Application note 1903 JULY 2006 Advanced IGBT Driver APPLICATION MANUAL Alain Calmels Product Engineer (Power Modules) Microsemi® Power Module Products 33700 Merignac, France Introduction -Optimize turn-on and turn-off operation for switching losses reduction by selecting the appropriate gate resistances (RG(on) , RG(off)). -Prevent cross conduction by the input signal dead time calculation. -Eliminate gate rigging in case of paralleled IGBT modules operation. -Understand the short circuit protection operation including fault output and reset in case of short circuit detection. -Explain mounting procedure. To simplify the design of high power, high performance applications, MICROSEMI introduced a new advanced Dual IGBT Driver. Dedicated to drive high Power IGBT modules (up to 300A, 1200V, 50 kHz) in phase leg operation (as shown on Fig. 1), this circuit provides multiple functions to optimize IGBT performance. This application note describes some techniques to: -Verify the driver capacity by the total gate charge calculation. DUAL DRIVER CIRCUIT +5VDigital +VBUS VC1 V1 IN1 SHORTCIRCUIT 1nF 1K BUFFER FAULT PROTECT VCEsat Memorisation IN2 GND P WM G ENERAT O R TOP HIGH POW ER IGBT 0V1 1nF LOGIC And INTERLOCK DRIVE 1R 10W SOFT TURN OFF And UVLO -V1 VC2 OUT V2 2.7K FAULT Memorisation FAULT OUT 1nF BUFFER GND +15V + SHORTCIRCUIT PROTECT VCEsat 0V2 2R 5W Goff2 GND +5V BOTTOM 0V2 DRIVER 0V2 0.5R 5W HIGH POW ER IGBT 1R 10W + 47MF Gon2 1nF 1K GND 15V AUX. S UPPLY (1A) 0VBUS 0.5R 5W 0V1 CIRCUIT GND RESET +5VDigital 2R 5W DRIVER 1K 2.7K BUFFER Gon1 Goff1 +5V BUFFER 0V1 ISOLATED DC/DC CONVERTERS SOFT TURN OFF And UVLO 0/15V -V2 0VBUS GND Figure 1 Typical Phase Leg Operation Description: Among other functions, this high speed circuit integrates galvanic isolation of logic level inputs signals, positive and negative isolated auxiliary power supplies and short circuit protection by VCE(sat) monitoring. Due to the compact design, this circuit is easy to mount on a PC board close to the power module in order to minimize parasitic elements. Isolated screw-on spacers guarantee good vibration withstand capability. www.advancedpower.com www.microsemi.com 1/12 Application note 1903 JULY 2006 Pin Description Sym bol Function +15V Supply V oltage 0/15V Power G round H1 Channel 1 Input H2 Channel 2 Input Reset Fault Reset Input FAU LT OU T Fault O utput GND Input Signal Ground V C1 Collector D esat Channel 1 G on1 T urn-on G ate O utput 1 G off1 T urn-off G ate O utput 1 0V 1 G off2 Common O utput Supply V oltage Common O utput Supply V oltage T urn-off G ate O utput 2 G on2 T urn-on G ate O utput 2 V C2 Collector D esat Channel 2 0V 2 D escription Positive power-supply voltage Input. All internal Aux. Power supplies are made from this V oltage including isolated secondary supplies. T he range of this voltage is 14.5V to 15.5V ( decoupling capacitor required) Internally connected to the G N D pin and the primary ground plane, T his pin must be connected to the Supply voltage Reference Channel 1 Input signal has a Schmitt T rigger Characteristics to provide improved signal noise immunity. Logic H igh (5V ) turn-on the IG B T In addition Low impedance ( typical 1K and 1nF) guarantees good noise immunity A parallel 5V zener diode increase the Electrostatic D ischarge Protection Channel 2 Input signal has a Schmitt T rigger Characteristics to provide improved signal noise immunity. Logic H igh (5V ) turn-on the IG B T In addition Low impedance ( typical 1K and 1nF) guarantees good noise immunity A parallel 5V zener diode increase the Electrostatic D ischarge Protection A logic H igh input for at least 20µ s, resets fault output high and enable O utputs 1 and 2 to follow the respective Input level Fault change from H igh Logic level ( 2,7K connected to +5V internal) to a logic Low following the voltage on V C1 or V C2 exceed 6.3V . Channel 1 and Channel 2 Fault outputs are open collectors connected together in a "wire O R" forming a single FAU LT O U T pin. D igital input ground pin should be connected to the low noise ground plane for optimum performances. D esaturation V oltage Input.W hen the voltage on V C1 exceeds 6.3V while the IG B T is O N , FAU LT O U T is changed from 5V to a Logic Low State and T urn-off the IG B T until Reset is brought hight Separate T urn-on and T urn-off gate D rive O utputs in order to Set T urn-on and T urn-off switching speed independently from each other. T hose pins are connected through a resistor to the gate of