PCAL9554B datasheet(20/42 Pages) NXP

20 / 42 page

PCAL9554B_PCAL9554C

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Product data sheet

Rev. 2 — 10 December 2012

20 of 42

NXP Semiconductors

PCAL9554B; PCAL9554C

Low-voltage 8-bit I2C-bus/SMBus low power I/O port

8.5 Device current consumption with internal pull-up and pull-down

resistors

The PCAL9554B; PCAL9554C integrates programmable pull-up and pull-down resistors

to eliminate external components when pins are configured as inputs and pull-up or

pull-down resistors are required (for example, nothing is driving the inputs to the power

supply rails. Since these pull-up and pull-down resistors are internal to the device itself,

they contribute to the current consumption of the device and must be considered in the

overall system design.

The pull-up or pull-down function is selected in register 44h, while the resistor is

connected by the enable register 43h. The configuration of the resistors is shown in

Figure 6.

If the resistor is configured as a pull-up, that is, connected to VDD, a current will flow from

the VDD pin through the resistor to ground when the pin is held LOW. This current will

appear as additional IDD upsetting any current consumption measurements.

In the same manner, if the resistor is configured as a pull-down and the pin is held HIGH,

current will flow from the power supply through the pin to the VSS pin. While this current

will not be measured as part of IDD, one must be mindful of the 200 mA limiting value

through VSS.

The pull-up and pull-down resistors are simple resistors and the current is linear with

voltage. The resistance specification for these devices spans from 50 k

 with a nominal

100 k

 value. Any current flow through these resistors is additive by the number of pins

held HIGH or LOW and the current can be calculated by Ohm’s law. See Figure 24 for a

graph of supply current versus the number of pull-up resistors.

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