THS3120EVM: THS3120EVM setup for LDO PSRR measurement

Leo Chow

Part Number: THS3120EVM
Other Parts Discussed in Thread: THS3120, THS4021

Hi,

After reading through the following app notes, it seems that THS3120EVM can be configured & setup to measure PSRR of LDOs.

http://www.ti.com/lit/an/slaa414a/slaa414a.pdf

In order to do this setup, is it necessary for me to make changes such as resistor values to match the app notes? As i was reading through THS3120 Datasheet pg/23 & 24 it seems that layout are slightly different so as the passive component values. Please verify. Thanks.

Regards,

Leo

over 5 years ago

0 Karan Kotadia over 5 years ago

TI__Genius 16725 points

Hi Leo,

The app note you provided has a circuit designed to measure PSRR of an LDO. The layout and EVM design mentioned in the datasheet is for optimal use of the THS3120. It is not necessary that the circuit for measuring PSRR will look the same or have the same values?

Thanks!
-Karan

0 Karan Kotadia over 5 years ago in reply to Karan Kotadia

TI__Genius 16725 points

Hello Leo,

Do you still have some questions?

Thanks!
-Karan

0 Michael Steffes over 5 years ago in reply to Karan Kotadia

Guru 48395 points

Hi guys,

Actually that app note is pretty odd, the circuit is using a CFA THS3120 for this? Actually might want a VFA with a 50ohm input resistor to terminate the RF source. that R across the inputs is probably them trying to raise the noise gain? That does not work with CFA.

If you want a lot of DC bias range on +/-15V low noise VFA, try the THS4021 with an input resistor of 50ohm, no resistor across the inputs, and a 1kohm feedback - simulate with load in place (removing caps at the LDO input) for stablity. Just need to drive with much lower RF out with that gain of -20V/V

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THS3120EVM: THS3120EVM setup for LDO PSRR measurement