AN3978 STMICROELECTRONICS | Alldatasheet
Document overview
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Technical content
Datasheet sections
- 1 Schematic design
- 1.1 Input interface
- 1.2 Diagnostic signal interface
- 1.3 Supply voltage line protection
- 1.4 Short-circuit current limit settings
- 1.5 ON-DELAY configuration
- 2 PCB layout
- 2.1 Supply voltage filter layout
- 2.2 Earth coupling
- 3 EMC requirements
- 3.1 Description of the procedure to evaluate the robustness
- 3.2 Burst tests (according to the IEC61000-4-4)
- 3.3 Surge test (according to the IEC61000-4-5)
- 4 EMC testing
- 5 Ordering information
- 6 Conclusion
December 2011 Doc ID 022179 Rev 1 1/19 AN3978 Application note Designing a digital output module with the L6370Q intelligent power switch STEVAL-IFP020V1 Introduction The L6370Q is a single channel high-side driver chip intended for driving resistive, inductive or capacitive loads in industrial environments. It provides an embedded fast demagnetization feature for inductive load switch-off. The chip evaluates load disconnection (in channel ON state), output short connection to V CC or GND, overtemperature, supply voltage undervoltage and provides feedback to a control unit. An integrated extensive set of electrical protections makes the application safe and reliable for use in harsh conditions. This application note documents an example of an application design with the L6370Q component. It guides the user on how to choose application external components, provides appropriate schematic diagrams and PCB design, and an overview of immunity test results. Application main features
- Galvanic isolated digital output module
- Single channel topology
- 2.5 A output current
- 100 mΩ output MOSFET RDSON
- 9.5 V to 35 V supply voltage range
- Output current limiting
- Thermal shutdown
- Open ground protection
- Internal negative voltage clamping to V S - 50 V for fast demagnetization
- Undervoltage lockout with hysteresis
- Open load detection
- Two diagnostic outputs
- Output status LED indication
- Non-dissipative short-circuit protection
- Protection against surge pulses (IEC61000-4-5)
- Immunity against burst transient (IEC61000-4-4)
- ESD protection (IEC61000-4-2)
- Compact design thanks to small component packages (L6370Q in QFN 7 x 7 mm)
1 Schematic design
A complete application schematic diagram is visible in Figure 1. Figure 1. Application schematic diagram
external components are used, and how they are dimensioned.
1.1 Input interface
effective, compact size optocouplers (TLP281) have been selected.
- Collector-emitter voltage higher than 80 V - which exceeds the L6370Q absolute maximum ratings and therefore doesn't limit supply voltage range
- Isolation voltage higher than 2500 Vrms - usually sufficient for this kind of application
- Current transfer ratio (depends on LED current) - LED and output phototransistor currents must be adjusted accordingly.
Figure 2. Input interface circuit approximately 2.4 mA, considering a 3.3 V signal level, and 4.3 mA for 5 V logic level. 18 kΩ). This means that CTR of the optocoupler must be at least ~5% (0.11 mA / 2.4 mA). This is in accordance with the TLP281 datasheet which shows a much higher CTR.
1.2 Diagnostic signal interface
appropriate part of the schematic diagram can be seen in Figure 3. Figure 3. Diagnostic signals circuit accordance with TLP281 characteristics.
1.3 Supply voltage line protection
disturbances with the external filter, as shown in Figure 4. Figure 4. Supply voltage protection filter
A Transil™ diode is used to clamp high energy surge pulses followed by a capacitive filter to suppress noise disturbance and limit application EMI. Capacitor C1 (100 μF) has a low ESR parameter in order to effectively suppress supply voltage fluctuations.
1.4 Short-circuit current limit settings
Configuration of the current limit is done by the external resistor connection between the RSC pin and GND. A 470 Ω resistor is used in the STEVAL-IFP020V1 application to adjust the maximum current limit, which is 3.2 A (typ.), due to the fact that 0 < RSC < 5 k Ω according to the L6370Q datasheet.
