PCA9550DP datasheet(11/26 Pages) NXP

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PCA9550_5

Product data sheet

Rev. 05 — 13 October 2008

11 of 26

NXP Semiconductors

PCA9550

2-bit I2C-bus LED driver with programmable blink rates

Application design-in information

8.1 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 14. 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 the I/O pins greater than or equal to VDD when the LED is off.

Figure 15 shows a high value resistor in parallel with the LED. Figure 16 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.

Fig 14. Typical application

PCA9550

LED0

LED1

SDA

SCL

RESET

5 V

I2C-BUS/SMBus

MASTER

SDA

SCL

VDD

VSS

5 V

10 k

Ω

10 k

Ω

10 k

Ω

002aad271

Fig 15. High value resistor in parallel with

the LED

Fig 16. Device supplied by a lower voltage

002aac189

LED

VDD

LEDn

100 k

Ω

VDD

002aac190

LED

VDD

LEDn

3.3 V

5 V

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