Points For Caution; Internal Regulator; Handling Of Unused Pins - Renesas R-IN32M3 Series User Manual

R-IN32M3 Series: Board design edition
25.3

Points for Caution

This section describes points of incorrect design that may lead to abnormal heating.
25.3.1

Internal Regulator

The 1.5V regulator incorporated in the R-IN32M3-EC requires an external smoothing circuit. This smoothing circuit not
operating stably (e.g. oscillating around 1.5 V) reduces the efficiency of the regulator and may lead to the supply of a
current above the rated value. Inappropriate equivalent series resistances (ESRs) for capacitors are the most likely source
of such problems. Thus, when using components other than those recommended, use a capacitor with an ESR in the
range from about 75 mΩ to 300 mΩ and check that the output voltage is stable. When using tantalum capacitors is not
possible, a ceramic capacitor and a combination of a 100-mΩ resistor and ceramic capacitor can be used for C2 and C1,
respectively.
25.3.2

Handling of Unused Pins

If an unused pin is clamped to the GND or power supply on the board, the corresponding pin must have the input
attribute as a fixed setting. If it is set as an output, and the level of the point where it is clamped is opposite that of the pin,
a large steady-state current will continuously flow through the output buffer.
On the other hand, if an unused pin is open-circuit on the board, the corresponding pin can have either a fixed output
attribute or an input attribute with enabling of pull-up or pull-down resistors. Setting a pin as an input without enabling a
pull-up or pull-down resistor may lead to the pin being in a floating state and the flow of a through-type current.
Since the above factors lead to unnecessary heating, be sure to check the settings made by the software.
R-IN32M3
Output mode enabled
R18UZ0021EJ0400
Dec. 28, 2018
VDD33 (3.3 V)
VDD33 (3.3 V)
Steady-state
current
R-IN32M3
VDD33 (3.3 V)
Through-type
current
VDD33 (3.3 V)
Output mode disabled
25. Thermal Design <R>
Open-circuit
(floating)
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