LMR16030: LMR16030SDDAR

ilya tashaev

Prodigy 95 points

Part Number: LMR16030
Other Parts Discussed in Thread: TPS563210A

Hello

i would like to use the LMR16030SDDAR and i have 2 questions about this part:

attached are my schematic and the datasheet...

my parameters are : input = 18-60V , output = 15V (3A)

1) for the EN/UVLO enable threshold is 1.2 V as stated in the datasheet (page 13), so i have used 2 resistor divider (R22=RENT, R=23RENB) to make this pin 1.2V when VIN is 18V,

BUT in the datasheet (page 14) there is a different formula for the 2 resistor divider (R22=RENT, R=23RENB) which is not understood.

what is the correct way to set UVLO for 18V ?

2) can the Soft Start be more than 10mS (WEBENCH® POWER DESIGNER limit to 10mS only) ?

what is the Css or the Soft Start time limit ?

thanks in advance

lmr16030.pdf

5 months ago

0 Frank De Stasi 5 months ago

TI__Guru 58995 points

Hello

The equations in the data sheet are correct.

If you wish a Von=18V and a Voff=17V (example)

then you would use RT=274k and RB=19.1k (standard values)

What soft-start time are you looking for ?

Thanks

0 ilya tashaev 5 months ago in reply to Frank De Stasi

Prodigy 95 points

Hi Frank

thank you for your fast reply, can you tell me please how and what values did you use in the equations to get these resistors ?

about the soft start i would like to know what is the IC limit, there is no reference about it in the datasheet also Vref is also not known ?

i would like it to be as long as possible but below the limit for proper operation...

0 Frank De Stasi 5 months ago in reply to ilya tashaev

TI__Guru 58995 points

Hello

See attached calculation.

I don't know why Webench limits the soft-start to 10ms.

One thing to be careful about is the size of the soft-start

capacitor. The discharge current may become large with

larger values of capacitor.

I think I would limit the time to 50ms or 100ms.

Thanks

0 ilya tashaev 5 months ago in reply to Frank De Stasi

Prodigy 95 points

Hi Frank

thank you very much, about the soft start WEBENCH is limiting to 10mS also other DC/DC converters IC this is very strange (example tps563210a) !

anyway if i want to increase the soft start what would be the value because in the datasheet Vref is not mentioned ?

220nF ? and if yes isn't it a high value ?

0 Frank De Stasi 5 months ago in reply to ilya tashaev

TI__Guru 58995 points

Hello

The reference voltage is 0.75V

I think that 220nF is OK; that would give about 55ms.

Thanks

0 ilya tashaev 5 months ago in reply to Frank De Stasi

Prodigy 95 points

i also though but are you sure that they mean Vref = Vfb ?

0 Frank De Stasi 5 months ago in reply to ilya tashaev

TI__Guru 58995 points

Hello

Yes, for the LMR device it is 0.75V.

Thanks

0 ilya tashaev 5 months ago in reply to Frank De Stasi

Prodigy 95 points

Hi Frank

thank you very much for your help !!!

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LMR16030: LMR16030SDDAR