AN3401 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 18
Technical content
Datasheet sections
- 1 Application overview
- 2 SPV100x functionalities
- 3 Operating modes: forwar d and reverse
- 4 Thermal runaway
- 5 Application information
- 6 SPV100x test description
- 6.1 Purpose
- 6.2 Instrumentation used
- 6.3 Procedure
- 7 Test results and device compar ison
- 7.1 Free devices at ambient temperature
- 7.2 Devices soldered on the PCB at ambient temperature
- 7.3 Devices soldered on the PCB at 85 °C chamber temperature
- 7.4 Devices soldered on the PCB at 105 °C chamber temperature (Junction
- 8 Conclusion
- 9 References
- 10 Revision history
December 2011 Doc ID 018842 Rev 1 1/18 AN3401 Application Note SPV1001/SPV1002 performance evaluation in a typical photovoltaic application Introduction The SPV1001 and SPV1002 are system-in-package solutions for photovoltaic applications, designed to increase system efficiency by implementing a bypass function through a power MOSFET transistor instead of a conventional Schottky diode. The SPV1002 differs from the SPV1001 in having a lower R DSon. This application note provides an evaluation of the performance comparison between the SPV100x and two standard Schottky diodes, in order to supply proper guidelines for the correct use of both devices.
1 Application overview
depend on the cell technology, cell size, and irradiation level. connecting in series a proper number of PV cells. same current, assuming negligible the spread among each PV cell. whole series operates at the lowest current level forced by the shaded PV cell. a bypass device is connected in parallel to each string, as shown in Figure 1. Figure 1. Bypass diodes internal connection
- To prevent the hot spot issue, bypass devices are connected in parallel to the cell string
- During normal operation (no shadows) the reverse leakage current must be very low
- When the cells are shaded the voltage drop must be very low. 393DQHO -XQFWLRQ ER[
2 SPV100x functionalities
Figure 4. SPV100x internal architecture
- To charge the integrated tank capacitor during the power MOSFET OFF time (Toff), boosting, with a charge pump, the voltage drop on the body diode of the power MOSFET itself.
- To drive the gate of the power MOSFET with the charge previously stored in the tank capacitor during the ON time (T on). So, the forward voltage drop between anode (source) and cathode (drain) terminals during the MOSFET switching, is shown in Figure 5 below:
Figure 5. SPV100x forward voltage drop
Operating modes: forward and reverse AN3401 6/18 Doc ID 018842 Rev 1
3 Operating modes: forward and reverse
In forward mode the average voltage drop between anode (source) and cathode (drain) (Vak) is: Equation 1 with T = Ton + Toff. During the ON time the voltage drop is: Equation 2 While in the OFF time the voltage drop is equal to the MOSFET body diode voltage drop. The average power is calculated using the relation: Equation 3 In reverse mode the leakage current results from the standard MOSFET value: Ir < 1 µA @ Tj = 25 °C Ir <10 µA @ Tj = 125 °C Vak Vakoff Toff⋅ Vakon + Ton⋅ Vakon RdsON Iak⋅= Pak Vak Iak⋅=
4 Thermal runaway
application comes also from a trade-off between forward voltage drop and leakage current. current due to the high temperature coming from the previous condition. mode, then the diode goes into thermal runaway until permanent damage occurs. Figure 6. Thermal runaway positive loop device, may be dangerous because of the risk of thermal runaway. where RthJA is the junction to ambient thermal resistance. the new junction temperature trend.
In Figure 7 the details for the temperature increase that destroys the device is shown. Figure 7. Thermal runaway detail
5 Application information
layers. Layer thickness is 35 µm. drop, in four different operative conditions.
- Device only, without any heat sinker @ oven temperature.
- Just one device soldered on the PCB @ ambient temperature.
- Three devices soldered on the PCB, at the temperature defined by IEC 61215
- The same as point 3 but at a different temperature (105 °C, to emulate the temperature
inside a junction box when ambient temperature is 85 °C). mentioned above. But note that the performances are strictly related to the PCB design. Figure 8. Typical junction box PCB to solder and connect the devices on PANEL
SPV100x test description AN3401 10/18 Doc ID 018842 Rev 1
6 SPV100x test description
6.1 Purpose
To assess the device thermal performance, checking the adequacy of the PCB thermal design and relative long-term reliability of the SPV100x diodes versus two standard Schottky diodes with comparable current capability (20 A and 30 A) and reverse voltage (40 V).
6.2 Instrumentation used
- Thermal chamber MAZZALI SYSTEM model TESYS 1200h.
- Data Logging PicoLog, high resolution until 1/100 °C
- Thermocouples interconnected with PicoLog.
- Power supply and current probe.
6.3 Procedure
Set up the environment in order to measure the following parameters:
- For free devices: The Tj (junction devices temperatures), and power in forward mode
- For the devices soldered in the PCB: The Tj and power in forward mode
- For the devices soldered in the PCB in the heat chamber @ 85 °C and @105 °C: The Tj and power in forward mode. All of the current values are checked in order to keep the SPV100x Tj temperature below its maximum operative value (150 °C).
7 Test results and device comparison
dissipation and junction temperature.
7.1 Free devices at ambient temperature
For the average power the values are calculated using Equation 2. Figure 9. Power vs. Iak Figure 10. Junction temp. vs. Iak
7.2 Devices soldered on the PCB at ambient temperature
Figure 11. Power dissipation vs. Iak Figure 12. Junction temp vs. Iak
7.3 Devices soldered on the P CB at 85 °C chamber temperature
Figure 13. Power dissipation @ 85 °C vs. Iak Figure 14. Junction temp @ 85 °C vs. Iak
7.4 Devices soldered on the PCB at 105 °C chamber temperature
Figure 15. Power dissipation @ 105 °C vs. Iak Figure 16. Junction temp. @ 105 °C vs. Iak
8 Conclusion
According to the results shown in the plots, the thermal and power performances of the SPV1001 and SPV1002 are better than the standard Shottky diodes. The above results can be improved by changing the PCB heat-sinking characteristics (increasing size, increasing thickness, increasing copper layers, changing number and size of thermal vias). Finally, from the application point of view it should be noted that the performance is strongly influenced by the specific junction box where the devices are placed. So, for every panel, device integration in the junction box, the material and the internal PCB design, is an important key to reaching the target current capability.
9 References
- CEI EN 61215-2006/08 2. SPV1001/SPV1002 datasheet 3. AN1542 application note 4. AN836 application note 5. AN869 application note
Table 1. Document revision history