PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -1- IR3897 DESCRIPTION FEATURES Single 5V to 21V application Wide Input Voltage Range from 1.0V to 21V with external Vcc Output Voltage Range: 0.5V to 0.86× Vin Enhanced Line/Load Regulation with Feed‐Forward Programmable Switching Frequency up to 1.5MHz Internal Digital Soft‐Start/Soft‐Stop Enable input with Voltage Monitoring Capability Thermally Compensated Current Limit with robust hiccup mode over current protection Smart Internal LDO to improve light load and full load efficiency External Synchronization with Smooth Clocking Enhanced Pre‐Bias Start‐Up Precision Reference Voltage (0.5V+/‐0.5%) with margining capability Vp for Tracking Applications (Source/Sink Capability +/‐4A) The IR3897 SupIRBuckTM is an easy‐to‐use, fully integrated and highly efficient DC/DC regulator. The onboard PWM controller and MOSFETs make IR3897 a space‐efficient solution, providing accurate power delivery. IR3897 is a versatile regulator which offers programmability of switching frequency and internal current limit while operates in wide input and output voltage range. The switching frequency is programmable from 300kHz to 1.5MHz for an optimum solution. It also features important protection functions, such as Pre‐Bias startup, thermally compensated current limit, over voltage protection and thermal shutdown to give required system level security in the event of fault conditions. APPLICATIONS Netcom Applications Integrated MOSFET drivers and Bootstrap Diode Embedded Telecom Systems Thermal Shut Down Server Applications Programmable Power Good Output with tracking capability Storage Applications Monotonic Start‐Up Distributed Point of Load Power Architectures Operating temp: ‐40 C < Tj < 125 C o o Small Size: 4mm x 5mm PQFN Lead‐free, Halogen‐free and RoHS Compliant Efficiency (%) BASIC APPLICATION 97 95 93 91 89 87 85 83 81 79 77 75 73 12Vin,Internal bias,Frequency 600KHz 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 Load Current (A) 1.2Vout Figure 1: IR3897 Basic Application Circuit 1 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 3.3Vout Figure 2:IR3897 Efficiency 3.6 4 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -2- IR3897 ORDERING INFORMATION IR3897 ― Package M Tape & Reel Qty 750 Part Number IR3897MTR1PBF M 4000 IR3897MTRPBF PBF – Lead Free TR/TR1 – Tape and Reel M – Package Type PIN DIAGRAM 4mm x 5mm POWER QFN TOP VIEW JA 32o C / W J - PCB 2o C / W 2 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -3- BLOCK DIAGRAM Figure 3: IR3897 Simplified Block Diagram 3 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -4- IR3897 PIN DESCRIPTIONS PIN # PIN NAME PIN DESCRIPTION 1 Fb Inverting input to the error amplifier. This pin is connected directly to the output of the regulator via resistor divider to set the output voltage and provide feedback to the error amplifier. 2 Vref 3 Comp 4 Gnd Internal reference voltage , it can be used for margining operation also. In normal and sequencing mode operation, a 100pF ceramic capacitor is recommended between this pin and Gnd. In tracking mode operation, Vref should be tied to Gnd. Output of error amplifier. An external resistor and capacitor network is typically connected from this pin to Fb to provide loop compensation. Signal ground for internal reference and control circuitry. 5 Rt/Sync Multi‐function pin to set switching frequency. Use an external resistor from this pin to Gnd to set the free‐running switching frequency. Or use an external clock signal to connect to this pin through a diode, the device’s switching frequency is synchronized with the external clock. 6 S_Ctrl Soft start/stop control. A high logic input enables the device to go into the internal soft start; a low logic input enables the output soft discharged. Pull this pin high if this function is not used. 7 PGood Power Good status pin. Output is open drain. Connect a pull up resistor (49.9k) from this pin to the voltage lower than or equal to the Vcc. 8 Vsns Sense pin for over‐voltage protection and PGood. It is optional to tie this pin to FB pin directly instead of using a resistor divider from Vout. 9 Vin Input voltage for Internal LDO. A 1.0µF capacitor should be connected between this pin and PGnd. If external supply is connected to Vcc/LDO_out pin, this pin should be shorted to Vcc/LDO_out pin. 10 Vcc/LDO_Out Input Bias for external Vcc Voltage/ output of internal LDO. Place a minimum 2.2µF cap from this pin to PGnd. 11 PGnd Power Ground. This pin serves as a separated ground for the MOSFET drivers and should be connected to the system’s power ground plane. 12 SW 13 PVin Input voltage for power stage. 14 Boot Supply voltage for high side driver, a 100nF capacitor should be connected between this pin and SW pin. 15 Enable Enable pin to turn on and off the device, if this pin is connected to PVin pin through a resistor divider, input voltage UVLO can be implemented. 16 Vp Input to error amplifier for tracking purposes. In the normal operation, it is left floating and no external capacitor is required. In the sequencing or the tracking mode operation, an external signal can be applied as the reference. 17 Gnd Signal ground for internal reference and control circuitry. 4 Switch node. This pin is connected to the output inductor. JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -5- IR3897 ABSOLUTE MAXIMUM RATINGS Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not implied. PVin, Vin ‐0.3V to 25V Vcc/LDO_Out ‐0.3V to 8V (Note 2) Boot ‐0.3V to 33V SW ‐0.3V to 25V (DC), ‐4V to 25V (AC, 100ns) Boot to SW ‐0.3V to VCC + 0.3V (Note 1) S_Ctrl, PGood ‐0.3V to VCC + 0.3V (Note 1) Other Input/Output Pins ‐0.3V to +3.9V PGnd to Gnd ‐0.3V to +0.3V Storage Temperature Range ‐55°C to 150°C Junction Temperature Range ‐40°C to 150°C (Note 2) ESD Classification (HBM JESD22‐A114) 2kV Moisture Sensitivity Level JEDEC Level 2@260°C Note 1: Must not exceed 8V Note 2: Vcc must not exceed 7.5V for Junction Temperature between ‐10°C and ‐40°C 5 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -6- IR3897 ELECTRICAL SPECIFICATIONS RECOMMENDED OPERATING CONDITIONS FOR RELIABLE OPERATION WITH MARGIN UNITS SYMBOL MIN MAX Input Voltage Range* PVin 1.0 21 Input Voltage Range** Vin 5 21 Supply Voltage Range*** VCC 4.5 7.5 Supply Voltage Range Boot to SW 4.5 7.5 Output Voltage Range VO 0.5 0.86xVin Output Current Range IO 0 ±4 A Switching Frequency FS 300 1500 kHz Operating Junction Temperature TJ ‐40 125 °C V *Maximum SW voltage should not exceed 25V. ** For internally biased single rail operation. When Vin drops below 6.8V, the internal LDO enters dropout. Please refer to Smart LDO section and Over Current Protection for detailed application information. *** Vcc/LDO_Out can be connected to an external regulated supply. If so, the Vin input should be connected to Vcc/LDO_Out pin. ELECTRICAL CHARACTERISTICS Unless otherwise specified, these specifications apply over, 6.8V < Vin = PVin < 21V, Vref = 0.5V in 0°C < TJ < 125°C. Typical values are specified at Ta = 25°C. PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNIT PLOSS 17.5 22.5 17.9 23.3 260 470 mV 1 µA 30 ns 100 µA Power Stage Top Switch Rds(on)_Top Vin = 12V, VO = 1.2V, IO = 4A, Fs = 600kHz, L = 1.5uH, Vcc = 6.4V, Note 4 VBoot‐Vsw=6.4V,IO= 4A,Tj = 25°C Bottom Switch Rds(on)_Bot Vcc = 6.4V, IO = 4A, Tj = 25°C Power Losses Bootstrap Diode Forward Voltage SW Leakage Current Dead Band Time I(Boot) = 10mA ISW Tdb SW = 