MIC4604 85V Half Bridge MOSFET Drivers with up to 16V Programmable Gate Drive General Description Features The MIC4604 is an 85V Half Bridge MOSFET driver. The MIC4604 features fast 39ns propagation delay times and 20ns driver rise/fall times for a 1nF capacitive load. The low-side and high-side gate drivers are independently controlled. The MIC4604 has TTL input thresholds. It includes a high-voltage internal diode that helps charge the high-side gate drive bootstrap capacitor. • 5.5V to 16V gate drive supply voltage range. • Drives high-side and low-side N-Channel MOSFETs with independent inputs • TTL input thresholds • On chip bootstrap diode • Fast 39ns propagation times • Drives 1000pF load with 20ns rise and fall times • Low power consumption • Supplies undervoltage protection • –40°C to +125°C junction temperature range A robust, high-speed, and low-power level shifter provides clean level transitions to the high-side output. The robust operation of the MIC4604 ensures that the outputs are not affected by supply glitches, HS ringing below ground, or HS slewing with high-speed voltage transitions. Undervoltage protection is provided on both the low-side and high-side drivers. The MIC4604 is available in an 8-pin SOIC package and a tiny 10-pin 2.5mm × 2.5mm TDFN package. Both packages have an operating junction temperature range of –40°C to +125°C. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Applications • • • • • Power inverters High-voltage step-down regulators Half, full and 3-phase bridge motor drives Distributed power systems Computing peripherals Typical Application Motor Door Lock Solution Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com June 25, 2013 Revision 1.0 Micrel, Inc. MIC4604 Ordering Information Part Number Part Marking Input Junction Temperature Range Package MIC4604YMT 463 TTL –40° to +125°C 10-Pin 2.5mm × 2.5mm TDFN MIC4604 YM TTL –40° to +125°C 8-Pin SOIC MIC4604YM Pin Configurations MIC4604YMT 10-Pin 2.5mm x2.5mm TDFN (MT) (Top View) MIC4604YM 8-Pin SOIC (M) (Top View) Pin Description Pin Number TDFN SOIC Pin Name 1 1 VDD 2, 10 Pin Function Input supply for gate drivers. Decouple this pin to VSS with a >2.2µF capacitor. Anode connection to internal bootstrap diode. NC No Connect 3 2 HB High-side bootstrap supply. External bootstrap capacitor is required. Connect bootstrap capacitor across this pin and HS. Cathode connection to internal bootstrap diode. 4 3 HO High-side drive output. Connect to gate of the external high-side power MOSFET. 5 4 HS High-side drive reference connection. Connect to source of the external high-side power MOSFET. Connect this pin to the bootstrap capacitor. 6 5 HI High-side drive input. 7 6 LI Low-side drive input. 8 7 VSS 9 8 LO EP June 25, 2013 EPAD Driver reference supply input. Connected to power ground of external circuitry and to source of low-side power MOSFET. Low-side drive output. Connect to gate of the external low-side power MOSFET. Exposed pad. Connect to VSS. 2 Revision 1.0 Micrel, Inc. MIC4604 Operating Ratings(2) Absolute Maximum Ratings(1, 4) Supply Voltage (VDD) [decreasing VDD] ........... 5.25V to 16V Supply Voltage (VDD) [increasing VDD] .............. 5.5V to 16V Voltage on HS .................................................... −1V to 85V Voltage on HS (repetitive transient) ................... −5V to 90V HS Slew Rate ............................................................ 50V/ns Voltage on HB ................................ VHS + 4.5V to VHS + 16V and/or.......................................... VDD − 1V to VDD + 85V Junction Temperature (TJ) ........................ –40°C to +125°C Junction Thermal Resistance 2.5mm x 2.5mm TDFN-10L (θJA) ....................... 75°C/W SOIC-8L (θJA) .................................................. 98.9°C/W Supply Voltage (VDD, VHB – VHS) ..................... −0.3V to 18V Input Voltages (VLI, VHI, VEN) ................. −0.3V to VDD + 0.3V Voltage on LO (VLO) ............................. −0.3V to VDD + 0.3V Voltage on HO (VHO) ..................... VHS − 0.3V to VHB + 0.3V Voltage on HS (continuous) ............................... −1V to 90V Voltage on HB .............................................................. 108V Average Current in VDD to HB Diode ....................... 100mA Storage Temperature (Ts) ......................... −60°C to +150°C (3) ESD Rating HBM ...................................................................... 