NORMAL TERMINATION OF CHARGING

As you can see in

Figure 1, the cell voltage must exceed

V

turned OFF (1). Once V

increases to 4 Hz. The sampling rate will return to 1 Hz only

after 4 consecutive samples result in V

the MOSFET pair is OFF (2), the voltage across the cell(s)

relax and the cell voltage will drop below V

sample, (3), the MOSFET pair will turn ON. As long as the

charger is applied and the MOSFET pair turn ON, the cell

voltage will exceed V

a 1 samples OFF will continue until the cell voltage equals

V

gerates the rate of these events. The actual operation would

result in many ON/OFF cycles at a decreasing duty cycle

prior to complete termination of charge. The cell bypass re-

sistor will discharge the cell enough to turn on the GATE over

a period of minutes.

NORMAL TERMINATION OF DISCHARGING

The cell voltage must go below V

samples before the MOSFET pair is turned OFF (1), which is

shown in

Figure 2. Once the MOSFET pair is OFF and the

current is interrupted, the voltage across the cell(s) will in-

crease and the cell voltage could exceed V

MOSFET pair remain off until a charger is applied to the

pack (3). The presence of a charger turns the MOSFET pair

ON. Deeply discharged cells will be charged, although for

some narrow bands of V

pulse OFF momentarily.

TERMINATION OF ILLEGALLY HIGH CHARGING

Should a high charge current be applied to the pack near the

end of charge, the cell voltage could exceed V

approximately 100 mV greater than V

On the first detection of a cell voltage in excess of V

SAFE-

OVERCHARGE

, the MOSFET pair will be turned OFF (2). The

sample rate increases to 4 Hz after the first detection of

V

the MOSFET pair to turn ON for only the shortest allowed

time period, which is 0.25 seconds. Each sample exceeding

V

cell voltage not drop below V

OFF, the MOSFET pair remain OFF (4). This example exag-

gerates the rate of these events. The actual operation would

result in many ON/OFF cycles at a decreasing duty cycle

prior to complete termination of charge.

LOAD APPLIED IN OVERCHARGED STATE

If a load is momentarily applied while the cell is in over-

charged state, then the MOSFET pair is momentarily turned

ON, see

Figure 4. The MOSFET pair will stay ON only as

long as the load is applied. The MOSFET pair will stay ON

after the load is removed only if the cell voltage remains be-

low V

shown as examples of operation:

(1) A momentary load is applied to an overcharged cell, the

MOSFET pair stay ON only as long as the load is applied.

The gate drive is limited so that the MOSFET pair ON volt-

age will match a bias voltage generated internal to the IC,

V

voltage that allows for the detection of a load. This mode of

operation is

Active Rectification. Note that the MOSFET pair

do not turn ON for the momentary application of a charger.

(2) A load is applied for less than 4 samples. The MOSFET

pair is ON for the load period, but turn OFF after the load is

removed. Only after the 4th sample of V

MOSFET pair turn ON, this time will full drive potential.

(3) Assume the application of a charger. Conduction is al-

lowed because the FETs are ON, but the MOSFET pair will

stay ON only for 4 consecutive overcharge samples. See the

diagram for the “Normal Termination of Charging”.

(4) The MOSFET pair will turn OFF after the 4 consecutive

overcharge samples.

(5) A load is applied and after V

tive samples, the MOSFET pair turn ON full. As long as

V

Should a load be applied that exceeds the overcurrent-

discharge current limit while the IC is in active rectification

mode, the MOSFET pair will turn OFF. Recovery requires

that either the IC detects a load greater than 3–7 M

Ω or that

the cell voltage remains under V

load that caused overcurrent remains after the cell voltage

drops under V

turn ON once more and normal overcurrent mode is entered.

DS012931 12

FIGURE 1. Normal Termination of Charging

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