CAT9557 Datasheet, PDF(13/17 Page) ON Semiconductor – 8-Bit I2C-Bus and SMBus I/O Port

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CAT9557 Datasheet, PDF (13/17 Pages) ON Semiconductor – 8-Bit I2C-Bus and SMBus I/O Port

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CAT9557

Minimizing IDD when the I/Os are Used to Control LEDs

When the I/Os are used to control LEDs, they are normally

connected to VDD through a resistor as shown in Figure 15.

Since the LED acts as a diode, when the LED is off the I/O

VI is about 1.2 V less than VDD. The supply current, IDD,

increases as VI becomes lower than VDD.

Designs needing to minimize current consumption, such

as battery power applications, should consider maintaining

VDD

the I/O pins greater than or equal to VDD when the LED is

off. Figure 16 shows a high value resistor in parallel with the

LED. Figure 17 shows VDD less than the LED supply

voltage by at least 1.2 V. Both of these methods maintain the

I/O VI at or above VDD and prevents additional supply

current consumption when the LED is off.

3.3 V

VDD

IOn

LED 100 kW

VDD

IOn

LED

Figure 16. High Value Resistor in

Parallel with the LED

Figure 17. Device Supplied by a Lower Vol

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