1.5kV MM ......................................................................... 200V Electrical Characteristics(4) VDD = VHB = 12V; VSS = VHS = 0V; No load on LO or HO; TA = +25°C; unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤ +125°C Symbol Parameter Condition Min. Typ. Max. Units Supply Current IDD VDD Quiescent Current LI = HI = 0V 48 200 µA IDDO VDD Operating Current f = 20kHz 136 300 µA IHB Total HB Quiescent Current LI = HI = 0V or LI = 0V and HI = 5V 20 75 µA IHBO Total HB Operating Current f = 20kHz 29 200 µA IHBS HB to VSS Quiescent Current VHS = VHB = 90V 0.5 5 µA 0.8 V Input (LI, HI) VIL Low-Level Input Voltage VIH High-Level Input Voltage VHYS Input Voltage Hysteresis RI Input Pull-Down Resistance 2.2 V 0.05 V 100 240 500 kΩ 4.0 4.4 4.9 V Undervoltage Protection VDDF VDD Falling Threshold VDDH VDD Threshold Hysteresis VHBF HB Falling Threshold VHBH HB Threshold Hysteresis Rising VDD Threshold; VDDR = VDDF + VDDH 0.21 4.0 4.4 V 4.9 V Rising VHB Threshold; VHBR = VHBF + VHBH 0.23 V IVDD-HB = 100µA 0.42 0.70 V Ω Bootstrap Diode VDL Low-Current Forward Voltage VDH High-Current Forward Voltage IVDD-HB = 50mA 0.75 1.0 RD Dynamic Resistance IVDD-HB = 50mA 2.8 5.0 V Notes: 1. Exceeding the absolute maximum ratings may damage the device. 2. The device is not guaranteed to function outside its operating ratings. 3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF. 4. Specification s are for packaged product only. June 25, 2013 3 Revision 1.0 Micrel, Inc. MIC4604 Electrical Characteristics(4) (Continued) VDD = VHB = 12V; VSS = VHS = 0V; No load on LO or HO; TA = +25°C; unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤ +125°C Symbol Parameter Condition Min. Typ. Max. Units LO Gate Driver VOLL Low-Level Output Voltage ILO = 50mA 0.17 0.4 V VOHL High-Level Output Voltage ILO = −50mA, VOHL = VDD – VLO 0.25 1.0 V IOHL Peak Sink Current VLO = 5V 1 A IOLL Peak Source Current VLO = 5V 1 A HO Gate Driver VOLH Low-Level Output Voltage IHO = 50mA 0.2 0.6 V VOHH High-Level Output Voltage IHO = −50mA, VOHH = VHB – VHO 0.22 1.0 V IOHH Peak Sink Current VHO = 5V 1.5 A IOLH Peak Source Current VHO = 5V 1 A (5) Switching Specifications tLPHL Lower Turn-Off Propagation Delay (LI Falling to LO Falling) 37 75 ns tHPHL Upper Turn-Off Propagation Delay (HI Falling to HO Falling) 34 75 ns tLPLH Lower Turn-On Propagation Delay (LI Rising to LO Rising) 39 75 ns tHPLH Upper Turn-On Propagation Delay (HI Rising to HO Rising) 33 75 ns tRC/FC Output Rise/Fall Time CL = 1000pF 20 ns tR/F Output Rise/Fall Time (3V to 9V) CL = 0.1µF 0.8 µs tPW Minimum Input Pulse Width that Changes the Output 50 ns tBS Bootstrap Diode Turn-On or Turn-Off Time 10 ns Note: 5. Guaranteed by design. Not production tested. June 25, 2013 4 Revision 1.0 Micrel, Inc. MIC4604 Timing Diagrams Note: 6. All propagation delays are measured from the 50% voltage level. Block Diagram Figure 1. MIC4604 Block Diagram June 25, 2013 5 Revision 1.0 Micrel, Inc. MIC4604 Typical Characteristics Quiescent Current vs. Input Voltage T = -40°C T = 25°C 60 40 T = 125°C 20 HS = 0V Freq = 20kHz HS = 0V VHB = VDD 250 VHB OPERATING CURRENT (µA) VDD OPERATING CURRENT (µA) T = -40°C T = 25°C 200 150 100 T = 125°C 50 6 8 10 12 14 4 16 6 8 12 10 14 20 T = -40°C 4 6 8 10 12 14 INPUT VOLTAGE (V) Quiescent Current vs. Temperature VDD Operating Current vs. Temperature VHB Operating Current vs. Temperature VDD = 12V 60 40 VDD = 9V HS = 0V 0 250 VDD = 16V 200 VDD = 12V 150 VDD = 9V 100 50 0 25 50 75 100 125 Freq = 20kHz HS = 0V VHB = VDD 40 VHB = 16V 35 30 25 VHB = 12V 20 VHB = 9V 15 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) VDD Operating Current vs. Frequency VHB Operating Current vs. Frequency Low Level Output Voltage vs. Temperature 8 VHB OPERATING CURRENT (mA) T = -40°C 6 T = 25°C 4 2 T = 125°C 0 HS = 0V ILO, IHO = 50mA HS = 0V VHB = VDD = 12V 400 0.6 T = 125°C T = 25°C 0.4 400 600 FREQUENCY (kHz) June 25, 2013 800 1000 VDD = 12V VDD = 9V 300 200 0.2 VDD = 16V 100 T = -40°C 0 0 200 125 500 0.8 HS = 0V VHB = VDD =12V 16 45 Freq = 20kHz HS = 0V VHB = VDD VHB OPERATING CURRENT (µA) VDD OPERATING CURRENT (µA) 80 0 30 INPUT VOLTAGE (V) VDD = 16V -25 T = 25°C 16 300 -50 T = 125°C 40 INPUT VOLTAGE (V) 100 20 Freq = 20kHz HS = 0V VHB = VDD 50 10 0 4 VOLL, VOLH (mV) QUIESCENT