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PMP11536: PMP 11536

Part Number: PMP11536
Other Parts Discussed in Thread: PMP, BQ25895, , TL431

Hello,

As I am student engineer I work for a project with PMP 11536.

I spend a while to analyze the schematic and I understand the most part.

But there are still two questions that stay mystery for me.

1. GND and PGND are linked by a Net-Tie.

Why GND and PGND are not the same ground plane ?

2. in this part of the circuit :

I understand Input is PMID from BQ25895 and Output is USB VBUS to charge devices. But I do not understand how it works ...

Thank you

Best Regards,

Theo

  • Hi, Theo,

    Glad to see you are interested in PMP11536.

    1. GND and PGND are linked by a Net-Tie

    Net-Tie is similar to a 0ohm resistor. This is a common power ground and digital ground connection style called single point grounded. The benefit for this ground connection is avoiding more noise from power ground interfering MCU digital ground. If you check most of DC-DC power IC, the power ground(PGND) is connected to analog ground(AGND) with single point.

    2. This circuit is for OTG function of BQ25895.

    In this OTG function, BQ25895 will boost battery voltage to 5V on PMID. On your attached circuit, there is a P-channel MOSFET between PMID and Vo_A. It is a low cost protection circuit. We can consider TL431 one comparator.

          (1) When PMID voltage is under 5.5V, the P-channel will turn on. there will be power on A port.

          (2) When PMID voltage is above 5.5V, there will be more than 2.5V on TL431 Pin 3 bigger than internal 2.5V reference. The voltage of TL431 Vka will be decreased from PMID, then Q2 will turn on and Q2 source gate voltage increase from 0V to PMID, the P-channel will turn off. there will no power on A port.

  • Hi, David,

    Thank you very much for your answer.

    I think it is clear now