AND8116/D

http://onsemi.com

5

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

°C of

ambient temperature. It results in an on−voltage drop of only

125 mV at 120 mA of current.

Figure 7. Waveforms Generated Across the

NUD3124 when Driving OMRON Relay

G8TB−1A−64

Inductor

kick back

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 =

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.

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).