0V, Enable = 0V SW = 0V, Enable = high, Vp = 0V Note 4 Iin(Standby) EN = Low, No Switching Iin(Dyn) EN = High, Fs = 600kHz, Vin = PVin = 21V 0.5 180 5 10 W mΩ Supply Current VIN Supply Current (standby) VIN Supply Current (dynamic) 9.5 12.5 6.4 6.7 mA Vcc/ LDO_Out Vcc Output Voltage LDO Dropout Voltage Vcc_drop Short Circuit Current Ishort 6 Vin(min) = 6.8V, Icc = 0‐30mA, Cload = 2.2uF, DCM = 0 6.0 Vin(min) = 6.8V, Icc = 0‐30mA, Cload = 2.2uF, DCM = 1 4.0 V 4.4 Icc=30mA,Cload=2.2uF JANUARY 18, 2013 |DATA SHEET | Rev 3.5 4.8 0.7 70 V mA PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -7PARAMETER SYMBOL CONDITIONS Zero‐crossing Comparator Delay Tdly_zc Note 4 Zero‐crossing Comparator Offset Vos_zc Note 4 MIN IR3897 TYP MAX 256/Fs ‐4 0 UNIT s 4 mV Oscillator Rt Voltage Vrt Frequency Range Fs Ramp Amplitude Vramp 1.0 V Rt = 80.6K 270 300 330 Rt = 39.2K 540 600 660 Rt = 15.0K 1350 1500 1650 Vin = 7.0V, Vin slew rate max = 1V/µs, Note 4 1.05 Vin = 12V, Vin slew rate max = 1V/µs, Note 4 1.80 Vin = 21V, Vin slew rate max = 1V/µs, Note 4 3.15 Vin=Vcc=5V, For external Vcc operation, Note 4 0.75 0.16 Ramp Offset Ramp(os) Note 4 Min Pulse Width Tmin(ctrl) Note 4 Max Duty Cycle Dmax Fixed Off Time Toff Fs = 300kHz, PVin = Vin = 12V Vp‐p V 60 86 Note 4 Fsync 270 Sync Pulse Duration Tsync 100 Sync Level Threshold High 3 ns % 200 Sync Frequency Range kHz 250 ns 1650 kHz 200 Low ns 0.6 V Error Amplifier Input Offset Voltage Vos_Vref Vos_Vp VFb – Vref, Vref = 0.5V ‐1.5 +1.5 VFb – Vp, Vp = 0.5V ‐1.5 +1.5 % Input Bias Current IFb(E/A) ‐1 +1 Input Bias Current IVp(E/A) 0 +4 Sink Current Isink(E/A) 0.4 0.85 1.2 mA Isource(E/A) 4 7.5 11 mA Source Current Slew Rate Gain‐Bandwidth Product DC Gain µA SR Note 4 7 12 20 V/µs GBWP Note 4 20 30 40 MHz Gain Note 4 100 110 120 dB 1.7 2.0 2.3 V 100 mV 1.2 V Maximum output Voltage Vmax(E/A) Minimum output Voltage Vmin(E/A) Common Mode input Voltage 0 Reference Voltage Feedback Voltage Accuracy Vfb Vref and Vp pin floating 0°C < Tj < +70°C 7 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 0.5 ‐0.5 V +0.5 % PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -8PARAMETER SYMBOL CONDITIONS ‐40°C < Tj < +125°C, Note 3 MIN IR3897 TYP MAX ‐1.0 +1.0 0.4 1.2 Vref Margining Voltage Vref_marg Sink Current Isink_Vref Vref = 0.6V 12.7 16.0 19.3 Source Current Isrc_Vref Vref = 0.4V 12.7 16.0 19.3 Vref Comparator Threshold Vref_disable Vref pin connected externally 0.15 Vref_enable 0.4 Soft Start Ramp Rate Ramp(SS_start) 0.16 0.2 0.24 Soft Stop Ramp Rate Ramp(SS_stop) ‐0.24 ‐0.2 ‐0.16 High 2.4 UNIT V µA V Soft Start/Stop S_Ctrl Threshold Low 0.6 mV/µs V Power Good PGood Turn on Threshold PGood Lower Turn off Threshold VPG(on) VPG(lower) Vsns Rising, 0.4V < Vref < 1.2V 85 90 95 % Vref Vsns Rising, Vref < 0.1V 85 90 95 % Vp Vsns Falling, 0.4V < Vref < 1.2V 85 85 95 % Vref Vsns Falling, Vref < 0.1V 80 85 90 % Vp PGood Turn on Delay VPG(on)_Dly Vsns Rising,see VPG(on) PGood Upper Turn off Threshold VPG(upper) Vsns Rising, 0.4V < Vref < 1.2V 115 120 125 % Vref Vsns Rising, Vref < 0.1V 115 120 125 % Vp 1 2 3.5 µs 0.5 V PGood Comparator Delay VPG(comp)_ Dly Vsns < VPG(lower) or Vsns > VPG(upper) PGood Voltage Low PG(voltage) IPgood = ‐5mA 1.28 Tracker Comparator Upper Threshold VPG(tracker_ upper) Vp Rising, Vref < 0.1V 0.4 Tracker Comparator Lower Threshold VPG(tracker_ lower) Vp Falling, Vref < 0.1V 0.3 Tracker Comparator Delay Tdelay(tracker) Vp Rising, Vref < 0.1V,see VPG(tracker_upper) 1.28 ms V ms Under‐Voltage Lockout Vcc‐Start Threshold VCC_UVLO_Start Vcc Rising Trip Level 4.0 4.2 4.4 Vcc‐Stop Threshold VCC_UVLO_Stop Vcc Falling Trip Level 3.7 3.9 4.1 Enable‐Start‐Threshold Enable_UVLO_Start Supply ramping up 1.14 1.2 1.26 Enable‐Stop‐Threshold Enable_UVLO_Stop Supply ramping down 0.95 1 1.05 Enable Leakage Current Ien Enable = 3.3V V V 1 µA Over‐Voltage Protection OVP Trip Threshold OVP Comparator Dely 8 OVP_Vth Vsns Rising, 0.45V < Vref < 1.2V 115 120 125 % Vref Vsns Rising, Vref < 0.1V 115 120 125 % Vp 1 2 3.5 µs OVP_Tdly JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator -9PARAMETER SYMBOL CONDITIONS IR3897 MIN TYP MAX UNIT 5.8 7.0 8.2 A Over‐Current Protection Current Limit ILIMIT Hiccup Blanking Time Tj = 25°C, Vcc = 6.4V Tblk_Hiccup Note 4 20.48 Ttsd Note 4 145 Ttsd_hys Note 4 20 ms Over‐Temperature Protection Thermal Shutdown Threshold Hysteresis Note 3: Cold temperature performance is guaranteed via correlation using statistical quality control. Not tested in production. Note 4: Guaranteed by design but not tested in production. 9 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 °C PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 10 - IR3897 TYPICAL EFFICIENCY AND POWER LOSS CURVES PVin = 12V, Vcc = Internal LDO (4.4V/6.4V), Io = 0A‐4A, Fs = 600KHz, Room Temperature, No Air Flow. Note that the efficiency and power loss curves include the losses of IR3897, the inductor losses and the losses of the input and output capacitors.The table below shows the inductors used for each of the output voltages in the efficiency measurement. VOUT (V) 1.0 LOUT (µH) P/N DCR (mΩ) 1.5 PCMB065T-1R5MS(Cyntec) 6.7 1.2 1.5 PCMB065T-1R5MS(Cyntec) 6.7 1.8 2.2 7443340220(Wurth Elektronik) 4.4 3.3 3.3 7443340330(Wurth Elektronik) 6.5 5 3.3 7443340330(Wurth Elektronik) 6.5 97 95 93 91 Efficiency (%) 89 87 85 83 81 79 77 75 73 71 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 Load Current (A) 1.0V 1.2V 1.8V 3.3V 5.0V 0.9 0.8 Power Dissipation(W) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 Load Current (A) 1.0V 10 1.2V JANUARY 18, 2013 |DATA SHEET | Rev 3.5 1.8V 3.3V 5.0V 3.6 4 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 11 - IR3897 TYPICAL EFFICIENCY AND POWER LOSS CURVES PVin = 12V, Vcc = External 5V, Io = 0A‐4A, Fs = 600KHz, Room Temperature, No Air Flow. Note that the efficiency and power loss curves include the losses of IR3897, the inductor losses and the losses of the input and output capacitors. The table below shows the inductors used for each of the output voltages in the efficiency measurement. VOUT (V) 1.0 LOUT (µH) P/N DCR (mΩ) 1.5 PCMB065T-1R5MS (Cyntec) 6.7 1.2 1.5 PCMB065T-1R5MS (Cyntec) 6.7 1.8 2.2 7443340220 (Wurth Elektronik) 4.4 3.3 3.3 7443340330 (Wurth Elektronik) 6.5 5 3.3 7443340330 (Wurth Elektronik) 6.5 98 96 94 Efficiency (%) 92 90 88 86 84 82 80 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 3.2 3.6 4 Load Current (A) 1.0V 1.2V 1.8V 3.3V 5.0V 0.9 0.8 Power Dissiation(W) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.4 0.8 1.2 1.6 2 2.4 2.8 Load Current (A) 1.0V 11 1.2V JANUARY 18, 2013 |DATA SHEET | Rev 3.5 1.8V 3.3V 5.0V PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 12 - IR3897 TYPICAL EFFICIENCY AND POWER LOSS CURVES PVin = 5.0V, Vcc = 5.0V, Io = 0A‐4A, Fs = 600KHz, Room Temperature, No Air Flow. Note that the efficiency and power loss curves include the losses of IR3897, the inductor losses and the losses of the input and output capacitors. The table below shows the inductors used for each of the output voltages in the efficiency measurement. VOUT (V) 1.0 LOUT (µH) P/N DCR (mΩ) 1 SPM6550T-1R0M (TDK) 4.7 1.2 1 SPM6550T-1R0M (TDK) 4.7 1.8 1.5 PCMB065T-1R5MS (Cyntec) 6.7 3.3 1.5 PCMB065T-1R5MS (Cyntec) 6.7 97 95 Efficiency (%) 93 91 89 87 85 83 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 3.2 3.6 4 Load Current (A) 1.0V 1.2V 1.8V 2 2.4 3.3V 0.7 Power Dissipation(W) 0.6 0.5 0.4 0.3 0.2 0.1 0 0.4 0.8 1.2 1.6 2.8 Load Current (A) 1.0V 