PCA9550 datasheet(8/17 Pages) PHILIPS

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Philips Semiconductors

Product data

PCA9550

2-bit I2C LED driver with programmable blink rates

2003 May 02

APPLICATION DATA

PCA9550

VSS

SDA

SCL

RESET

VDD

I2C/SMBus MASTER

SW00929

SDA

SCL

LED0

LED1

5 V

Figure 12. Typical application

Minimizing IDD when the I/O is 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 12. Since the LED acts as a

diode, when the LED is off the I/O VIN is about 1.2 V less than VDD. The supply current, IDD, increases as VIN becomes lower than VDD and is

specified as

∆IDD in the DC characteristics table.

Designs needing to minimize current consumption, such as battery power applications, should consider maintaining the I/O pins greater than or

equal to VDD when the LED is off. Figure 13 shows a high value resistor in parallel with the LED. Figure 14 shows VDD less than the LED supply

voltage by at least 1.2 V. Both of these methods maintain the I/O VIN at or above VDD and prevents additional supply current consumption when

the LED is off.

VDD

LEDx

LED

100 k

Ω

SW02086

Figure 13. High value resistor in parallel with the LED

VDD

3.3 V

LEDx

LED

SW02087

5 V

Figure 14. Device supplied by a lower voltage

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