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| TCA9539_15 Datasheet, PDF (26/42 Pages) Texas Instruments – Low Voltage 16-Bit I2C and SMBus Low-Power I/O Expander | |||
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TCA9539
SCPS202B â OCTOBER 2009 â REVISED OCTOBER 2015
www.ti.com
Typical Application (continued)
9.2.1 Design Requirements
9.2.1.1 Minimizing ICC When I/Os Control LEDs
When an I/O is used to control an LED, normally it is connected to VCC through a resistor (see Figure 34).
Because the LED acts as a diode, when the LED is off, the I/O VIN is about 1.2 V less than VCC. The ÎICC
parameter in Electrical Characteristics shows how ICC increases as VIN becomes lower than VCC. For battery-
powered applications, it is essential that the voltage of I/O pins is greater than or equal to VCC, when the LED is
off, to minimize current consumption.
Figure 35 shows a high-value resistor in parallel with the LED. Figure 36 shows VCC less than the LED supply
voltage by at least 1.2 V. Both of these methods maintain the I/O VCC at or above VCC and prevent additional
supply-current consumption when the LED is off.
VCC
VCC
Pn
LED
100 k
Figure 35. High-Value Resistor In Parallel With Led
3.3 V
5V
VCC
Pn
LED
Figure 36. Device Supplied By Lower Voltage
26
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