9.2.1.2 Minimizing I_CC When I/Os Control LEDs

When the I/Os are used to control LEDs, normally they are connected to V_CC through a resistor as shown in Figure 33. For a P-port configured as an input, I_CC increases as V_I becomes lower than V_CC. The LED is a diode, with threshold voltage V_T, and when a P-port is configured as an input the LED is off but V_I is a V_T drop below V_CC.

For battery-powered applications, it is essential that the voltage of P-ports controlling LEDs is greater than or equal to V_CC when the P-ports are configured as input to minimize current consumption. Figure 34 shows a high-value resistor in parallel with the LED. Figure 35 shows V_CC less than the LED supply voltage by at least V_T. Both of these methods maintain the I/O V_I at or above V_CC and prevents additional supply current consumption when the P-port is configured as an input and the LED is off.

Figure 34. High-Value Resistor in Parallel With LED

Figure 35. Device Supplied by a Lower Voltage