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© 2022 ROHM Co., Ltd.
No. 64UG116E Rev.002
Feb.2022
User’s Guide
1.3.2.2
IO_VDD Sensor Select and VR2 Voltage Regulator
The RKX-A3-EVK-001 provides flexibility for selecting the IO_VDD source for the connected sensors independent of the VDD_SENSOR if desired.
As shown in Figure 6, the selection is made using the Single Poll Double Throw (SPDT) switch SW3. The default option for IO_VDD is to be
connected to the VDD_SENSOR rail. In this case, the IO_VDD voltage will follow the VDD_SENSOR voltage. The alternative selection of the
SW3 switch would connect IO_VDD rail to the output of the VR2 voltage regulator.
Figure 6. IO_VDD Sensor Select and VR2 Voltage Regulator
The VR2 voltage regulator is also a variable output Low Dropout (LDO) linear voltage regulator. By default, it is configured to output 3.3V using the
preset values of R5 and R6 feedback resistors. However, the user can modify the output of the VR2 voltage regulator if desired by replacing the
R6 resistor (13.7k) with another value (Table 3).
Table 3. Voltage Regulator (VR2) Output Option
VR2_OUT
3.3V (default)
3.0V
2.8V
2.5V
1.8V
1.7V
3.6V
R6
13.7k
15.4k
17.4k
20k
34k
38.3k
12.4k
R5
43.2k
43.2k
43.2k
43.2k
43.2k
43.2k
43.2k
1.3.2.3
External Power Supply Connection
In some cases, it may be required to provide an external voltage source for the VDD_SENSOR. To accomplish this, please remove the R64 zero-
ohm resistor. The positive terminal of the external power supply can then be attached to the test point TP3 and negative terminal can be attached
to any GND location on the RKX-A3-EVK-001. One such convenient location is a test point TP1 shown in Figure 7.
Figure 7. External Voltage Source Recommended Connection
