LM74722-Q1: TVS Selection/ peak surge current

MAKOTO HADA

Part Number: LM74722-Q1

Tool/software:

Hello, I am Makoto.

Datasheet says,

The SMBJ33CA TVS diode can be used for 12-V battery protection application. The breakdown voltage of 36.7
V meets the jump start, load dump requirements on the positive side and 16-V reverse battery connection on the
negative side. During ISO 7637-2 pulse 1 test, the SMBJ33CA clamps at –44 V with 12 A of peak surge current
and it meets the clamping voltage ≤ 44 V.

I cannot understand how to select TVS SMBJ33CA. It clamps at -44V with 12A peak surge current.

Where the 12A comes from?

SMBJ33CA is 11.3A of Ip-p.

over 1 year ago

0 Shiven Dhir over 1 year ago

TI__Guru 58295 points

Hi Makota,

There might be an error in the datasheet.

Datasheet states that SMBJ33CA clamps at -44V at 12A. But in reality, it clamps at -42V only. Current flown through is ~10.8A. For a -150V pulse1, current through the TVS will be:

(150-42)/10ohms = 10.8 where 10ohms is the impedance of pulse generator. Which tells we still have margin of 2V.

Regards,

Shiven Dhir

0 MAKOTO HADA over 1 year ago in reply to Shiven Dhir

Prodigy 20 points

Hello Shiven,

Thank you for the feedback.

Why "But in reality, it clamps at -42V only. "? I cannot understand 2V margin.

Regards,

Makoto

0 Shiven Dhir over 1 year ago in reply to MAKOTO HADA

TI__Guru 58295 points

Hi Makota,

According to calculation, we had to clamp under -44V but we clamp at -42V only. This is the 2V margin that I am referring to.

Regards,

Shiven Dhir

0 MAKOTO HADA over 1 year ago in reply to Shiven Dhir

Prodigy 20 points

Hello Shiven,

10.8A would be max, therefore SMBJ33CA with Maximum Peak Pulse Current 11.3A can behave correctly. Is my understanding correct?

Regards,

Makoto

+1 Shiven Dhir over 1 year ago in reply to MAKOTO HADA

TI__Guru 58295 points

Hi Makota,

Understanding is correct.

Regards,

Shiven Dhir

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LM74722-Q1: TVS Selection/ peak surge current