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NEED LDO

Other Parts Discussed in Thread: TPS7A7100, TPS795

HI,

I need low drop voltage regulator adjustable 0.5A output: Vin is between 4.8-5.2V (USB host voltage), and Vout need to be minimum of 4.65-4.7 (the higher the better.....)

there is the TPS79501, but at the data sheet there is no data regarding its dropout voltage (Vi-Vo).

please advice ASAP

  • Hi Golan,

    Figure 18 of the datasheet shows the dropout (Vi - Vo) curve vs. current. At 500mA, the dropout is about 160mV which means for an input voltage of 4.8 and output voltage of 4.7, the device will be in dropout.

    Have you looked into the TPS7A7100? It is one of our newer, higher performing low dropout regulators. Below is the link to its product page. On Figure 6 of its datasheet, it shows the VDO vs. current curve.

    http://www.ti.com/product/tps7a7100

    Regards,

    Darwin

  • HI,

    WHAT DO U MEAN BY "THE DEVICE WILL BE IN DROPOUT"

    So the 79501 do not suit for the application?

    as for the LDO u suggested at page 3 the drop out voltage is 350mV if Vout higher then 3.3V. the Vin/Vout minimum difference is 0.5V, so its not suitable for my basic turms:

    Vin=4.8-5V ; Vout=4.65 minimum

  • Hello Golan,

    The TPS795 is a good part but please consider all the sources of inaccuracies, not forgetting the +/-1.5% contribution from 1% feedback resistors, as well as decreasing regulation as the Vin-Vout difference approaches dropout (where measured dropout, Vdo, scales with output current) - in other words as you enter dropout the output voltage will roll off.  It might be a good idea to use 0.1% resistors.

    An alternative might be to use the TPS7A7100 which has a programmable output voltage with 50mV resolution - but even here you must consider the inaccuracies involved.

    Try ordering Evaluation modules (EVM) for each to see what you like.

    Regards

    Bill

  • Hi Golan,

    When an LDO is in dropout, it can no longer regulate the output voltage. VDO is the minimum VIN-VOUT voltage differential to regulate the output. This means you need a lower dropout voltage if you want a higher output voltage for the given VIN. We have an app note that describes dropout in detail. http://www.ti.com/lit/ml/slup239/slup239.pdf

    As Bill stated, the dropout voltage is a function of current. The 350mV dropout voltage in the electrical characteristics table is for 1A. The dropout at 500mA will be lower. Please refer to Figures 6 and Figure 7 of the TPS7A100 datasheet for VDO at lower currents.

    Regards,

    Darwin