Datasheet

V
CC
V
CC
LED
Pn
100 kW
V
CC
3.3 V 5 V
LED
Pn
V
CC
Ramp-Up Re-Ramp-Up
Time to Re-Ramp
Time
Ramp-Down
V
CC_RT
V
CC_RT
V
CC_FT
V
CC_TRR_GND
PCA9539
www.ti.com SCPS130F –AUGUST 2005–REVISED JANUARY 2011
Minimizing I
CC
When I/O Is Used to Control LED
When an I/O is used to control an LED, normally it is connected to V
CC
through a resistor (see Figure 15).
Because the LED acts as a diode, when the LED is off, the I/O V
IN
is about 1.2 V less than V
CC
. The ΔI
CC
parameter in Electrical Characteristics shows how I
CC
increases as V
IN
becomes lower than V
CC
. For
battery-powered applications, it is essential that the voltage of I/O pins is greater than or equal to V
CC
, when the
LED is off, to minimize current consumption.
Figure 16 shows a high-value resistor in parallel with the LED. Figure 17 shows V
CC
less than the LED supply
voltage by at least 1.2 V. Both of these methods maintain the I/O V
CC
at or above V
CC
and prevent additional
supply-current consumption when the LED is off.
Figure 16. High-Value Resistor in Parallel With LED
Figure 17. Device Supplied by Lower Voltage
Power-On Reset Requirements
In the event of a glitch or data corruption, PCA9539 can be reset to its default conditions by using the power-on
reset feature. Power-on reset requires that the device go through a power cycle to be completely reset. This
reset also happens when the device is powered on for the first time in an application.
The two types of power-on reset are shown in Figure 18 and Figure 19.
Figure 18. V
CC
is Lowered Below 0.2 V or 0 V and Then Ramped Up to V
CC
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