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LM74610-DQEVM: LM74610-DQEVM

Timothy Tran2
Intellectual 420 points
Part Number: LM74610-DQEVM
Other Parts Discussed in Thread: LM74610-Q1, LM74700-Q1, , LM74700EVM

Hi,

Figure 12 (schematic) on pg. 16 shows using a single FET (SQJ422EP-T1-GE3) per path (FET1_A, FET2_A), which is rated 75A max - If I use 2 x of those FET's in parallel per path then the current rating would be double ~ 150A (2x 75A), right?

Figure 6 on pg.10 - What is the send voltage drop/dip after the FET has fully turned on

Thanks,

Tim

  • 0
    TI__Guru 57737 points

    Hi Tim,

    Yes, Increasing the Number of FETs in parallel will increase the current handling capability. The actual current that can flow through the FET depends of layout (RQJA), Air flow/ Cooling, Max Ambient Temperature in the system, etc,..

    The drop in output voltage occasionally (approx. 2% duty cycle) is because the GATE is turned OFF by the LM74610-Q1. This is done intentionally so that the internal charge pump can charge the capacitor using the FET body diode drop. For more understanding, please refer to datasheet section '7.3 Feature Description'

    In case you do not want the voltage drop on Vout, you can consider using LM74700-Q1 which has a steady gate drive but comes with a GND pin and higher Iq when compared to that of LM74610-Q1.

  • 0 in reply to Praveen GD
    Intellectual 420 points

    Hi Praveen,

    Thanks the feedback and pointing on the LM74700-Q1.  what's minimum load current  in order ORing FET conducting at initial turn-on ?

    Is there any evaluation board for ORing application similar to the LM74610-DQEVM?  

    Thanks,

    Tim

  • 0 in reply to Timothy Tran2
    TI__Guru 57737 points

    Hi Tim,

    LM74700-Q1 has Linear Gate ORing control to ensure zero reverse current flow. This control regulates the FET gate voltage such that the voltage drop across the FET is maintained at 20mV.

    RDS(ON) x ILOAD = VAK(REG) = 20mV

    • Higher the load current, higher the gate voltage and lower the FET resistance. 
    • Lower the load current, lower the gate resistance and higher the FET resistance.

    For more understanding on this topic, please refer to e2e FAQ: Ideal Diode Controller or ORing Controller gate voltage is lower than expected

    To evaluate ORing functionality of LM74700-Q1, you need to use 2x  LM74700EVM and tie the outputs to together.

  • 0 in reply to Praveen GD
    Intellectual 420 points

    Hi Praveen,

    LM74700-Q1, if I'm using 3 or 4 FETs in parallel with each FET Rdson around 1mOhm for my application load 12V/90-100A, then I would need a very high load current > 70A to in order to maintain 20mV drop across the FETs otherwise the FETs will not fully turn on, right?  Is there other controller that requires much lower than 20mV?

    Thanks,

    Tim     

  • 0
    Intellectual 420 points

    Hi Praveen,

    Just wanted to clarify -  either LM74610-Q1 or LM74700-Q1 will require 20mV drop across FET (D-S) in order to controller to fully turn on the FET's , right?  if so, it will require load to be at least 20A  (20mV/1mOhm Rdson) for FET with low Rdson 1mOhm.   Is there way to have FETs fully turn on FETs with low Rdson (1mOhm, for example)  at light load (< 20A , for example)?

    Thanks,

    Tim  

  • 0 in reply to Praveen GD
    Intellectual 420 points

    Hi Praveen,

    Just wanted to clarify about the 20mV drop across FET (D-S) -  Either LM74610-Q1 or LM74700-Q1 will require 20mV  in order to controller to fully turn on the FET's , right?  If so, it will require load to be at least 20A  (20mV/1mOhm Rdson) for FET with low Rdson 1mOhm, for example.   So, is there way to fully turn on FETs with low Rdson (1mOhm, for example)  at light load (< 20A , for example)?

    Thanks,

    Tim  

  • 0 in reply to Timothy Tran2
    TI__Guru 57737 points

    Hi Timothy,

    LM74700-Q1 has linear gate control because of which the gate voltage is regulated so that the FET RDS(ON) x ILOAD  is maintained at 20mV. So, even though the FET is not fully ON/ Enhanced the voltage drop across the FET is constant because of which the power loss is not so significant. 

    In case customer wants completely ON gate irrespective of load current, them they can consider using LM74801-Q1 in Ideal diode only configuration. 

    To understand more about differences between Linear Gate control and Hysteretic ON/OFF control, customer can have a look at '6.1 Linear Regulation Control Vs Hysteretic ON/OFF Control' section '' of  Basics of Ideal Diodes Application note

  • 0 in reply to Praveen GD
    Intellectual 420 points

    Hi Praveen, 

    I couldn't find or locate your explanation..., or have you sent me yet?

    Thanks, Tim

  • 0 in reply to Timothy Tran2
    TI__Guru 57737 points

    Hi Timothy,

    LM74700-Q1 has linear gate control because of which the gate voltage is regulated so that the FET RDS(ON) x ILOAD  is maintained at 20mV. So, even though the FET is not fully ON/ Enhanced the voltage drop across the FET is constant because of which the power loss is not so significant. 

    In case customer wants completely ON gate irrespective of load current, them they can consider using LM74801-Q1 in Ideal diode only configuration. 

    To understand more about differences between Linear Gate control and Hysteretic ON/OFF control, customer can have a look at '6.1 Linear Regulation Control Vs Hysteretic ON/OFF Control' section '' of  Basics of Ideal Diodes Application note