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TPS61288: Design verification and Enable pin function

Balasubramani M
Prodigy 20 points
Part Number: TPS61288

Tool/software:

Hi,

I am using the Boost converter module TPS61288 to generate 9.0V from battery source whose typical voltage is 7.4V and it may range from 5.8V to 8.4V. The discharge capacity of the battery is 7.5A peak current and 1A continuous current. The current drawn by the load is 6.2A during surge and 0.8A during continuous operation.

I have attached the schematic for the reference, please confirm if the schematic is good to go

And also confirm if pulling the Enable pin to low will disable the output completely or still Vout=Vin like in most of the boost converter modules. In my application, I need to turn off the 9V output completely when not is use. If the enable on pulled low will disable only the set output voltage and still the Vin will be seen on the Vout pin, I need to implement a separate logic for turning off the Vout completely, please confirm

Thank you

  • 0
    TI__Genius 16265 points

    Hi Balasubramani,

    Thanks for reaching out.

    1. the device is not true load disconnected and when EN is low, the VO=VIN like most Boost converters.

    2.  When the load is 6.2A and the input current reaches 12A when 5.4Vinput and 8A when 7.4Vinput.

    This triggers the battery's current limit 7.5A and will it cause any protection?

    3. What is the part FB_50ohm? 

    A device with 50ohm at input/output side will be a large voltage drop and power loss.

    4. It is recommended to add more capacitors (polar capacitors) at input/output side to improve the sharp current transient from 0.8A to 6.2A.

    Considerations depends on the source response (input side) and current slew rate and required voltage drop/overshoot (output side).

    Best Regards,

    Fergus

  • 0 in reply to Fergus He
    Prodigy 20 points

    Hi Fergus,

    Thank you for the prompt reply

    The battery pack has over current protection at 7.5A which will kick in during over load current, but the surge on the load current may last to few milliseconds. Please suggest if we can compensate it by adding polar capacitors

    FB_50Ohm is ferrite bead part to improve high frequency noise immunity in the power plane, which has 10mOhm DCR and 50 Ohm is the impedance of the bead @100MHz

     

    Thank you,

    Balasubramani

  • 0 in reply to Balasubramani M
    TI__Genius 16265 points

    Hi Balasubramani,

    Milliseconds is already stable state for Boost.

    When the battery limits its output current, but the device will continue try to output such high power,

    the input capacitor's voltage will decrease due to power imbalance and device will shut down due to VIN under voltage protection.

    We can calculate the demanded capacitance needed in worst case Vin=5.8V:

    ΔP=(9V*6.2A/0.9-5.8V*7.5A)*1ms=0.019J=1/2*C(5.8V^2-2V^2)

    C=1.248mF

    That is, when the input capacitance is larger than 1.25mF, the input voltage will not drop to 2V(UVLO point) in 1ms.

    Best Regards,

    Fergus

  • 0 in reply to Fergus He
    Prodigy 20 points

    Hi Fergus,

    Thank you for the reply

  • 0 in reply to Balasubramani M
    TI__Genius 16265 points

    Hi Balasubramani,

    Please tell me if you have any more questions.

    Best Regards,

    Fergus