12 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 1.2V 1.8V 3.3V PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 13 - IR3897 THERMAL DERATING CURVES Measurement done on Evaluation board of IRDC3897.PCB is 4 layer board with 2 oz Copper, FR4 material, size 2.23"x2" PVin = 12V, Vout=1.2V, Vcc = Internal LDO (6.4V), Fs = 600kHz 5.6 5.4 Iout(A) 5.2 5 4.8 4.6 Lout-1.5uH,6.7mΩ(Cyntec PCMB065T-1R5MS) 4.4 25 30 35 40 45 50 55 60 65 70 75 80 85 TAmb 0 LFM PVin = 12V, Vout=3.3V, Vcc = Internal LDO (6.4V), Fs = 600kHz 5.6 5.4 Iout(A) 5.2 5 4.8 4.6 Lout-3.3uH,6.5mΩ(Wurth Elektronik 7443340330) 4.4 25 30 35 40 45 50 55 60 65 70 75 80 85 TAmb 0 LFM Note: International Rectifier Corporation specifies current rating of SupIRBuck devices conservatively. The continuous current load capability might be higher than the rating of the device if input voltage is 12V typical and switching frequency is below 750 kHz.The above derating curves are generated at 12V input ,600kHz with 0-200LFM air flow and ambient temperature up to 85°C.Detailed thermal derating information can be found in the Application Note AN-1174 “Thermal Derating of DC DC Convertors using IR3899/98/97”. However, the maximum current is limited by the internal current limit and designers need to consider enough guard bands between load current and minimum current limit to guarantee that the device does not trip at steady state condition. 13 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 14 - RDSON OF MOSFETS OVER TEMPERATURE AT Vcc=6.4V RDSON OF MOSFETS OVER TEMPERATURE AT Vcc=5.0V 14 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 15 - TYPICAL OPERATING CHARACTERISTICS (‐40°C to +125°C) 15 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 16 - IR3897 TYPICAL OPERATING CHARACTERISTICS (‐40°C to +125°C) Internal LDO is in regulation With an External 5V Vcc Voltage 16 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 Internal LDO is in dropout mode PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 17 - TYPICAL OPERATING CHARACTERISTICS (‐40°C to +125°C) 17 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 18 - THEORY OF OPERATION DESCRIPTION The IR3897 uses a PWM voltage mode control scheme with external compensation to provide good noise immunity and maximum flexibility in selecting inductor values and capacitor types. The switching frequency is programmable from 300kHz to 1.5MHz and provides the capability of optimizing the design in terms of size and performance. IR3897 provides precisely regulated output voltage programmed via two external resistors from 0.5V to 0.86*Vin. The IR3897 operates with an internal bias supply (LDO) which is connected to the Vcc/LDO_out pin. This allows operation with single supply. The bias voltage is variable according to load condition. If the output load current is less than half of the peak‐to‐peak inductor current, a lower bias voltage, 4.4V, is used as the internal gate drive voltage; otherwise, a higher voltage, 6.4V, is used. This feature helps the converter to reduce power losses. The device can also be operated with an external supply from 4.5 to 7.5V, allowing an extended operating input voltage (PVin) range from 1.0V to 16V. For using the internal LDO supply, the Vin pin should be connected to PVin pin. If an external supply is used, it should be connected to Vcc/LDO_Out pin and the Vin pin should be shorted to Vcc/LDO_Out pin. The device utilizes the on‐resistance of the low side MOSFET (synchronous Mosfet) for the over current protection. This method enhances the converter’s efficiency and reduces cost by eliminating the need for external current sense resistor. IR3897 The POR (Power On Ready) signal is generated when all these signals reach the valid logic level (see system block diagram). When the POR is asserted the soft start sequence starts (see soft start section). ENABLE The Enable features another level of flexibility for start up. The Enable has precise threshold which is internally monitored by Under‐Voltage Lockout (UVLO) circuit. Therefore, the IR3897 will turn on only when the voltage at the Enable pin exceeds this threshold, typically, 1.2V. If the input to the Enable pin is derived from the bus voltage by a suitably programmed resistive divider, it can be ensured that the IR3897 does not turn on until the bus voltage reaches the desired level (Fig. 4). Only after the bus voltage reaches or exceeds this level and voltage at the Enable pin exceeds its threshold, IR3897 will be enabled. Therefore, in addition to being a logic input pin to enable the IR3897, the Enable feature, with its precise threshold, also allows the user to implement an Under‐Voltage Lockout for the bus voltage (PVin). This is desirable particularly for high output voltage applications, where we might want the IR3897 to be disabled at least until PVIN exceeds the desired output voltage level. Pvin (12V) 10. 2 V Vcc Enable Threshold= 1.2V Enable Intl_SS IR3897 includes two low Rds(on) MOSFETs using IR’s HEXFET technology. These are specifically designed for high efficiency applications. UNDER‐VOLTAGE LOCKOUT AND POR The under‐voltage lockout circuit monitors the voltage of Vcc/LDO_Out pin and the Enable input. It assures that the MOSFET driver outputs remain in the off state whenever either of these two signals drop below the set thresholds. Normal operation resumes once Vcc/LDO_Out and Enable rise above their thresholds. 18 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 Figure 4: Normal Start up, device turns on when the bus voltage reaches 10.2V A resistor divider is used at EN pin from PVin to turn on the device at 10.2V. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 19 Pvin(12V) IR3897 Figure 5a shows the recommended start‐up sequence for the normal (non‐tracking, non‐sequencing) operation of IR3897, when Enable is used as a logic input. Figure 5b shows the recommended startup sequence for sequenced operation of IR3897 with Enable used as logic input. Figure 5c shows the recommended startup sequence for tracking operation of IR3897 with Enable used as logic input. Vcc Vp>1V Enable >1.2V Intl_SS Figure 5a: Recommended startup for Normal operation In normal and sequencing mode operation, Vref is left floating. A 100pF ceramic capacitor is recommended between this pin and Gnd. In tracking mode operation, Vref should be tied to Gnd. It is recommended to apply the Enable signal after the VCC voltage has been established. If the Enable signal is present before VCC, a 50kΩ resistor can be used in series with the Enable pin to limit the current flowing into the Enable pin. Pvin (12V) PRE‐BIAS STARTUP IR3897 is able to start up into pre‐charged output, which prevents oscillation and disturbances of the output voltage. Vcc Enable > 1. 2 V Intl_SS Vp Figure 5b: Recommended startup for sequencing operation (ratiometric or simultaneous) The output starts in asynchronous fashion and keeps the synchronous MOSFET (Sync FET) off until the first gate signal for control MOSFET (Ctrl FET) is generated. Figure 6a shows a typical Pre‐Bias condition at start up. The sync FET always starts with a narrow pulse width (12.5% of a switching period) and gradually increases its duty cycle with a step of 12.5% until it reaches the steady state value. The number of these startup pulses for each step is 16 and it’s internally programmed. Figure 6b shows the series of 16x8 startup pulses. [V] Vo Pre-Bias Voltage [Time] Figure 6a: Pre‐Bias startup HDRv ... 