IR2277S

Data Sheet No. PD60233 revB IR2277S/IR2177S(PbF) Phase Current Sensor IC for AC motor control Features • Floating channel up to 600 V for IR2177 & 1200 V for IR2277 Product Summary VOFFSET (max) Vin range Bootstrap supply range Floating channel quiescent current (max) Sensing latency (max) Throughput Over Current threshold (max) IR2277 IR2177 1200 V 600 V ±250mV 8-20 V 2.2 mA 7.5 µsec (@20kHz) 40ksample/sec (@20kHz) ±470 mV • • • • • • • Synchronous sampling measurement system High PWM noise (ripple) rejection capability Digital PWM output Fast Over Current detection Suitable for bootstrap power supplies Low sensing latency ( 16 kHz * VB VB 16 / 10 kHz VS VB 10 / 6 kHz VB VS < 6 kHz VS VS * 40 kHz Table 1: G0, G1 gain settings 2 Sizing tips 2.1 Bootstrap supply The VBS1,2,3 voltage provides the supply to the high side drivers circuitry of the IR2277S/IR2177S. VBS supply sit on top of the VS voltage and so it must be floating. The bootstrap method to generate VBS supply can be used with IR2277S/IR2177S current sensors. The bootstrap supply is formed by a diode and a capacitor connected as in Figure 20. Figure 20: bootstrap supply schematic 17 www.irf.com IR2277S or IR2177S IR2277S/IR2177S(PbF) This method has the advantage of being simple and low cost but may force some limitations on dutycycle and on-time since they are limited by the requirement to refresh the charge in the bootstrap capacitor. Proper capacitor choice can reduce drastically these limitations. high side freewheeling diode get forwarded biased ILOAD = 0; the IGBT is not loaded while being on and VCE can be neglected VBS = VCC − VF ILOAD > 0; the load current flows through the freewheeling diode Bootstrap capacitor sizing Given the maximum admitted voltage drop for VBS, namely ∆VBS, the influencing factors contributing to VBS decrease are: − − − − Floating section quiescent current (IQBS); Floating section leakage current (ILK) Bootstrap diode leakage current (ILK_DIODE); Charge required by the internal level shifters (QLS); typical 20nC − Bootstrap capacitor leakage current (ILK_CAP); − High side on time (THON). V BS = VCC − VF + VFP In this case we have the highest value for VBS. Turning on the high side IGBT, ILOAD flows into it and VS is pulled up. b) Bootstrap Resistor A resistor (Rboot) is placed in series with the bootstrap diode (see Figure 20) to limit the current when the bootstrap capacitor is initially charged. We suggest not exceeding some Ohms (typically 5, maximum 10 Ohms) to avoid increasing the VBS time-constant. The minimum on time for charging the bootstrap capacitor or for refreshing its charge must be verified against this time-constant. c) Bootstrap Capacitor For high THON designs where an electrolytic tank capacitor is used, its ESR must be considered. This parasitic resistance develops a voltage divider with Rboot generating a voltage step on VBS at the first charge of bootstrap capacitor. The voltage step and the related speed (dVBS/dt) should be limited. As a general rule, ESR should meet the following constraint: ILK_CAP is only relevant when using an electrolytic capacitor and can be ignored if other types of capacitors are used. It is strongly recommend using at least one low ESR ceramic capacitor (paralleling electrolytic and low ESR ceramic may result in an efficient solution). Then we have: QTOT = QLS + ( I QBS + + I LK + I LK _ DIODE + I LK _ CAP ) ⋅ THON The minimum size of bootstrap capacitor is then: C BOOT min = QTOT ∆V BS ESR ⋅ VCC ≤ 3V ESR + RBOOT Parallel combination of small ceramic and large electrolytic capacitors is normally the best compromise, the first acting as fast charge tank for the gate charge only and limiting the dVBS/dt by reducing the equivalent resistance while the second keeps the VBS voltage drop inside the desired ∆VBS. d) Bootstrap Diode The diode must have a BV> 600V (or 1200V depending on application) and a fast recovery time (trr < 100 ns) to minimize the amount of charge fed back from the bootstrap capacitor to VCC supply. Some important considerations a) Voltage ripple There are three different cases making the bootstrap circuit get conductive (see Figure 20) ILOAD < 0; the load current flows in the low side IGBT displaying relevant VCEon VBS = VCC − VF − VCEon In this case we have the lowest value for VBS. This represents the worst case for the bootstrap capacitor sizing. When the IGBT is turned off the Vs node is pushed up by the load current until the 18 www.irf.com IR2277S/IR2177S(PbF) 3 PCB LAYOUT TIPS 3.3 Antenna loops and inputs connection Current loops behave like antennas able to receive EM noise. In order to reduce EM coupling loops must be reduced as much as possible. Figure 21 shows the high side shunt loops. Moreover it is strongly suggested to use Kelvin connections for Vin+ and Vin- to shunt paths and starconnect VS to Vin- close to the shunt resistor as explained in Fig. 22. 3.1 Distance from H to L voltage The IR2277S/IR2177S package (wide body) maximizes the distance between floating (from DCto DC+) and low voltage pins (VSS). It is strongly recommended to place components tied to floating voltage in the respective high voltage portions of the device (VB, VS) side. 3.2 Ground plane Ground plane must NOT be placed under or nearby the high voltage floating side to minimize noise coupling. VB VB VS V in V in + VS VinVin+ Antenna Loop Figure 22: Recommended shunt connection Figure 21: antenna loops 3.4 Supply capacitors The supply capacitors must be placed as close as possible to the device pins (VCC and VSS for the ground tied supply, VB and VS for the floating supply) in order to minimize parasitic traces inductance/resistance 19 www.irf.com IR2277S/IR2177S(PbF) Case Outline WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245 Tel: (310) 252-7105 This part has been qualified for the Industrial Market Data and specifications subject to change without notice. 8/18/2005 20 www.irf.com