Datasheet

PCAL6408A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 18 September 2013 22 of 49
NXP Semiconductors
PCAL6408A
Low-voltage translating, 8-bit I
2
C-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 V
DD
, a current flows from the
V
DD(P)
pin through the resistor to ground when the pin is held LOW. This current appears
as additional I
DD
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 V
SS
pin. While this current is
not measured as part of I
DD
, one must be mindful of the 200 mA limiting value through
V
SS
.
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.