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LMR23630: Problem with regulator LMR23630

Part Number: LMR23630
Other Parts Discussed in Thread: BQ24070, , LM2576

Regulator issue
For a tracking device we implement the attached power scheme

the device processor is a MT7688AN

The MT7688AN processor has a Linux operating system (openwrt) and when energizing the device with a discharged battery or without battery, the following behavior occurs, the MT7688AN starts to load the kernel and all its components, but when the modem is energized, the MT7688AN is it restarts and does not finish loading the operating system (this process is repeated indefinitely), when the BQ24070 regulator has a charged battery connected, the MT7688AN does not restart when the modem is energized, so I can assume that the problem is in the current which can supply the LMR23630 regulator or the BQ24070 regulator.

Another fact to mention is that the device's coils emit a hum when the modem is sending information.

The peak consumption of the MT7688AN together with its peripherals (memories, regulators, etc.) is 800mA, the average consumption is 300mA. The LT1963EST3.3 regulator supplies a maximum current of 1.5A, enough for the MT7688AN processor to work.

The peak consumption of the 2G modem can reach 1.6A, the average consumption is around 400mA, the SC4215A regulator supplies a maximum current of 2A, enough for the 2G modem to work.

The steps you took to identify the problem were as follows.

1. remove the battery regulator BQ24070, and feed the regulators LT1963EST3.3 (3.3v) and SC4215A (3.8v) with the 5v of the LMR23630 regulator, in this case the behavior was the same, the MT7688AN restarts when the modem is energized 2G.

When monitoring the oscilloscope I could not observe any voltage drop in the 3.3v line to which the MT7688AN is connected

2. Al replace the LMR23630 regulator with the LM2576S regulator.
With this change, the MT7688AN processor works without problems, it no longer restarts when the modem is started and no sound is heard from the device's coils.

My questions are the following:

The LMR23630 and LM2576S regulators can supply a current of 3A (according to the datasheet), when measuring the consumption of the device I obtained a maximum measurement of 0.61A with a voltage of 5v between the LMR2360 regulator and the BQ24070 regulator, this measurement is carried out with a fluke 117 multimeter in current measurement and maximum measurement configuration.
Which tells me that the consumption of the device is very far from the maximum current of the LMR23630 and LM2576S regulators.

Why does the device work correctly with the LM2576S regulator and not with the LMR23630 regulator?

What component should I add / change to the LMR23630 regulator circuit in order to use this regulator in the device?

The schematic circuit used for the LMR23630 regulator and the LM2576S regulator are those indicated by their datasheets in the example circuit.

  • Hi Jose,

    I'm a bit confused on your application. LMR23630 is a synchronous converter while LM2576 regulator is a non-synchronous. There must be a difference in circuitry if swapping out for testing. Thanks for the clarification.

    Regards,
    Alejandro

  • Hello Alejandro,


    Regulator circuits are different,


    The device PCB was designed with the LMR23630 regulator and the components it requires for its operation.

    Then for the test I did with the LM2576 I used a PCB that had the circuit for that regulator, remove the regulator LMR23630 from the device PCB (along with inductor and capacitors) and with cables I made the connection from the LM2576 regulator to the device PCB


    I did not know that one regulator was synchronous and the other was not.

  • Jose,

    Can you please provide circuit schematic used for LM2576? Can we please try the following tests:

    • I would recommend to swap Cout with a ceramic 100uF. Share results. Cout affects the steady-state output-voltage ripple, loop stability, and the voltage over/undershoot during load-current transients. I'm curious/speculating that the output capacitance is not large enough to supply the transients. (See section 9.2.2.5 in datasheet for more info)
    • Keep in mind that the cout value on Figure 9-1 (Table 9-1) is after derating.
    • Can you clarify the following? "When measuring the consumption of the device", what device?

      when measuring the consumption of the device I obtained a maximum measurement of 0.61A with a voltage of 5v between the LMR2360 regulator and the BQ24070 regulator

      Thanks,
      Alejandro

  • Hello Alejandro, 

    This is the circuit I used with the LM2576 regulator

    This is the measurement I get on Cout from the LM2576 regulator.

    These are the results of the tests you requested.

    1. Change Cout for a 100uf ceramic capacitor.

    This is the oscilloscope measurement before the change:

    This is the oscilloscope measurement on the capacitor, after swapping the Cout for a 100uF tantalum capacitor.

    This is the oscilloscope measurement on the capacitor, after swapping the Cout for a 100uF ceramic capacitor

     

    2. The tracking device has a processor based on an MT7688AN, a flash memory, a RAM memory, a 2G modem, a GPS, a 4-channel optocoupler, and the regulators that I have included in the block design of the power supply. device.

    I did the current measurement at the following point:

  • Hi Jose,

    This is strange. I have reached out to the team internally for further input, but in the meantime: When swapping to ceramic cap values, did you test if any failures occurred? What about increasing your ceramic cap values? Sincewe would like cout =100uF effective capacitance and currently it might be de-rating too low.

    Thanks,
    Alejandro

  • Hi iAlejandro,

    I did a test with the 100uF ceramic capacitor, and the device reset the same as with the electrolytic capacitor.

    then I did a second test with 200uF Cout (two 100uF capacitors in parallel) and this time the device did not reset, and it works correctly, do this test 10 times.

    I did a third test with a 1000uF tantalum capacitor but the device also reboots.

    I should use a ceramic capacitor in Cout, but what would be the correct value for this capacitor?

  • Hi Jose,

    That's good to hear! So, increasing the ceramic cap helped solve the problem. The effective capacitance value can be found in the datasheets of the individual capacitor. For example, there should be a figure/curve that indicates "DC Bias Characteristics". If data curve is not found within the datasheet, it might be something to contact the vendor about.

    Take a look at this link for an example which explains in detail about "nominal value" and "effective capacitance".

    Thanks,
    Alejandro