Datasheet

PCA9551_8 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 08 — 31 July 2008 11 of 26
NXP Semiconductors
PCA9551
8-bit I
2
C-bus LED driver with programmable blink rates
8. Application design-in information
8.1 Minimizing I
DD
when the I/Os are used to control LEDs
When the I/Os are used to control LEDs, they are normally connected to V
DD
through a
resistor as shown in Figure 14. Since the LED acts as a diode, when the LED is off the
I/O V
I
is about 1.2 V less than V
DD
. The supply current, I
DD
, increases as V
I
becomes
lower than V
DD
and is specified as ∆I
DD
in Table 12 “Static characteristics”.
Designs needing to minimize current consumption, such as battery power applications,
should consider maintaining the I/O pins greater than or equal to V
DD
when the LED is off.
Figure 15 shows a high value resistor in parallel with the LED. Figure 16 shows V
DD
less
than the LED supply voltage by at least 1.2 V. Both of these methods maintain the I/O V
I
at or above V
DD
and prevents additional supply current consumption when the LED is off.
LED0 to LED5 are used as LED drivers.
LED6 and LED7 are used as regular GPIOs.
Fig 14. Typical application
PCA9551
LED0
LED1
SDA
SCL
RESET
5 V
I
2
C-BUS/SMBus
MASTER
002aac510
SDA
SCL
V
DD
A2
A1
A0
V
SS
5 V
10 kΩ
LED2
LED3
LED4
LED5
LED6
LED7
GPIOs
10 kΩ10 kΩ
Fig 15. High value resistor in parallel with
the LED
Fig 16. Device supplied by a lower voltage
002aac189
LED
V
DD
LEDn
100 kΩ
V
DD
002aac190
LED
V
DD
LEDn
3.3 V 5 V