We are switching from AD5541A to AD5542A in our products due to ic shortages. Our DSP runs at +1.8V. We assumed we could change the voltage at the VLogic pin to run AD5542 with our 1.8v DSP. However, in our tests, we are unable to lower the digital VINH by changing the VLogic voltage. Can you help or provide clarity on why this may be the case?
For our test, we bought an eval board (EVAL-AD5542A), cut the trace on your 2-layer eval board PCB right before the entrance to the Vlogic pin to inject our own logic voltage. (Pretty sure we did a good job in isolating this trace from rest of the board). The voltage at the VL pin is ~4.3 volts by default if no logic input is provided. If we try to inject our own VLogic at a level below 4.3 volts, the +5 VDD and our external power supply for Vlogic start fighting one another. The Vlogic pin seems to work only when the injected logic voltage is higher than roughly +4.3V. This is not how 5541A works and we scanned the datasheet for 5542A to see if there were any differences. We could not find any.
Question: Can we lower VINH by injecting external voltage in AD5542A? If not, why is this input provided?