CURRENT (µA) 80 0 QUIESCENT CURRENT (µA) 60 300 100 VDD OPERATING (mA) VHB Operating Current vs. Input Voltage VDD Operating Current vs. Input Voltage 0 200 400 600 FREQUENCY (kHz) 6 800 1000 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) Revision 1.0 Micrel, Inc. MIC4604 Typical Characteristics (Continued) High Level Output Voltage vs. Temperature 500 HS = 0V HS = 0V 4.7 THRESHOLDS (V) VDD = 12V VDD = 9V 300 200 0.26 VHB Rising HYSTERESIS (V) 400 4.6 VDD Rising 4.5 VDD Falling 4.4 VHB Hysteresis 0.24 0.22 0.20 VDD Hysteresis VDD = 16V 100 VHB Falling 4.3 0 0.18 0.16 4.2 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 TEMPERATURE (°C) TEMPERATURE (°C) Propagation Delay vs. Input Voltage Propagation Delay vs. Temperature 80 100 -50 125 DELAY (ns) 50 tLPHL 50 35 50 75 100 125 HS = 0V tLPLH tLPHL 40 tHPHL 30 tHPHL 25 1000 VDD = VHB = 12V HS = 0V tLPLH 0 Bootstrap Diode I-V Characteristics 60 TAMB = 25°C HS = 0V 65 -25 TEMPERATURE (°C) FORWARD CURRENT (mA) VOHL, VOHH (mV) 0.28 4.8 HS = 0V ILO ,IHO = -50mA DELAY (ns) UVLO Hysteresis vs. Temperature UVLO Thresholds vs. Temperature tHPLH T = 25°C 100 T = 125°C 10 T = -40°C 1 tHPLH 20 20 4 6 8 10 12 14 16 INPUT VOLTAGE (V) 0.1 -50 -25 0 25 50 75 TEMPERATURE (°C) 100 125 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FORWARD VOLTAGE (V) Bootstrap Diode Reverse Current 100 REVERSE CURRENT (µA) HS = 0V 10 1 T = 125°C 0.1 T = 85°C 0.01 T = 25°C 0.001 0.0001 0 10 20 30 40 50 60 70 80 90 100 REVERSE VOLTAGE (V) June 25, 2013 7 Revision 1.0 Micrel, Inc. MIC4604 Functional Description The MIC4604 is a high-voltage, non-inverting, dual MOSFET driver that is designed to independently drive both high-side and low-side N-Channel MOSFETs. The block diagram of the MIC4604 is shown in Figure 1. Both drivers contain an input buffer with hysteresis, a UVLO circuit, and an output buffer. The high-side output buffer includes a high-speed level-shifting circuit that is referenced to the HS pin. An internal diode is used as part of a bootstrap circuit to provide the drive voltage for the high-side output. Startup and UVLO The UVLO circuit forces the driver output low until the supply voltage exceeds the UVLO threshold. The low-side UVLO circuit monitors the voltage between the VDD and VSS pins. The high-side UVLO circuit monitors the voltage between the HB and HS pins. Hysteresis in the UVLO circuit prevents noise and finite circuit impedance from causing chatter during turn-on. Figure 2. Low-Side Driver Block Diagram High-Side Driver and Bootstrap Circuit A block diagram of the high-side driver and bootstrap circuit is shown in Figure 3. This driver is designed to drive a floating N-channel MOSFET, whose source terminal is referenced to the HS pin. Input Stage Both the HI and LI pins of the MIC4604 are referenced to the VSS pin. The voltage state of the input signal does not change the quiescent current draw of the driver. The MIC4604 has a TTL-compatible input range and can be used with input signals with amplitude less than the supply voltage. The threshold level is independent of the VDD supply voltage and there is no dependence between IVDD and the input signal amplitude with the MIC4604. This feature makes the MIC4604 an excellent level translator that will drive high-threshold MOSFETs from a low-voltage PWM IC. Low-Side Driver A block diagram of the low-side driver is shown in Figure 2. The low-side driver is designed to drive a ground (VSS pin) referenced N-channel MOSFET. Low driver impedances allow the external MOSFET to be turned on and off quickly. The rail-to-rail drive capability of the output ensures a low RDsON from the external MOSFET. Figure 3. High-Side Driver and Bootstrap Circuit Block Diagram A high level applied to LI pin causes the upper driver MOSFET to turn on and VDD voltage is applied to the gate of the external MOSFET. A low level on the LI pin turns off the upper driver and turns on the low side driver to ground the gate of the external MOSFET. June 25, 2013 A low-power, high-speed, level-shifting circuit isolates the low side (VSS pin) referenced circuitry from the high-side (HS pin) referenced driver. Power to the high-side driver and UVLO circuit is supplied by the bootstrap circuit while the voltage level of the HS pin is shifted high. 8 Revision 1.0 Micrel, Inc. MIC4604 The bootstrap circuit consists of an internal diode