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PCAL6408A

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Product data sheet

Rev. 3 — 18 September 2013

22 of 49

NXP Semiconductors

PCAL6408A

Low-voltage translating, 8-bit I2C-bus/SMBus I/O expander

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

resistors

The PCAL6408A 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 9.

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

VDD(P) pin through the resistor to ground when the pin is held LOW. This current appears

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 flows from the power supply through the pin to the VSS pin. While this current is

not 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 26 for a

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

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