IG BT with short wire length ( see "G ate resistors calculation") T his pin is directly connected to the Emetter of the IG BT or throught a resistor to minimize G ate ringing in case of paralleling operations T his pin is directly connected to the Emetter of the IG BT or throught a resistor to minimize G ate ringing in case of paralleling operations Separate T urn-on and T urn-off gate D rive O utput in order to Set T urn-on and T urn-off switching speed independently from each other. T hose pins are connected through a resistor to the gate of IG BT with short wire length ( see "G ate Resistors Calculation" ) D esaturation V oltage Input.W hen the voltage on V C2 exceeds 6.3V while the IG B T is O N , FAU LT O U T is changed from 5V to a Logic Low State and T urn off the IG BT until Reset is brought hight Table 1 Pin Function and Description Features: - Common mode rejection higher than 10 kV/µs for very high noise immunity. - 2500V galvanic isolation between primary and secondary and between the two secondary. - 5V logic level with Schmidt trigger input. - Low speed over current cut off (coupled with short circuit protection) to limit over voltage. - Separate sink & Source outputs for turn-on and turn-off switching optimisation. - Single VDD=15V supply required. - Secondary auxiliary power supplies under voltage lockout with hysteresis. The +15V bias voltage ensures low IGBT saturation voltage while the –5V guarantees fast turn-off and good noise immunity, even in an electrically noisy environnement. www.advancedpower.com www.microsemi.com 2/12 Application note 1903 JULY 2006 switching frequency, the higher the driver consumption is. This effective gate capacitor may be calculated by the relation: 1- Drive Power Calculation To determine if the IGBT driver is well suited for the application the main parameter is the total gate charge of the IGBT (Qg). Most of power semiconductor data sheet specify the IGBT total gate charge with the corresponding gate voltage applied. C = Qg V (@ 15V ) with VGE=15V GE Application: The Total Gate charge Curve ( see APTGF300A120 data sheet for example) gives a Qg of 2200µC @ VGE=15V. By the formula the effective capacitor can be calculated: In this application note we will also examine some simple methods to determine the Total Gate charge. 1-1 Effective Gate Determination EFF CEFF = 146 nF. Capacitor So the “Frequency vs. Effective Gate Capacitance” curve (see Fig. 2) allows verifying if the driver is well suited to the application. In our example, the frequency at 25°C is close to 40 kHz. During each turn-on and turn off operation the driver must charge and discharge the effective gate capacitor, so the higher the Frequency Vs Gate effective Capacitor 110 100 90 Tamb=25°C F RQ (Khz) 80 Tamb=70°C 70 60 50 40 30 20 10 0 0 25 50 75 100 125 150 175 200 225 250 275 300 CEFF (nF) Figure 2 Switching Frequency vs. Effective Gate Capacitance The driving power per channel and the consumption in the primary auxiliary power supply are: P (W ) = C EFF × ( ∆V Gate) × F RQ 2 perchannel (Normally the power necessary to charge a capacitor is ½ CV2f, but in this case, during a switching period the driver must charge and discharge the effective capacitance, resulting in twice the power). www.advancedpower.com www.microsemi.com 3/12 Application note 1903 JULY 2006 1-2 Example operation of phase The maximum steady state power dissipation of the driver is close to 1.2W (due to biasing the device). So the total primary power consumption (gate driver supply voltage=15V) is: leg The total amplitude generated by the IGBT driver is 20V (15V positive, -5V negative). So the power per channel at 40 kHz and 146nF is: P = 2.3W Additional losses like gate driver’s DC/DC converter efficiency must also be added (it represents around 30% of total losses). 60 PTOTAL(primary) =7.2W @ Frq=40 kHz and CEFF=146nF The maximum switching frequency is also dependent on the ambient temperature. The following Figure 3 “Switching Frequency vs. Ambient Temperature” gives the derating to observe. Maximum Switching Frequency Vs Ambiant Temperature APTGF300A120(Ceff=150nF) PHASE LEG OPERATION 50 Frq (KHz) 40 Absolute Max. Rating 30 Typical 20 10 0 -50 -25 0 25 50 75 85 100 Tamb (°C) Figure 3 Switching Frequency vs. Ambient Temperature 1-3 Total gate Measurement Charge - In general the effective capacitance (CEFF) is close to the input capacitance value (Cies) increased by a factor 5. C EFF ≅ 5 × C ies And Qg ( nC ) = C EFF ( nF ) × VoltageRise(V ) The difference is more particularly due the the Miller plateau effect (as shown in Fig. 4) corresponding to the flat portion of the curve. www.advancedpower.com www.microsemi.com 4/12 Application note 1903 JULY 2006 1-4 Measurement methodology If a more accurate value is needed, the following method based on the Gate current measurement is very simple (see Fig. 5). Important: The gate charge is increasing with the IGBT Collector voltage amplitude. So it is important to apply the same collector voltage as in the final application. 