and external capacitor, CB. In a typical application, such as the synchronous buck converter shown in Figure 4, the HS pin is at ground potential while the low-side MOSFET is on. The internal diode allows capacitor CB to charge up to VDD-VF during this time (where VF is the forward voltage drop of the internal diode). After the low-side MOSFET is turned off and the HO pin turns on, the voltage across capacitor CB is applied to the gate of the upper external MOSFET. As the upper MOSFET turns on, voltage on the HS pin rises with the source of the high-side MOSFET until it reaches VIN. As the HS and HB pin rise, the internal diode is reverse biased preventing capacitor CB from discharging. (total of 10.8V) to exceed the minimal VDD range. As an additional benefit, the low 5.5V gate drive capability allows a longer run time. This is because the Li-ion battery can run down to 5.5V, which is just above its 4.8V minimum recommended discharge voltage. This is also a benefit in higher current power tools that use five or six cells. The driver can be operated up to 16V to minimize the RDSON of the MOSFETs and use as much of the discharge battery pack as possible for a longer run time. For example, an 18V battery pack can be used to the lowest operating discharge voltage of 13.5V. Application Information Power Dissipation Considerations Power dissipation in the driver can be separated into three areas: Internal diode dissipation in the bootstrap circuit • Internal driver dissipation • Quiescent current dissipation used to supply the internal logic and control functions. Bootstrap Circuit Power Dissipation Power dissipation of the internal bootstrap diode primarily comes from the average charging current of the CB capacitor multiplied by the forward voltage drop of the diode. Secondary sources of diode power dissipation are the reverse leakage current and reverse recovery effects of the diode. Figure 4. High-Side Driver and Bootstrap Circuit Block Diagram The average current drawn by repeated charging of the high-side MOSFET is calculated by: Programmable Gate Drive The MIC4604 offers programmable gate drive, which means the MOSFET gate drive (gate to source voltage) equals the VDD voltage. This feature offers designers flexibility in driving the MOSFETs. Different MOSFETs require different VGS characteristics for optimum RDSON performance. Typically, the higher the gate voltage (up to 16V), the lower the RDSON achieved. For example, a 4899 MOSFET can be driven to the ON state at 4.5V gate voltage but RDSON is 7.5mΩ. If driven to 10V gate voltage, RDSON is 4.5mΩ. In low-current applications, the losses due to RDSON are minimal, but in high-current applications such as power hand tools, the difference in RDSON can cut into the efficiency budget. IF( AVE ) = Q gate × f S Eq. 1 Where: Qgate = total gate charge at VHB fs = gate drive switching frequency The average power dissipated by the forward voltage drop of the diode equals: Pdiode fwd = IF( AVE ) × VF Eq. 2 Where: VF = diode forward voltage drop The value of VF should be taken at the peak current through the diode; however, this current is difficult to calculate because of differences in source impedances. The peak current can either be measured or the value of VF at the average current can be used, which will yield a good approximation of diode power dissipation. In portable hand tools and other battery-powered applications, the MIC4604 offers the ability to drive motors at a lower voltage compared to the traditional MOSFET drivers because of the wide VDD range (5.5V to 16V). Traditional MOSFET drivers typically require a VDD greater than 9V. The MIC4604 drives a motor using only two Li-ion batteries (total 7.2V) compared to traditional MOSFET drivers which will require at least three cells June 25, 2013 • The reverse leakage current of the internal bootstrap diode is typically 2µA at a reverse voltage of 85V at 125C. Power 9 Revision 1.0 Micrel, Inc. MIC4604 dissipation due to reverse leakage is typically much less than 1mW and can be ignored. Reverse recovery time is the time required for the injected minority carriers to be swept away from the depletion region during turn-off of the diode. Power dissipation due to reverse recovery can be calculated by computing the average reverse current due to reverse recovery charge times the reverse voltage across