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AFE5828: 1V8 logic input Voltage Level Compatibility question

Genius 3870 points
Part Number: AFE5828
Other Parts Discussed in Thread: SN74LVC8T245

Hi there

we are designing FPGA to control AFE5828, here is a concern about IO standard Voltage level compatible. FPGA  IO output pins are LVCMOS1V8 (JESD 8C.01 ) standard, directly connect to AFE's 1.8V-logic inputs (like reset, PDN_GBL, .....and SEN, SCLK, SDIN ...etc)。

Below is the voltage level of AFE and FPGA, as I cycled out, there seems RISK that FPGA's VoL(max 0.45V) > AFE's ViL(max 0.4V), and FPGA's VoH(min 1.35V) < AFE's ViH(min 1.5V). which means that AFE may not receive correct logic inputs under some boundary conditions. How do you think?

One possible solution is to insert a logic buffer (1.8V  to 1.8V) ,such as TI SN74LVC8T245. However, its VoL and VoH is dependent on load current(as below pic).

So, how could we estimate the load current based on AFE's 1.8V-logic input s parameters, especially on AFE's SPI inputs ( SPI works on 20MHZ frequency)?

By the way, does AFE5828's 1.8V-logic inputs / outputs compliant to JESD LVCMOS1V8 standard? 

Thanks a lot.

  • hi, anyone could help ? thanks!

  • Hi,

    Yes, there could be a boundary condition where the logic levels may not get registered by the device.

    You have to ensure that the conditions of VIH of 1.5V and VIL of 0.4V of these pins should be met.  

    As you suggested, you can place a level shifter and for the leakage current you can refer to IIH and IIL numbers from the device datasheet., the value of these leakage currents is 150 uA.

    Yes. the device is LVCMOS1V8 standard.

    Thanks & regards,

    Abhishek