LM25149-Q1EVM-2100: heavy load startup, see overshoot on current

Mona Guo

Hi, team

when start up with heavy load(13A), see overshoot on Iout. Is it normal? and what can cause this overshoot? (such as test method?)

test condition: Vin=12V Vout=3.3V Iload=13A

0 Orlando Murray over 2 years ago

Hi Mona,

No that is not normal, the EVM has a peak current limit setpoint of 12A, did you modify the EVM?

Do you have scope shots of VOUT? Also please scope COMP in this condition.

-Orlando

0 Mona Guo over 2 years ago

Hi, Orlando

The Vout don't have overshoot, only current has overshoot even under 3A load condition.

another question,

1. When the EN=4.5~5.5V, under light load condition, the output voltage random change, and under heavy load, don't have this problem.

2. for the AEFVDDA pin connection, both 100n connect to ground and pull up resistor to VCC?

0 Orlando Murray over 2 years ago in reply to Mona Guo

Hi Mona,

Do you have any scope shots of the EN behavior?

For Active EMI power capacitor pin place a 4.7µF capacitor close to AEFVDDA and AVSS pins. Pullup AEFVDDA node with a 3Ω resistor to VCC.

Let me know,

-Orlando

0 Mona Guo over 2 years ago in reply to Orlando Murray

Hi, Orlando

What's this 3ohom resistor used for? Is this mandatory?

0 Orlando Murray over 2 years ago in reply to Mona Guo

Hi Mona,

The 3Ω resistor is for filtering noise between VCC and AEF, and also helps with measuring AEF current.

It is also useful to remove AEF from VCC completely.

-Orlando

0 Mona Guo over 2 years ago in reply to Orlando Murray

the current on resistor is a portion of AEFVDDA? Is there any other path from VCC to AEFVDDA?

0 Orlando Murray over 2 years ago in reply to Mona Guo

Mona,

No there is no other path from VCC to AEFVDDA. The AEF pins are isolated from the Controller pins.

-Orlando

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