Hardware Reference
In-Depth Information
While we have focused on GPIO inputs in this section, the clamping diodes also
apply to outputs. Outputs can be forced beyond their limits by external circuits like
pull-up resistors. Pull-up resistors should not be attached to +5 V, for example, when the
MCP23017 is operating from a +3.3 V supply.
Standby Current
If the MCP23017 device is not sourcing or sinking output currents, the standby current
is stated as 3 μA (for 4.5 to 5.5 V operation). This operating parameter is important to
designers of battery-operated equipment.
Input Logic Levels
Since the device operates over a range of supply voltages, the datasheet defines the logic
levels in terms of the supply voltage. For example, the GPIO input low level is listed as
0.2 ×
V
DD
. So if we operate with
V
DD
= +3.3
V
, the input low voltage is calculated as follows:
V
=´
=´
=
02
02 33
066
.
.
V
IL
DD
max
.
.
V
Therefore, a voltage in the range of 0 to 0.66 V is guaranteed to read as a 0 bit.
Likewise, let's calculate the input high voltage threshold, where the multiplier is
given as 0.8:
V
=´
=´
=
08
08 33
264
.
.
V
IH
DD
min
.
.
V
Thus any voltage greater than or equal to 2.64 V is read as a 1 bit, when powered from
a +3.3 V supply. Any voltage between
V
ILmax
and
V
IHmin
is undefined and reads as a 1 or a 0,
and perhaps randomly so.
Output Logic Levels
The output logic levels are stated differently. The datasheet simply states that the output
low voltage should not exceed a fixed limit. The high level is also stated as a minimum
value relative to
V
DD
. This pair of parameters is listed here:
V
=
=
=
=
06
.
V
OLma
OHmi
x
n
V
V
-
-
07
.
V
DD
33
.
07
.
27
.
V
