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TM4C129EKCPDT: TM4C129EKCPDTI3R USE?

Simba Su
Prodigy 240 points
Part Number: TM4C129EKCPDT

We use  TM4C129EKCPDTI3R,  The POWER indicator light of our equipment is always on when powered by the POWER supply of 3V3, and the POWER supply of the chip is also powered by the POWER supply of 3V3. We use the chip VBAT pin and the chip register to save the POWER off data. When the POWER supply of the equipment is disconnected, the POWER light of the equipment will keep a slightly bright state.By testing the voltage and current, the chip VBAT pin current is significantly increased (the current is from the battery). The 3V3 loop has a voltage of 1V6, but the 3V3 loop has no power supply.The VBAT pin is connected to the battery positive pole, and the battery voltage is 3V3.TI support to solution the problem, analyze the reason for the pin to electricity rate is not greater than 0.7 V/us, by the RC circuit, reduce electricity rate, confirm the resistance value of 51 r, capacitance value is 100 nf follow-up until solve the problem, but in a batch production and found that the power lamp light phenomenon, by adjusting the resistance, we further reduce electricity speed of the pin, the issue is resolved for the time being.May I ask: can we solve the problem by increasing the resistance value and reducing the power loading speed? What is the reason for the recurrence of this phenomenon?

  • 0
    TI__Guru*** 127995 points

    Hello Simba,

    The suggestions in the System Design Guidelines assume no other components are meant to be a quick set of values for all customers to use in a basic application. By introducing the diode, you need to recharacterize the behavior when the Vbat ramps up. Changes to resistance are fine to handle this, but it is a system specific requirement then so you need to do the system evaluation and pick the right values based on the ramp voltage observed in your system.

  • 0 in reply to Ralph Jacobi
    Prodigy 240 points

    To analyze the reason for the pin to electricity rate is not greater than 0.7 V/us, by the RC circuit, reduce electricity rate, confirm the resistance value of 51 r, capacitance value is 100 nf follow-up until solve the problem, but in a batch production and found that the power lamp light phenomenon, by adjusting the resistance value is 1 k ohm, we further reduce electricity speed of the pin, the issue is resolved for the time being.May I ask whether our measures to increase the resistance value and reduce the power loading speed can solve the problem?What is the reason for this recurrence?

  • 0 in reply to Simba Su
    TI__Guru*** 127995 points

    Hello Simba,

    Simba Su said:
    May I ask whether our measures to increase the resistance value and reduce the power loading speed can solve the problem?

    As I've said before, you need to characterize this on your system. We cannot characterize your system behavior for you.

    You need to assess the voltage rise at the MCU I/O and ensure it is less than 0.7V/us.

    If it is, then your system design is fine.

    If it is faster, then you need to adjust your component values (maybe the capacitor is easiest here, so you can keep the same R).

    That is not a question that we can answer though the full circuit including the diode impacts this.

    Simba Su said:
    What is the reason for this recurrence?

    By adding the diode you changed the circuitry beyond what we documented, and the voltage drop across the diode is impacting your system setup. So you need to re-evaluated your system for the 0.7V/us condition.