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Original question:

TPS63031: Current Consumption (Load and No Load) is more than expectation

TPS63031: Unable to get expected Low Power

Amit Kotal
Intellectual 535 points
Part Number: TPS63031

Hi,

I am designing a Battery Operated Low Power Device, battery used will be of 3.6V Li-Po. TPS63031 is used as a buck boost converter. I have designed a custom PCB for the project. 

During Initial Tests, the TPS63031 was showing a current consumption of 40uA at no load, which is approx similar to quiescent current in datasheet specs. But after I connect a micro controller and an LED, the current consumption measured is quite high and unstable ranging between 250uA to 120 uA.

Points to note,

1. The micro controller is put in to low power sleep mode, making the PSCTL Pin of TPS Low to enter power save mode.

2. During Run Mode of Micro controller, PSCTL Pin is pulled high to disable power save mode.

3. The measured current test values always differ for different attempts.

For reference I am attaching the circuit schematic pdf  of TPS63031.

Thank You,

Amit Kotal

tps63031 schematic.pdf

  • 0
    TI__Expert 7925 points
    Hi Amit,

    Firstly, just as a note, the Iq in the datasheet is not the no-load input current. See this application note for clarification:

    www.ti.com/lit/an/slyt412/slyt412.pdf

    Nevertheless, 40 μA seems fine for no-load input current of the TPS63031.

    I assume you refer to PS/SYNC pin. If you disable power save mode, the converter will operate in forced PWM mode, which results in higher input current. Why do you disable power save mode?

    Best regards,
    Milos
  • 0 in reply to Milos
    Intellectual 535 points
    Hi Milos,
    Thanks for the reply.
    Yes, PSCTL refers to the PS/SYNC pin. I may be wrong in understanding the Power Save Mode. I intend to keep the power consumption as low as possible to conserve battery. Hence, during Run Mode of the System, I Disable Power Save mode, in order to meet the load power requirements and during the Sleep Mode of the System, I Enable the Power Save Mode via the PS/SYNC Pin.
    So Is this approach the right way?
    Also kindly elaborate the Forced PWM mode and how can it affect the power consumption. I am a noobie in Low Power Design and Applications.

    Regards,
    Amit Kotal
  • 0 in reply to Amit Kotal
    TI__Expert 7925 points

    Hi Amit,

    As described in the datasheet, there are 3 modes of operation:
    1. Power-save mode enabled (PS/SYNC=LOW): for light loads (resulting in inductor current lower than 100 mA) the converter operates in short bursts, just frequently enough to sustain the output voltage. The no-load input current is lowest and the light-load efficiency is higher (Figure 6), but the output voltage ripple is higher.
    2. Power-save mode disabled (PS/SYNC=HI): the converter is always switching, resulting in lower ripple, but poor efficiency below 100 mA (Figure 7).
    3. Shutdown mode (EN=LOW): The device is turned off and the load is disconnected from the source.

    If you just have an MCU with an LED as a load I would keep the device always in power save mode (PS/SYNC=LOW), as the load is likely not sensitive to somewhat higher ripple in power save mode.

    Is the MCU itself controlling the PS/SYNC pin?

    Best regards,
    Milos

  • 0 in reply to Milos
    Intellectual 535 points
    Hi Milos,
    Thanks for the in depth elaboration.
    Yes the MCU itself will be controlling the PS/SYNC Pin, and also a Pull Down Arrangement is made.
    The MCU and LED are only used for testing, the complete board will be having approx load of 600 - 700 mA, with certain spikes,
    So will it be fine if TPS is used in Power Save Mode ?
    Also I have a query, Will it be an issue, if the PS/SYNC Pin is Switched from High to Low or vice versa, during system run time??

    Regards,
    Amit Kotal
  • 0 in reply to Amit Kotal
    TI__Expert 7925 points
    Hi Amit,

    Just a side note, check Figure 2 in the datasheet if the device can deliver the required load current under all input voltages.

    The device can be freely switched between the modes during run time. Just make sure that your load can tolerate somewhat larger ripple in the power save mode, if the load current is low. For high load currents, the device will always operate in PWM mode with small ripple.

    Best regards,
    Milos
  • 0 in reply to Milos
    Intellectual 535 points
    Hi Milos,
    Now majority of my queries are clear. I am very grateful for your help. Just last thing I wish to know. If in hardware itself the PS/SYNC Pin is kept low via a Pull Down Resistor and My system includes, various RF modules, wherein Total Load Current During boot can reach up to 300 - 400 mA, and I will be Disabling the Power Save Mode via the MCU during Boot. So during this boot interval, will the TPS handle the load spikes?

    Best Regards,
    Amit Kotal
  • 0 in reply to Amit Kotal
    TI__Expert 7925 points
    Hi Amit,

    For such output currents, the device will likely work in PWM mode anyway, regardless of the PS/SYNC pin state. I think it would be safe to leave PS mode always enabled, but even if you want to change the mode during boot-up that should not make any problems.

    Best regards,
    Milos
  • 0 in reply to Milos
    Intellectual 535 points
    Hi Milos,
    I am very much grateful for your time and support.

    Regards,
    Amit Kotal