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# LTC3129 Efficiency loss

Dear Analog Team,

I recently tested your evaluation board and I faced efficiency loss issue for low output voltage.

Please refer the evaluation board and test condition details below,

Evaluation Board:  LTC3129 Demo Circuit 1922A.

Test Condition:

Input Voltage: 2.4 to 4

Configured Output Voltage: 1.438V

Mode: Burst

Obtained Efficiency: 66.22%

Please refer below table for tested results,

As per datasheet graph efficiency would be greater than 80% but practically I couldn’t achieve it. Please refer below image,

What is the reason for efficiency loss? Could you clarify me?

• This post is incorrectly categorized.  Please move to Power by Linear

• Could you any one give a solution for the above problem?

• Given your operating conditions, I would not expect 80% efficiency.  The curves in the datasheet, and in the demo manual show efficiency for a given output voltage.  Since your output voltage is significantly lower it is hard to compare those graphs directly.  However, if you compare the curves for similar output power you can see the efficiency is between 60-70% depending on Vin.  For example if you take your Vout= 1.44V and Iout =   17mA your Po= 24.5mW.  If you compare that operating point to one where Vout =2.5V (one of the curves in the datasheet) that corresponds to a load current of 9.8mA.  You can see from the curve in the datasheet on the bottom of page 4, for Vin=5V and Vout =2.5V that gives an efficiency of about 60%, and for Vin=2.5V about 70%.  While not exactly your operating mode, it is close enough for a general comparison.

I would recommend measuring the efficiency on the demo board under the demo board operating conditions, i.e. with Vout=5V and at an input voltage corresponding to 3V.  See if you get similar efficiency as is shown in the curve in the demo manual.  That way you can verify your measurement technique.