IR21771STRPBF

Data Sheet No. PD60234 revB IR22771S/IR21771S(PbF) Phase Current Sensor IC for AC motor control Features • Floating channel up to 600V for IR21771 and 1200V for Product Summary VOFFSET (max) IR22771 • • • • • • IR22771 1200 V IR21771 600V Vin range ±250mV Bootstrap supply range 8-20 V 2.2 mA Fast Over Current detection Floating channel quiescent current (max) Sensing latency (max) Suitable for bootstrap power supplies Throughput Synchronous sampling measurement system High PWM noise (ripple) rejection capability Digital PWM output Low sensing latency ( 16 kHz * VB VB 16 / 10 kHz VS VB 10 / 6 kHz VB VS < 6 kHz VS VS *Æ 40 kHz Table 1: G0, G1 gain settings www.irf.com IR22771S/IR21771S(PbF) 2 Sizing tips 2.1 Bootstrap supply The VBS1,2,3 voltage provides the supply to the high side drivers circuitry of the IR22771S/IR21771S. 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 IR22771S/IR21771S current sensors. The bootstrap supply is formed by a diode and a capacitor connected as in Figure 16. 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 ∆VBS Some important considerations IR22771S or IR21771S a) Voltage ripple There are three different cases making the bootstrap circuit get conductive (see Figure 16) ‚ ILOAD < 0; the load current flows in the low side IGBT displaying relevant VCEon VBS = VCC − VF − VCEon Figure 16: bootstrap supply schematic 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. 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). 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). 14 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 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 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 bootstrap diode (see Figure 16) so to limit the current when the bootstrap capacitor is initially charged. We suggest not exceeding some Ohms (typically 5, maximum 10 Ohm) to avoid increasing the VBS timeconstant. The minimum on time for charging the bootstrap capacitor or for refreshing its charge must be verified against this time-constant. www.irf.com IR22771S/IR21771S(PbF) c) Bootstrap Capacitor For high THON designs where is used an electrolytic tank capacitor, 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: 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 thank 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. 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 17 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. 18. VB VS VinVin+ 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. 3 PCB LAYOUT TIPS 3.1 Distance from H to L voltage Figure 18: Recommended shunt connection 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. The IR22771S/IR21771S package (wide body) maximizes the distance between floating (from DCto DC+) and low voltage pins (VSS). It’s 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 VS Vin- Antenna Loop Vin+ Figure 17: antenna loops 15 www.irf.com IR22771S/IR21771S(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. 8/17/2005 16 www.irf.com