NXP Semiconductors
PCA9538
8-bit I2C-bus and SMBus low power I/O port with interrupt and reset
7.1 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 11. 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 12 shows a high value resistor in parallel with the LED. Figure 13 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
IOn
LED
100 kΩ
VDD
LED
IOn
002aac660
002aac661
Fig 12. High value resistor in parallel with Fig 13. Device supplied by a lower voltage
the LED
PCA9538_5
Product data sheet
Rev. 05 — 28 May 2009
© NXP B.V. 2009. All rights reserved.
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