What voltage range is supported by VADJ on the Kintex-7 FPGA KC705 Evaluation Kit?
How can this voltage be adjusted?
The KC705 FMC banks are HR banks, therefore they can support a supply voltage of up to 3.3V.
The VADJ for KC705 can be 1.8V, 2.5V, or 3.3V. The default value for VADJ on the KC705 is 2.5V and FMC_VADJ rail is set to 2.5V when the KC705 is shipped to customers.
Voltage control is achieved as follows:
When the KC705 is powered on, the state of the FMC_VADJ_ON_B signal (wired to header J65) is sampled by the TI UCD9248 controller, U55.
By default, a jumper exists on J65, therefore the signal FMC_VADJ_ON_B is held low, ensuring U55 energizes the FMC_VADJ rail at power on.
The rail turn on decision is made at power-on time (based on the J65 jumper setting). Removing J65 after the KC705 is powered up will not affect 2.5V power delivered to FMC_VADJ rail.
At power on, if no jumper is present on J65, the FMC_VADJ_ON_B signal is set to high and the KC705 will not energize FMC_VADJ 2.5V at power on.
The user can then control when to turn on FMC_VADJ and to what voltage level (1.8V - 3.3V).
With FMC_VADJ off, the Kintex-7 FPGA will still configure and has access to the TI controller PMBUS and VADJ_ON_B signal.
Users can develop code to command the FMC_VADJ rail to be set to something other than the default (2.5V). That code would program the FMC_VADJ voltage level into U55.
The VADJ_ON_B signal can then be driven low by user logic, and the FMC_VADJ rail comes up at the new FMC_VADJ voltage level.
The responsibility to develop code to achieve this rests with the individual customer, however this can be adjusted manually using TI tools and the TI USB adapter.
Care is advised if making any changes to power levels on the board.
Documentation describing PMBUS programming for the UCD9248 digital power controller is available at http://www.ti.com/fusiondocs
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