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LM5145: VIN vs Efficiency

Kai Nomiyama
Expert 5545 points
Part Number: LM5145

Hi Team,

My customer is evaluating LM5145.
In order to reduce internal 7.5V regulator power loss, they want to use separated power for VIN_5145 and VIN_FET.

When they use 12.5, 14.0, 24.0VIN_5145, efficiency at 12.5VIN_5145 shows the lowest efficiency even though we expect lower VIN_5145 shows higher efficiency.

Do you have any idea why LM5145 shows that result?

[Test condition]
device: LM5145
VIN_5145: 12.5V, 14V, 24V
VIN_FET: 24V
Vout: 3.3V
Iout: 3A
efficiency:
- 91.4% at 24VIN_5145
- 92.4% at 14VIN_5145
- 90.9% at 12.5VIN_5145

LM5145.pptx

Regards,
Kai

  • 0
    TI__Mastermind 27470 points

    Kai:

    1. do you know how customer test the efficiency, Does Vin close to input capacitor?

    2. can customer add 8V voltage at VCC pin like below, Dvin don't need if Vin not lower than 8V. and test the efficiency again. 

    Thanks

    Daniel Li

  • 0 in reply to Daniel Li14
    TI__Expert 5545 points

    Hi Daniel,

    Regarding #1, here is customer test conddition. they don't take Vin close to input capacitor but are there any DC voltage sensitive components on VIN line?

    Regarding #2, i will share that information with customer.

    Regards,

    Kai

  • 0 in reply to Kai Nomiyama
    TI__Guru 73072 points

    Hi Kai-san,

    Is this with the LM5145 EVM? Note the input filter inductor is in series, so it has higher loss at low Vin (higher Iin) -- try measuring Vin at the regulator side to avoid that drop. However, this really shouldn't be a factor for a 3.3V x 3A output, < 10W.

    Also, note the Rdson of the high-side FET is higher in anticipation of a lower duty cycle operating point. Again, this shouldn't have a major impact given the light-load condition. 

    Is DEMB tied high or low here?

    Regards,

    Tim.