Datasheet

PCA9538A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 1 — 28 September 2012 12 of 37
NXP Semiconductors
PCA9538A
Low-voltage 8-bit I
2
C-bus I/O port with interrupt and reset
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 11
. 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 12
shows a high value resistor in parallel with the LED. Figure 13 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.
8.2 12 V tolerant I/Os
The PCA9538A device SCR group reference diode can go up to 10 V before latch back to
8 V. The ESD gate oxide will protect the device, but not if used continually. Therefore, to
achieve 12 V tolerant I/Os, the external protection circuitry (diode) must be used as shown
in Figure 14
.
Fig 12. High value resistor in parallel with
the LED
Fig 13. Device supplied by a lower voltage
002aag164
LED
V
DD
Pn
100 kΩ
V
DD
002aag165
LED
V
DD
Pn
3.3 V 5 V
Fig 14. External protection circuitry
PCA9538A
A0 V
DD
A1 SDA
RESET SCL
P0 INT
P1 P7
P2 P6
P3 P5
V
SS
P4
002aah421
+5 V +12 V