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# LM53603-Q1: Accurate Estimation of Max Dropout Voltage

Part Number: LM53603-Q1

Hello,

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?

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.

----Ambreesh