the diode. The average reverse current and power dissipation due to reverse recovery can be estimated by: IRR( AVE ) = 0.5 × IRRM × t rr × f S Pdiode RR = IRR( AVE ) × VREV Eq. 3 Where: IRRM = peak reverse recovery current trr = reverse recovery time The total diode power dissipation is: Pdiode total = Pdiode fwd + Pdiode RR Eq. 4 Figure 5. Optional Bootstrap Diode An optional external bootstrap diode may be used instead of the internal diode (Figure 5). An external diode may be useful if high gate charge MOSFETs are being driven and the power dissipation of the internal diode is contributing to excessive die temperatures. The voltage drop of the external diode must be less than the internal diode for this option to work. The reverse voltage across the diode will be equal to the input voltage minus the VDD supply voltage. The above equations can be used to calculate power dissipation in the external diode; however, if the external diode has significant reverse leakage current, the power dissipated in that diode due to reverse leakage can be calculated as: Pdiode REV = IR × VREV × (1 − D) Gate Driver Power Dissipation Power dissipation in the output driver stage is mainly caused by charging and discharging the gate to source and gate to drain capacitance of the external MOSFET. Figure 6 shows a simplified equivalent circuit of the MIC4604 driving an external MOSFET. Eq. 5 Where: IR = reverse current flow at VREV and TJ VREV = diode reverse voltage D = duty cycle = tON × fS The on-time is the time the high-side switch is conducting. In most topologies, the diode is reverse biased during the switching cycle off-time. Figure 6. MIC4604 Driving an External MOSFET Dissipation during the External MOSFET Turn-On Energy from capacitor CB is used to charge up the input capacitance of the MOSFET (Cgd and Cgs). The energy delivered to the MOSFET is dissipated in the three resistive components, Ron, Rg and Rg_fet. Ron is the on resistance of the upper driver MOSFET in the MIC4604. June 25, 2013 10 Revision 1.0 Micrel, Inc. MIC4604 Rg is the series resistor (if any) between the driver IC and the MOSFET. Rg_fet is the gate resistance of the MOSFET. Rg_fet is usually listed in the power MOSFET’s specifications. The ESR of capacitor CB and the resistance of the connecting etch can be ignored since they are much less than Ron and Rg_fet. The same energy is dissipated by Roff, Rg and Rg_fet when the driver IC turns the MOSFET off. Assuming Ron is approximately equal to Roff, the total energy and power dissipated by the resistive drive elements is: Edriver = Qg × Vgs and Pdriver = Qg × Vgs × fs The effective capacitances of Cgd and Cgs are difficult to calculate because they vary non-linearly with Id, Vgs, and Vds. Fortunately, most power MOSFET specifications include a typical graph of total gate charge versus Vgs. Figure 7 shows a typical gate charge curve for an arbitrary power MOSFET. This chart shows that for a gate voltage of 10V, the MOSFET requires about 23.5nC of charge. The energy dissipated by the resistive components of the gate drive circuit during turn-on is calculated as: E= 1 2 × Ciss × Vgs Where: Edriver = energy dissipated per switching cycle Pdriver = power dissipated per switching cycle Qg = total gate charge at Vgs Vgs = gate to source voltage on the MOSFET fs = switching frequency of the gate drive circuit The power dissipated inside the MIC4604 is equal to the ratio of Ron and Roff to the external resistive losses in Rg and Rg_fet. Letting Ron = Roff, the power dissipated in the MIC4604 due to driving the external MOSFET is: 2 but Q = C× V Eq. 6 so E = 1/2 × Qg × Vgs Pdiss drive = Pdriver Where Ciss = total gate capacitance of the MOSFET VGS - Gate-to-Source Voltage (V) Ron Ron + Rg + Rg _ fet Eq. 8 Supply Current Power Dissipation Power is dissipated in the MIC4604 even if nothing is being driven. The supply current is drawn by the bias for the internal circuitry, the level shifting circuitry, and shootthrough current in the output drivers. The supply current is proportional to operating frequency and the VDD and VHB voltages. The typical characteristic graphs show how supply current varies with switching frequency and supply voltage. Gate Charge 10 VDS = 50V ID = 6.9A 8 Eq. 7 6 The power dissipated by the MIC4604 due to supply current is 4 2 Pdiss sup ply = VDD × IDD + VHB × IHB Eq. 9 0 0 5 10 15 20 Total Power Dissipation and Thermal Considerations Total power dissipation in the MIC4604 is equal to the power dissipation caused by driving the external MOSFETs, the supply current and the internal bootstrap diode. 