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LM2941: Adjusting multiple LM2941s with a single control

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Replies: 3

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Part Number: LM2941

Hi - I'm trying to setup two LM2941 regulators to operate with one control. I have built a prototype of a simple setup using a  single pair of resistors (OUT to ADJ (1.8k) and ADJ to GND (470 ohm)) on one of the LM2941 regulators and connected a second LM2941 so that its connected to the same input, control (on/off), GND and ADJ  - the outputs are separate and there is no OUT to ADJ resistor on the second LM2941 . I get very different output voltages from the two regulator outputs. Obviously they are not tracking at all closely. If I use the same setup with two LM317s it works fine.  Is there something else needed or a different arrangement required (for LDOs) to allow two LM2941s to share a single control

thanks charlie

  • Hi Charlie,

    LM317 and LM2941 have different design typologies. The LM317 regulates when the Vref is across the top resistor in the external resistor divider, while LM2941 regulates when Vref is across the bottom resistor in the resistor divider.

    While there is no issue with tying the two inputs, GNDs, and ON/OFF pins for each regulator, there is risk when you break the feedback loop for the linear regulator.

    We do have LDOs such as TPS743 and TPS7B5x-Q1 devices that are designed for voltage tracking. For these families you will note that in order to achieve voltage tracking, it is the voltage reference that is adjusted rather than the feedback loop.

    Very Respectfully,
    Ryan
  • In reply to Ryan Eslinger:

    I was after an LDO that could handle at least an input of 12 v and outputs of 6v to 10.5 - using a 3 bit digital control to parallel resistors . The LDOs you mention TPS743 doesn't support my input voltage ...not sure the TPS7B5x-Q1 as I could not find a reference to the family on the TI site ..is the part number right? could you provide a link to any of the devices in that TPS7B5x-Q1 family and I can check out the data sheets from there.

    thanks again

  • In reply to Charlie Azz:

    Hi Charlie,

    My apologies, I was intending to refer to the TPS7B425x-Q1 family (TPS7B4254-Q1, TPS7B4253-Q1, TPS7B4250-Q1). I am not sure what happened to my "42." These devices have an operating input voltage range up to 40 V.

    Very Respectfully,
    Ryan

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