16 VDRV VGS, Gate-To-Source Voltage (V) 14 12 10 Miller Plateau VCE A digital oscilloscope combined with “Integral” math function analysis on the Gate current waveform gives the gate charge value by the formula: 8 6 Q = idt 4 The measurement gives: Q = 2400nAs 2 QG C 0 Qg, Total Gate Charge (nC) Figure 4 Typical Gate Charge Curves EFF = Q = 120nF 20 By comparison, the total gate charge for VGE = 0 to 15V is: Q G @ 15V = 1800nC G a t e C h a r g e M e a s u r e m e n t (n A s ) ∆ -0V - -0nAs-0A- T im e ( 1 µ S / D iv ) Figure 5 Gate Charge Measurement www.advancedpower.com www.microsemi.com 5/12 Application note 1903 JULY 2006 2- Gate Resistors Calculation The choice of the turn-on and turn-off gate resistors is critical in order to optimise the IGBT switching losses without exceeding the current capability of the driver. The typical values of Ron and Roff are given in Table 2, “Typical External Components Values”. Typical External Components Values APT - Modul SP6 package Technology IGBT Turn-on speed of an IGBT can be increased only up to a level compatible with the reverse recovery of a free wheeling rectifier. Too fast turn-on could also cause oscillations in the collector current. On the other hand, turn-off time must be as short as possible to reduce power loss. For theses reasons (and others like EMI limitation), the APTRG8A120 integrates Gon and Goff output connections in order to adjust separately the Ron and Roff gate resistors. Ron (ohms) Roff (ohms) Total gate charge (nC) @15V Frequency up to (Khz) ** R return (ohms) NPT Trench/Fieldstop Trench/Fieldstop 6.8 4.7 2.2 6.8 4.7 2.2 1320 2150 4300 50 20 10 0 0 0 NPT Trench/Fieldstop Trench/Fieldstop NPT Trench/Fieldstop 10 10 6.8 3.9 3.3 10 10 6.8 3.9 3.3 850 700 950 2250 1850 50 20 20 25 20 0 0 0 0 0 Trench/Fieldstop Trench/Fieldstop 6.8 3.3 6.8 3.3 850 1700 20 20 0 0 Additional Diode * 600V APTGF350A60 APTGT300A60 APTGT600A60 1200V APTGF150A120 APTGT150A120 APTGT200A120 APTGF300A120 APTGT400A120 1700V APTGT150A170 APTGT300A170 X X Caution : A dead time must be observed between H1 and H2 input signals ( see" dead time" Chapter) * : This external diode ( STTH112U from STM for example) must be connected between VC pins and IGBT collector to increase voltage capability ** : due to the driver and/or the power module switching frequency limitation ( Tamb = 85°C, Tcase module = 80°C) Table 2 Typical External Component Values 2-1 Gate resistors Minimum Value Calculation A minimum gate resistor value must be observed to avoid IGBT Driver damage. The peak current is limited at 8A during turn-on and 15A during turn-off. To calculate the minimum “ON” and “OFF” gate resistors (see Fig. 6 and Fig. 7), it should be considered that the APTRG8A120 is turned-on at +15V and turned-off at –5V therefore the gate voltage amplitude is 20V during every switching procedure. RG ON min RG OFF min = = ∆VG I PEAKon ∆VG I PEAKoff = 20 = 2.5Ω 8 = 20 = 1.33Ω 15 In fact the IGBT gate model integrates a series resistance, so in practice: RGONmin=2 And www.advancedpower.com www.microsemi.com RGOFFmin=1 6/12 Application note 1903 JULY 2006 Also the wire length between the driver and the power module must be as short as possible. Parasitic elements in the drive loop (like emitter inductance) clearly alter the performance. In general IGBT power modules integrate a Kelvin emitter sense terminal to minimize this drive loop effect. 