LM61480: LM61480 Design Review

Manikandan M M

Part Number: LM61480

I am using LM61480 to generate -3.3V from 12V of load current 4A. Inductor part Number - IHLP2525CZER2R2MA1. Kindly find the attached Schematic for review

over 2 years ago

0 Jimmy Hua over 2 years ago

TI__Guru 50120 points

Hello,

Please refer to the app note for IBB conversion (SNVA856).
For the nRESET (pgood) functionality, you would also need to have a level shifter circuit as shown in Figure 7-3.
Input capacitor selection should have both Cin and Cio following Figure 5-1 (IBB External components).
What is the desired output voltage regulation? Output looks like VCC_N3V3 which I assume is a -3.3V rail but the top/bottom resistors ( 100k/10k) result in a regulation of -11V. If you want to regulate to -3.3V, replace R334 resistor with a 43.2k.

Regards,

Jimmy

0 Sai Kiranmai Maramraju over 2 years ago in reply to Jimmy Hua

Prodigy 80 points

Hi,

1. Please review attached updated schematic.

2. I will not connect PGOOD output signal to any of my external Component.So, please let me know just a pull up alone is sufficient there are not instead of level shifter circuit?

3. Please let me know the functionality of SPSP pin.

Thank you.

0 Jimmy Hua over 2 years ago in reply to Sai Kiranmai Maramraju

TI__Guru 50120 points

Hi,

1. Schematic looks okay.

2. Are you trying to just measure the PGOOD flag with respects to the IC in this case? If so then this should be fine. However, if not then it will need be to level-shifted to system ground if they are to be utilized by the system.

3. SPSP pin is to enable/disable the spread spectrum feature for improved EMI performance. Please refer to Section 8.3.10 for more details on the spread spectrum control.

Regards,

Jimmy

0 Sai Kiranmai Maramraju over 2 years ago in reply to Jimmy Hua

Prodigy 80 points

Hi,

Can u please tell efficiency and max load current of LM61480?

0 Sai Kiranmai Maramraju over 2 years ago in reply to Jimmy Hua

Prodigy 80 points

Please suggest external output inductor for 4A load.

0 Jimmy Hua over 2 years ago in reply to Sai Kiranmai Maramraju

TI__Guru 50120 points

Hello,

Please use the WEBENCH designer tool to help with part selection and simulation of efficiency at your target application.

You can also modify any component in the schematic to a custom part and resimulate efficiency.

To learn more how to use WEBENCH designer tool refer to this video : https://www.ti.com/video/5859518204001

Regards,

Jimmy

0 Sai Kiranmai Maramraju over 2 years ago in reply to Jimmy Hua

Prodigy 80 points

hii,

For part LM61480 we are unable load negative output value in WEBENCH designer tool, please give solution for this.

0 Jimmy Hua over 2 years ago in reply to Sai Kiranmai Maramraju

TI__Guru 50120 points

Unfortunately the LM61480 WEBENCH designer tool does not have the IBB simulation capability.

Please follow the IBB conversion design app note (https://www.ti.com/lit/an/snva856b/snva856b.pdf).

0 Roy T over 2 years ago in reply to Sai Kiranmai Maramraju

Prodigy 95 points

Hi Sai,

I was wondering if you can tell me if the LM61480 is working in IBB mode for you? I just received a board using the LM61480 (20V to -4.7V) and it is not working correctly. Wondering if yours is. output on our unit is -19V

I see on Rboot/Cboot you do not have a capacitor to SW. Is this intentional? if yes would you be able to tell me what documentation indicated to remove this capacitor? Other than that My schematic looks similar to yours.

Thank you!

-Roy

0 Jimmy Hua over 2 years ago in reply to Roy T

TI__Guru 50120 points

Since there is no further question regarding Sai's schematic, I will be closing this thread now.

Thank you for using the E2E forum.

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LM61480: LM61480 Design Review