B2
. These values, however, must not be
Negative
Negative
and 500k
Yes
No
*
V
V
Battery Sense Voltage
B
Voltage
Voltage
, C
Max
Max
Yes
Yes
Yes
to prevent these prob-
B1
B
B1
) may be needed to
and R
B1
/ R
Time
Time
Max
Max
B2
Yes
Yes
Yes
+ R
B2
) + 1
B2
, shown in
) should
Temp.
Temp.
Max
Max
Yes
Yes
Yes
B
x