Philips Semiconductors
2-bit I2C LED dimmer
Preliminary data
PCA9530
APPLICATION DATA
3.3 V
SDA
SCL
5V
SDA
VDD
LED0
SCL
RESET
LED1
I2C/SMBus MASTER
A0
VSS
PCA9530
Figure 12. Typical application
SW02043
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
3.3 V
5V
VDD
LEDx
LED
100 k
SW02086
Figure 13. High value resistor in parallel with the LED
VDD
LEDx
LED
SW02087
Figure 14. Device supplied by a lower voltage
2002 Dec 12
8