AND8116/D

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6

The 73 V waveform shown in the oscilloscope picture

(Figure 9) resulted from the 60 V load dump transient plus

the vehicle’s battery voltage (13 V). In the application field,

the relay driver (NUD3124) is always connected to relays,

therefore if a load dump condition occurs, the current is

limited by the relay’s coil resistance which reduces the

amount of energy that the relay driver (NUD3124) needs to

drain to ground. Figure 10 shows an oscilloscope picture

with the waveforms generated across the NUD3124 device

when it is subjected to a load dump transient. For this case,

the device is controlling an OMRON relay (G8TB−1A−64)

The most stressful and aggressive requirement for

automotive transients is load dump. Therefore if a device is

able to comply with this requirement, it is assured that it will

sustain all the other less aggressive transients such as 240 V

(10

W source impedance), 350 ms time−duration type.

In addition to complying with the load dump transient

requirements and all the other smaller automotive transients,

the NUD3124 device also complies with other automotive

requirements such as reverse battery (−14 V, 1 minute or

more) and dual voltage jump start (24 V

"10%).

If a reverse battery condition occurs, it will cause the body

diode of the FET to be forward biased and hence conduct.

During this condition, the current will be limited by the

relay’s coil resistance to a safe level causing the relay be

energized. With the traditional discrete approach, damage

can occur to the control logic circuitry due to a possible

current path from a reverse connected battery through the

driver to the logic’s output. This possibility is eliminated

when the NUD3124 device is used.

If a dual voltage jump start is used (24 V or more), the

NUD3124 device will remain in its off−state and therefore

the relays will too. This is the ideal operation required during

a dual voltage jump start condition, otherwise the relays

would be activated and could create serious operation

problems in the equipment or functions that they are

controlling (windows, seats, etc.).

RELAY MODULE

The benefits of the ON Semiconductor’s relay driver

devices (NUD3105, NUD3112 and NUD3124) are even

more unique and useful if they are integrated inside the relay

body to create relay modules that can be driven directly from

the logic circuitry. The advantages are:

All the previous advantages will result in costs reduction

for industrial and automotive applications which have the

need for mechanical relays. Figure 10 describes graphically

the design of the relay module. Some relay manufacturers

already integrate a diode connected in parallel with the

relay’s coil to simplify the driver circuitry. Others are

considering to develop the concept of the relay module. The

major goal of the relay’s manufacturers is to offer more

added value to their customers for design optimization and

cost reduction.

Load Dump Transient – 20 V/div

Conversion factors:

Ch1 – Direct (Volts)

Ch2 – Max * 20 (Amp)

Ch3 – Direct (Volts)

M1 – Area * 20 (Joules)

= 73 mJ

Figure 10. Waveforms Generated Across the

NUD3124 Device During a Load Dump Transient