Xilinx KCU105 User Manual page 15

Encryption Key Battery Backup Circuit
The XCKU040 device U1 implements bitstream encryption key technology. The KCU105
board provides the encryption key backup battery circuit shown in
TS518FE rechargeable 1.5V lithium button-type battery B1 is soldered to the board with the
positive output connected to the XCKU040 device U1 VBATT pin AD7. The battery supply
current I specification is described in the Kintex UltraScale Architecture Data Sheet: DC
BATT
and AC Switching Characteristics (DS892)
RAM-based encryption key when the board power is off. B1 is charged from the SYS_1V8
1.8V rail through a series diode with a typical forward voltage drop of 0.38V and 4.7 KΩ
current limit resistor. The nominal charging voltage is 1.42V. The VBATT is only required for
use with encrypted bitstreams as it provides backup power to a RAM-based encryption key
in the absence of powering the entire FPGA. The stored key is used for decrypting an
encrypted bitstream during configuration.
See UltraScale Architecture Configuration User Guide (UG570)
Xilinx UltraScale bitstream encryption solutions.
X-Ref Target - Figure 1-4
KCU105 Board User Guide
UG917 (v1.4) September 25, 2015
[Ref 1]. The battery provides backup power to a
Figure 1-4: Encryption Key Backup Circuit
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Chapter 1: KCU105 Evaluation Board Features
Figure
[Ref 3] for more details about
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