PCA9557
NXP Semiconductors
8-bit I2C-bus and SMBus I/O port with reset
9. Application design-in information
V
(5 V)
DD
100 kΩ
(× 5)
620 Ω
1.8 kΩ
1.8 kΩ
2 kΩ
2 kΩ
V
V
DD
DD
MASTER
CONTROLLER
PCA9557
SUBSYSTEM 1
IO0
(e.g., temp. sensor)
SCL
SCL
SDA
INT
SDA
IO1
IO2
IO3
IO4
IO5
IO6
IO7
RESET
RESET
RESET
SUBSYSTEM 2
(e.g., counter)
V
SS
A
controlled switch
(e.g., CBT device)
enable
A2
A1
A0
B
V
SS
ALARM
SUBSYSTEM 3
(e.g., alarm system)
V
DD
002aad285
Device address configured as 0011 100x for this example.
IO0, IO2, IO3 configured as outputs.
IO1, IO4, IO5 configured as inputs.
IO6, IO7 are not used.
Fig 18. Typical application
9.1 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 18. 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 19 shows a high value resistor in parallel with the LED. Figure 20 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.
PCA9557
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2013. All rights reserved.
Product data sheet
Rev. 7 — 10 December 2013
13 of 30
NXP [ NXP ]
