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TPS2549: Datasheet questions

SRW
Intellectual 370 points

Part Number: TPS2549

Hi,

I have a few questions about the TPS2549 datasheet specs.

  1. Is there leakage/error associated with low levels of cable compensation? For example, if the load current were 100mA would the Ics be reasonable close to (75uA/A)(100mA) = 7.5uA?
  2. Pg 18 of the datasheet section 8.3.2.1 #4 says:
    1. "C(COMP) in parallel with R(FA) is needed to stablilize V(OUT) when C(OUT) is large. Start with C(COMP) ≥ 3 × G(CS) × C(OUT), then adjust C(COMP) to optimize the load transient of the voltage regulator output."
    2. What Cout is this referring to? Is it the Cout to the "right" and/or "left" of the TPS2549?
  3. If configured as CDP per Table 2 CTL1-3 as '111', will the status output be active when the ILIM_LO threshold is met per section 8.3.5.2?
  4. If configured as CDP per Table 2 CTL1-3 as '111', but auto-switches to SDP because device didn't enumerate, will the status output be active when the ILIM_LO threshold is met per section 8.3.5.2?

Thanks!

  • 0
    TI__Intellectual 2685 points

    Hi,

    1. yes, the CS current will be close to 7.5uA.

    2. Cout is the capacitor connected on the OUT pin.

    3. yes, when the load current exceeds the threshold determined by the ILIM_LO, STATUS pin will assert.

    4. No, STATUS will not assert in SDP mode.

  • 0 in reply to Yongqiang Sun
    Intellectual 370 points
    Thank you for the quick response, this completely answers my questions.
  • 0
    Intellectual 370 points
    I have another question about this device. The datasheet says the TPS2549 can support divider 3 mode, which I believe is 2.4A.

    1. Is divider 3 mode 2.4A?
    2. What happens if you configure for DCP_AUTO and the device wants 2.4A, or even 2.0A, but the current limit is set to 1.5A? How will the connected device realize it can only draw 1.5A when the handshaking told it 2.4A? Is there a standard or typical way a device will handle this situation?

    Thank you.
  • 0 in reply to SRW
    TI__Intellectual 2685 points

    1. yes, divider3 is 2.4A

    2. if the device wants 2.4A but the current limit is 1.5A, then TPS2549 will limit the current to 1.5A, so the device can only sink 1.5A.

  • 0 in reply to Yongqiang Sun
    Intellectual 370 points

    Thank you for the response.

    Yongqiang Sun said:

    2. if the device wants 2.4A but the current limit is 1.5A, then TPS2549 will limit the current to 1.5A, so the device can only sink 1.5A.

    I understand that (in this example) the device will current limit to 1.5A. But if TPS2549 is in divider3 mode, presumably the device thinks it can sink 2.4A. When it tries to draw 2.4A, it instead gets current limited at 1.5A, so the device gets less current and the bus voltage starts to drop. How will the typical device handle this situation? Will it realize that it can't actually draw 2.4A, even though divider3 mode was advertised, and draw the 1.5A instead? Or will it do smoothing more drastic, such as give up and stop charging?