AND8116 Datasheet, PDF (5/8 Pages) ON Semiconductor – Integrated Relay/Inductive Load Drivers for Industrial and Automotive Applications

AND8116/D
Figure 7 shows the voltage and current waveforms
generated across the NUD3124 relay driver when it is
controlling an OMRON relay (G8TB−1A−64). This relay
has the following coil characteristics: L = 46 mH, Rdc =
100 W. The current that the OMRON relay takes for 12 V of
supply voltage is 120 mA. The integrated FET has a typical
on−resistance of 1.0 W, therefore the power dissipation
generated in the FET is around 15 mW (P=I²R) at 25°C of
ambient temperature. It results in an on−voltage drop of only
125 mV at 120 mA of current.
V_SUPPLY – 10 V/div
V_GS – 10 V/div
Inductor
kick back
V_DS – 10 V/div
I_D – 50 mA/div
Figure 7. Waveforms Generated Across the
NUD3124 when Driving OMRON Relay
G8TB−1A−64
Unlike the NUD3105 and NUD3112 devices (industrial
version), the unique design of the NUD3124 device
(automotive version) provides the active clamp feature that
allows higher reverse avalanche energy capability by
activating the FET anytime transient voltage conditions
exceed the breakdown voltage of the clamp Zener diodes
(28 V). The energy capability of the NUD3124 device is
350 mJ typically. Figure 8 shows an oscilloscope picture of
a surge test applied to the device when it was characterized
to find its maximum reverse avalanche energy capability.
The high reverse avalanche energy capability of this
device (350 mJ) allows to control most of the relays used in
automotive applications since they usually have coils
between 50 mA and 150 mA with inductance values lower
than 1 Henry. These type of coils do not transfer high levels
of energy to the NUD3124 device (E = ½ L I²⁾, and therefore
each of them can be controlled with the same device
(NUD3124). Big advantages are obtained when a common
relay driver product is used to control the majority of the
relays used in a particular application circuit. PC board
space is saved and the circuit design is optimized. In
addition, components count purchasing operations are also
simplified.
The active clamp characteristic of the NUD3124 device
also allows it to comply with automotive requirements of
load dump and other voltage transients required by the
automotive specifications. Load dump transients are
generated by the vehicle’s alternator when the battery
connection fails during heavy charging. These type of
transients could occur when the relay is on or off. Although
automotive requirements for load dump vary between
suppliers, it has been learned that most of the load dump
requirements can be covered by devices which can sustain
a load dump transient of 60 V with 350 msec of duration.
Figure 9 shows a load dump transient of 60 V and 350 msec
of duration.
V_GS – 10 V/div
I_D – 100 mA/div
P_pk = Ch2 x Ch3
Conversion Factors:
Ch2 – Max * 100
Ch3 – Max * 10
M1 – Area * 1000
= 351 mJ
Figure 8. Waveforms Generated Across the
NUD3124 Device During Surge Test
Figure 9. Load Dump Transient Waveform
(60 V, 350 msec).
http://onsemi.com
5