N11
Hardware User Guide
Copyright © Neoway Technology Co., Ltd
17
Figure 3-11
Level shifting circuit 1
UART_TXD
VDDIO_2P8
VCC_IO
4.7 k
Ω
10 k
Ω
Q1
R2
R3
MCU_RXD
MCU_TXD
VDDIO_2P8
VCC_IO
4.7 k
Ω
10 k
Ω
Q2
R4
R1
UART_RXD
Components:
⚫
R2/R4: 2 kΩ-10 kΩ.
The greater the UART baud rate is, the lower the R2/R4 value is.
⚫
R1/R3: 4.7 kΩ-10 kΩ.
The greater the UART baud rate is, the higher the R1/R3 value is.
⚫
Q1/Q2: MMBT3904 or MMBT2222
High-speed transistor is better.
If the low level at MCU_UART (V
IL
) is greater than 200mV, use level shifting circuit in Figure 3-12.
Otherwise, low level at UART might be higher than required, resulting in failure to identify signals.
