PCF8575CDGVR datasheet(18/38 Pages) TI1

18 / 38 page

LED

3.3 V

5 V

LEDx

VCC

LED

LEDx

VCC

100 k

VCC

PCF8575C

SCPS123F – MARCH 2005 – REVISED JANUARY 2015

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Typical Application (continued)

9.2.1 Design Requirements

9.2.1.1 Minimizing ICC When I/Os Control LEDs

When the I/Os are used to control LEDs, normally they are connected to VCC through a resistor as shown in

Figure 15. For a P-port configured as an input, ICC increases as VI becomes lower than VCC. The LED is a diode,

with threshold voltage VT, and when a P-port is configured as an input the LED will be off but VI is a VT drop

below VCC.

For battery-powered applications, it is essential that the voltage of P-ports controlling LEDs is greater than or

equal to VCC when the P-ports are configured as input to minimize current consumption. Figure 16 shows a high-

value resistor in parallel with the LED. Figure 17 shows VCC less than the LED supply voltage by at least VT.

Both of these methods maintain the I/O VI at or above VCC and prevents additional supply current consumption

when the P-port is configured as an input and the LED is off.

Figure 16. High-Value Resistor in Parallel With LED

Figure 17. Device Supplied by a Lower Voltage

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PCF8575CDGVR Datasheet(PDF) 18 Page - Texas Instruments