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AN2208
APPLICATION NOTE
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ST AN2208 APPLICATION NOTE

AN2208
APPLICATION NOTE
Designing Industrial Applications with
VN808/VN340SP High-side Drivers
Introduction
VN808/VN340SP high-side drivers are teste d mounted on their respecti ve ref eren ce design board (RDB).
Note: Additional information concerning the L5970D DC/DC converter, based on BCD technology, is
included in Section Appendix C: L5970D DC/DC converter on page 46.

Figure 1. VN808 and VN340SP reference design boards

Rev. 1
September 2005 1/51
http:/www.st.com
1
AN2208
Contents
1 High-side driver description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 VN808 reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Surge suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Isolation recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Heatsink recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5 Schematic diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 VN340SP reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1 Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Schematic diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Load switching tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5 Thermal stress tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6 Electromagnetic compatibility (EMC) tests . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.2 List of EMC test equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.3 Requested test levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.3.1 IEC 61000-4-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.3.2 IEC 61000-4-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.3.3 IEC 61000-4-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.4 IEC 61000-4-4 EFT test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.4.1 Power supply tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.4.2 Input port tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.4.3 Output port tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.5 IEC 61000-4-5 surge test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5.1 Power supply tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5.2 Output port tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.6 IEC 61000-4-6 conducted immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.6.1 Power supply tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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6.6.2 Input port tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.6.3 Output port tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7 Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1 VN808 HSD test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1.1 Load switching test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1.2 Thermal stress test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.1.3 EMC test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.2 VN340SP HSD test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.2.1 Load switching test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.2.2 Thermal stress test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.2.3 EMC test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Appendix A VN808 reference design board (RDB) . . . . . . . . . . . . . . . . . . . . . . . 42
A.1 VN808 RDB bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
A.2 Recommended VN808 PCB Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Appendix B VN340SP reference design board (RDB). . . . . . . . . . . . . . . . . . . . . 44
B.1 VN340SP RDB bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
B.2 Recommended VN340SP RDB PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . 45
Appendix C L5970D DC/DC converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
C.1 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
C.2 L5970D layout recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
C.3 L5970D DC/DC converter load test results . . . . . . . . . . . . . . . . . . . . . . . . . . 48
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
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List of figures
Figure 1. VN808 and VN340SP reference design boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. VN808 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 3. VN340SP block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 4. VN808 reference design board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 5. Surge Suppression Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 6. Typical input/status isolation by optocouplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 7. Burst pulse affecting one input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 8. Recommended layout for High Power Dissipation capability . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 9. DC/DC part of the application circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 10. Current and voltage conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 11. Complete application circuit with VN808 and L5970D devices. . . . . . . . . . . . . . . . . . . . . . 13
Figure 12. Switching part of the application circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 13. VN340SP reference design board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 14. Switching part of the application circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 15. Complete application circuit with VN340SP and L5970D devices . . . . . . . . . . . . . . . . . . . 17
