LM5018 and LM5008A

ismail jorio1

Other Parts Discussed in Thread: LM5018, LM5008A, LM50, LM5008

Hello,

I am trying to use a high input voltage converter ( up to 65V) for a 3.3V at 200mA. I am currently using LM5008A which has the ripple config options. i am still getting about 30mV ripple on the Eval. Board. Do you have any ripple values on the LM5018. Webench gives about 2 to 3 mV andi just want to confirm with an apps engineer. My requirement is lower than 20mV.

I am open to recommendations.

Regards,

Ismail

over 12 years ago

0 Vijay86929 over 12 years ago

TI__Genius 11490 points

Hi Ismail,

Which configuration are you using for ripple. If you use type III configuration (minimum ripple), the ripple is only dependent on the output capacitor and can be easily reduced below 10mV. Same goes for LM5018.

Regards,

Vijay

0 ismail jorio1 over 12 years ago in reply to Vijay86929

Prodigy 40 points

Hi Vijay,

i have tried all configuration and specifically the third one. I am using a 22uF ceramic in series with a 0 Ohm.

Vin = 57V

Vout =3.3V

Iout = 20 mA

Regards,

ismail

0 Vijay86929 over 12 years ago in reply to ismail jorio1

TI__Genius 11490 points

Hi Ismail,

With this small load, the converter is is DCM with reduced frequency, hence the higher ripple. LM5018 is always in CCM so it should have lower ripple at that load.

Thanks and regards,

Vijay

0 ismail jorio1 over 12 years ago in reply to Vijay86929

Prodigy 40 points

20mA is the lowest load i have, it can be up to 200mA.

I thought LM5008A is a Constant on time so it should just change to lower frequency at low duty cycle and low load current.

How can i reach the bay area local sales rep for an LM5018 eval board?

Regards,

ismail

0 Vijay86929 over 12 years ago in reply to ismail jorio1

TI__Genius 11490 points

Hi Ismail,

It does. And most converters with DCM mode will have higher ripple at light load.

You can order it from http://www.ti.com/tool/lm5018eval

Thanks and regards,

Vijay

0 ismail jorio1 over 12 years ago in reply to Vijay86929

Prodigy 40 points

Hi Vijay,

I have increased the load to about 200mA and the part is currently running in CCM (LM5008). the ripple has improved to about 20mV. I am using a ceramic 22uF, what type of capacitor you recommend to reach 10mV ripple at this type of duty cycle?

Regards,

Ismail

0 Vijay86929 over 12 years ago in reply to ismail jorio1

TI__Genius 11490 points

Ceramic capacitor is the right type. From here it depends on the type of ripple. If the ripple is capacitive type (rounded waves) than increasing the capacitace will help reduce it further.

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LM5018 and LM5008A