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| PCA9550 Datasheet, PDF (11/26 Pages) NXP Semiconductors – 2-bit I2C-bus LED driver with programmable blink rates | |||
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NXP Semiconductors
PCA9550
2-bit I2C-bus LED driver with programmable blink rates
8. Application design-in information
5V
5V
I2C-BUS/SMBus
MASTER
SDA
SCL
10 kâ¦
10 kâ¦
10 kâ¦
VDD
PCA9550
SDA
LED0
SCL
LED1
Fig 14. Typical application
RESET
A0
VSS
002aad271
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.
VDD
3.3 V
5V
VDD
LEDn
LED
100 kâ¦
VDD
LED
LEDn
002aac189
Fig 15. High value resistor in parallel with
the LED
002aac190
Fig 16. Device supplied by a lower voltage
PCA9550_5
Product data sheet
Rev. 05 â 13 October 2008
© NXP B.V. 2008. All rights reserved.
11 of 26
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