Figure 16. Description of the switching inductor loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 17. IPS simplified structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 18. Simplified thermal models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 19. Power supply tests (IEC 61000-4-4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 20. Switch diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 21. Test on input ports (IEC 61000-4-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 22. Output port tests (IEC 61000-4-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 23. Power supply tests (IEC 61000-4-5). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 24. Test on Output Ports (IEC 61000-4-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 25. Power supply tests (IEC 61000-4-6). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 26. Input port tests (IEC 61000-4-6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 27. Output port tests (IEC 61000-4-6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 28. VN808 Waveforms (Part 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Figure 29. VN808 Waveforms (Part 2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 30. GND_Power disconnection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 31. Switching lamps: VCC = 24V, f = 0.5 Hz, Wave1 = VINOPT,
Wave2 = VOUT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 32. Waveform tOFF inductor load: VCC = 24V, L = 130mH, RLOAD = 63W,
tOFF = 1.2101 ms, Wave2 = VOUT, Wave1 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . 32
Figure 33. Waveform switching inductive load: VCC = 24V, L = 130mH, RLOAD = 48W,
f = 0.5Hz, Wave2 = VOUT, Wave1 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . 33
Figure 34. Switching with short circuit: VCC = 24V, f = 0.5Hz, Wave2 = VSTATUSOPT,
Wave1 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 35. Time delay between VINOPT and VOUT: VCC = 24V, Load = Lamp,
Wave2 = VOUT, Wave3 = VINOPT, Dt = 58.462 µs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 36. GND_Power disconnection for VN808: VCC = 25V, Load = Lamp,
Wave1 = VCC, Wave2 = VOUT, Wave3 = GND of power supply . . . . . . . . . . . . . . . . . . . 33
Figure 37. Waveform ITOT and VINOPT during the test with short circuit VCC = 28V,
TA = 85°C, Wave4 = ITOT, Wave1 = VINOPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 38. Waveform on ITOT and VINOPT during the test with short circuit VCC = 28V,
TA = –25°C, Wave4 = ITOT, Wave1 = VINOPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 39. Case temperature dependency vs. current ITOT (TA = 25°C and VCC = 24 V) . . . . . . . . 34
Figure 40. Burst applied on the power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
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Figure 41. Burst applied on the output channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 42. Positive surge applied on power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 43. Negative surge applied on power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 44. Switching lamps: Vcc = 24V, f = 0.5Hz, Wave3 = VINOPT,
Wave2 = VOUT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 45. Waveform tOFF inductor load: Vcc = 24V, L = 130mH, RLOAD = 60W,
tOFF = 1.2276ms, Wave2 = VOUT, Wave3 = VINOPT, Wave4 = ICH1OUT. . . . . . . . . . . 38
Figure 46. Time delay between VINOPT and VOUT: Vcc = 24V, Load = Lamp,
Wave2 = VOUT, Wave3 = VINOPT, Dt = 139µs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 47. Switching with short circuit: Vcc = 24V, f = 0.5Hz, Wave2 = VSTATUSOPT,
Wave3 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 48. Waveform switching inductive load: Vcc = 24V, L = 130mH, RLOAD = 48W,
f = 0.5Hz, Wave2 = VOUT, Wave3 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . 39
Figure 49. Switching with short circuit: Vcc = 24V, f = 0.5Hz, Wave2 = VSTATUSOPT,
Wave3 = VINOPT, Wave4 = ICH1OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 50. Waveform ITOT and VSTATUSOPT during the test with short circuit:
Vcc = 28V, TA = 85°C, Wave4 = ITOT, Wave1 = VSTATUSOPT . . . . . . . . . . . . . . . . . . . 39
Figure 51. Waveform on ITOT and VSTATUSOPT during the test with short circuit:
Vcc = 28V, TA = –25°C, Wave4 = ITOT, Wave1 = VSTATUSOPT . . . . . . . . . . . . . . . . . . 39
Figure 52. VN808 RDB PCB layout (top and bottom) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 53. VN808 RDB PCB layout (component side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 54. VN340SP RDB PCB layout (Top side) and (Bottom side) . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 55. VN340SP RDB PCB layout (component side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 56. L5970D block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 57. L5970 DC/DC converter layout example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Figure 58. Efficiency vs. output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Figure 59. Output voltage stability of L5970D, Vss = 24 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Figure 60. Voltage ripple on capacitor C30, IOUTDC = 0.4A, Vss = 24V . . . . . . . . . . . . . . . . . . . . . . 49
Figure 61. Waveform on coil L1, IOUTDC = 0.4A, Vss = 24V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Figure 62. Voltage ripple on capacitor C33, Vss = 24V, IOUTDC = 0.4 A. . . . . . . . . . . . . . . . . . . . . . 49
Figure 63. Waveform on coil L1, without load, Vss = 24V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
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List of tables
Table 1. VN808 and VN340SP main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. EMC industrial compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 4. Equipment list for EMC tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 5. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 6. EMC test IEC 61000-4-4 EFT test results (VN808 RDB) . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 7. EMC test IEC61000-4-5 surge test results (VN808 RDB) . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 8. EMC test IEC 61000-4-6 conducted immunity test results (VN808 RDB) . . . . . . . . . . . . . 37
Table 9. EMC test IEC 61000-4-4 EFT test results (VN340SP RDB). . . . . . . . . . . . . . . . . . . . . . . . 40
Table 10. EMC test IEC61000-4-5 surge test results (VN340SP RDB) . . . . . . . . . . . . . . . . . . . . . . . 40
Table 11. EMC test IEC 61000-4-6 conducted immunity test results (VN340SP RDB) . . . . . . . . . . . 41
Table 12. VN808 RDB bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Table 13. VN340SP RDB bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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AN2208 1 High-side driver description

