LP8555: Soft-start function

Kouassi KRA

Part Number: LP8555

Hi,

The datasheet that there is a soft-start function in LP8555 section 8.3.1.1.

What are the specifications about this soft-start function?

With an inductance 10uH I measure a peak inductance current during start-up at 1.5A and a rising time of Boost output voltage at 100us.

Have you recommendation to reduce this peak current?

Vin= 5,25V

VOUT=VINIT= 14.45V

Thanks in advance.

Regards,

Kouassi KRA

over 3 years ago

0 Yuting Shao over 3 years ago

TI__Genius 13001 points

Hi Kouassi,

The soft star current limit is set internally, and pls. refer to register CONF0[1:0] to set required current limit.

BR,

Robin

0 Kouassi KRA over 3 years ago in reply to Yuting Shao

Prodigy 70 points

Hi,

Thank you for your prompt response. I'm using USB connection, to power the LP8555, so the peak current must not exceed reach 500 mA to comply with USB requirement.

The register CONF0 specifies a current limit at mimum 0.9A. Have you recommandation to drop below 500mA?

Regards,

Kouassi KRA

0 Yuting Shao over 3 years ago in reply to Kouassi KRA

TI__Genius 13001 points

Hi Kouassi,

The actual inductor current can be decreased with lower output current and larger inductor. That means lower average current and lower current ripple results in lower inductor peak current.

BR,

Robin

0 Kouassi KRA over 3 years ago in reply to Yuting Shao

Prodigy 70 points

Hi,

I try with a 22uH inductance. It's didn't change much on peak current at boost startup( 1,4A).

I also tried to modify the register CONF0[0:1], but it doesn't work. After writing value 0x88 at address 0x76, I read 0x00. Is this register write protected ?

Regards,

Kouassi KRA

0 Yuting Shao over 3 years ago in reply to Kouassi KRA

TI__Genius 13001 points

Hi Kouassi,

You need set the CONF0[7] firstly.

BR,

Robin

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LP8555: Soft-start function