12.5% ... LDRv Figure 5c: Recommended startup for memory tracking operation (VTT‐DDR4) 16 ... ... 25% ... 16 ... 87.5% ... ... ... ... Figure 6b: Pre‐Bias startup pulses 19 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 End of PB PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 20 - IR3897 TABLE 1: SWITCHING FREQUENCY (FS) VS. EXTERNAL RESISTOR (RT) SOFT‐START IR3897 has an internal digital soft‐start to control the output voltage rise and to limit the current surge at the start‐up. To ensure correct start‐up, the soft‐start sequence initiates when the Enable and Vcc rise above their UVLO thresholds and generate the Power On Ready (POR) signal. The internal soft‐start (Intl_SS) signal linearly rises with the rate of 0.2mV/µs from 0V to 1.5V. Figure 7 shows the waveforms during soft start (also refer to Fig. 20). The normal Vout start‐up time is fixed, and is equal to: Tstart 0.65V-0.15V 2.5ms(1) 0.2mV/s During the soft start the over‐current protection (OCP) and over‐voltage protection (OVP) is enabled to protect the device for any short circuit or over voltage condition. Rt (KΩ) 80.6 60.4 48.7 39.2 34 29.4 26.1 23.2 21 19.1 17.4 16.2 15 Freq (KHz) 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 OVER CURRENT PROTECTION POR 3.0V 1.5V 0.65V 0.15V Intl_SS Vout t1 t 2 t3 Figure 7: Theoretical operation waveforms during soft‐start (non tracking / non sequencing) OPERATING FREQUENCY The switching frequency can be programmed between 300kHz – 1500kHz by connecting an external resistor from Rt pin to Gnd. Table 1 tabulates the oscillator frequency versus Rt. SHUTDOWN IR3897 can be shutdown by pulling the Enable pin below its 1.0V threshold. This will tri‐state both the high side and the low side driver. 20 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 The over current (OC) protection is performed by sensing current through the RDS(on) of the Synchronous Mosfet. This method enhances the converter’s efficiency, reduces cost by eliminating a current sense resistor and any layout releated noise issues. The current limit is pre‐set internally and is compensated according to the IC temperature. So at different ambient temperature, the over‐current trip threshold remains almost constant. Note that the over current limit is a function of the Vcc voltage. Refer to the typical performance curves of the OCP current limit with the internal LDO and the external Vcc voltage. Detailed operation of OCP is explained as follows. Over Current Protection circuit senses the inductor current flowing through the Synchronous Mosfet closer to the valley point. OCP circuit samples this current for 40nsec typically after the rising edge of the PWM set pulse which has a width of 12.5% of the switching period.The PWM pulse starts at the falling edge of the PWM set pulse.This makes valley current sense more robust as current is sensed close to the bottom of the inductor downward slope where transient and switching noise are lower and helps to prevent false tripping due to noise and transient. An OC condition is detected if the load current exceeds the threshold, the converter enters into hiccup mode. PGood will go low and the internal soft start signal will be pulled low. The converter goes into hiccup mode with a 20.48ms (typ.) delay as shown in Figure 8. The convertor stays in this mode until the over load or short circuit is removed. The actual DC output current limit point will be greater PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 21 than the valley point by an amount equal to approximately half of peak to peak inductor ripple current. The current limit point will be a function of the inductor value, input, output voltage and the frequency of operation. IOCP ILIMIT i 2 (2) IOCP= DC current limit hiccup point ILIMIT= Current limit Valley Point Δi=Inductor ripple current IR3897 When an external clock is applied to Rt/Sync pin after the converter runs in steady state with its free‐running frequency, a transition from the free‐running frequency to the external clock frequency will happen. This transition is to gradually make the actual switching frequency equal to the external clock frequency, no matter which one is higher. On the contrary, when the external clock signal is removed from Rt/Sync pin, the switching frequency is also changed to free‐running gradually. In order to minimize the impact from these transitions to output voltage, a diode is recommended to add between the external clock and Rt/Sync pin, as shown in Figure 9a. Figure 9b shows the timing diagram of hese transitions. IR3897 Rt/Sync Gnd Figure 8: Timing Diagram for Current Limit and Hiccup Figure 9a: Configuration of External Synchronization THERMAL SHUTDOWN Temperature sensing is provided inside IR3897. The trip threshold is typically set to 145oC. When trip threshold is exceeded, thermal shutdown turns off both MOSFETs and resets the internal soft start. Automatic restart is initiated when the sensed temperature drops within the operating range. There is a 20oC hysteresis in the thermal shutdown threshold. EXTERNAL SYNCHRONIZATION IR3897 incorporates an internal phase lock loop (PLL) circuit which enables synchronization of the internal oscillator to an external clock. This function is important to avoid sub‐harmonic oscillations due to beat frequency for embedded systems when multiple point‐of‐load (POL) regulators are used. A multi‐function pin, Rt/Sync, is used to connect the external clock. If the external clock is present before the converter turns on, Rt/Sync pin can be connected to the external clock signal solely and no other resistor is needed. If the external clock is applied after the converter turns on, or the converter switching frequency needs to toggle between the external clock frequency and the internal free‐running frequency, an external resistor from Rt/Sync pin to Gnd is required to set the free‐running frequency. 21 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 Figure 9: Timing Diagram for Synchronization to the external clock (Fs1>Fs2 or Fs1<Fs2) An internal circuit is used to change the PWM ramp slope according to the clock frequency applied on Rt/Sync pin. Even though the frequency of the external synchronization clock can vary in a wide range, the PLL circuit will make sure that the ramp amplitude is kept constant, requiring no adjustment of the loop compensation. Vin variation also affects the ramp amplitude, which will be discussed separately in Feed‐Forward section. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 22 FEED‐FORWARD Feed‐Forward (F.F.) is an important feature, because it can keep the converter stable and preserve its load transient performance when Vin varies in a large range. In IR3897, F.F. function is enabled when Vin pin is connected to PVin pin. In this case, the internal low dropout (LDO) regulator is used. The PWM ramp amplitude (Vramp) is proportionally changed with Vin to maintain Vin/Vramp almost constant throughout Vin variation range (as shown in Fig. 10). Thus, the control loop bandwidth and phase margin can be maintained constant. Feed‐forward function can also minimize impact on output voltage from fast Vin change. The maximum Vin slew rate is within 1V/µs. If an external bias voltage is used as Vcc, Vin pin should be connected to Vcc/LDO_Out pin instead of PVin pin. Then the F.F. function is disabled. A re‐calculation of control loop parameters is needed for re‐compensation. IR3897 chattering. Figure 11a shows the timing diagram. Whenever device turns on, LDO always starts with 6.4V, then goes to 4.4V/6.4V depending upon the load condition. For internally biased single rail operation, Vin pin should be connected to PVin pin, as shown in Figure 11b. If external bias voltage is used, Vin pin should be connected to Vcc/LDO_Out pin, as shown in Figure 11c. ... IL ... ... 