1 High-side driver description
The VN808 (Figure 2) is a high-side driver (HSD) us ed to driv e eight ind epend ent l oads . Act ive current limitation combined with thermal shutdown and automatic restart functions protect the device against ov erload. A thermal case substrat e protection is implemented to prot ect the FRx substrate under short circuit and worst case ambient conditions in terms of reliability. The device automatically turns off when the ground pin is disconnected. The VN340SP and VN808 are especially suitable for use with programmable logic controllers (PLC) in industrial applications.
The VN340SP (Figure 3) is used to drive four independent resistive, capacitive and inductive loads in high-side configurations. Active current limitation prevents the system power supply from dropping in the event of a short load. A built-in thermal shutdown circuit protects the chip from high temperatures and short circuits. Each I/O is pulled down when an over-temperature condition of the relative channel is detected and restarts after reaching the lower thermal threshold. The system oscillates depending on the thermal impedance of the application.

Table 1. VN808 and VN340SP main characteristics

VN340SP HSD VN808 HSD
Output current per channel 0.5A at 24V
Built-in current limiter
Short-load and overtemperature (Junction) protection
Under-voltage shutdown Open-drain diagnostic output Status output current 2 to 4 mA DC supply voltage 36V DC supply voltage 45V
V e ry low stand-by current
Short-load and overtemperature (Junction and Case) protection
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1 High-side driver description AN2208

Figure 2. VN808 block diagram

INPUT 1 INPUT 2 INPUT 3 INPUT 4 INPUT 5 INPUT 6
INPUT 7
LOGIC CONTROL
INPUT 8
STATUS

Figure 3. VN340SP block diagram

I/O1
I/O2
I/O3
I/O4
DIAG
GROUND
Overtemp 1
Overtemp 2
Overtemp 3
Overtemp 4
UNDERVOLTAGE DETECTION
CLAMP POWER
CURRENT LIMITER
JUNCTION TEMP. DETECTION
Same struct ure f or al l channels
CASE TEMP. DETECTION
V
CC
Undervoltage
Control
Logic
Driver 1
I Limit 1
Driver 2
I Limit 2
Driver 3
I Limit 3
Driver 4
I Limit 4
V
CC
CLAMP
VCC
GND
OUTPUT 1 OUTPUT 2 OUTPUT 3 OUTPUT 4 OUTPUT 5 OUTPUT 6 OUTPUT 7 OUTPUT 8
Ai11606
OUTPUT 1
OUTPUT 2
OUTPUT 3
OUTPUT 4
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AN2208 2 VN808 reference design board

2 VN808 reference design board
This is a practical example how the VN808 high-side driver (HSD) can be used in applications for an industrial environment.

Figure 4. VN808 reference design board

2.1 Circuit description

In order to protect the high-side driver (HSD) from the harsh industrial conditions of power supply lines, usually optocouplers and Transil diodes are used to separate the ap plic at ion control circuits from the power supply. Figure 11 shows a complete schematic diagram of the VN808 reference design board.
The VN808 reference design board uses multi-channel TLP281-4 and TLP181 optocouplers. The TLP281-4 and TLP181 are small and thin couplers, suitable for surfa ce-mounted assemblies that consist of a photo transistor optically coupled to a gallium-arsenide infrared emitting diode. The isolation voltage for this type of optocoupler is 2500 V
The clamping function of Transil diodes protect the HSD against transient overvoltages. The reference design board is assembled with uni-directional SM15TXXA Transil diodes because they protect the HSD against both positi ve and negative surge pulses. For more information about SM15TXXA Transil diodes from STMicroelectronics, please refer to the SM15T36A Datasheet av ailable at www.st.com.
Refer to Section A.2: Recommended VN808 PCB Layout on page 43 for more information about designing boards to improve EMC immunity and performance in industrial environments.

