LM3424 buck boost LED driver uncompensated dc loop gain

Anand Vivek Ravi

Other Parts Discussed in Thread: LM3424

Hi,

This question is regarding the uncompensated dc gain of buck-boost converter given in the datasheet of LM3424. I have attached a pdf which contains a block diagram of the peak current control using the LM3424 (may be generic). The uncompensated open loop gain contains all the parameters given in the datasheet except 500V. I do not get where the 500V comes from. I would like to know 1. Whether the attached control structure is correct and 2. Where does the 500V come from? Any Help would be appreciated.

Thanks,

Anand V R

over 7 years ago

0 Clinton Jensen over 7 years ago

TI__Mastermind 25500 points

The “500V” in the dc gain equation (equation 15 in the datasheet) is the dc gain of the error amplifier. This dc gain equals to gm x Ro (gm is 100uA/V from datasheet and Ro is estimated as 5Mohm, see equation 18 in the datasheet).

0 Anand Vivek Ravi over 7 years ago in reply to Clinton Jensen

Prodigy 70 points

Thanks Clinton. One final question - Why does gm X Ro have the units of 'V'. Shouldn't it be dimensionless (A X ohm / V).

0 Clinton Jensen over 7 years ago in reply to Anand Vivek Ravi

TI__Mastermind 25500 points

Good question. I believe that is a typo and you are correct.

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LM3424 buck boost LED driver uncompensated dc loop gain