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LM53603-Q1: Accurate Estimation of Max Dropout Voltage

Part Number: LM53603-Q1


I'd like to accurately estimate the Max dropout voltage of LM53603-Q1 under the following conditions.

  • Output voltage drops down to 4.95 V.
  • Output current: 3 A
  • Switching frequency: It is acceptable that fSW goes below 1.85 MHz.

Alternatively, the worst case of Figure 25 (Drop-out for -1% Regulation) on the data sheet is OK.

Is there any equation or tool to calculate the number? Or, is actual measurement needed to get the number?

Please give me advice.

Best regards,
Shinichi Yokota

  • Yokota-san,

    The dropout is  dependent on three  factors -  98% duty limit  , I*R drop across High side FET and Drop across Inductor DCR.

    The worst case drop out can be calculated as (Vin*0.98) - (290 mOhm high side FET RDson + Inductor DCR)* Iout where 0.98 is the max duty cycle limit , 290mohm is the worst case Rdson of high side FET .

    4.95 =  (Vin*0.98) - (290 mOhm high side FET RDson + Inductor DCR)* Iout , Iout=3A and suppose DCR=10mohm

    Here Vin comes out to be 5.96V and hence the dropuout is 5.96V-4.95V= 1V approx.