2.2 Surge suppression

When designing your application, VCC and ground lines should lay on top of ea ch other, minimizing the closed loop area and increasing the ability of the application to reject
RMS
.
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2 VN808 reference design board AN2208
environmental noise. Figure 5 shows a surge suppression block using a un i-directional SM15T36A Transil diode.
The Transil diode provides overvoltage protection for the HSD. The SM15T36A has a peak pulse power dissipation of 1500 W, stand-off voltage of 36 V and breakdown voltage of 37.8 V. Depending on the application, a Transil diode with a different v a lue (for example, betw een 2 8 V and 40 V) may be used.
An electrolytic capacitor (C1) must be placed immedi a tely afte r th e sur g e sup p re ssio n block. The size of the electrolytic capacitor is selected based on the slope of the output current, the impedance of the complex power supply cables, as well as the maximum allowed voltage drop across the device . The C1 v a lue is ge ner ally 25 µF per chip. For more inf ormation about th e C1 value, please refer to Application Note AN1351: VIPower and BCDMultipower: Making life easier with ST's high-side drivers.
A low ESR SMD capacitor (C2) must be placed as close as possib le to the HSD in order to f ilter the power supply line for electromagnetic compatibility concerns. The suggested C2 value is 100 nF.

Figure 5. Surge Suppression Block

24V DC Input
C14
4.7 nF
GND_EARTH GND_POWER
C13
4.7 nF

2.3 Isolation recommendations

Industrial environments require good isolation between digital and power supply parts. Optocouplers are widely used and multi-channel optocouplers represent a very attractive solution. Figure 6 shows a schematic diagram with optocouplers connected to ground.
Although optocouplers are good isolators, they may lower the category of the Electrical Fast Transients (EFT) immunity tests as the primary and secondary sides of the optocouplers may still have parasitic capacitance “bonding” to each other, even though they are isolated. This parasitic capacitance may inject a current through the base emitter junction of the phototransistor when one half of the optocoupler is “tight” due to fast voltage transients with respect to the other side as shown in Figure 7.
C1
22 µF
50V
VCC 24V
+
C2
100 nF
GND_POWER
D1
SM15T36A
Ai11615
If an optocoupler is used in an emitter-follower configuration, as in most industrial applications, a high emitter voltage sig nal ma y b e induced b y applying EFTs e ven after opening the collector termination. An efficient way to prevent this high emitter voltage signal is to provide a conducting plane connected to gro und on both the top and bo ttom la y ers of th e PCB (under the optocouplers) as shown in Figure 52: VN808 RDB PCB layout (top and bottom).
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AN2208 2 VN808 reference design board

Figure 6. Typical input/status isolation by optocouplers

Figure 7. Burst pulse affecting one input

2.4 Heatsink recommendations

Depending on ambient thermal conditions, HSD’s with a PowerSO10/SO36 package require external cooling as the copper bott om p lat e of t he PSO-Package, u sed to maint ain t he ju nctio n temperature during inductive switching, acts as a thermal capacitor.
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2 VN808 reference design board AN2208
The VN808 reference board is designed with an onboard heatsink capability (minimum heat sink area is 6 cm²). The recommended layout for Power SO packages is shown in Fig ure 8.

Figure 8. Recommended layout for High Power Dissipation capability

2.5 Schematic diagrams

Figure 9. DC/DC part of the application circuit

Figure 10. Current and voltage conventions

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AN2208 2 VN808 reference design board

Figure 11. Complete application circuit with VN808 and L5970D devices

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2 VN808 reference design board AN2208

Figure 12. Switching part of the application circuit

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AN2208 3 VN340SP reference design board

3 VN340SP reference design board
This is a practical example how the VN340SP high-side driver (HSD) can be used in applications for an industrial environment.

Figure 13. VN340SP reference design board

3.1 Circuit description

The application described below is very similar to that of the VN808 reference design board; only the type of HSD and the optocoupler inter-co nn e ctio n is different. Figure 15 shows a complete schematic diagram of the VN340SP reference design board. The optocouplers and Transil diodes are the same as those used in the VN808 reference design board.
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3 VN340SP reference design board AN2208

3.2 Schematic diagrams

Figure 14. Switching part of the application circuit

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