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LMG3422R030: Clarification regarding the application and implementation

Neha Agarwal
Prodigy 80 points
Part Number: LMG3422R030

Hi,

In the Typical half bridge application of LMG3422R030 I saw that the input to S1 and S2 have lot of differences. If I am not wrong, the only difference should be that when its high input to S1 input to S2 should be low. I am not sure if there is some other difference in the 2 inputs. However, when I look at the circuit implementation I see that the isolator used has different pins, also there is a MOSFET MGSF1N02LT1G, to name few differences. 

Could you please tell me why are the two branches different.

Thank you for your help,

Neha Agarwal

  • 0
    TI__Expert 5855 points

    Hi Neha,

    S1 and S2 will be mostly similar like you've said above. They will both use reference grounds of the node their source pin is connected to, this means the low side device will use ground as its reference ground and the high side device will use the switch node as its reference ground. In addition to this the EVM which the schematics are for offer the options of using either isolated bias supplies or bootstrap power supply to power the devices. When choosing the isolated bias supply the MOSFET isn't used and does not need to be populated. This allows you to reduce the isolator down to a four channel isolator, the same as the high side. When using the bootstrap supply for the high side device, the MOSFET is necessary to slow down the slew rate of the low side device during the initial switching cycles of startup in order to build up charge. This is only necessary when using the bootstrap supply and a slew rate ≥100V/ns.

    Best,
    Kyle Wolf