The EVK includes a number of programable current sources and switched resistive loads on board.
Net names:
SD3 - BUCK3 Output.
VIL_SD3 - Output of the current shunt amplifier for Buck3's programable current sink.
BUCK 3 - Configuration
Buck 3 is left in its default configuration for a 900 mV output.
(BUCK3) SD3 - 0 A to 1 A
(BUCK3) SD3 - 100 mA to 1 A
(BUCK3) SD3 - Random 0 mA to 2.2 A
LDO2 PSRR
For this test we will evaluate how well LDO2 can post regulate the output of BUCK 3. First, we must remove R6 from the EVK:
Connect the output of BUCK 3 to in the input of LDO2:
BUCK 3 is configured to output 3.3V:
LDO2 is configured to output 2.5V:
To give LDO2 a fair chance, I will add a 1 mA static load with the unused programable current sink on the EVK:
LDO2 PSRR with a 1 mA Load
LDO2 PSRR with a 33 Ohm load
Enable the onboard 33 ohm load resistor in the EVK's GUI:
I was using the alligator ground clips of my scope probes in 1x mode for convenience. If one were to employ alternate probing techniques with a smaller loop-area, the results of the MAX77714 would likely exceed what was demonstrated in this blog post.
Clarification on the EVK's LDO Loads
The EVK includes a diverse set of discrete switchable loads on board:
One should note that the loads are being high side switched with an NFET. The gate drive signal for each of the NFETs originates from a I2C GPIO expander with its outputs referenced to VLOGIC.
When VLOGIC is set for 1.8V as recommended in the user's guide for the EVK, the switchable loads will behave as current sinks when for LDO voltages greater than approximately 1 V.
Just something to bear in mind, as it is not explicitly stated in the GUI or documentation that these loads may very well behave as current sinks.