0 ... 256/Fs Vcc/ LDO 6.4V 4.4V 6.4V 0 Figure 11a: Time Diagram for Smart LDO Vin Vin PVin IR3897 VCC/ LDO_OUT PGnd Figure 10: Timing Diagram for Feed‐Forward (F.F.) Function SMART LOW DROPOUT REGULATOR (LDO) Figure 11b: Internally Biased Single Rail Operation IR3897 has an integrated low dropout (LDO) regulator which can provide gate drive voltage for both drivers. In order to improve overall efficiency over the whole load range, LDO voltage is set to 6.4V (typ.) at mid‐ or heavy load condition to reduce Rds(on) and thus MOSFET conduction loss; and it is reduced to 4.4 (typ.) at light load condition to reduce gate drive loss. The smart LDO can select its output voltage according to the load condition by sensing switch node (SW) voltage. At light load condition when part of the inductor current flows in the reverse direction (DCM=1), VSW > 0 on LDrv falling edge in a switching cycle. If this case happens for consecutive 256 switching cycles, the smart LDO reduces its output to 4.4. If in any one of the 256 cycles, Vsw < 0 on LDrv falling edge, the counter is reset and LDO voltage doesn’t change. On the other hand, if Vsw < 0 on LDrv falling edge (DCM=0), LDO output is increased to 6.4V. A hysteresis band is added to Vsw comparison to avoid 22 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 Figure 11c: Use External Bias Voltage When the Vin voltage is below 6.8V, the internal LDO enters the dropout mode at medium and heavy load. The dropout voltage increases with the switching frequency. Figure 11d shows the LDO voltage for 600 kHz and 1500 kHz switching frequency respectively. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 23 - IR3897 regulated with Vref.The final Vp voltage after sequencing startup should between 0.7V ~ 3.3V. Figure 11d: LDO_Out Voltage in dropout mode OUTPUT VOLTAGE TRACKING AND SEQUENCING IR3897 can accommodate user programmable tracking and/or sequencing options using Vp, Vref, Enable, and Power Good pins. In the block diagram presented on page 3, the error‐amplifier (E/A) has been depicted with three positive inputs. Ideally, the input with the lowest voltage is used for regulating the output voltage and the other two inputs are ignored. In practice the voltage of the other two inputs should be about 200mV greater than the low‐voltage input so that their effects can completely be ignored. Vp is internally biased to 3.3V via a high impedance path. For normal operation, Vp and Vref is left floating (Vref should have a bypass capacitor). Therefore, in normal operating condition, after Enable goes high, the internal soft‐start (Intl_SS) ramps up the output voltage until Vfb (voltage of feedback/Fb pin) reaches about 0.5V. Then Vref takes over and the output voltage is regulated. Tracking‐mode operation is achieved by connecting Vref to GND. In tracking‐mode, Vfb always follows Vp, which means Vout is always proportional to Vp voltage (typical for DDR/VTT rail applications). The effective Vp variation range is 0V~1.2V. Fig. 5c illustrates the start‐up of VTT tracking for DDR4 application. Vp is proportional to VDDQ. After Vp is established, asserting Enable initiates the internal soft‐start. VTT, which is the output of POL, starts to ramp up and tracks Vp. In sequencing mode of operation (simultaneous or ratiometric), Vref is left floating and Vp is kept to ground level until Intl_SS signal reaches the final value. Then Vp is ramped up and Vfb follows Vp. When Vp>0.5V the error‐ amplifier switches to Vref and the output voltage is 23 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 5 V < Vin < 21 V Vref S_Ctrl EN Vin PVin Boot Vcc/LDO RE RF PGood PGood Vo2 (Salve) SW Vo1 (master) Vsns Vp RC Rt/ Sync Fb Gnd PGnd Comp RD Figure 12: Application Circuit for Simultaneous and Ratiometric Sequencing Tracking and sequencing operations can be implemented to be simultaneous or ratiometric (refer to Fig. 13 and 14). Figure 12 shows typical circuit configuration for sequencing operation. With this power‐up configuration, the voltage at the Vp pin of the slave reaches 0.5V before the Fb pin of the master. If RE/RF =RC/RD, simultaneous startup is achieved. That is, the output voltage of the slave follows that of the master until the voltage at the Vp pin of the slave reaches 0.5 V. After the voltage at the Vp pin of the slave exceeds 0.5V, the internal 0.5V reference of the slave dictates its output voltage. In reality the regulation gradually shifts from Vp to internal Vref. The circuit shown in Fig. 12 can also be used for simultaneous or ratiometric tracking operation if Vref of the slave is connected to GND. Table 2 summarizes the required conditions to achieve simultaneous/ratiometric tracking or sequencing operations. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 24 Vcc VREF Vref=0.5V Enable (slave) 1.2V Soft Start (slave) Vo1 (master) (a) Vo2 (slave) Vo1 (master) (b) IR3897 Vo2 (slave) Figure 13: Typical waveforms for sequencing mode of operation: (a) simultaneous, (b) ratiometric This pin reflects the internal reference voltage which is used by the error amplifier to set the output voltage. In most operating conditions this pin is only connected to an external bypass capacitor and it is left floating. A 100pF ceramic capacitor is recommended for the bypass capacitor. To keep stand by current to minimum, Vref is not allowed to come up until EN starts going high. In tracking mode this pin should be pulled to GND. For margining applications, an external voltage source is connected to Vref pin and overrides the internal reference voltage. The external voltage source should have a low internal resistance (<100Ω) and be able to source and sink more than 25µA POWER GOOD OUTPUT (TRACKING, SEQUENCING, VREF MARGINING) IR3897 continually monitors the output voltage via the sense pin (Vsns) voltage. The Vsns voltage is an input to the window comparator with upper and lower threshold of 0.6V and 0.45V respectively. PGood signal is high whenever Vsns voltage is within the PGood comparator window thresholds. The PGood pin is open drain and it needs to be externally pulled high. High state indicates that output is in regulation. Figure 14: Typical waveforms in tracking mode of operation: (a) simultaneous, (b) ratiometric TABLE 2: REQUIRED CONDITIONS FOR SIMULTANEOUS/RATIOMETRIC TRACKING AND SEQUENCING (FIG. 12) Operating Mode Normal (Non‐sequencing, Non‐tracking) Simultaneous Sequencing Ratiometric Sequencing Simultaneous Tracking Ratiometric Tracking 24 Vref (Slave) 0.5V (Floating) 0.5V 0.5V 0V 0V Vp Required Condition Floating ― Ramp up from 0V Ramp up from 0V Ramp up before En Ramp up before En RA/RB>RE/ RF=RC/RD RA/RB>RE/ RF>RC/RD RE/RF =RC/RD RE/RF >RC/RD JANUARY 18, 2013 |DATA SHEET | Rev 3.5 The threshold is set differently at different operating modes and the results of the comparison sets the PGood signal. Figures 15, 16, and 17 show the timing diagram of the PGood signal at different operating modes.Vsns signal is also used by OVP comparator for detecting output over voltage condition. Vref 0 0.5 V 1.2*Vref