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WEBENCH® Tools/LP2980-ADJ: The pass element of LDO

chentsu chung
Mastermind 6180 points
Part Number: LP2980-ADJ

Tool/software: WEBENCH® Design Tools

Hi,

From datasheet, I know the pass element of LDO is a PNP FET,.

1. compare with other vendor's LDOs, some of them use MOSFET as pass element, so what is the reason to use PNP FET in side?

2. In datashhe page9. there is inherent diode connected between the regulator output and input.  As I know, the body diode is come from MOSFET, so could you help to let us know how the body diode be exist.

  • 0
    TI__Genius 10490 points

    Hi,

    1. Note that the pass element of the LP2980-ADJ is a Vertically Integrated PNP (VIP) BJT, not a FET. BJTs offer better performance in applications that require high voltage and low noise, like telecommunications equipment. This type of pass device was chosen for the LP2980-ADJ as it was able to deliver the desired performance based on the requirements of the target applications and end equipment. This paper explains the VIP10 process in detail and touches on some more advantages that it has over CMOS processes:

    2. The diode shown in Figure 21 of the datasheet is an inherent diode that was created during the layout and fabrication process. It is not a body diode associated with the pass PNP BJT. It is included in the datasheet to show that additional Schottky diode protection is required if the LP2980-ADJ is being used in an application where the output voltage could be higher than the input voltage. 

    Thanks,

    Gerard