Logic selection guide 2016

OPEN-DRAIN OUTPUTS
Open-drain outputs
An open-drain output can be pulled up to a voltage level
that matches the requirements of the device it’s driving.
As shown in the figure, a pull-up resistor (R PU
) is used
between the output and the pull-up voltage (V PU
). V PU
can be set higher or lower than V CC
, making open-drain
outputs suitable for both low-to-high and high-to-low
voltage-level translation.
Where you’ll find it
The AHCT and HCT families support legacy TTL levels.
They operate at 5 V and can be used to interface with
3.3 V inputs. AUP1T devices operate at 3.3 V and can be
used to interface with 1.8 V inputs. The LVT and ALVT
families operate at 3.3 V and can be used to interface
with 2.5 V inputs. Many of NXP’s buffer, inverter, and
gate devices include open-drain outputs.
V PU
5 V 3.3 V 2.5 V 1.8 V 1.2 V 0.8 V
Input
Level shifter
with open-drain
output
Pull-up
resistor
(R PU
)
Opendrain
outputs
HEF4000B,
NPIC,
HC(T),
AHC(T),
LV, LVC
HC,
AHC,
LV, LVC,
AUP
LVC,
AUP,
AXP
AUP,
AXP
AUP,
AXP
AXP
GND
Open-drain output and pull-up resistor for level translation
INPUT-CLAMPING DIODES
What they do
Provide overvoltage and ESD protection, and enable
high-to-low level translation.
Inputclamping
diodes
5 V 3.3 V 2.5 V 1.8 V 1.2 V
HEF4000B,
HC(T),
LV
HC, LV HC, LV LV LV
Why they’re important
In families that have an input-clamping diode to V CC
, the
diode is a critical part of the input ESD-protection circuit.
Clamping
diode
The clamping property of the diode can also be used
with an external current-limiting resistor so the input
V CC2 = 5 V
can be interfaced to higher voltages. On some NXP
logic devices, the inputs have input-clamping diodes
V CC1
= 15 V
to V CC
and GND. When using CMOS devices that have
Device A
current-limiting resistors at the inputs, the input voltage
can exceed maximum specified values as long as the
maximum current rating is observed.
R CL
GND
Where you’ll find them
The HEF4000B, HC(T), NPIC, and LV families all utilize
ESD-protection circuits that include input-clamping
diodes to V CC
.
R CL
=
15 V - (5.0 V + 0.7 V)
I IK
ESD
protection
I IK
is found in the limiting values table of the datasheet
Input
buffer
Input-clamping diodes support high-to-low level translation
NXP Logic selection guide 2016
23