Vsns 0.85*Vp 0 0.9*Vp OVP Latch PGood 0 1.28ms 1.28ms Figure 15: Non‐sequence, Non‐tracking Startup and Vref Margin (Vp pin floating) PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 25 0.4V 0.3V Vp 0 1.2*Vp Vsns IR3897 18b. If either of the above conditions is not satisfied, OVP is disabled. Vsns voltage is set by the voltage divider connected to the output and it can be programmed externally. Figure 18c shows the timing diagram for OVP in non‐tracking mode. 0.9*Vp 0 PGood 0 1.28ms Figure 16: Vp Tracking (Vref =0V) Figure 18a: Activation of OVP in non‐tracking mode Figure 17: Vp Sequence and Vref Margin OVER‐VOLTAGE PROTECTION (OVP) OVP is achieved by comparing Vsns voltage to an OVP threshold voltage. In non‐tracking mode, OVP threshold voltage is 1.2×Vref; in tracking mode, it is set at 1.2×Vp. When Vsns exceeds the OVP threshold, an over voltage trip signal asserts after 2us (typ.) delay. Then the control FET is latched off immediately, PGood flags low. The sync FET remains on to discharge the output capacitor. When the Vsns voltage drops below the threshold, the sync FET turns off to prevent the complete depletion of the output capacitor. The control FET remains latched off until user cycle either Vcc or Enable. Figure 18b: Activation of OVP in tracking mode 1.2*Vref 1.15*Vref 0 0 0 OVP comparator becomes active only when the device is enabled. Furthermore, for OVP to be active Vref has to exceed 0.2V in non‐tracking mode, or Vp has to exceed the threshold in tracking‐mode, as illustrated in Fig 18a and Fig 0 Figure 18c: Timing Diagram for OVP in non‐tracking mode 25 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 26 - IR3897 SOFT START/SOFT‐STOP (S_CTRL) MINIMUM ON TIME CONSIDERATIONS Soft‐stop function can make output voltage discharge gradually. To enable this function, S_Ctrl is kept low first when EN goes high. Then S_Ctrl is pulled high to cross the logic level threshold (typ. 2V), the internal soft‐start ramp is initiated. So Vo follows Intl_SS to ramp up until it reaches its steady state. In soft‐stop process, S_Ctrl needs to be pulled low before EN goes low. After S_Ctrl goes below its threshold, a decreasing ramp is generated at Intl_SS with the same slope as in soft‐start ramp. Vo follows this ramp to discharge softly until shutdown completely. Figure 19 shows the timing diagram of S_Ctrl controlled soft‐start and soft‐stop. The minimum ON time is the shortest amount of time for Ctrl FET to be reliably turned on. This is very critical parameter for low duty cycle, high frequency applications. Conventional approach limits the pulse width to prevent noise, jitter and pulse skipping. This results to lower closed loop bandwidth. If the falling edge of Enable signal asserts before S_Ctrl falling edge, the converter is still turned off by Enable. Both gate drivers are turned off immediately and Vo discharges to zero. Figure 20 shows the timing diagram of Enable controlled soft‐start and soft‐stop. Soft stop feature ensures that Vout discharges and also regulates the current precisely to zero with no undershoot. IR has developed a proprietary scheme to improve and enhance minimum pulse width which utilizes the benefits of voltage mode control scheme with higher switching frequency, wider conversion ratio and higher closed loop bandwidth, the latter results in reduction of output capacitors. Any design or application using IR3897 must ensure operation with a pulse width that is higher than this minimum on‐time and preferably higher than 60 ns. This is necessary for the circuit to operate without jitter and pulse‐skipping, which can cause high inductor current ripple and high output voltage ripple. ton Vout D (3) Fs Vin Fs Enable In any application that uses IR3897, the following condition must be satisfied: 0 S_Ctrl ton (min) ton (4) 0 0.65V 0.65V Intl _SS 0.15V 0.15V ton (min) Vout (5) Vin Fs 0 Vin Fs Vout 0 Figure 19: Timing Diagram for S_Ctrl controlled Soft Start/Soft Stop Enable Vin Fs 1.2V 1.0V 0 0.65V Intl _SS 0.15V 0 Vout 0 Figure 20: Timing Diagram for Enable controlled Soft Start/Shutdown 26 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 ton (min) (6) The minimum output voltage is limited by the reference voltage and hence Vout(min) = 0.5 V. Therefore, for Vout(min) = 0.5 V, S_Ctrl 0 Vout Vout (min) Vin Fs t on (min) 0.5 V 8.33 V/uS 60 ns Therefore, at the maximum recommended input voltage 21V and minimum output voltage, the converter should be designed at a switching frequency that does not exceed 396 kHz. Conversely, for operation at the maximum recommended operating frequency (1.65 MHz) and minimum output voltage (0.5V). The input voltage (PVin) should not exceed 5.05V, otherwise pulse skipping will happen. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 27 MAXIMUM DUTY RATIO A certain off‐time is specified for IR3897. This provides an upper limit on the operating duty ratio at any given switching frequency. The off‐time remains at a relatively fixed ratio to switching period in low and mid frequency range, while in high frequency range this ratio increases, thus the lower the maximum duty ratio at which IR3897 can operate. Figure 21 shows a plot of the maximum duty ratio vs. the switching frequency with built in input voltage feed forward mechanism. Figure 21: Maximum duty cycle vs. switching frequency. 27 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 28 - DESIGN EXAMPLE The following example is a typical application for IR3897. The application circuit is shown in Fig.28. Vin =12 V ( 10% ) Vo =1.2 V Io = 4 A Ripple Voltage= 1% *Vo ΔVo = 5% *︵ Vo for 50% load transient ) Fs =600 kHz Enabling the IR3897 As explained earlier, the precise threshold of the Enable lends itself well to implementation of a UVLO for the Bus Voltage as shown in Fig. 22. IR3897 Output Voltage Programming Output voltage is programmed by reference voltage and external voltage divider. The Fb pin is the inverting input of the error amplifier, which is internally referenced to 0.5V. The divider ratio is set to provide 0.5V at the Fb pin when the output is at its desired value. The output voltage is defined by using the following equation: R Vo Vref 1 5 (9) R6 When an external resistor divider is connected to the output as shown in Fig. 23. Vref R6 R5 V V o ref (10) For the calculated values of R5 and R6, see feedback compensation section. Figure 22: Using Enable pin for UVLO implementation For a typical Enable threshold of VEN = 1.2 V Vin (min) * R2 R1 R2 VEN 1.2(7) R1 R2 VEN (8) Vin( min ) VEN For Vin (min)=9.2V, R1=49.9K and R2=7.5K ohm is a good choice. Programming the frequency For Fs = 600 kHz, select Rt = 39.2 KΩ, using Table 1. Figure 23: Typical application of the IR3897 for programming the output voltage Bootstrap Capacitor Selection To drive the Control FET, it is necessary to supply a gate voltage at least 4V greater than the voltage at the SW pin, which is connected to the source of the Control FET. This is achieved by using a bootstrap configuration, which comprises the internal bootstrap diode and an external bootstrap capacitor (C1). The operation of the circuit is as follows: When the sync FET is turned on, the capacitor node connected to SW is pulled down to ground. The capacitor charges towards Vcc through the internal bootstrap diode (Fig.24), which has a forward voltage drop VD. The voltage Vc across the bootstrap capacitor C1 is approximately given as: Vc Vcc VD (11) 28 