25 Qg - Total Gate Charge (nC) Figure 7. Typical Gate Charge vs. VGS Pdiss total = Pdiss sup ply + Pdiss drive + Pdiode total June 25, 2013 11 Eq. 10 Revision 1.0 Micrel, Inc. MIC4604 The die temperature can be calculated after the total power dissipation is known. TJ = TA + Pdiss total × θ JA minimum capacitance value should be increased if low voltage capacitors are used because even good quality dielectric capacitors, such as X5R, will lose 40% to 70% of their capacitance value at the rated voltage. Eq. 11 Placement of the decoupling capacitors is critical. The bypass capacitor for VDD should be placed as close as possible between the VDD and VSS pins. The bypass capacitor (CB) for the HB supply pin must be located as close as possible between the HB and HS pins. The etch connections must be short, wide, and direct. The use of a ground plane to minimize connection impedance is recommended. Refer to the section on Grounding, Component Placement and Circuit Layout for more information. Where: TA = maximum ambient temperature TJ = junction temperature (°C) Pdisstotal = power dissipation of the MIC4604 θJA = thermal resistance from junction to ambient air Propagation Delay and Other Timing Considerations Propagation delay and signal timing are important considerations. Many power supply topologies use two switching MOSFETs operating 180° out of phase from each other. These MOSFETs must not be on at the same time or a short circuit will occur, causing high peak currents and higher power dissipation in the MOSFETs. The MIC4604 output gate drivers are not designed with anti-shoot-through protection circuitry. The output drive signals simply follow the inputs. The power supply design must include timing delays (dead-time) between the input signals to prevent shoot-through. The voltage on the bootstrap capacitor drops each time it delivers charge to turn on the MOSFET. The voltage drop depends on the gate charge required by the MOSFET. Most MOSFET specifications specify gate charge versus Vgs voltage. Based on this information and a recommended ΔVHB of less than 0.1V, the minimum value of bootstrap capacitance is calculated as: CB ≥ Make sure the input signal pulse width is greater than the minimum specified pulse width. An input signal that is less than the minimum pulse width may result in no output pulse or an output pulse whose width is significantly less than the input. ∆VHB Eq. 12 Where: Qgate = total gate charge at VHB ∆VHB = voltage drop at the HB pin The maximum duty cycle (ratio of high side on-time to switching period) is controlled by the minimum pulse width of the low side and by the time required for the CB capacitor to charge during the off-time. Adequate time must be allowed for the CB capacitor to charge up before the high-side driver is turned on. The decoupling capacitor for the VDD input may be calculated in with the same formula; however, the two capacitors are usually equal in value. Grounding, Component Placement and Circuit Layout Nanosecond switching speeds and ampere peak currents in and around the MIC4604 drivers require proper placement and trace routing of all components. Improper placement may cause degraded noise immunity, false switching, excessive ringing, or circuit latch-up. Decoupling and Bootstrap Capacitor Selection Decoupling capacitors are required for both the low side (VDD) and high side (HB) supply pins. These capacitors supply the charge necessary to drive the external MOSFETs and also minimize the voltage ripple on these pins. The capacitor from HB to HS has two functions: it provides decoupling for the high-side circuitry and also provides current to the high-side circuit while the high-side external MOSFET is on. Ceramic capacitors are recommended because of their low impedance and small size. Z5U type ceramic capacitor dielectrics are not recommended because of the large change in capacitance over temperature and voltage. A minimum value of 0.1µF is required for each of the capacitors, regardless of the MOSFETs being driven. Larger MOSFETs may require larger capacitance values for proper operation. The voltage rating of the capacitors depends on the supply voltage, ambient temperature and the voltage derating used for reliability. 