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The Vlogic pin of the AD5316R is not working

When the AD5316R is connected to VDD=5V, a voltage of 4.25V is automatically generated on the Vlogic. While the I2C pull-up voltage I want to use is 3.3V, Vlogic cannot connect the digital voltage of 3.3V externally, because it will raise 3.3V on the microcontroller power supply.Does the Vlogic have to be supplyed? Will floating affect IC working? If I have to access it, how do I do it?

  • Hi, 

    The Vlogic pin should be supplied to operate normally. Have you tried connecting it first to a 3.3V supply? It shouldn't be affected by the voltage seen while it is floating. 


  • Hi,

    Thank you for your answer. At first, I connected 3.3V to Vlogic pin as power supply, but I found that the 3.3V bus on the MCU was raised to 3.9V during detection. Later, I found that the 3.3V bus was restored only after the Vlogic pin was floating. Therefore, I do not know how to deal with the Vlogic pin, so as to use the AD5316R normally, and does not affect the MCU power supply.

  • Hi, 

    The Vlogic pin should not cause the bus voltage to increase. This is not a normal response. Can you check your schematic, might be that there are logic pins that are connected or pulled-up to VDD instead of Vlogic. 

    Are you using the evaluation board or a different hardware?

  • I use AD5316R to generate voltage. As shown in the schematic diagram, the original intention is to use 3.3V as Vlogic power supply, so that I2C can also be 3.3V pull-up, which can be controlled by MCU.

  • Hi, 

    The gain pin is categorized as a digital pin, and the max input should be Vlogic +0.3V. If you want to set it high, this should be tied to Vlogic instead. Tying it to VDD has violated the absolute max rating of this pin so I'm not sure if this has damaged the device. 

    Another point is, that you are using the AD5316R, which has an internal reference. I don't see the need to connect the VREF pin to VLOGIC. If you want to use an external reference, I suggest using a reference IC that provides less noise as compared to Vlogic. 


  • Datasheet indicate that the Gain pin needs to be connected to the VDD for gain. The Vref pins are my miscalculations. During debugging, the AD5316R also works when the Vlogic pin is floating. What are the possible problems caused by such use?

  • When you connected the gain pin to VDD, the protection diode of the gain pin which is internally connected to Vlogic, and with VDD higher than vlogic, now allows current to flow from VDD to Vlogic. THis is why the device works even with Vlogic floating in yout setup. 

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