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TPS82740B: Load current

Andrew V
Intellectual 270 points
Part Number: TPS82740B

I am considering a step down converter TPS82740B, which is set for Vout = 3V. The system is powered from a Li-ion battery Vin = 3.2- 4.2V. The total load current requirement is typically around 100mA but can go up to 150-160mA for 20-30min. This presents a problem because according to the recommended operating conditions on page 4, the converter output capability is limited, depending on the input voltage:

  • For VOUT nom + 0.7V ≤ VIN ≤ 5.5V the output current is 200mA
  • For VOUT nom ≤ VIN ≤ VOUTnom +0.7V the output current is 100mA

If I follow the specs, the device can provide 200mA if the input voltage is 3.7V and above. For the input voltage between 3.2V and 3.7V the output current will be limited to 100mA.

TPS82740B is a very attractive option in terms of its size, and it would be great if I could use it, however the 100mA current limit is a major concern. I did some load stress testing on the eval board and the device fine at Vin 3.2V, 200mA. Can somebody from TI clarify the current limits issue?

 

  • 0
    TI__Guru*** 144060 points

    Hi Andrew,

    It sounds like you've tested the device for your application and it is suitable.  This is the most important item.

    The 100 mA and 200 mA are merely recommended operating ranges.  It is not the current limit.  The idea behind those limits is that we want the device's internal 100% mode circuit (D/S section 9.4.4) to engage before the operating frequency gets too low, as this can negatively impact the radio (which we assume is on the output).  Since you have a bit under the 200 mA current rating and a much higher Vout and Vin, the voltage drop across the module is lower and the 100% mode circuit should engage normally.

  • 0 in reply to Chris Glaser
    Intellectual 270 points

    Thank you. I didn't find 9.4.4 but found a chart of frequency vs current on Figure 17.  Its still odd that nowhere in the datasheet it defines the max output current.

  • 0 in reply to Andrew V
    TI__Guru*** 144060 points

    Section 9.4.4 is on page 19.

    This module is designed for 200 mA load currents.  This is supported by its internal switch current limit (page 5).