L9680 datasheet(43/286 Pages) STMICROELECTRONICS

Teilenummer	L9680

Bauteilbeschribung	Automotive advanced airbag for mid/high end applications and cut-off battery IC

PDF	286 Pages

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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43 / 286 page

DS11615 Rev 7

43/286

L9680

Start-up and power control

285

The user can decide the charge and discharge time based on the ER CAP used in

application, in order to maximize the differential voltage and then improve the accuracy.

Anyway, a timeout on ER Discharge current has been implemented to prevent thermal

issue, so the discharge time cannot be longer than 350 ms.

Figure 17. ER CAP measurement timing diagram

The following formulas can be used to retrieve the ER CAP value from the voltage and

timing measurements.

T1 = discharge time

T2 = charge time, same as discharge time

T1 = T2 = T



V1 = Vstart - Vstop



V2 = Vend - Vstop

I1 = discharge current

I2 = charge current, same as discharge current

I1 = I2 = I

ILEAK = leakage current



V1 V2

I1 ILEAK

---------------------------T1

I2 ILEAK

–

--------------------------T2

2 I T

 

Vstart Vend 2 Vstop



–

----------------------------------------------------------------

ESR > 0

VER (t)

ER_DISCHARGE

ER_CHARGE

ESR = 0

Vstart

Vstop

Vend

GAPGPS02262

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