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INA195: Current Limiter Circuit for 10mA

Part Number: INA195
Other Parts Discussed in Thread: TLV3201, LM27761, LMP8646, LP38693-ADJ, LP38693

I want to limit o/p current limit at 10mA for -3.5V supply regulator.

Can we use current sense INA195 and comparator TLV3201 to control the EN pin of -3.5V regulator to limit the current at 10mA ?

please ASAP

  • Is this a switching regulator? Can you provide us more details regarding the complete circuit?
    We have a couple of devices with built in comparator that might be a better choice (smaller footprint, built in hysteresis)
    The INA195 and the TLV3201 might work, what accuracy are you looking into?
  • we are planing to use LM27761 regulator to generate -3.5V O/P. The only thing we want to control O/P current to 10mA.

    -3.5V Supply spec are :- 

    Vin = 5V

    Vout = -3.5V (Negative voltage) +/-5%

     Current limit power up = 10mA 

    Steady State current = 5mA

    Ripple   =  10mV RMS @ 1MHZ.

    Please suggest the suitable approach to meet this requirement.

  • For the required accuracy, the correct approach is to modify the feedback loop on your chosen regulator to throttle back the output should the maximum current be exceeded. 

    A standard current sense amplifier cannot be used for this purpose, since both loops (voltage and current) need to be combined using a diode, which would introduce errors due to the non linear current versus forward voltage characteristics and the associated voltage drop. The LMP8646 was designed with this in mind and has an internal diode compensated by the feedback loop.

    I suggest a read to the LMP8646 datasheet, which explains in detail how to implement a current source using an existing constant voltage regulator and how to calculate all the required parameters.

    Under the required application, which uses a negative output voltage, the device should be powered from the 5V line and the sense resistor should be placed in series with ground and the negative load as shown below:

    Do be aware that your chosen voltage regulator has a min output of -1.5V, and therefore current throttling will only occur on the range Vout {-1.5...-3.5V}.

    I suggest a device whose output can be adjusted all the way down to zero.

  • Is this current source we should connect after -3.5V regulator?

    How will it limit the current at 10mA?

    It would be really helpful if you share some connectivity diagram of the complete solution.

  • Hi Rahul,
    Please see my updated post above.
  • We need to limit current for the following supplies as well ..please suggest regulator compatible with LMP8646 current limiter:

    1. VOUT = +1.8V

    Vin = 3V

    Vout = +1.8V +/-15%

    Current limit power up = 150mA

    Steady State current = 80mA

    Ripple = 30mV RMS @ 1MHZ

    2. VOUT = +6.5V

    Vin = 9V

    Vout = +6.5V +/-5%

    Current limit power up = 100mA

    Steady State current = 80mA

    Ripple = 10mV RMS @ 1MHZ

    For -3.5V current limit as discussed earlier, Can we simulate the full circuit ?
    We got pSpice model for LMP8646 but did not find model for regulator LM27761.
  • Can we use LP38693-ADJ voltage regulator with LMP8646 current limiter to for 1.8V & 6.5V for 150mA current limit ?
    If yes please suggest simulation method
  • The LP38693 has a minimun regulation voltage of 1.25V, therefore the circuit can be implemented to limit current as long as the limitation occurs above this voltage level.

    For Vout >0 and <1.25V the output will be limited by the regulator itself. Please refer to Section 7.3.3 of the device datasheet for further details.

    I would suggest posting a new question on the buck converter forums section for help on choosing an appropriate regulator. In the meanwhile, here is a resource that can help.

    Please note that there will always be a voltage drop across the sense resistor used to monitor the current, so be aware of this when selecting a value so that the output stays within the specifications, when loaded at your desired current level.

  • As you suggested the LMP8646 for -3.5V@10mA current limiting.
    How to connect Vout pin of LMP8646 to the negative LM27761 regulator Feedback (FB) pin ?
    How we can calculate components for LMP8646 for negative supply since Online tool of LMP8646 is not supporting negative regulator O/P ?
  • Hi Rahul,

    The output of the LMP8646 goes directly into the regulator feedback pin, just as it does on the positive regulator.  Remember both the LMP8646 and the buck boost converter used to generate the negative rail are powered from the positive 5V voltage.

  • Can we connect load in other configuration because in the user connector there is only -3.5V supply pins and common ground.
    please suggest some other options and also suggest simulation scheme.
  • Hi Rahul,

    The load configuration we showed earlier is, sadly, the only one we are able to support, achieving your design criteria and our device specs.
  • Ok..Can you please suggest some external current limiting circuitry which we can connect at the o/p of regulator?

    Please share some application note or any method.

  • Hi Rahul,

    I'm afraid adding a external circuit to the output of the regulator would add an additional voltage drop to the supply that would put it right out of the specs. This is fine in applications such as LED lightning, where the voltage is only coarsely regulated for safety (open circuit) but the actual device operates in constant current mode.

    For your specs, the only option is to use a current sense comparator to add an additional error signal to the reference of the regulator thus limiting the voltage once a given current is exceeded (hence CC operation).

    The only application note we have is that shown on the LMP8646 Datasheet that goes into detail regarding the required modifications and I also explained what are the required modifications to make the circuit operate at a negative supply. Should you have any questions after building that circuit I may be able to assist further.

  • Ok, Actually my requirement is to limit the O/P current of regulator (LM27761) when load demands more current (>10mA@-3.5V) not to stop the output voltage of regulator. In this case can i use current sense amplifier with mosfet kind of circuitory ?

    I saw some kind of circuits using opamp and mosfet with error amplifiers but in my case i am finding difficulty in the right selection of components.

    Actually i am comfortable with TI parts so, can you please suggest me some current sense amplifier and additional components which i can use to control the feedback pin of regulator to limit the o/p current ?

    I would be really helpful if you give some interface diagram kind of ....