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 29 When the control FET turns on in the next cycle, the capacitor node connected to SW rises to the bus voltage Vin. However, if the value of C1 is appropriately chosen, the voltage Vc across C1 remains approximately unchanged and the voltage at the Boot pin becomes: VBoot Vin Vcc VD (12) IR3897 Ceramic capacitors are recommended due to their peak current capabilities. They also feature low ESR and ESL at higher frequency which enables better efficiency. For this application, it is advisable to have 3x10uF, 25V ceramic capacitors, C3216X5R1E106M from TDK. In addition to these, although not mandatory, a 1x330uF, 25V SMD capacitor EEV‐FK1E331P from Panasonic may also be used as a bulk capacitor and is recommended if the input power supply is not located close to the converter. Inductor Selection The inductor is selected based on output power, operating frequency and efficiency requirements. A low inductor value causes large ripple current, resulting in the smaller size, faster response to a load transient but poor efficiency and high output noise. Generally, the selection of the inductor value can be reduced to the desired maximum ripple current in the inductor (Δi). The optimum point is usually found between 20% and 50% ripple of the output current. Figure 24: Bootstrap circuit to generate Vc voltage A bootstrap capacitor of value 0.1uF is suitable for most applications. Input Capacitor Selection The ripple current generated during the on time of the control FET should be provided by the input capacitor. The RMS value of this ripple is expressed by: I RMS I o D (1 D )(13) D Vo (14) Vin Where: D is the Duty Cycle IRMS is the RMS value of the input capacitor current. Io is the output current. For Io=4A and D = 0.1, the IRMS = 1.8A. 29 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 For the buck converter, the inductor value for the desired operating ripple current can be determined using the following relation: Vin Vo L i 1 ; t D t Fs Vo L Vin Vo Vin i * Fs (15) Where: Vin = Maximum input voltage V0 = Output Voltage Δi = Inductor Peak‐to‐Peak Ripple Current Fs = Switching Frequency Δt = ON time D = Duty Cycle If Δi ≈ 30%*Io, then the output inductor is calculated to be 1.5μH. Select L=1.5μH, PCMB065T‐1R5MS, from Cyntec which provides a compact, low profile inductor suitable for this application. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 30 - IR3897 Output Capacitor Selection Feedback Compensation The voltage ripple and transient requirements determine the output capacitors type and values. The criteria is normally based on the value of the Effective Series Resistance (ESR). However the actual capacitance value and the Equivalent Series Inductance (ESL) are other contributing components. These components can be described as: The IR3897 is a voltage mode controller. The control loop is a single voltage feedback path including an error amplifier and error comparator. To achieve fast transient response and accurate output regulation, a compensation circuit is necessary. The goal of the compensation network is to close the control loop at high crossover frequency with phase margin greater than 45o. Vo Vo(ESR) Vo(ESL) Vo(C) The output LC filter introduces a double pole, ‐40dB/decade gain slope above its corner resonant frequency, and a total phase lag of 180o . The resonant frequency of the LC filter is expressed as follows: Vo(ESR) IL *ESR V V Vo(ESL) in o *ESL L IL Vo(C) 8*Co *Fs FLC (16) Where: ΔV0 = Output Voltage Ripple ΔIL = Inductor Ripple Current Since the output capacitor has a major role in the overall performance of the converter and determines the result of transient response, selection of the capacitor is critical. The IR3897 can perform well with all types of capacitors. As a rule, the capacitor must have low enough ESR to meet output ripple and load transient requirements. The goal for this design is to meet the voltage ripple requirement in the smallest possible capacitor size. Therefore it is advisable to select ceramic capacitors due to their low ESR and ESL and small size. Four of TDK C2012X5R0J226M (22uF/0805/X5R/6.3V) capacitors is a good choice. It is also recommended to use a 0.1µF ceramic capacitor at the output for high frequency filtering. 30 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 1 (17) 2 Lo Co Figure 25 shows gain and phase of the LC filter. Since we already have 180o phase shift from the output filter alone, the system runs the risk of being unstable. Phase Gain 0dB 00 -40dB/Decade -900 FLC Frequency -1800 FLC Frequency Figure 25: Gain and Phase of LC filter The IR3897 uses a voltage‐type error amplifier with high‐gain (110dB) and high‐bandwidth (30MHz). The output of the amplifier is available for DC gain control and AC phase compensation. The error amplifier can be compensated either in type II or type III compensation. Type II compensation is shown in Fig. 26. This method requires that the output capacitors have enough ESR to satisfy stability requirements. If the output capacitor’s ESR generates a zero at 5kHz to 50kHz, the zero generates acceptable phase margin and the Type II compensator can be used. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 31 The ESR zero of the output capacitor is expressed as follows: FESR Use the following equation to calculate R3: R3 1 (18) 2π * ESR* Co VO U T Z IN C P O LE R3 C3 R5 Zf Fb E /A R6 C om p Vosc * Fo * FESR * R5 (23) 2 Vin * FLC Where: Vin = Maximum Input Voltage Vosc = Amplitude of the oscillator Ramp Voltage Fo = Crossover Frequency FESR = Zero Frequency of the Output Capacitor FLC = Resonant Frequency of the Output Filter R5 = Feedback Resistor Ve VR EF G ain(dB ) IR3897 To cancel one of the LC filter poles, place the zero before the LC filter resonant frequency pole: Fz 75 % *FLC H(s) dB Fz 0.75* F FZ P O LE 1 (24) 2 Lo *Co Frequency Use equations (20), (21) and (22) to calculate C3. Figure 26: Type II compensation network and its asymptotic gain plot The transfer function (Ve/Vout) is given by: Zf 1 sR 3C3 Ve H ( s) (19) Vout Z IN sR 5C3 The (s) indicates that the transfer function varies as a function of frequency. This configuration introduces a gain and zero, expressed by: H s R3 (20) R5 1 (21) Fz 2 * R 3 * C3 First select the desired zero‐crossover frequency (Fo): Fo FESR and Fo 1/5~1/10 * Fs (22) 31 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 One more capacitor is sometimes added in parallel with C3 and R3. This introduces one more pole which is mainly used to suppress the switching noise. The additional pole is given by: FP 1 (25) C *C 2 * R3 * 3 POLE C3 CPOLE The pole sets to one half of the switching frequency which results in the capacitor CPOLE: CPOLE 1 * R 3 * Fs 1 C3 1 (26) * R 3 * Fs For a general solution for unconditional stability for any type of output capacitors, and a wide range of ESR values, a type III compensation network can be used, as shown in Fig. 27. