mc33348d ON Semiconductor, mc33348d Datasheet - Page 9

• Manufacturer Part Number: mc33348d
• Description: Lithium Battery Protection Circuit For One Cell Smart Battery Packs
• Manufacturer: ON Semiconductor

description, charge MOSFET Q1 is held off during an
overvoltage fault condition. When this condition is present,
the discharge current limit protection function is internally
disabled. This is required, since the voltage across Q1, in the
off state, would exceed the current sense threshold. This
would cause Q2 to turn off as well, preventing both charging
and discharging of the cell. Discharge current limit protection
is enabled whenever an overvoltage fault is not present.
response delay of 3.0 ms. This helps to prevent fault
activation when the battery pack is subjected to pulsed
currents during discharging. An additional current sense
delay can be added as shown in Figure 12. If the battery pack
is subjected to extremely high discharge current pulses or is
shorted, the V CC pin must be decoupled from the cell. This is
required so that the protection circuit will have sufficient
operating voltage during the load transient, to ensure turn off
of discharge MOSFET Q2. Figure 13 shows the placement of
decoupling components.
Charge Pump and MOSFET Switches
ensure that the MOSFET switches are fully enhanced for
reduced power losses. An external reservoir capacitor
normally connects from the Charge Pump output to ground,
Pins 8 and 3. The capacitor value is not critical and is usually
within the range of 10 nF to 100 nF. The Charge Pump output
is regulated at 10.2 V allowing the use of the more
economical logic level MOSFETs. The main requirement in
selecting a particular type of MOSFET switch is to consider
the desired on–resistance at the lowest anticipated operating
voltage of the battery pack. A table of small outline surface
mount devices is given in Figure 14. When using extremely
MOTOROLA ANALOG IC DEVICE DATA
MMFT3055VL
MMDF3N03HD
MMDF4N01HD
MMSF5N02HD
MMDF6N02HD
As previously stated in the voltage sensing operating
The discharge current protection circuit contains a built in
The MC33348 contains an on chip Charge Pump to
Device
Type
0.047 Ω
0.043 Ω
2.5 V
–
–
–
Figure 14. Small Outline Surface Mount MOSFET Switches
0.525 Ω
0.042 Ω
0.065 Ω
0.035 Ω
3.0 V
–
On–Resistance (Ω) versus Gate to Source Voltage (V)
0.080 Ω
0.037 Ω
0.023 Ω
0.029 Ω
4.0 V
MC33348
–
low threshold MOSFETs, it may be desirable to disable the
Charge Pump so that the maximum gate to source voltage is
not exceeded. This can be accomplished by connecting Pin 6
to Pin 5, and will result in an additional cell drain current of
approximately 8.0 µA.
Testing
battery pack testing. By grounding Pin 2, the internal logic is
held in a reset state and both MOSFET switches are turned
on. Upon release, the logic becomes active and the cell
voltage is polled within 1.0 ms.
Battery Pack Application
Figure 7 contains a capacitor labeled C I that connects
directly across the battery pack terminals. This component
prevents excessive currents from flowing into the MC33348
when the battery pack terminals are shorted or arced, and is
mandatory. Capacitor C I is a 100 nF 20% ceramic leaded
or surface mount type. It must be placed directly across the
battery pack plus and minus terminals with extremely short
lead lengths ( 1/16 ).
are used, the protection circuit may take a considerable
amount of time to reset from an overcurrent fault after the
load is removed. This situation can be remedied by providing
a small leakage path for charging C I , thus allowing Pin 5 to
rapidly fall below the discharge current limit threshold. A
1.0 megohm resistor placed across the MOSFET switches
accomplishes this task with a minimum increase in cell
discharge current when the battery pack is connected to a
load.
A test pin is provided in order to speed up device and
The one cell smart battery pack application shown in
In applications where inordinately low leakage MOSFETs
0.120 Ω
0.065 Ω
0.035 Ω
0.021 Ω
0.028 Ω
5.0 V
0.063 Ω
0.034 Ω
0.020 Ω
0.026 Ω
0.115 Ω
6.0 V
0.108 Ω
0.062 Ω
0.033 Ω
0.018 Ω
0.025 Ω
7.5 V
0.100 Ω
0.060 Ω
0.033 Ω
0.018 Ω
0.023 Ω
9.0 V
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