AND8116 Datasheet, PDF (4/8 Pages) ON Semiconductor – Integrated Relay/Inductive Load Drivers for Industrial and Automotive Applications

AND8116/D
Based on the relay coil specifications, the energy that is
transferred to the driver by the relay’s coils can be
theoretically calculated by using the formula E = ½ L I2,
which results in 0.331 mJ. The avalanche energy capability
of the NUD3105 and NUD3112 devices is 50 mJ, so the
0.331 mJ transferred by the OMRON relay only represents
a 0.65% of their energy capability. The same theoretical
principle (E = ½ L I2) can be used to find out the type of
relay’s coils that the NUD3105 and NUD3112 devices can
drive. For these purposes, one needs to know the inductance
and current characteristics of the relay’s coil to calculate the
energy that will be transferred. The resulting energy should
not exceed the 50 mJ at which the devices are rated.
Automotive Version
Figure 5 describes the automotive relay driver version
(device NUD3124).
This device also integrates several discrete components in
a single SOT−23 three leaded surface mount package to
achieve a simpler and even more robust solution than the
conventional discrete relay drivers. The characteristics of
the integrated devices are listed below:
• N−channel FET 40 V, 150 mA
• ESD protection Zener diodes (14 V)
• Bias resistors (10 kW in the gate and 100 kW between
gate and source)
• Clamping protection Zener diodes (28 V) to perform as
an active clamp function.
Drain (3)
Clamp Zener
28 V
Clamp Zener
28 V
Gate (1)
10 k
ESD
Zener
14 V
ESD
Zener
14 V
100 k
ESD
Zener
14 V
ESD
Zener
14 V
Source (2)
Figure 5. Automotive Relay Driver Description
(NUD3124 Device)
The 40 V N−channel FET is designed to switch on and off
the relay’s coil for currents up to 200 mA. The clamping
protection Zener diodes (28 V) provides an active clamp
function to drain to ground the voltage spikes generated by
the relay’s coils during the turn−off interactions (V = Ldi/dt).
This function is achieved by partially activating the FET
through the clamp Zener diodes anytime the voltage across
them reaches their breakdown voltage level (28 V). 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 6 illustrates the typical connection diagram of the
NUD3124 device.
+12 V (Car’s Battery)
NUD3124
Gate (1)
LOGIC
Clamp Zener
28 V
Clamp Zener
28 V
10 k
ESD
Zener
14 V
ESD
Zener
14 V
100 k
ESD
Zener
14 V
ESD
Zener
14 V
RELAY
Source (2)
Figure 6. Typical Connection Diagram for
Automotive Relay Driver (NUD3124 Device)
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 causes the clamp Zener
diodes (28 V) to breakdown which partially activates the
FET to drain this condition to ground. This operation
sequence is repeated for all the on and off operations of the
relay driver.
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