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A few questions related to TPS61325...

Soren Steen Christensen
Genius 3685 points
Other Parts Discussed in Thread: TPS61325

Hi TI Power/LED Support Team,

I'm current finalizing a design using a TPS61325 for driving a super cap for a LED based flash light (2x2A + torch mode) and unfortunately having a few questions after having read the datasheet (http://www.ti.com/lit/ds/symlink/tps61325.pdf) several times...

  1. Page 32 table 2 seems to indicate that TX-mask only affect the 30 and 250mA modes and not the high current modes, which I would assume is the ones to be "cut" for best possible protection of battery when TX burst is ongoing. Can you please elaborate on the meaning of this table, as it's unfortunately not clear to me?
  2. Page 45 have the following text which I find very unclear as well?
    110: 166.5mA, 249.75mA current level can be activated simultaneously with Tx-MASK = 1
    111: 194.25mA, 360.75mA current level can be activated simultaneously with Tx-MASK = 1
    Again - Why/How would current be highest when TX-MASK=1?
  3. Page 53 states that minimum usable inductor is 1,3uH, but Murata series LQM32PN mentioned in the table just below does AFAICT only exist in a 1uH version? Can you please confirm if this is OK or a mistake? I'm already using the given part another place in my design, so being able to reuse the part BOM-wise would of cause be beneficial if possible...

I hope you can easily help me forward with the 3 questions above? Best regards and thanks in advance
  Søren

  • 0
    TI__Guru*** 146640 points

    Updating this thread to convey what was explained via email:

    Q1)  Table 2 refers to the power stage inductor valley-current limit (e.g. Ivalley set to 30mA, 250mA meaning the DC input current is limited to a value roughly 100 to 150mA above theses thresholds). To enable dynamic input current limitation control (i.e. vs Tx_MASK input state), Tx-MASK bit needs to be set high.

    Q2) This mode is rather meant for direct-drive operation, i.e. in a circuit w/o EDLC cap. at the converter’s output (HC_SEL = 0). In case of a Tx-MASK masking event, the LED current is instantaneously to the DC light level. Depending on the DCLC bits settings the current during the flash blanking period can be adjusted. Fig 32 illustrates the behavior.

    Q3) There should be a 2.2uH inductor out of the muRata LQM32PN series … otherwise you can also consider TOKO DFE322512-2R2 product.