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I'm looking for a Supervisor circuit for monitoring both negative and possitive power supply

Mateusz Kaluzny17
Expert 1065 points
Other Parts Discussed in Thread: UC1903, TPS3701

Hello dear Ti community.

I've got a dual rail power supply which will power up my amplifier.
Both of them got enable PIN (TPS7A4701 and TPS7A3301) so I want to use them better than with simple voltage divider which is not enough in my case.

What I'm looking for? I'm looking for a simple solution to monitor both negative and positive voltage which will be presented at regulators input pins.
It would be nice to achieve one thing, lets assume that one of power rail will go down below 20/-20V (I've got both regs adjusted to symetrical 18V) if that happen one of two regs will be off till malfunction will be removed. I'm looking for a solution that will turn off both regs even if one of them can be properly powered up, no matter which voltage will be below threshold (pos or neg).

I never done that before so I'm looking for a solution, IC proposition etc. I neved had that kind of issue in the past, but it would be nice to be protected anyway :)

  • 0
    TI__Genius 12630 points

    Mateusz,

    I think the best solution is UC1903 device family. This device has wide input voltage range and can monitor 4 voltages for undervoltage and overvoltage in addition to 1 negative voltage monitor.

    http://www.ti.com/product/uc1903

    Please provide feedback if this device will work for your application!

    -Michael

  • 0 in reply to Michael_DeSando
    Expert 1065 points

    Michal, thank you for suggestion :)
    That IC look very nice, it's even suitable for negative voltage - one IC for all my needs.

    But there is a question, with this chip I will be able to monitor my positive and negative supply (undervoltage option), so I can add some LEDs for easy visual control.

    Michael could you help me adjust everything to suit my needs?

    I've got a power supply based on TPS7A4701 and TPS7A3301 both are adjusted for symetrical 18V per line.
    So it would be nice to use features of this kinda expensive UC1903.

    I assume that UV and OV control works for all sensing inputs, so how to set it properly?
    Lets assume that I want to stay in range of 20-25V, everything below will be triggered as a UV and everything above will be recognized as a OV.
    Similiar situation for negative voltage.

    I also assume that power ok signal should be tied with EN pins of both regs to power it on and turn it off if there will be any OV or UV at least on one power line or both?

  • 0 in reply to Mateusz Kaluzny17
    TI__Genius 12630 points

    Mateusz,

    The reference voltage for this device is 2.5V. So if you are sensing 22.5V as your center point and 20V is the UV and 25V is the OV (so +/- 2.5V), you could set the following:

    Vs (nom) = 22.5V, V_UV = 20V, V_OV = 25V so the fault window in percent is (1- (20/22.5)) * 100 =  11%

    Set R2 to 10 kohm. Solve for R1 = 80 kohm.

    Solving for R3 with 11% fault window gives R3 = approx 88.8 kohm.

    If you do not want to use R3 and want to use the standard 10% fault window, the UV will be approx. 20.25V and the OV will be 24.75V.

    Please try this out and let me know your feedback.

    -Michael

  • 0 in reply to Michael_DeSando
    Expert 1065 points

    Michael.

    How about using TPS3701 for each rail (even negative) then I will need two of these :)

    Let's assume I need to disable LDO when voltage fall below 20V or rise above 25V.

    That chip should do the trick? Or maybe I will need to add some mosfet.
    There is two outputs, should I pull up both to my VDD?

    That chip is rather cheap and very small which is good for my design, I need only UV and OV to be honest.

    Could you help me calculate exact resistor values? Both rails are almost the same (TPS7A4701 and TPS7A3301).
    I will need output of 3V to enable TPS7A4701 and 2v (or -2V) to do the same for TPS7A3301.

    I never done that before, I used some supervisors for simple reset when voltage below some level, but that was all in one IC like MCP130.

  • 0 in reply to Mateusz Kaluzny17
    TI__Genius 12630 points

    Mateusz,

    TPS3701 is an excellent choice, one of our top performing devices.

    Using the application section in the datasheet, section 8.1.1

    Setting Vmon(OV) at 25V and Vmon(UV) at 20V, I calculated:

    R1 = ~980kohm, R2 = ~4kohm, R3 = ~16kohm.

    Let me know if that works for you. Thanks!

    -Michael

  • 0 in reply to Michael_DeSando
    Expert 1065 points

    Ok. Thank you.

    Both outputs should be pulled up via resistor (should I care about value, 10K-50K?).
    And then tied together to EN pin of my reg?

    How about driving some LEDs for OV and UV indicator?

    Will it work like in this picture (actually it's diffrent chip, but doing similiar job).

    I just don't want to use another chip and resistors for LED indicator if I'm able to use those two TPS3701, instead of MC34161 (picture taken from his app note).

    Both outputs should be pulled up via one resistor in my case?
    How about output voltage of TPS3701? What should I expect when everything is fine (no UV/OV lockout).

  • 0 in reply to Mateusz Kaluzny17
    TI__Genius 12630 points
    You can use a single pull-up resistor and you select the value to ensure the output current is less than the recommended output current MAX which is 10mA for both outputs. So scale your resistor accordingly. Also, the LED will work so long as there is enough current to drive it ON. When no UV or OV condition, output will be pulled "high" to the pull-up voltage. So in the LED case, the LED will be off (no current flowing through it) when no UV or OV condition detected. Then when either of the outputs drops "low", this should turn on the LED.

    Does this answer all your questions?

    -Michael
  • 0 in reply to Michael_DeSando
    Expert 1065 points

    I know almost everything ;)

    Would you please take a look in to my schematic?
    It's for both rails VEE and VCC.
    One diode for faulty condition and one for "OK" state.

  • 0 in reply to Mateusz Kaluzny17
    TI__Genius 12630 points

    Mateusz,

    I looked over the schematic and there are some concerns.

    1. LED4 will not work I don't think. When OUT is high (no undervoltage or overvoltage is detected), LED4 will pull the output low which is going to incorrectly change the output logic.. and when the output is low due to UV or OV, LED4 will be shorted out because internal FET will be on. I recommend using just LED1 for the top circuit. When LED is off, voltage is OK and when LED1 is on, this is undervoltage or overvoltage condition. Keep in mind that LED1 provides an addition path from VDD to OUT when OUT is low.

    2. For the bottom circuit, LED2 and LED5 are in opposite directions. Is this intentional? I have not seen this device configured for monitoring negative voltages but again, I would recommend using a single LED configuration.

    To see my simulation results, please email me directly at michaeldesando@ti.com

    -Michael