AIC1803CCS datasheet(10/12 Pages) AIC

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AIC1803

TC ‚CTD(F)

10n

22n

33n

OC ‚T OD(S)

21m

52m

132m

253m

347m

TC ‚CTD(F)

47n

68n

82n

100n

OC ‚T OD(S)

617m

748m

1004m

1630m

The

delay

time

can

also

approximately

calculated by the following equations (if C

TC , CTD

≤ 82nF) :

OC (mS) = 11.8 x CTC(nF)

OD (mS) = 11.8 x CTD(nF)

Setting the Overcurrent Delay Time 1

The overcurrent delay time 1 (T

OI1)

at 0.15V <

CC-VCS < 0.3V is set by the external capacitor CTI,

while the overcurrent delay time 2 and 3 (T

OI2 and

OI3) is fixed by IC internal circuit.The relationship

between capacitance of the external capacitor and

delay time is tabulated as below.

TI(F)

2.2n

3.3n

6.8n

10n

OI(mS)

4.8

15.0

18.8

23.6

31.0

61.8

Selection

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 of the external control MOSFETs can

be determined by the equation: R

ON=V

OIP/IT (IT is

the overcurrent threshold current). For example, if

the overcurrent threshold current I

T is designed to

be 5A, the turn-on resistance of 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

overcurrent

threshold

current

will

change

accordingly.

Suppressing

the

Ripple

and

Disturbance from Charger

To suppress the ripple and disturbance from

charger, connecting R1 to R4 and C1 to C4 is

recommended.

Controlling

the

Charge

Control

MOSFET

R5, R6, R7 and NPN transistor Q1 are used to

switch

the

charge

control

MOSFET

M2.

overcharge does not occur, no current flows into

OC pin and Q1 is turned off, then M2 is turned on.

When overcharge occurs, current flows into OC

pin and Q1 is turned on, which turns off M2 in turn.

Protection at CS Pin

R8 is used for protection of IC when charger is

connected

reverse.

The

charge

detection

function after overdischarge is possibly disabled

by larger value of R8. Resistance of 1K

Ω is

recommended.

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