KCU105 Board User Guide www.xilinx.com 15
UG917 (v1.4) September 25, 2015
Chapter 1: KCU105 Evaluation Board Features
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 Figure 1-4. The Seiko
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
BATT
specification is described in the Kintex UltraScale Architecture Data Sheet: DC
and AC Switching Characteristics (DS892) [Ref 1]. The battery provides backup power to a
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) [Ref 3] for more details about
Xilinx UltraScale bitstream encryption solutions.
X-Ref Target - Figure 1-4
Figure 1-4: Encryption Key Backup Circuit
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