Verdin Carrier Board Design Guide
Preliminary
– Subject to Change
Toradex AG l Ebenaustrasse 10 l 6048 Horw l Switzerland l +41 41 500 48 00 l
l
Page | 93
3.5.5.12 Level Shifter
Level shifters can be an effective method for preventing backfeeding. Especially if you anyway need
a level shifter in the signal path. Even if both sides have the same IO voltage level, a level shifter
can still be a good option. It is important to select a level shifter that allows both power rails to be
switched off individually. Not all level shifters allow that without causing backfeeding. A good
candidate for preventing backfeeding is the SN74AVC4T774 from TI. For open-drain signals such
as the I
2
C bus, the FXMA2102L8X from ON Semiconductor prevents backfeeding.
Figure 85: Level shifter for preventing backfeeding
3.5.5.13 Galvanic Isolation
Galvanic isolations in the signal path can be achieved by transformers, optocouplers, or specialized
ICs. Especially in harsh environments, galvanic isolation is a preferred method for isolating power
domains of different devices. The so-called magnetics inside the Ethernet connector is also a
galvanic isolator and prevents backfeeding over the Ethernet cable. Galvanic isolators are also
preferred way for protecting different power domains of CAN interfaces.
Figure 86: Galvanic isolation between input and output
Peripheral
SoC
IO Rail (off)
RX
Peripheral Rail (on)
TX
0V
1.8V
1.8V
0V
High
Level Shifter
PWR_1V8_MOCI (off)
0V
VCC_B
VCC_A
B
A
GND
Peripheral
SoC
IO Rail (off)
RX
Peripheral Rail (on)
TX
0V
1.8V
1.8V
0V
High
