|
Details, datasheet, quote on part number:NUD3112
| |
Datasheet text preview:
AND8116/D Integrated Relay/Inductive Load Drivers for Industrial and Automotive Applications
http://onsemi.com Prepared by: Alejandro Lara ON Semiconductor
APPLICATION NOTE
Abstract Most PC board mounted relays are driven by microprocessors or other sensitive electronic devices. A successful coil drive circuit requires isolation between the relay and the microprocessor circuitry. Effective drive circuits must account for drive current and voltage requirements as well as effective suppression of L di/dt transients which can destroy microprocessor circuits. While it is easy to over-design an effective drive circuit, today's designs must be cost competitive. Integrating a monolithic IC driver device into the relay will provide significant value to the system designer. This paper describes the operation of ON Semiconductor's integrated relay driver products to interface sensitive electronic devices with mechanical relays to accomplish different control/power functions. Important benefits such as PC board space savings and components count reduction are also explained.
Introduction
Industrial and Automotive Application Requirements
The device requirements for industrial and automotive applications are different and must be addressed in different manner. While the requirements for automotive applications are the most difficult to comply with, industrial requirements traditionally allow more latitudes. Relay coil currents vary considerably depending on the applications. The largest class of industrial and automotive relays have coils with current consumption between 50 and 150 mA. Selection of a suitable relay driver requires many constraints to be evaluated. For automotive applications, it is necessary to put special attention in the following requirements: · Load dump (80 V, 300 msec) · Dual voltage jump start (24 V or more) · Reverse battery (-14 V, 1minute or more) · ESD immunity (according AEC-Q100 specification) · Operating ambient temperature (-40°C to 85°C) Meeting these automotive requirements usually results in specifying an oversized and non-cost effective relay driver, or one requiring many protection components. Industrial applications on the other hand do not have many requirements different than the standard ones such as ESD immunity (usually 2.0 kV HBM), and a given range of operating ambient temperature (usually between 0°C to 85°C). However, some applications also call for protection devices against transient voltage conditions, which creates the need for extra protection components too.
Although the advances in the electronics industry are increasing day by day, mechanical relays are still extensively used in industrial and automotive applications to control high current loads. Their low cost and excellent fault tolerance make relays to be an useful and reliable solution in industrial and automotive applications environments. The integrated relay driver devices NUD3105, NUD3112 and NUD3124 offered by ON Semiconductor are considered to be the ideal device solution to control mechanical relays used in industrial and automotive applications. Their integrated design allows significant simplification and cost reductions when replacing traditional discrete solutions such as bipolar transistors plus free-wheeling diodes.
© Semiconductor Components Industries, LLC, 2003
1
September, 2003 - Rev. 1
Publication Order Number: AND8116/D
AND8116/D
Standard Discrete RELAY DRIVERS For both type of applications industrial and automotive, the most traditional and popular relay drivers are the ones formed discretely with a bipolar transistor, two bias resistors and a free-wheeling diode. In some cases, it is required to add extra components such as MOVs (metal oxide varistors) and extra diodes to ensure proper protection. Figure 1 shows a typical discrete relay driver with the extra protection devices. Diode D1 provides reverse supply protection and diode D2 provides a clamp function to suppress the voltage spike generated by the relay's coil during the turn-off interactions (V = Ldi/dt). A power MOV device is used to limit positive transients to within the bipolar transistor's breakdown voltage. The saturation voltage of the bipolar transistor (typically over 1.0 V) causes high power dissipation which in some cases eliminates the option to use inexpensive surface mount package devices such as SOT-23 or smaller, therefore the need for bigger packages such as TO220 is always present. The resulting discrete circuit is expensive because it takes several components and a big space in the PC board.
+12 V D1 Gate (1) RELAY ESD Zener 7V 300 k R1 LOGIC R2 Source (2) 0 Q1 VARISTOR ESD Zener 7V 1.0 k Clamp Zener 7 V or 14 V Clamp Zener 7 V or 14 V
ON Semiconductor's RELAY DRIVERS The ON Semiconductor's relay drivers portfolio is divided in two main categories: · Industrial version (devices NUD3105, NUD3112) · Automotive version (device NUD3124)
Industrial Version
Figure 2 describes the industrial relay driver version (devices NUD3105, NUD3112). This device integrates several discrete components in a single SOT-23 three leaded surface mount package to achieve a simpler and more efficient solution than the conventional discrete relay drivers. The characteristics of the integrated devices are listed below: · N-channel FET 40 V, 500 mA · ESD protection Zener diodes (7.0 V) · Bias resistors (1.0 K W in the gate and 300 K W between gate and source) · Clamping protection Zener diodes (7.0 V for 5.0 V relay's coils, and 14 V for 12 V coils)
Drain (3)
D2 +5 V/3.3 V
Figure 1. Typical Discrete Relay Driver
Figure 2. Industrial Relay Driver Description (NUD3105 and NUD3112 Devices)
http://onsemi.com
2
AND8116/D
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:
+12 V/5.0 V
RELAY NUD3105, NUD3112 +5 V/3.3 V 1.0 k LOGIC ESD Zener 14 V 300 k ESD Zener 14 V Clamp Zener 7 V or 14 V Clamp Zener 7 V or 14 V
0
Figure 3. Typical Connection Diagram (NUD3105 5.0 V Relay's Coils and NUD3112 for 12 V)
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 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.
VSUPPLY 10 V/div VGS 10 V/div
VDS 10 V/div
Inductor kick back
ID 50 mA/div
Figure 4. Traces Generated Across NUD3112 Device when Driving OMRON Relay G8TB-1A-64
http://onsemi.com
3
|
|