3- Dead Time and Drive Interlock In case of phase leg operation, a dead time must be applied between the two input signals (H1 and H2) to ensure the complete turn-off of the active IGBT switch before turn-on of the opposite switch. If not, then short cross conductions appear which increase the losses and may destroy the IGBTs. Generally those cross conductions are short enough to disappear before the end of the necessary VCE(sat) detection blanking time, so the short circuit protection will not be activated. Figure 6 Turn-On Operation 3-1 Minimum Calculation Figure 7 Turn-Off Operation 2-2 Gate Resistors Determination Power Note that most of the drive losses are dissipated in the external gate resistors independently of the resistors values. In the previous example (primary power consumption calculation in phase leg operation) the Ron and Roff power will be: P=2.3/2 = 1.15 W In order to have good safety margin we propose: dead Time The dead time is the difference between the maximum total turn-off delay time and minimum total turn-on delay time (see Fig. 8 and Fig. 9 “Tdon and Tdoff measurements”). This includes driver, gate resistors and IGBT delay times. Note that the driver data sheet gives the “Propagation Delay Difference Between any Two Drivers” (PDD) which simplifies this calculation. Rgon, Rgoff = PR02 series (2W metal layer) Low inductance metal layer resistors are recommended. www.advancedpower.com www.microsemi.com 7/12 Application note 1903 JULY 2006 So the equation of the Minimum dead time becomes (ns): DTmin= (RGoff.Cies(max)log2+TdoffIGBT+Toff) -(RGon.Cies(min)log2+TdonIGBT+Ton)+PDD 3-2 APTGF300A120 Example With Cies = Input Capacitance Rgoff = Turn-off gate resistor Rgon= Turn-on gate resistor 90% With Rgon=Rgoff= 2R and RE (emitter resistor) = 0R DTmin (nS) = (41 + 500 + 30) – (30 + 70 + 50) + 350 = 771 ns Dead Time Calculation - 5V - 1 1 - H (Input Driver Signal) 2 - Output Collector Current (A) -0- This function prevents two IGBT’s in the same leg from being turned on at the same time as shown in Table 3, “Operation Table”. 10% -0TOTAL TDON Figure 8 Total Tdon Measurement for Dead Time Calculation Dead Time Calculation - 5V - 1 -01 - H (Input Driver Signal) 2 - Output Collector Current 2 10% -0- Recommended Dead Time: 1µs 3-3 Drive Interlock 2 90% Calculation TOTAL TDOFF 4- Suppression of gate ringing by R return When IGBT module paralleling is necessary it is best to use a common gate drive. Using different driver circuits introduces additional variation in turn-on and turn-off time and possible imbalance between each power module. To avoid gate ringing during the switching transient (collector voltage transition), an additional resistor may be connected between emitter sense connection and the common supply (0V) of the driver. Figure 9 Total Tdoff Measurement for Dead Time Calculation www.advancedpower.com www.microsemi.com 8/12 Application note 1903 JULY 2006 Operation Table Inputs H1 H2 Low High Low High X X X X X X Low Low High High X X X X X X Secondary UVLO Channel 1 Channel 2 X X X X Active X X X X X X X X X X Active X X X X Desat Condition Detected Channel 1 Channel 2 X X X X X X Yes X Yes X X X X X X X X Yes X Yes Reset Not Active Not Active Not Active Not Active Not active Not active Low Low High High Fault Output High High High High High High Low ** Low ** High** High** OUT G1 OUT G2 Low High Low Low/High * Low X Low ** X X X Low Low High High/Low * X Low X Low** X X * : in all of the cases only one of the two outputs may be High at the same time, generally the first channel high will keep hight Output level but un case of sychonise input signal the reponse time of each internal component will determind the high level channel and could not be garanty. ** : The fault condition is memorized until Reset input is brought low, then a logic hight for at least 20µS reset fault output and enable Inputs. A period of time ( 100 mS minimum) must be observe between each reset pulse in order to avoid the destruction of Power IGBT by over heating. Table 3 Operation Table This additional “return” resistor combined with the traditional gate resistor permits driving each power device gate input in a differential mode that helps to eliminate the effects of possible oscillations (see Fig. 10, “Paralleling of Power Modules Block Diagram”). Generally the power modules integrate emitter sense connections that reduce the driving loop effects. In case of discrete semiconductors never forget that parasitic elements like inductance in the drive loop clearly alter the circuit performance and will increase switching losses. Note that separate distributed resistors (Ron, Roff and Rreturn) must be matched for best synchronization. A bi-directional tranzorb should also be added to protect the IGBT gate from over voltage spikes (Z1, Z2 in Fig. 10). Figure 10 Paralleling of Power Module Block Diagram www.advancedpower.com www.microsemi.com 9/12 Application note 1903 JULY 2006 5- Protections 5-1 Short circuit protection by VCEsat monitoring Each driver