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LM25117 EVM

user4768469
Intellectual 290 points
Other Parts Discussed in Thread: LM25117

Hi,

Below appears in the user's guide of LM25117 EVM：

3.2 Source Power
The power supply and cabling must present low impedance to the evaluation board. Insufficient cabling or
a high impedance power supply will droop during power supply application with the evaluation board
inrush current. If large enough, this droop will cause a chattering condition upon power up. During power
down, this insufficient cabling or a high impedance power supply will overshoot, results in a nonmonotonic
decay on the output.

Why does the high impedance source cause these issues?would you please tell me more details?

Thanks!

  • 0
    TI__Genius 13700 points
    Hello,

    The chattering will most likely be caused by under-voltage protection on the LM25117 or over current limiting on the power supply.

    The reason why high impedance sources can cause this issue is can be understood in the following hypothetical situation:

    Your source is supplying 5V and as a result of the source impedance+connector+cable+connector impedance there is a total of 0.1ohms of inline loop impedance.
    During operation you LM25117 starts asking for >10A of input current. As a result of the inline impedence a voltage drop results in the LM25117 seeing <4.5V which is where under-voltage protection kicks in. With the protection kicking in the LM25117 reduces how much power it is drawing to get out of under-voltage lockout. Once it is out of lockout it tries to pull >10A again causing the part to lock out again.
    The result can be the chattering condition described.