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LTM4622 &LTM4705 Frequency Set for Dual Output voltage

Category: Hardware
Product Number: LTM4622 LTM4705

Hi 

We are using LTM4622 Dual Output Voltage part for Vout1 3.3V and Vout2 - 1.8V.

The datasheet specifies Frequency pin  : For 1.8V, FREQ Pin should be left open to set 1MHz and For 3.3V FREQ Pin to be connected ground with 324K to set 2MHz

Q1: In Two different output (LTM4622) Switching frequency Fsw of regulator will be same for both output, Right?

Q2: In my case, Where I've Vout1-3.3V and Vout2- 1.8V, What should be the Switching frequency set to?

If I set Fsw- 1 MHz, For 3.3V, Inductor ripple current as per the datasheet calculation, it results 2.392 A which is exceeding "1.2A peak-to-peak inductor ripple current" 

Same for LTM4705, Vout1-3.3V and Vout2- 1.35,

What should be Fsw?

Top Replies

  • FormerMember
    FormerMember
Mar 6, 2023 in reply to KLN +1 verified

You should use the higher switching frequency if you wish to use the parts you mentioned.

Regards,

Jhun

on Mar 6, 2023 12:56 AM

Hello,

What is your input/output requirement?

Q1: In Two different output (LTM4622) Switching frequency Fsw of regulator will be same for both output, Right?

Yes.

Q2: In my case, Where I've Vout1-3.3V and Vout2- 1.8V, What should be the Switching frequency set to?

If you insist on using the part numbers you mentioned, you should set the switching frequency to 2MHz to not violate the maximum peak current requirement.

Regards,

Jhun

  • Hi  

    For All case, Input voltage is 12V

    What is the case for "LTM4705" part?- Switching frequency will be same for both output?

  • FormerMember
    0 FormerMember on Mar 6, 2023 3:31 AM in reply to KLN

    It is the same case.

    What is your output current requirement?

  • The Output current 

    LTM4622-    VIN-12V, Vout1- 3.3V, 0.34A : Vout2- 1.8V,1.4A

    LTM4705-    VIN-12V, Vout- 3.3V,2.83A : Vout2- 1.35V, 3.56A

  • FormerMember
    +1 FormerMember on Mar 6, 2023 11:23 PM in reply to KLN

    You should use the higher switching frequency if you wish to use the parts you mentioned.

    Regards,

    Jhun