provides a short circuit protection by VCEsat monitoring. If the drive senses that the voltage across the IGBT (at ON state only and from the VC pins) is greater than 6.3V, the short circuit conditions has been detected, the Figure 11 Short Circuit Protection Operation The fault outputs of each channel are connected together in a “Wired OR” forming a single fault output pin. This is an open collector with an integrated pull up resistor of 2.7K. The other side of this pull up resistor is connected to the internal 5V supply. In order to increase the immunity it is recommended to add an external pull-up resistor close to the digital components. Due to the switching over-voltage spikes (in spite of decoupling capacitors) or following a short circuit (in spite of slow turn-off) a safety margin must be observed between the VBUS voltage and corresponding driver output is slowly turned off as shown in Fig. 11 and the fault output immediately activated. The fault conditions are stored until a logic high signal for at least 20µs is applied to the reset input. The total driver reaction time in case of short circuit is 5µs, with a short circuit duration that will not exceed 6µs. the IGBT breakdown voltage (BVCES) like the Vc pins maximum voltage (1200V). See Fig. 1 “Phase Leg Operation Block Diagram”. Note that in normal operation (no fault) the reset input may be high or low without any action inside the driver. A period of 100ms must be considered as a minimum between each reset signal to prevent the destruction of the IGBT by over heating. www.advancedpower.com www.microsemi.com 10/12 Application note 1903 JULY 2006 For 1700V applications an additional fast diode (STTH112U from STM for example) must be connected between the Vc pins and the IGBT collector. 5-2 Secondary Auxiliary power supplies under voltage The APTRG8A120 under-voltage lockout (UVLO) feature is designed to prevent against insufficient IGBT gate voltage. The IGBT saturation voltage is increased significantly when the gate voltage amplitude is under 13V and dramatically when below 11V. In this case the conduction losses are so important that they may damage the IGBT by over heating. The UVLO will turn off the output if the secondary power supply voltage falls below 12.3V (typical) with a hysteresis of 0.4V minimum to prevent erratic operation. 6- Mounting Instructions The IGBT driver is dedicated to be mounted on a PC Board and fixed with 4x M3 screws in order to increase the vibration withstand capability. The recommended diameters for drill holes are 1 mm for the 18x 0.6mm square @2.54 mm raster gold plated connectors. To minimize parasitic elements, the driver and other external components must be as close as possible to the IGBT Power module. For this reason the PC Board will be fixed on the same support as the module (the heat sink generally). See Fig. 12 “Recommended Layout and Mounting”. In the case of SP6 power module, keep a distance of at least 5cm between the 2.8mm fast-on connectors and the spacer, which supports the PCB, to avoid mechanical stress. See “SP6 Mounting Instructions” application note APT0601. Note that the screw-on spacers are totally isolated from the rest of the circuit and are also isolated from each other. Figure 12 Recommended Layout and Mounting www.advancedpower.com www.microsemi.com 11/12 Application note 1903 JULY 2006 Conclusion The APTRG8A120 Drivers Circuit simplifies the power systems design by offering most of the functions necessary to set up and protect power IGBTs. This application note describes how to use this circuit to obtain the best performance. We also demonstrate that IGBT operating parameters must be considered to design a reliable power system. The parameters can be summarized by the following checklist: -Total Gate charge (Qg) -Input capacitance (CIES) -Turn-on and Turn-off delay times (Tdon, Tdoff) -Turn-on and Turn-off times (Ton, Toff) -Breakdown Voltage (BVCES) -Maximum switching Frequency (Frq ) References 1 Ralph McArthur “Making Use of Gate Charge Information in MOSFET and IGBT Data Sheets” Application Note APT0103 Advanced Power Technology. 2 “Use Gate Charge to Design the Gate Drive Circuit” AN944 International Rectifier 3 Jonathan Dodge, P.E., John Hess “IGBT Tutorial” Application note APT0201 Advanced Power Technology. 4 Serge Bontemps Product Manager “Parallel Connection of IGBT and MOSFET Power Modules” Application Note APT0405 Advanced Power Technology. www.advancedpower.com www.microsemi.com 12/12