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Question with CC2541 working with TPS62730.

Hongxiang Ji
Prodigy 130 points
Other Parts Discussed in Thread: TPS62730, CC2541

 In TPS62730 datasheet(SLVSAC3C-MAY 2011- REVISED DECEMBER 2012), it mentiones"Once the device is turned from ultra low power bypass mode into buck converter operation for a RF transmission, all the internal circuits of the regulator are activated within a start up time tStart of typ 50µs. During this time the bypass switch is still turned on and maintains the output VOUT connected to the input VIN. Once the DC/DC converter is settled and ready to operate, the internal bypass switch is turned off and the system is supplied by the output capacitor and the other decoupling capacitors. The buck converter kicks in once the capacitors connected to VOUT are discharged to the level of the nominal buck converter output voltage." in page 14. My question is that in this period from "bypass" mode to "on" mode, or in the reverse direction, the output voltage of TPS62730 changes ,and in the meantime the CC2541 still works and also with its inner processor 8051, will the supply voltage vary cause some uncontrollable errors or states that takes place in CC2541. thanks! 

  • 0
    TI__Expert 3595 points

    Internally the CC2541 works on lower voltages.  Its regulators can handle the transition in supply when the TPS62730 turns on. 

  • 0
    TI__Genius 12545 points

    Thing to remember here is that there are internal LDOs in the CC2541 that in the absence of a regulated voltage convert the external voltage (2.0V-3.6V) to 1.8V. Therefore the operations will not be as adversely affected when the supply voltage is transitioning from 2.1V to whatever the supply voltage is or the other way round. Yes there will be transition glitches which are reduced by the the caps on the supply lines. The internal voltage regulator acts as a level of shielding preventing any catastrophic errors on the CC2541. The supply glitches can affect the clock and so the BLE stack provides time buffers to prevent failed operations.

  • 0 in reply to Chatto
    Prodigy 130 points

    Hi Chatto,

    Thanks! Your answer is very good removing my puzzle. But can you explain "The supply glitches can affect the clock and so the BLE stack provides time buffers to prevent failed operations. " more clearly?  as to "BLE stack provides time buffers? " I do not understand this and do not find it in any TI technical documents. and how it realize "prevent failed operations"?

    thanks!

  • 0 in reply to Chris M
    Prodigy 130 points

    thanks! your answer is good resolving my problem.

  • 0 in reply to Chatto
    Prodigy 130 points

    hello Chatto, 

    Another question related to the voltage shift is the cc2541's pins' voltage is 0-3v when the supply voltage VDD=3V, so when the vdd changes to 2.1V , will the outputs of CC2541 change accordingly? Is the cc2541's pins' voltage 0-2.1v when VDD changes to 2.1v?

    thanks!

  • 0 in reply to Hongxiang Ji
    TI__Genius 12545 points

    When the supply voltage to the chip is 2.1V, the GPIO's range would be from 0-2.1V

    In general, the GPIO's range will always be 0-VDD, whatever the VDD to the chip

  • 0 in reply to Hongxiang Ji
    TI__Genius 12545 points

    While developing the combination boards of the CC254x-TPS62730, we came across connection issues. These were cause by the real time clock being disrupted by the supply change glitch. The answer to which was, allowing some settling time for the supply transition, before waking up or putting to sleep the CC254x. Waking up or putting to sleep the CC254x too early would cause the real time sync to be lost sometimes, causing the connection to randomly be dropped. So we added additional delays in the stack before and after every voltage transition to ensure stability. This is not mentioned in documentation as we don't see the need for it as the stack handles the wake up and sleep sequences anyway.