PCA9534A datasheet(23/39 Pages) TI

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LED

LEDx

VCC

100 kW

VCC

LED

3.3 V

5 V

LEDx

VCC

Ramp-Up

Re-Ramp-Up

Time to Re-Ramp

Time

Ramp-Down

VCC_RT

VCC_FT

VCC_TRR_GND

PCA9534A

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SCPS141F – SEPTEMBER 2006 – REVISED JUNE 2010

Minimizing ICC When the I/O Controls LEDs

When the I/Os are used to control LEDs, they normally are connected to VCC through a resistor as shown in

Figure 14. 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

supply current, ICC, increases as VIN becomes lower than VCC and is specified as ΔICC in Electrical

Characteristics.

For battery-powered applications, it is essential that the voltage of the I/O pins is greater than or equal to VCC

when the LED is off to minimize current consumption. Figure 15 shows a high-value resistor in parallel with the

LED. Figure 16 shows VCC less than the LED supply voltage by at least 1.2 V. Both of these methods maintain

the I/O VIN at or above VCC and prevents additional supply-current consumption when the LED is off.

Figure 15. High-Value Resistor in Parallel With the LED

Figure 16. Device Supplied by a Lower Voltage

Power-On Reset Requirements

In the event of a glitch or data corruption, PCA9534A 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 17 and Figure 18.

Figure 17. VCC is Lowered Below 0.2 V or 0 V and Then Ramped Up to VCC

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