LTC4357 100V Application

Hello, 

Is it possible to use LTC4357 for 80V+ voltage oring by ground shifting as shown below?

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  • +1
    •  Analog Employees 
    on Apr 18, 2019 9:40 PM over 1 year ago

    Hello ek09,  The above circuit needs to be within the 9V to 80V operating and 100V absolute maximum rating of the LTC4357 but device should also not spend extended time near absolute maximum rating (per Note 1 on datasheet page 3). For example, with V1 input at 0V and Vout = 100V, U1 GND pin will be around 0.7V. Therefore, OUT – GND is close to 100V absolute maximum even under normal operation. For your application, please see Figure 11, 200V Ideal Diode, on page 13 of LTC4359 datasheet.

  • Hi PSachdev,  it seems to me your argument against ek09's circuit, also applies to Figure 11 of the data sheet- if Vin=0, it will pull Vss to about 0.7V through D1, forcing (Vout-Vss =~200).  I guess the assumption behind Fig 11 (and the app note by Mitchell Lee) is that Vin has to stay higher than Vout-100, or be open-circuit.  This might be a realistic assumption in some systems, e.g. with battery banks.  Or am I missing something?

    Also, I have a related question: the LTC4359 data sheet says it's rated for an operating range up to 80V, and its absolute max limit on Vin is 100V.  Can I infer that one should avoid operating between these two voltages?  (Murphy's law in play: I have an application that is spec'd up to 90V.)

    Thanks,

    JoePb

  • 0
    •  Analog Employees 
    on Aug 20, 2019 5:47 PM over 1 year ago in reply to JoePb

    Hi JoePb,  In LTC4359 Figure 11 circuit, when VIN1 = 0V, the depletion mode transistor Q3 clamps LTC4359 OUT pin to a few volts above 0V. This preserves the IN - OUT absolute maximum rating of the device. Yes, LTC4359 operating range is limited to 80V but Figure 11 shows a way to use it above 80V.

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