Datasheet

PCA9537_5 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 05 — 7 May 2009 10 of 24
NXP Semiconductors
PCA9537
4-bit I
2
C-bus and SMBus low power I/O port with interrupt and reset
7. Application design-in information
7.1 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 9. 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
.
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 10 shows a high value resistor in parallel with the LED. Figure 11 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.
Device address is 1001 001x for this example.
IO0, IO2, IO3 configured as outputs.
IO1 configured as input.
Fig 9. Typical application
PCA9537
IO0
IO1
SCL
SDA
V
DD
(5 V)
MASTER
CONTROLLER
SCL
SDA
INT
IO2
V
DD
V
DD
V
SS
INT
10 kΩ
SUB-SYSTEM 1
(e.g., temp sensor)
IO3
INT
SUB-SYSTEM 2
(e.g., counter)
RESET
controlled
switch
(e.g., CBT device)
A
B
enable
V
SS
002aae640
10 kΩ10 kΩ 2 kΩ 100 kΩ
RESET RESET
10 kΩ
Fig 10. High value resistor in parallel with
the LED
Fig 11. Device supplied by a lower voltage
002aac660
LED
V
DD
IOn
100 kΩ
V
DD
002aac661
LED
V
DD
IOn
3.3 V 5 V