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TPS61291: At which state should the EN/BYP pin at startup?

Danilo A.
Mastermind 24715 points
Part Number: TPS61291
Other Parts Discussed in Thread: CC1352P

Hi Team,

A customer asked the following questions about the EN/BYP pin.

1. Which state should the EN/BYP pin at start-up.

2. Does it matter if EN/BYP pin is at high or low state during start-up.

3. Can we set the EN/BYP pin in low at startup (Bypass mode).

Regards,

Danilo

  • 0
    TI__Mastermind 21565 points

    Hi Danilo:

    What's the customer condition? Please share the Vin, Vout, load condition, and describe what's they expected for startup.

  • 0 in reply to Minqiu Xie
    Intellectual 340 points

    Hello,

    Section 7.4.5 states:

    After the EN/BYP pin is tied high, the device starts to operate. If the input voltage is not high enough to supply the control circuit properly, a startup oscillator starts to operate the switches. During this phase, the switching frequency is controlled by the oscillator and the switch current is limited. As soon as the device has built up the output voltage to about 1.8 V, high enough for supplying the control circuit, the device switches to its normal hysteretic current mode operation.

    My questions?

    Does it mean at the startup, the EN/BYP pin should be connected to a pullup?

    Does it matter the state of the EN/BYP pin at the startup?

    Can EN/BYP pin be connected to MCU GPIO without any pullup or pulldown? (We are very sensitive to the leakage currents.)

    Our system requirement?

    EN/BYP comes from MCU GPIO (CC1352P).

    Battery voltage is 3.1V to 2V.

    Boost output: For battery 3.1V to 2.2V (Bypass mode). Under 2.2V battery, Output=3V (Boost mode)

    Best Regards,

    Ramin

  • 0 in reply to Ramin Rahamim
    TI__Mastermind 21565 points

    Hi Ramin:

    May I know what's meaning of "startup" in your understand? As the converter has bypass mode, so that pull up or pull down the EN/BYP pin, there is always a voltage at output side with battery. So, I will recommend you divide the situations into bypass mode or boost mode. (We usually just call start to operate with boost mode as "Startup" for such type part.)

    If you need the boost mode, (when Vbat<2.2V), you need to pull up(set high) the EN/BYP pin. If not, then pull down it (set low).

    The leakage current of this pin is 0.1uA max. It depends on the MCU port configuration if whether the pull up or pull down resistance is needed.

    The Fig 9 in datasheet shows an example.You can take it for reference.  

  • 0 in reply to Minqiu Xie
    Intellectual 340 points

    Hi Minqiu,

    I mean the state that there is no battery and first time the battery is inserted. At this state, is it important to have any pullup/down on EN/BYP pin? Because after MCU power-on, its GPIO will be at 3-state until the MCU changes the GPIO to low or high state. Does the 3-state can cause any problem to this device?

    Best Regards,

    Ramin

  • 0 in reply to Ramin Rahamim
    TI__Mastermind 21565 points

    Hi Ramin:

    Got it.

    The EN/BYP pin should not be float. So if the GPIO will be high-Z in some case, it's better to add the pull up or pull down resistance to ensure this pin with a certain level.

  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points

    Hi Ramin:

    One question:

    If there is no battery, if there any power for MCU?

  • 0 in reply to Minqiu Xie
    Intellectual 340 points

    Hi Minqiu,

    No power for MCU.

    If the MCU receives power at the first time, then after its power-on Reset, it changes its GPIO from 3-state to any low/high level, a pullup is still needed?

    I don't see such pullups in any of the examples in the datasheet. The examples are for MSP430 (figure 9) that its GPIO is also at 3-state at first time after a battery is inserted.

    Please advise

    Ramin

  • 0 in reply to Ramin Rahamim
    TI__Mastermind 21565 points

    Hi Ramin:

    The purpose that EN/BYP should float is to ensure it has a certain status for bypass or boost mode. 

    If there is no battery and no power for MCU, it doesn't matter which state the converter is.