This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS82671: Operating quiescent current during PWM mode

Part Number: TPS82671
Other Parts Discussed in Thread: TPS82085, , TPS82740A

I am evaluating buck converters between TI parts. As I reviewed the specs between 82085 and 82671,

they are compatible in terms of input voltages, operating frequency (2.4 vs. 5.5Mhz) and etc. However,

the operating quiescent current is totally different between them. On the condition, devices are NOT

switching, they are identical, but 82671 jumps to 5.8mA as Iout = 0 in PWM mode (show below). The 82085 device

is also the similar scheme for power conversion, but it does not show any data in supply current category.

I would like to know the value of 5.8mA (shown above) as typo or real data during PWM operation. If it is in

PWM, why 82085 does not have any similar current consumption during this operation.

I am looking forward to hearing from you.

Warm Regards.

  • Please see my paper for a detailed explanation of Iq: www.ti.com/.../slyt412.pdf

    The TPS82085 does not offer a forced PWM mode.

    These are very different devices: 3A vs. 600 mA and an all in one device vs. a solution which is ~5x the size. As well, the TPS82671 does not support a 5V input voltage. What do you need in your system?
  • Hello Chris. Thank you for your reply. My application consumes 30mA at the peak. After reviewing the specs, 82671 would be an ideal candidate.
    Therefore, the device would be operated in PFM/PWM mode all the time. Is it true? Looking at the figure 14 from 82671 specs, I assume my input voltage at 3.5V, Iout ~ 10mA, then the operating current (from the power loss) would be ((1/.86) -1)Pout/Vin ~ 2.93mW/3.5 = 0.84mA. Is this correct? Please let me know. I am looking forward to hearing from you. Warm Regards.
  • Thanks for coming back to this thread after the holiday.

    Yes, for your low load currents you need a device which has a PFM mode and you would operate the device in PFM for best efficiency.

    I'm not sure where your 2.93 mW value comes from, but your thinking seems to be basically correct. You can use the efficiency graphs in the D/S to determine the input current consumption. You might also see Figure 12 and use the 3.6V curve, which will be very close to your 3.5V level. From that curve, we have about 85% efficiency at 30 mA, which results in an input current of ~18.1 mA.

    Since you have a lower load current, you might also look at the TPS82740A which has much better efficiency at loads under 1 mA.