This article explores the connection of the gate driver with the controller and IGBT modules. This information should support in minimizing malfunctions of gate driver and IGBT modules due to electromagnetic interference, signal oscillation, or induced noise. The information given in this application note is not exhaustive.
Connection between gate driver and controller
Control signals for the gate driver should not be interfered by disturbances. Electrical disturbances arise because of many reasons. One of them is the switching of IGBTs resulting in high di/dt and dv/dt. Theoretically, there should not be any induction of other signals into the control signals, which may cause malfunction. But practically, this is not possible. Proper routing of cables should be done for minimising such effects. Following are some hints to design the connection between gate driver and controller.
Tracks on the printed circuit board should be kept as short as possible. Loops should be avoided.
- Length of cable should be as short as possible and should not exceed three meters. The cable should be twisted pair.
- Do not group control signals (low power signal) with high power signal (power supply). Use signal ground and power supply ground separately. Both should be tied only at one point (mostly at driver) to avoid looping.
- Signal cable should be placed as far as possible away from power terminals, power cables, ground cables, DC-link capacitors and all other noise sources.
- Control signal cable should not run parallel with power cable. Minimum distance between control signal cable and power cable should be 30cm and the cables should cross vertical only.
- It is recommended to keep all cables close to ground (e.g. heat sink or the like).
- In noise intensive applications, it is recommended to improve the noise immunity with shielded cable or the usage of fibre optic interfaces.
- For differential mode noise suppression uses a low value capacitor (1nF) between signal and power supply ground of the gate driver.
- Use of open collector
Use of Filter Capacitors
A capacitor is connected tothe input of the gate driver to obtain high noise immunity. This capacitor can cause for current limited line drivers a small delay of few ns, which can be neglected besides paralleling of control signals. The capacitors have to be placed as close as possible to the gate driver interface.
Connection between gate driver and IGBT module
The gate driver must be located very close to the IGBT module to minimize stray inductance between gate driver and IGBT module. An advantageous solution, even for high power IGBT modules, is directly mounting of the gate driver onto the IGBT module.
Besides reliable electric circuits for driver and monitoring functions, another key requirement for power electronic systems is to provide an optimum connection between gate driver and power module. In conventional solutions, drivers and power modules are connected by wires that are as short and as low-inductive as possible and twisted pair. Due to design restrictions, however, an optimum connection is not always possible. Complex wiring and solder and plug-in connections are the result.
A connection that does not require soldering and complex wiring would enable to develop and to produce solutions in which the gate driver can be reliably connected to the power semiconductors and the gate driver can be connected at any stage of the manufacturing process. There is a fast and easy way to achieve this. Using the standard gate driver SKYPER, an application specific adapter board and the IGBT module SEMiX. Unlike integrated systems (IPM), this solution offers electrical design flexibility.
With the SEMiX IGBT module, the adapter board and gate driver are mounted directly on top of the power module, in doing so keeping the connection paths as short and reliable as possible. This type of connection requires no soldering due to spring-based connecting technology. The adapter board, which is adapted to meet the requirements of the individual application and the used IGBT module, is screwed onto the SEMiX module. The springs, integrated in the module, provide the connection through solder pads on the bottom side of the adapter board. The driver is then simply snapped on to the adapter board from above. This is possible due to the robust standard interface in SKYPER modules which is suitable for use with plug-in connectors.
The following are some hints to design the connection between gate driver and IGBT, if wire connections are used.
- Any parasitic inductances within the DC-link have to be minimized. Over voltages may be absorbed by C- or RCD snubbers between main terminals for plus and minus of the power module.
- Make power patterns short and thick to reduce stray inductance and stray resistance.
- The connecting leads between gate driver and IGBT module must be kept as short as possible. Gate and emitter wiring must be twisted pair to minimize mutual induction, because magnetic field will be compensated by equal current flow in opposite directions.
- The VCE-monitoring wiring must not be bundled together with the gate and emitter wiring.
- Gate wiring for top and bottom IGBT or other phases must not bundle together.
- It is recommended to place a 10kΩ resistance (RGE) between the gate and emitter. If wire connection is used, do not place the RGE between printed circuit board and IGBT module. RGE has to be placed very close to the IGBT module.
- Use auxiliary emitter contacts to minimize negative feedback effect on gate-emitter voltage.
- Use suppressor diode (back-to-back Zener diode) between gate and emitter. The diode has to be placed very close to the IGBT module.
- Use of a capacitor (CGE) between gate and emitter can be advantageous, even for high power IGBT modules and parallel operation. C GE should be approximately 10% of CGE of the used IGBT. CGE has to be placed very close to the IGBT module.
- Any current loops must be avoided.
- Place the gate resistances for turn-on and turn-off close together.
- Use an auxiliary printed circuit board with all components and solder to gate / emitter of the IGBT module, if the power is getting higher.
- If external boost capacitors are used, the capacitors must be placed as close as possible to the gate driver in order to minimize parasitic inductance.
- If the ground of the driver is connected to the power emitter terminal, voltage is induced across LES due to high di/dt of load current. This voltage decreases the gate turn-on voltage and voltage is added to the gate turn-off voltage to slow the turn-on / turn-off. Therefore, stray inductances between auxiliary emitter and power emitter should not be shared.
- In order to ensure locking of the IGBT even when the driver supply voltage is turned off and voltage is applied to the power circuit, a resistance (RGE) has to be integrated.
- The suppressor diode must be placed very close to the IGBT module. It can protect the gate of IGBT on over voltage as well as limit the short circuit current in short circuit event. During short circuit, there is a possibility of rise in gate emitter voltage due to miller capacitor between collector and gate. High dv/dt during short circuit causes a current to flow through the miller capacitor, which increase the gate emitter voltage. The suppressor diode will clamp that voltage. Furthermore, the suppressor diode can prevent the gate driver on consequential damage, if the IGBT module is failed.
- The gate emitter capacitor CGE is used as a smoothing capacitor, especially in a short circuit event, in order to reduce oscillation at the gate of the IGBT.
Please Note: it is recommended that user's technical experts perform tests to ensure that no oscillations occur in the IGBT control paths.
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