25V rated X5R or X7R ceramic capacitors are recommended for most applications. The June 25, 2013 Q gate Figure 8 shows the critical current paths when the driver outputs go high and turn on the external MOSFETs. It also helps demonstrate the need for a low impedance ground plane. Charge needed to turn-on the MOSFET gates comes from the decoupling capacitors CVDD and CB. Current in the low-side gate driver flows from CVDD through the internal driver, into the MOSFET gate, and out the source. The return connection back to the decoupling capacitor is made through the ground plane. Any inductance or resistance in the ground return path causes a voltage spike or ringing to appear on the source of the MOSFET. This voltage works against the gate drive voltage and can either slow down or turn off the MOSFET during the period when it should be turned on. 12 Revision 1.0 Micrel, Inc. MIC4604 Current in the high-side driver is sourced from capacitor CB and flows into the HB pin and out the HO pin, into the gate of the high side MOSFET. The return path for the current is from the source of the MOSFET and back to capacitor CB. The high-side circuit return path usually does not have a low-impedance ground plane so the etch connections in this critical path should be short and wide to minimize parasitic inductance. As with the low-side circuit, impedance between the MOSFET source and the decoupling capacitor causes negative voltage feedback that fights the turn-on of the MOSFET. It is important to note that capacitor CB must be placed close to the HB and HS pins. This capacitor not only provides all the energy for turn-on but it must also keep HB pin noise and ripple low for proper operation of the highside drive circuitry. Figure 9. Turn-Off Current Paths DC Motor Applications MIC4604 MOSFET drivers are widely used in DC motor applications. They address brushed motors in both halfbridge and full-bridge motor topologies as well as 3-phase brushless motors. As shown in Figure 10, Figure 11, and Figure 12, the drivers switch the MOSFETs at variable duty cycles that modulate the voltage to control motor speed. In the half-bridge topology, the motor turns in one direction only. The full-bridge topology allows for bidirectional control. 3-Phase motors are more efficient compared to the brushed motors but require three halfbridge switches and additional circuitry to sense the position of the rotor. The MIC4604 85V operating voltage offers the engineer margin to protect against Back Electromotive Force (EMF) which is a voltage spike caused by the rotation of the rotor. The Back EMF voltage amplitude depends on the speed of the rotation. It is good practice to have at least twice the HV voltage of the motor supply. 85V is plenty of margin for 12V, 24V, and 40V motors. Figure 8. Turn-On Current Paths Figure 9 shows the critical current paths when the driver outputs go low and turn off the external MOSFETs. Short, low-impedance connections are important during turn-off for the same reasons given in the turn-on explanation. Current flowing through the internal diode replenishes charge in the bootstrap capacitor, CB. June 25, 2013 13 Revision 1.0 Micrel, Inc. MIC4604 Figure 10. Half Bridge DC Motor Figure 12. 3-Phase Brushless DC Motor Driver – 24V Block Diagram The MIC4604 is offered in a small 2.5mm × 2.5mm TDFN package for applications that are space constrained and an SOIC-8 package for ease of manufacturing. The motor trend is to put the motor control circuit inside the motor casing, which requires small packaging because of the size of the motor. The MIC4604 offers low UVLO threshold and programmable gate drive, which allows for longer operation time in battery operated motors such as power hand tools. Cross conduction across the half bridge can cause catastrophic failure in a motor application. Engineers typically add dead time between states that switch between high input and low input to ensure that the lowside MOSFET completely turns off before the high-side MOSFET turns on and vice versa. The dead time depends on the MOSFET used in the application, but 200ns is typical for most motor applications. Power Inverter Power inverters are used to supply AC loads from a DC operated battery system, mainly during power