SS6802 datasheet(8/10 Pages) SSC

8 / 10 page

02/26/2008 Rev.1.00

www.SiliconStandard.com

CS pin and overcurrent delay time TOI is

tabulated as below.

VCS (V)

TOI (S)

150m

9.0m

200m

5.6m

300m

2.8m

360m

2.0m

540

290

270

Unbalanced Discharge after Overcharge

When either of the battery cells is overcharged,

the SS6802 will automatically discharge the

overcharged cell at about 7.7mA until the voltage

of the overcharged cell is equal to the voltage of

the other cell. If the voltage of the other cell is

below VOCR, the internal cell-balance “bleeding”

will proceed until the voltage of the overcharged

cell decreases to VOCR.

DESIGN GUIDE

Adjustment of Overcharge and

Overdischarge Delay Time

Both the overcharge and overdischarge delay

times default to 25mS and can be extended by

adding the external capacitors CTC and CTD,

respectively. Increasing the capacitance value will

increase

the

delay

time.

The

relationship

between capacitance of the external capacitors

and delay time is tabulated as below:

CTC (F)

TOC (S)

25m

0.1

320m

0.3

890m

0.47

1.12

0.57

1.43

CTD (F)

TOD (S)

25m

0.1

320m

0.3

820m

0.47

1.08

0.57

1.39

Selection of External Control MOSFETs

Because the overcurrent protection voltage is

preset, the threshold current for overcurrent

detection is determined by the turn-on resistance

of the discharge control MOSFET M1. The

turn-on

resistance

the

external

control

MOSFETs can be determined by the equation:

RON=VOIP/IT (IT is the overcurrent threshold

current).

For

example,

the

overcurrent

threshold current IT is designed to be 5A, the

turn-on

resistance

the

external

control

MOSFETs must be 30m

Ω. Users should be

aware that turn-on resistance of the MOSFET

changes with temperature variation due to heat

dissipation. It changes with the voltage between

gate and source as well. (Turn-on resistance of a

MOSFET increases as the voltage between gate

and

source

decreases).

Once

the

turn-on

resistance of the external MOSFET changes, the

SS6802

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