Preview:
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The Toshiba TPD2015FN features an advanced 8-pin high-side MOSFET driver designed for PLC application to power 24 VDC industrial loads including relays, solenoids, lamps, and small motors.
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The latest MIKROE CLICK TPD2015 provides a low-cost breakout board for the Toshiba TPD2015FN.
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The Toshiba TPD2015FN features advanced protection circuitry to mitigate overtemperature, overcurrent, and short circuit. External diodes are required for protection against inductive kick.
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The Toshiba solution encapsulates supporting circuitry such as voltage regulators and charge pumps for low MOSFET on-resistance. This can simplify the design of your industrial automation and control circuitry.
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Designing a robust 24 VDC PLC output driver is not a trivial circuit application. Considerable attention is required to produce a reliable circuit that will operate in extreme industrial environments subject to overloads, short circuits, and ESD.
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The Toshiba TPD2015FN is a sourcing (high-side) driver. The Toshiba TPD2017FN provides an alternative sinking (low-side) driver.
Introduction
This engineering brief introduces Programmable Logic Controller (PLC) digital output drivers by exploring the Toshiba TPD2015FN as installed on the MIKROE TPD2015. The CLICK provides a convenient breakout board and development platform facilitating an exploration of the Toshiba driver attributes.
This article is educational in nature, exploring applications of the MIKROE board along with code examples. It also provides a technical description of the IC as hosted on the CLICK board. This information is useful for a first experience with the MIKROE product and for designers reverse engineering the MIKROE CLICK design for future integration into their own industrial control or building automation projects. We recognize that this article may not present the most straightforward implementation of the MIKROE products. Please refer to mikroe.com for the latest libraries and time saving OS. Once again, our purpose is education with an emphasis on understanding the inner working of the IC featured on the MIKROE break out board.
Figure 1: Image of the MIKROE TPD2015 featuring the Toshiba TPD2015FN driver integrated circuit.
Tech Tip: The Toshiba TPD2015FN is classified as a sourcing (high-side) driver. A closely related product is the TPD2017FN,L1F sinking (low-side) driver. Recall that most PLCs feature modular construction allowing the user to select either sinking or sourcing semiconductor drivers to meet their needs. Note that the pinout between the 2015 and the 2017 is nearly identical, requiring minimal PCB modification to swap between devices. In fact, close inspection of the TPD2015 reveals jumper for the ’15 and the ’17 suggesting that the same board is used for the TPD2017.
What is a high side driver?
Industrial controls and automation systems often work within a 24 VDC ecosystem which includes sensors, actuators, control relays, indicator lamps, and small DC motors. As we focus on the smart relays and PLC, we encounter two unique configurations to control the field devices including the sinking and sourcing configurations.
Figure 2 (left) shows the sourcing (high-side) configuration. Observe that the load resistor is placed in the source leg of the MOSFET. The load is activated when the MOSFET gate is pulled to approximately 36 VDC relative to ground. This accounts for the 12 V_{GS} drive voltage stacked on top of a 24 VDC supply to ensure a low MOSFET on-resistance. This is reflected in Figure 3 from the Toshiba TPD2015FN datasheet. The load is connected to the source of the N-channel output MOSFET. An internal charge pump is used to develop the gate drive for the high-side MOSFET. While the voltage is not specified, we can expect the charge pump to deliver approximately 12 VDC over and above the VDD input voltage. Please refer to this article for a DIY charge pump circuit.
Figure 2 (right) shows a sinking (low-side) driver where the load resistor is connected to the drain of the MOSFET. As a general statement, the low-side driver is easier to construct as the controller and MOSFET share a common ground. Instead of using a charge pump or bootstrap circuit, the low-side driver requires a low impedance driver and a 12 VDC earth referenced power supply.
Tech Tip: The terms “sourcing driver” and “MOSFET source” describe two different things. To clarify the terms, let’s replace the MOSFET with a BJT. We now have a BJT sourcing current to the load via its emitter leg. When we switch back to the MOSFET, it sources current via its source leg.
Tech Tip: Up this point, we have carefully used the terms “sourcing” and “high-side” to refer to the circuitry of the TPD2015. This is necessary as the product serves two different communities each with their own terminology. The circuit designer will use the term “high-side” when referring to the circuitry. For example, they may purchase a high-side driver IC. The industrial control engineers and technicians will typically use the term “sourcing.” such as when they describe the circuit or purchase a PLC module. It’s important to keep these distinctions especially as you bridge communities.
Figure 2: Image showing the sinking and sourcing configuration for a MOSFET driver and load resistor.
Figure 3: Block diagram of the Toshiba TPD2015FN showing the location of the output MOSFET and critical circuitry such as the charge pump.
Control side connections for the TPD2015
The MIKROE TPD2015 is built to the MikroBUS socket standard. Recall that this bus features a pair of 8 pin headers with heavy focus on communication protocols such as SPI and I2C.
When compared to other CLICK boards, the TPD2015 is a minimalist design. Instead of including serial communication via an interposing microcontroller (serial to parallel converter), the MIKROE engineers allow direct connection to all eight of the TPD2015FN command pins:
- control for outputs 1 to 4 are available via the mikroBUS.
- control for outputs 5 to 8 are available on the 5-pin header (4 signal plus ground) as shown in Figure 1.
A minimalist implementation is used for our featured design. The CLICK - TPD2015 is placed into mikroBUS socket #2 of the MIKROE-5739 Arduino UNO shield. The control connections are very simple, as outlined in the code listing described later in this article. This implementation does not use outputs 4 to 8 or the plug and play ClickID authentication chip DS28E36BQ.
