MC33349N View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

MC33349N

Lithium Battery Protection Circuit for One Cell Battery Packs

ON Semiconductor 

MC33349

0.210

0.209

0.208

0.207

0.206

0.205

0.204

0.203

0.202

0

VDD = 3.0V

0.5

1

1.5

2

2.5

3

W EXTERNAL RESISTANCE R2(k )

Figure 20. Excess Current Threshold vs

External Resistance R2

MC33349N–3X / MC33349N–7X

4.258

4.256

C1 = 0 to 0.68µF

4.254

C3 = 0.22µF

C3 = 0.1µF

4.252

4.250

C3 = 0.01µF

4.248

4.246

0

200

400

600

800

1000

W EXTERNAL RESISTANCE R1( )

Figure 21. Overvoltage Threshold vs

External Resistance R1

MC33349N–3X

OPERATING DESCRIPTION

VD1 / Over–Charge Detector

VD1 monitors the voltage at the VCELL pin (VDD). When

it exceeds the over–charge detector threshold, VDET1. VD1

senses an over–charging condition, the CO pin goes to a

”Low” level, and the external charge control,

Nch–MOSFET turns off.

Resetting VD1 allows resumption of the charging

process. VD1 resets under two conditions, thus, making the

CO pin level ”High.” The first case occurs when the cell

voltage drops below ”VDET1 – VHYS1.” (VHYS1 is typically

200 mV). In the second case, disconnecting the charger from

the battery pack can reset VD1 after VDD drops between

”VDET1” and ”VDET1 – VHYS1”.

After detecting over–charge, connecting a load to the

battery pack allows load current to flow through the parasitic

diode of the external charge control FET. The CO level goes

”High” when the cell voltage drops below VDET1 due to load

current draw through the parasitic diode.

An external capacitor connected between the Gnd pin and

Ct pin sets the output delay time for over–charge detection.

The external capacitor sets up a delay time from the moment

of over–charge detection to the time CO outputs a signal,

which enables the charge control FET to turn off. If the

voltage fault occurs within the time delay window. CO will

not turn off the charge control FET. The output delay time

can be calculated as follows:

+ * ń tVDET1[sec] (Ct[F] (VDD[V] 0.7) (0.48 10*6)

A level shifter incorporated in a buffer driver for the CO

pin drives the ”Low” level of CO pin to the P– pin voltage.

A CMOS buffer sets the ”High” level of CO pin to VDD.

VD2 / Over–Discharge Detector

VD2 monitors the voltage at the VCELL pin (VDD). When

it drops below the over–discharge detector threshold,

VDET2, VD2 senses an over–discharge condition, the DO

pin goes to a ”Low” level, and the external discharge control

Nch MOSFET turns off. The IC enters a low current standby

mode after detection of an over–discharged voltage by VD2.

Supply current then reduces to approximately 0.3 µA.

During standby mode, only the charger detector operates.

VD2 can only reset after connecting the pack to a charger.

While VDD remains under the over–discharge detector

threshold, VDET2, discharge current can flow through the

parasitic diode of the external discharge control FET. The

DO level goes ”High” when the cell voltage rises above

VDET2 due to the charging current through the parasitic

diode. Connecting a charger to the battery pack will instantly

set DO ”High” if this causes VDD to rise above VDET2.

When cell voltage equals zero, one can charge the battery

pack if the voltage is greater than the minimum charge

voltage, VST.

Output delay time for the over–discharge detection

(tVDET2) is fixed internally. If the voltage fault occurs within

the time delay window, DO will not turn off the discharge

control FET.

A CMOS buffer sets the output of the DO pin to a ”High”

level of VDD and a ”Low” level of Gnd.

VD3 / Excess Current Detector, Short Circuit Detector

Both the excess current detector and the short circuit

detector can work when the two control FET’s are on. When

the voltage at the P– pin rises to a value between the short

circuit protection voltage, VSHORT, and the excess current

threshold, VDET3, the excess current detector operates.

Increasing V(P–) higher than VSHORT enables the short

circuit detector. The DO pin then goes to a ”Low” level, and

the external discharge control Nch MOSFET turns off.

Output delay time for excess current detection (tVDET3) is

fixed internally. If the excess current fault occurs within the

time delay window, DO will not turn off the discharge

control FET. However, when the short circuit protector is

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