LM1117 - the method of the measuring phase margin

Hirotaka Matsumoto

Other Parts Discussed in Thread: LM1117

Hello,

Would you mind if we ask the method of the measuring phase margin on LM1117?

In order to measure the phase margin, the resistor to inject small signal is inserted between R2 and GND
as following attached file.
6433.Attached file.pdf

<Q1>
Is this the method true as the measurement of LM1117-ADJ's phase margin?

<Q2>
In general, we think that the correct method(way) is following;
Method : The resistor to inject small signal is inserted between Vout and R1.

If you have any advice, could you tell us?

Kind regards,

Hirotaka Matsumoto

over 11 years ago

0 Ron Michallick over 11 years ago

TI__Guru**** 164976 points

Hirotaka-san,

The LM1117 is upside down compared to most regulator loops. If the circuit is isolated from ground then you may test phase gain.

Connect your reference and test probe grounds to schematic VOUT (not ground).
Test probe signal connects to schematic ground. Then you may inject an AC signal between R2 and schematic ground and use this as reference signal.

0 Hirotaka Matsumoto over 11 years ago in reply to Ron Michallick

Guru 27585 points

Hi Ron San,

Thank you for your updata.

We'd like to confirm the method of the measuring phase margin.
Our image is following attached file;
5270.Our image.pdf

If it is incorrect, please tell us proper way to measure.

Kind regards,

Hirotaka Matsumoto

0 Ron Michallick over 11 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 164976 points

Hirotaka-san,

Your picture is good except for one detail. See green wire.

0 Hirotaka Matsumoto over 11 years ago in reply to Ron Michallick

Guru 27585 points

Hi Ron San,

Thank you for your updata!

Kind regards,

Hirotaka Matsumoto

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LM1117 - the method of the measuring phase margin