Tech Tip: The Arduino UNO R4 Minima was used in place of the classic Arduino UNO R3. This new Arduino board features a 32-bit Arm Cortex M4 processor. The R4 and R3 have nearly identical I/O specification. Also, the new R4 has a lower DigiKey cost.
Output side connections for the TPD2015
The TPD2015 was installed on a Phase Dock trainer as shown in Figure 4 with the associated wire diagram shown in Figure 5. The circuit demonstrates compatibility with representative industrial components including two control relays and a bicolor red-green lamp. A 24 VDC fan is driven by CR2 as demonstrated in Video 1. This ladder logic diagram has the same look and feel as a PLC wiring diagram and will be familiar to industrial engineers and technicians.
Figure 4: Image of the MIKROE TPD2015 installed on a Phase Dock industrial trainer.
Figure 5: Wire diagram for the MIKROE TPD2015 for the system shown in Figure 4.
Arduino UNO Code for the TPD2015
The minimalist code is shown below. Recall that Toshiba TPD2015FN control inputs 1 to 4 are directly accessible on the mikroBus. The remaining (not used in this demonstration) are available in an independent header.
// Use mikroBUS socket #2 of the Arduino UNO CLICK shield (MIKROE-5739)
#define PL_GREEN 15 // TPD2015FN in 1
#define PL_RED 3
#define CR1 9
#define CR2 16 // TPD2015FN in 4
#define OFF LOW
#define ON HIGH
void setup() {
pinMode(PL_GREEN, OUTPUT);
pinMode(PL_RED, OUTPUT);
pinMode(CR1, OUTPUT);
pinMode(CR2, OUTPUT);
}
void loop() {
digitalWrite(PL_GREEN, ON);
delay(1000);
digitalWrite(CR1, ON);
delay(2000);
digitalWrite(CR2, ON);
digitalWrite(PL_GREEN, OFF);
digitalWrite(PL_RED, ON);
delay(2000);
digitalWrite(CR1, OFF);
digitalWrite(CR2, OFF);
digitalWrite(PL_RED, OFF);
delay(2000);
}
Video 1: Demonstration of the MIKROE TPD2015 in the Phase Dock trainer.
Limitations of the Toshiba TPD2015FN
The Toshiba TPD2015FN is designed to provide a fully integrated driver for 24 VDC industrial and building automation control systems. The result is a compact solution with eight independent drivers to save PCB space. The external circuit requirements are limited to supply decoupling capacitors. External diodes are required to protect against the flyback voltages associated with inductive loads.
Driving inductive loads
Freewheeling diodes, also known as flyback, inductive kickback, and EMFprotection, are an essential component required to protect a semiconductor switch against the high voltage spike associated with turning off an inductive load. Many, but not all industrial inductive loads such as relays include an integral freewheeling diode or an optional module featuring the protective diode. The Phoenix Contact 2903334 relays shown in Figure 4 include a 2900939 module to protect again the inductive kick when the relay deenergized.
Close inspection of the TPD2015FN datasheet shows that these essential diodes are not built-in. They are also absent from the MIKROE TPD2015. For maximum protection be sure to install Toshiba Schottky CRS20I40A(TE85L,QM diodes). Failure to include flyback protection while driving inductive loads will lead to the destruction of the TPD2015FN.
Look for a future article describing how to install the protection diodes on the MIKROE TPD2015 and TPD2017.
Overcurrent / Overload
The TPD2015FN is classified as a 0.5 A driver. It may also be operated with channels in parallel to drive 1 A loads. The device features internal protection to protect against short circuits. While the IC is designed to protect itself, it’s a good idea to include an appropriately sized fuse or circuit breaker.
Overtemperature
The MOSFET has a worst-case on-resistance of 0.55 Ω. With a typical overcurrent activation at 1.8 A, we can expect a single overloaded channel to exceed the absolute maximum power dissipating level of the IC. To prevent device damage the TPD2015FN will shut down when the die temperature (typical) exceeds 175 °C. We can then expect thermal cycling as the channel alternatively heats and cools below the typical 20 °C hysteresis.
Next steps
This article serves as a general introduction to the 24 VDC output drivers commonly featured in smart relays, PLC, and building automation equipment. To increase your knowledge:
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Be content knowing that engineers incorporate advanced protection features into PLC. Busy yourself with the wide and complex world of PLC applications.
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Reverse engineer PLC output stages with a focus on optical isolation to protect the sensitive logic.
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Explore application of ESD in industrial environments and techniques to improve the reliability of industrial I/O. Refer to the IEC 61131-2 and 61000- 4-X standards.
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Explore the impact of driving capacitive loads, such as long cables.
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Explore PWM techniques for reduced contactor holding current.
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Explore motor drives featuring a step plus direction interface with attention to the driver’s turn on and turn off times.
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Construct your own PCB featuring the Toshiba TPD2015 or TPD2017.
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Explore contactor turn off speed using TVS diodes and interposing relays
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Explore the active clamp techniques for elimination of the flyback diode, using advanced driver such as the Analog Devices MAX14912AKN+.
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Optimize the design to balance cost, performance, longevity.
Parting thoughts
The MIKROE TPD2015/17 provide an excellent launchpad to study the characteristics of 24 VDC PLC driver. The breakout board is very easy to use within the mikroBUS ecosystem from both the physical as well as a programming perspective.
Stay tuned as we will explore the MIKROE-6072 24 VDC digital input module. When combined with the TPD2015 we have the foundation for a DIY PLC featuring 8 digital inputs and 8 digital outputs. Add a MIKROE-5540 4-20 mA module for even more fun!
Don’t forget to protect against inductive kick.
Best wishes,
APDahlen
Related Information
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About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.