Negative Delta Voltage Termination

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

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.

Maximum Temperature Termination

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-

age is set externally at the TCO pin using a resistor

excessively low temperature will also terminate fast-

charge. The minimum temperature is the low tempera-

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-

for a detailed design example.

Maximum Voltage Termination

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-

age measured at BAT exceeds that at MCV, fast-

charge is terminated. For most applications using both

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.

Maximum Timeout Termination

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

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).

NiCd/NiMH Battery

Fast-Charge Controllers

______________________________________________________________________________________

11

*Enable

100

23

4C

Disable

100

23

*Enable

410

90

*Enable

200

45

2C

Open

C

GND

*Enable

820

180

C/2

Open

4C

Open

Open

Disable

410

90

Disable

200

45

2C

Open

GND

C

GND

Disable

820

180

C/2

GND

Open

Disable

Top-Off

Charge

140

Hold-Off

Time

∆V/MCV

(sec)

360

Fast-

Charge

Timeout

(min)

TM1

C/4

GND

GND

Fast-

Charge

Rate

TM2

Table 4. Programmable Inputs for

Timeout/Hold-Off/Fast-Charge/Top-Off/

0.5

1

0.5

0.5

0.5

1

1

1

Disable

MAX2003A

Trickle

Charge (s)

On/Off

* MAX2003 is on for 4sec and off for 30sec.

MAX2003A is on for 0.5sec and off for 3.5sec.

16

32

64

128

16

32

64

128

544

MAX2003A

Sampling

Interval

(sec)

544

136

68

68

544

136

68

68