1.5 ON-DELAY configuration
ON-DELAY pin functionality is well described in the L6370Q datasheet. Basically, it is used to disable the power stage if an overcurrent condition lasts longer than the adjusted t ON. This feature also suppresses diagnostic activation in case of short-time overload or short- circuit. A capacitor value of 680 pF connected between the ON-DELAY and GND adjusts the ON- DELAY time to: t ON = 1.28 * CON = 1.28 μs/pF * 680 pF = 870.4 μs
2 PCB layout
avoiding signal loops and minimizing track length. Figure 5. Demonstration board PCB layout - top side Figure 6. Demonstration board PCB layout - bottom side
2.1 Supply voltage filter layout
routes accordingly. A correct reference is visible in Figure 7. Figure 7. Supply voltage filter PCB design distribution for the application.
2.2 Earth coupling
charge/discharge current intervention of application reference supply points (TP1, TP2). environment or during EMC tests.
3 EMC requirements
3.1 Description of the procedure to evaluate the robustness of
The reference to evaluate the robustness of the L6370Q product is the IEC61131-2 international standard. This international standard gives all the requirements and conditions of tests that must be performed on the programmable logic controllers (PLC) and their associated peripherals. The IEC61131-2 standard specifies the Electromagnetic Compatibility (EMC) requirements and the nature of the tests to perform in order to determine if the system meets these requirements (paragraph 7: “Electromagnetic Compatibility EMC Requirements” and paragraph 8: “Electromagnetic Compatibility (EMC) Type Tests and Verifications” of the Ed2 of the standard). The levels of each test depend on the zone where the system is installed. The most typical industrial environmental levels correspond to zone B: local power distribution zone and dedicated power distribution zone (see table 28: “EMC immunity zones” of the IEC61131-2-Ed2 standard). The following paragraphs recall the test levels for this zone.
3.2 Burst tests (according to the IEC61000-4-4)
The fast transient burst tests must be ap plied on all the input pins of the system. A capacitive clamp-coupling device (50-200 pF) must be used as described in the IEC61000-4-4 standard. The required burst voltage le vels are: analog or digital I/O: +/-1 kV, dc power line: +/-2 kV. The PLC system continues to operate as intended. Temporary degradation of the performance is acceptable during the test, but the system must recover by itself after the test (B criterion according to the IEC61131-2 standard).
3.3 Surge test (according to the IEC61000-4-5)
Since the voltage surge consists of a single but energetic pulse, the L6370Q device embeds the appropriate protections. Moreover, additional external protection (filter) is necessary, see Section 2.1 for an example. The absorbed energy complies at least with the requirements of the IEC61131-2 standard. The high energy surge test must be applied on all output / supply voltage terminals of the system. For all digital outputs and I/O power, the coupling method is a 42 Ω serial resistance and a 0.5 μF capacitor. The required voltage surge levels are 0.5 kV (line-to-line and line-to-earth coupling modes). The PLC system continues to operate as intended. Temporary degradation of the performance is acceptable during the test, but the system must recover by itself after the test (B criterion according to the IEC61131-2 standard).
4 EMC testing
burst amplitude, the system then behaves according to criteria B. performance criteria A is fulfilled also for higher burst amplitudes. Table 1. Application EFT (burst) robustness, applied to supply voltage lines Table 2. Application EFT (burst) robustness, applied to output lines Table 3. Application surge test results, surge applied to supply lines
that high energy surge pulses cause short-time power interruptions on the chip supply. Immunity of the output in differential mode depends on the supply voltage capacitive filter. Selection of the supply capacitor (C1) dramatically influences the achieved test result. Table 4. Application surge test results, surge applied to output lines
5 Ordering information
The application board is orderable in the same way as all STMicroelectronics products. The appropriate ordering code is STEVAL-IFP020V1. It contains the application board assembled according to the descriptions above, board documentation, PCB fabrication data such as Gerber files, assembly files (Pick and Place), and component documentation.
6 Conclusion
This application note may be used as a guide when designing the L6370Q application. The document shows that the L6370Q application works in harsh environments without any problems and that the industrial standard requirements are fulfilled. Moreover, the test levels are higher than requested for the majority of final products. The L6370Q application requires a minimum amount of external components, which has a positive influence on the application costs.
Application components are listed in T able 5. Table 5. Bill of material
3 TLP281 Optocoupler HPMF4 Any
- IEC61131-2: Programmable Controllers - Equipment Requirements and Tests
- IEC61000-4-4: Electrical fast transient/burst immunity test
- IEC61000-4-5: Surge immunity test.
6 T est point T est_Point_Small Any
Table 5. Bill of material (continued)
Revision history
Table 6. Document revision history 05-Dec-2011 1 Initial release.