AND8116/D

http://onsemi.com

3

The 40 V N−channel FET is designed to switch the relay’s

coil for currents up to 500 mA. The clamping protection

Zener diodes (14 V) provides a clamp function to suppress

the voltage spike generated by the relay’s coil during the

turn−off interactions (V = Ldi/dt). The ESD protection

Zener diodes protects the gate−source silicon junction

against ESD conditions possibly induced by persons during

the handling or assembly of the device. And the bias resistor

provides the drive control signals to the FET.

Figure 3 illustrates the typical connection diagram of the

NUD3105 / NUD3112 devices:

Figure 3. Typical Connection Diagram

(NUD3105 5.0 V Relay’s Coils and NUD3112 for 12 V)

1.0 k

300 k

ESD

Zener

14 V

ESD

Zener

14 V

Clamp Zener

7 V or 14 V

Clamp Zener

7 V or 14 V

+5 V/3.3 V

LOGIC

+12 V/5.0 V

RELAY

0

NUD3105, NUD3112

When positive logic voltage is applied to the gate of the

device (5.0 V/3.3 V), the FET is turned−on which activates

the relay. When the FET is turned−off, the relay’s coil is

deactivated which causes it to kickback and generates a high

voltage spike, this voltage spike is suppressed by the clamp

Zener diodes placed across the FET. This operation

sequence is repeated for all the on and off operations of the

relay driver. Figure 4 shows the voltage and current

waveforms generated across the NUD3112 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 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 4. Traces Generated Across NUD3112 Device

when Driving OMRON Relay G8TB−1A−64

Inductor

kick back