failure. The battery voltage can be 12VDC, 24VDC, or up to 36VDC, depending on the power requirements. There two popular conversion methods, Type I and Type II, that convert the battery energy to AC line voltage (110VAC or 230VAC). Figure 11. Full Bridge DC Motor June 25, 2013 14 Revision 1.0 Micrel, Inc. MIC4604 Figure 13. Type I Inverter Topology As shown in Figure 13, Type I is a dual-stage topology where line voltage is converted to DC through a transformer to charge the storage batteries. When a power failure is detected, the stored DC energy is converted to AC through another transformer to drive the AC loads connected to the inverter output. This method is simplest to design but tends to be bulky and expensive because it uses two transformers. • Use a ground plane to minimize parasitic inductance and impedance of the return paths. The MIC4604 is capable of greater than 1A peak currents and any impedance between the MIC4604, the decoupling capacitors, and the external MOSFET will degrade the performance of the driver. • Trace out the high di/dt and dv/dt paths, as shown in Figure 14 and Figure 15, and minimize etch length and loop area for these connections. Minimizing these parameters decreases the parasitic inductance and the radiated EMI generated by fast rise and fall times. A typical layout of a synchronous Buck converter power stage (Figure 14) is shown in Figure 15 . Type II is a single-stage topology that uses only one transformer to charge the bank of batteries to store the energy. During a power outage, the same transformer is used to power the line voltage. The Type II switches at a higher frequency compared to the Type I topology to maintain a small transformer size. Both types require a half bridge or full bridge topology to boost the DC to AC. This application can use two MIC4604s. The 85V operating voltage offers enough margin to address all of the available banks of batteries commonly used in inverter applications. The 85V operating voltage allows designers to increase the bank of batteries up to 72V, if desired. The MIC4604 can sink as much as 1A, which is enough current to overcome the MOSFET’s input capacitance and switch the MOSFET up to 50kHz. This makes the MIC4604 an ideal solution for inverter applications. Figure 14. Synchronous Buck Converter Power Stage The high-side MOSFET drain connects to the input supply voltage (drain) and the source connects to the switching node. The low-side MOSFET drain connects to the switching node and its source is connected to ground. The buck converter output inductor (not shown) connects to the switching node. The high-side drive trace, HO, is routed on top of its return trace, HS, to minimize loop area and parasitic inductance. The low-side drive trace LO is routed over the ground plane to minimize the impedance of that current path. The decoupling capacitors, CB and CVDD, are placed to minimize etch length between the capacitors and their respective pins. This close placement is necessary to efficiently charge capacitor CB when the HS node is low. All traces are 0.025in wide or greater to reduce impedance. CIN is used to decouple the high current path through the MOSFETs. As with all half bridge and full bridge topologies, cross conduction is a concern to inverter manufactures because it can cause catastrophic failure. This can be remedied by adding the appropriate dead time between transitioning from the high-side MOSFET to the low-side MOSFET and vice versa. Layout Guidelines Use the following layout guidelines for optimum circuit performance: • Place the VDD and HB bypass capacitors close to the supply and ground pins. It is critical that the etch length between the high side decoupling capacitor (CB) and the HB and HS pins be minimized to reduce lead inductance. June 25, 2013 15 Revision 1.0 Micrel, Inc. MIC4604 Top Side Bottom Side Figure 15. Typical Layout of a Synchronous Buck Converter Power Stage June 25, 2013 16 Revision 1.0 Micrel, Inc. MIC4604 Package Information and Recommended Land Pattern(7) 8-Pin SOIC (M) Note: 7. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. June 25, 2013 17 Revision 1.0 Micrel, Inc. MIC4604 Package Information and Recommended Land Pattern (Continued)(7) 2.5mm × 2.5mm 10-Pin TDFN (MT) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2013 Micrel, Incorporated. June 25, 2013 18 Revision 1.0