7630 datasheet(73/238 Pages) RENESAS

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APPLICATION

2.1 I/O ports

2-7

7630 Group User’s Manual

2.1.3 Overvoltage conditions at digital input ports

This section describes how to use digital input ports of the 7630 group at overvoltages. The terms over

voltage refer to voltage levels beyond VCC+0.3V. When subjected to such input voltage levels, the built-

in protection circuit of the input port attempts to limit the input voltage in order to avoid permanent damage

to the device. This condition causes input current to the port. The built-in protection circuit tolerates input

currents up to specified limits (refer to “3.1 Electrical characteristics”). The input current levels must be

limited by appropriate design of the application circuit connected to the coresponding port. Figure 2.1.9

shows an example circuit.

Fig. 2.1.9 External circuit example applying overvoltage to digital inputs

Assume VIN the voltage to be connected to the MCU. The resistor R limits the input current to satisfy the

“recommended operatiing conditions”. For an estimation of the resistor, the port voltage VP should be

assumed to be VCC at overvoltage (VIN > VCC+0.3V). To determine the appropriate resistor size refer to

the below:

≥

VIN(max.) – VCC

(VIN > VCC+0.3V)

IIO

Notes: • Subjecting ports to overvoltage may effect the supply voltage and ground levels of the application

and the device. Ensure appropriate design (low impedance) of the power and ground supply to

keep VCC and VSS within the specified limits. In particular, avoid subjecting ports to overvoltage

causing VCC-VSS to rise above 5.5 V.

• Port P0 must not be subjected to overvoltage conditions.

• Overvoltages causing input current flowing through the internal port protection circuits have a

negative effect on the ports noise immunity. Therefore, careful and intense testing of the target

system’s noise immunity is required.

• Because of the above noise immunity issue, it is not recommended to subjects ports with interrupt

functions (such as ports for external interrupt) to overvoltage conditions.

• Refer to the “3.4 Countmeasures against noise”.

Internal

circuits

MCU

VCC

VIN

Protection

circuit

VSS

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