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.

TPS566231: I_FB

Part Number: TPS566231
Other Parts Discussed in Thread: TPS54J061, TPS543620

Hello TI,

What is I_FB (typ / max) for the above part, please? Could this be added to the datasheet?

  • Hi, why do you need this value? commonly the data is not shown in datasheet.

    Yuchang

  • Hello Yuchang,

    I_FB affects the output setpoint voltage. The larger I_FB is, the higher the output setpoint voltage will rise. This parameter is consistently included in TI DC/DC converter datasheets (for examples see: SLVSES3A page 6, or SLVSBB8B page 5, or SLVSDV2 page 6, etc etc).

    Please clarify I_FB (typ / max) for the TPS566231 so that its effect on the output setpoint voltage may be evaluated.

  • Hi Bernhard,

    I'm a little bit confused about your comments that "The larger I_FB is, the higher the output setpoint voltage will rise". Do you want to add an resistor between middle point of feedback voltage divider and the FB pin? If not, I would say the resistance of feedback trace on PCB has almost no impacts on the setpoint voltage. The impacts of uV level voltage drop is too small compared with 600mV voltage reference.

    By the way, I'm assuming that you might have a very high requirement of the reference voltage accuracy. If yes, I would recommend you to choose TPS54J061 (+/-1% accuracy over full temperature) or TPS543620 (+/-0.5%accuracy over full temperature range). Those two 6A devices have better reference voltage accuracy and are more suitable for application with high output voltage accuracy requirement. TPS566231 is targeted at cost effective market and its accuracy is +/-1% under room temp.

    Thanks,

    Andrew

  • Hello Andrew,

    I was not referring to an additional resistor. Any current demand I_FB required by the FB pin is drawn via Rtop, the top resistor in the standard feedback network. This results in an additional voltage drop over Rtop, lifting the output voltage due to the feedback action which is attempting to regulate the feedback voltage to e.g. V_FB=0.6V in this case. So to give an example, if Rtop = 100kΩ and I_FB(max) is 1µA, this will lift the output voltage by 0.1V worst case.

    So I_FB informs the choice of Rtop; a large I_FB would prefer correspondingly small FB resistor values to limit their contribution to the output error (which is also substantially affected by the accuracy of V_FB, as you mention).

    This is a relatively new TI part, so I expect I_FB to be 1 nA (typ) and 100 nA (max), so with Rtop around 10kΩ, the contribution should indeed be negligible.

  • Hi Bernhard,

    Yes, thanks for the explanation. That makes sense. The leakage current IFB is mainly due to device leakage of internal ESD. For the ESD structure of TPS566231, the leakage current is very small. As you can see on datasheet, the maximum Rtop in our recommended component is high as 220kohm.

    By the way, we can check internally with team for the value and we'll give you feedback later.

    Thanks,

    Andrew

  • Hi Bernhard,

    I checked internally, I_FB is about ± 10nA.