MC33348D-5 Просмотр технического описания (PDF) - ON Semiconductor

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MC33348D-5

Lithium Battery Protection Circuit for One Cell Battery Packs

ON Semiconductor 

MC33348

Figure 8. One Cell Smart Battery Pack

1

Cell

7

MC33348

3

84

65

Discharge

MOSFET Q2

Charge

MOSFET Q1

A functional description of the protection circuit blocks follows.

Refer to the detailed block diagram shown in Figure 7.

Voltage Sensing

Voltage sensing is accomplished by the use of the Cell Voltage

Sample Switch in conjunction with the Over/Under Voltage Detector

and Reference block. The Sample Switch applies the cell voltage to

the top resistor of an internal divider string. The voltage at each of the

tap points is sequentially polled and compared to an internal reference.

If a limit has been exceeded, the result is stored in the Over/Under

Data Latch and Control Logic block. The Cell Voltage Sample Switch

is gated on for a 1.0 ms period at a one second repetition rate. This low

duty cycle sampling technique reduces the average load current that

the divider presents across the cell, thus extending the useful battery

pack capacity. The cell voltage limits are tested in the following

sequence:

Figure 9. Cell Sensing Sequence

Polling

Sequence

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ 1

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ 2

Time

(ms)

0.5

0.5

Tested

Limit

Overvoltage

Undervoltage

By incorporating this polling technique with a single comparator

and voltage divider, a significant reduction of circuitry and trim

elements is achieved. This results in a smaller die size, lower cost, and

reduced operating current.

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