Hi,
I have a question on the interface for the digital input signals SCLK, SEN, SDI and CLPIN on the LM98640.
In the LM98640 device, are the circuits for the SCLK, SEN, SDI and CLPIN input signals 1.8V interfaces? Or are they 3.3V interfaces? The datasheet does not make that clear since it lists VIH and VIL levels for 3.3V but states that the digital power supply is 1.8V.
VDD18 corresponds to 1.8V and it is labeled as the digital supply. VDD33 is for 3.3V and it is labeled the analog supply.
Table 6.6 lists VIH as 2V and VIL as 0.8V for the input digital signals. Those levels correspond to a 3.3V interface typically. This is listed on page 9 of the datasheet for signals SCLK, SEN, SDI and CLPIN. Should we interface with these signals using a 3.3V interface or with a 1.8V interface? To add to the confusion, the output signal SDO lists VOH and VOL levels that correspond to 1.8V signaling.
We are developing a circuit board which has a LM98640 interfacing with an FPGA. The datasheet specifies a digital supply VDD18 voltage of 1.8V, but the Electrical Characteristics table shows that VIH max and VOH min is 2.0V and 1.8V, respectively. Based on the Electrical Characteristics table, the I/O voltage (digital) can't be 1.8V. I suspect it should be 3.3V, but I guess my question is: what FPGA I/Os (1.8V or 3.3V) should the LM98640 interface to? Should we use 1.8V signaling or 3.3V signaling to communicate with the LM98640 SCLK, SEN, SDI, and CLPIN signals?
I am guessing we have one of the following two conditions as the cause for my confusion and question:
1.Is the 3.3V analog supply VDD33 being used for the digital signaling interface? It seemed unlikely since it is named the Analog supply but is the 3.3V VDD33 supply used for the interface of the digital signals and the 1.8V VDD18 supply only used for the internal digital signals and the output signal SDO?
OR
2.Are there typographical errors for the listed VIH and VIL levels for logical “1” and “0” for the SCLK, SEN, SDI, and CLPIN digital signals in table 6.6 on page 9 of the datasheet? Should the levels correspond to 1.8V digital signaling instead of 3.3V?
Note 1 on page 9 under table 6.6 has an image for the analog input diode protection. Do digital signals have the same type of protection? If they do, can you state what voltage supply they are connected to please? Can you please provide the same image for the digital inputs SCLK, SEN, SDI, and CLPIN?
Thank you for your help,
Scott