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 32 VOUT ZIN C2 C4 R4 R3 C3 R5 Zf Fb R6 E/ A Ve Comp VREF Gain (dB) FZ1 FZ 2 FP2 FP3 Frequency Figure 27: Type III Compensation network and its asymptotic gain plot Again, the transfer function is given by: Zf Ve H (s) Vout Z IN By replacing Zin and Zf, according to Fig. 27, the transfer function can be expressed as: (1 sR3 C 3 ) 1 sC 4 R 4 R5 C * C3 H (s) sR5 ( C 2 C 3 ) 1 sR 3 2 (1 sR 4 C 4 ) C2 C3 (27) The compensation network has three poles and two zeros and they are expressed as follows: FP1 0(28) FP 3 1 (29) 2 * R4 * C4 1 1 (30) C2 * C3 2 * R3 * C2 2 * R3 C2 C3 32 FZ 1 1 (31) 2 * R3 * C3 FZ 2 1 1 (32) 2 * C4 * ( R4 R5 ) 2 * C4 * R5 Cross over frequency is expressed as: Fo R3 * C4 * Vin 1 * Vosc 2 * Lo * Co (33) Based on the frequency of the zero generated by the output capacitor and its ESR, relative to crossover frequency, the compensation type can be different. Table 3 shows the compensation types for relative locations of the crossover frequency. |H(s)| dB FP 2 IR3897 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 TABLE 3: DIFFERENT TYPES OF COMPENSATORS Compensator Type FESR vs FO Typical Output Capacitor Type II Type III FLC < FESR < FO < FS/2 FLC < FO < FESR Electrolytic SP Cap, Ceramic The higher the crossover frequency is, the potentially faster the load transient response will be. However, the crossover frequency should be low enough to allow attenuation of switching noise. Typically, the control loop bandwidth or crossover frequency (Fo) is selected such that: Fo 1/5 ~ 1/10 * Fs The DC gain should be large enough to provide high DC‐regulation accuracy. The phase margin should be greater than 45o for overall stability. For this design we have: Vin=12V Vo=1.2V Vosc=1.8V (This is a function of Vin, pls. see feed forward section) Vref=0.5V Lo=1.5uH Co=4x22uF, ESR≈3mΩ each It must be noted here that the value of the capacitance used in the compensator design must be the small signal value. For instance, the small signal capacitance of the 22uF capacitor used in this design is 10uF at 1.2 V DC bias and 600 kHz frequency. It is this value that must be used for all PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 33 computations related to the compensation. The small signal value may be obtained from the manufacturer’s datasheets, design tools or SPICE models. Alternatively, they may also be inferred from measuring the power stage transfer function of the converter and measuring the double pole frequency FLC and using equation (17) to compute the small signal Co. These result to: FLC=20.5 kHz FESR=5.3 MHz Fs/2=300 kHz Calculate R4, R5 and R6: R4 1 ; R4 106 Ω, Select: R4 100 Ω 2 * C4 * FP 2 1 - R4 ; R5 3.41 kΩ, 2 * C4 * FZ 2 R5 Select R5 = 3.32 kΩ: R6 Select crossover frequency F0=120 kHz Since FLC<F0<Fs/2<FESR, Type III is selected to place the pole and zeros. Detailed calculation of compensation Type III: Desired Phase Boost Θ = 70° FZ 2 Fo FP 2 Fo IR3897 1 sin 21.2 KHz 1 sin 1 sin 680.6 kHz 1 sin Select: Vref Vo - Vref * R5 ; R6 2.37 kΩ Select: R6 2.37 kΩ Setting the Power Good Threshold In this design IR3897 is used in normal (non‐tracking, non‐sequencing) mode, therefore the PGood thresholds are internally set at 90% and 120% of Vref. At startup as soon as Vsns voltage reaches 0.9*0.5V=0.45V (Fig. 15), after 1.28ms delay, PGood signal is asserted. As long as the Vsns voltage is between the threshold range, Enable is high, and no fault happens, the PGood remains high. The following formula can be used to set the threshold. VoutPGood_Th can be taken as 90% of Vout. Choose R7=3.32KΩ: R8 Vref * 0.9 * R 7 Vout PGood _ Th Vref * 0.9 (34) R8 2.37 K FZ1 0.5* FZ 2 10.6 kHzand FP 3 0.5*Fs 300 kHz Select C4 = 2.2nF. The PGood is an open drain output. Hence, it is necessary to use a pull up resistor, RPG, from PGood pin to Vcc. The value of the pull‐up resistor must be chosen such as to limit the current flowing into the PGood pin to less than 5mA when the output voltage is not in regulation. A typical value used is 49.9kΩ. Calculate R3, C3 and C2: 2 * Fo * Lo * Co *Vosc R3 ; R3 3.08kΩ C4 *Vin Vout _ OVP Vref *1.2 * ( R7 R8) / R8 1.44V Select R3 = 3.01 kΩ: C3 1 ; C3 4.9 nF, Select: C3 10 nF 2 *FZ 1 * R 3 C2 1 ; C2 176 pF, Select: C2 120 pF 2 * FP 3 * R3 33 OVP comparator also uses Vsns signal for over Voltage dectection.With above values for R7 and R8, OVP trip point (Vout_OVP) is JANUARY 18, 2013 |DATA SHEET | Rev 3.5 (35) Vref Bypass Capacitor A minimum value of 100pF bypass capacitor is recommended to be placed between Vref and Gnd pins.This capacitor should be placed as close as possible to Vref pin.. PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 34 - IR3897 APPLICATION DIAGRAM Figure 28a: Application Circuit for a 12V to 1.2V, 4A Point of Load Converter Suggested bill of materials for the application circuit Part Reference Cin Qty Value 2 10uF Description 1206, 25V, X5R, 20% Manufacturer Part Number TDK C3216X5R1E106M GRM188R71E104KA01B C1 C5 C6 4 0.1uF 0603, 25V, X7R, 10% Murata Cref 1 100pF 0603,50V,NP0, 5% Murata GRM1885C1H101JA01D C4 1 2200pF C2 1 120pF 0603,50V,X7R 0603, 50V, NP0, 5% Murata Murata GRM188R71H222KA01B GRM1885C1H121JA01D Co 4 22uF 0805, 6.3V, X5R, 20% TDK C2012X5R0J226M CVcc 1 2.2uF 0603, 16V, X5R, 20% TDK C1608X5R1C225M C3 1 10nF 0603, 25V, X7R, 10% Murata GRM188R71E103KA01J Cvin 1 1.0uF 0603, 25V, X5R, 10% Murata GRM188R61E105KA12D Lo 1 1.5H PCMB065T-1R5MS 1 3.01K SMD 7.05x6.6x4.8mm,6.7mΩ Thick Film, 0603,1/10W,1% Cyntec R3 Panasonic ERJ-3EKF3011V R5 R7 2 3.32K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF3321V R6 R8 2 2.37K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF2371V R4 1 100 Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF1000V Rt 1 39.2K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF3922V R1 Rpg 2 49.9K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF4992V R2 1 7.5K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF7551V U1 1 IR3897 PQFN 4x5mm IR IR3897MPBF 34 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 35 Vin=12 V IR3897 C6 0.1uF Cin = 3 X10uF R1 49.9K R2 7.5K U1 External VCC=5V 2.2uF CVcc Vin S_Ctrl Enable PVin Boot C1 0. 1 uF Lo 1.5 uH Vcc/LDO_out Vo=1.2V SW RPG 49.9K PGood IR3897 Vsns Vp R7 3.32k Rt/Sync 39.2 . K PGnd 100pF Cref Comp C3 10nF R3 1.78k C5 0.1uF C4 2.2nF R5 3.32k R4 143 Fb Rt Vref Gnd R8 2.37K Co=4X22uF R6 2.37K C2 120pF Figure 28b: Application Circuit for a 12V to 1.2V, 4A Point of Load Converter with External 5V VCC 35 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 36 Vin= 5 V IR3897 C6 0.1uF Cin = 3 X10uF Enable U1 2.2uF CVcc Enable PVin Vin S_Ctrl Boot C1 0. 1 uF Lo 1 uH Vcc/LDO_out Vo=1V SW RPG 49.9K PGood IR 3897 PGood Vsns Vp R7 3.32k R8 3.32k R5 3.32k R4 100 Fb Rt/Sync Rt 39.2 . K Vref Gnd PGnd Comp C3 5.6nF C5 0.1uF C4 2.2nF Co=4X22uF R6 3.32k R3 3.01k C2 100pF 100pF Cref Figure 29: Application Circuit for a 5V to 1V, 4A Point of Load Converter Suggested bill of materials for the application circuit 5V to 1V Part Reference Cin Qty Value Part Number 10uF Description 1206, 25V, X5R, 20% Manufacturer 3 TDK C3216X5R1E106M C1 C5 C6 3 0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01B Cref 1 100pF 0603,50V,NP0, 5% Murata GRM1885C1H101JA01D C4 1 2200pF C2 1 100pF 0603,50V,X7R 0603, 50V, NP0, 5% Murata Murata GRM188R71H222KA01B GRM1885C1H101JA01D Co 4 22uF 0805, 6.3V, X5R, 20% TDK C2012X5R0J226M CVcc 1 2.2uF 0603, 16V, X5R, 20% TDK C1608X5R1C225M C3 1 5.6nF 0603, 50V, X7R, 10% Murata GRM188R71H562KA01D Cvin 1 1.0uF 0603, 25V, X5R, 10% Murata GRM188R61E105KA12D Lo 1 1uH TDK SPM6550T-1R0M Panasonic ERJ-3EKF3011V R3 1 3.01k SMD 6.86x6.47x5mm,4.7mΩ Thick Film, 0603,1/10W,1% R5 R6 R7 R8 4 3.32K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF3321V R4 1 100 Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF1000V Rt 1 39.2K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF3922V Rpg 2 49.9K Thick Film, 0603,1/10W,1% Panasonic ERJ-3EKF4992V U1 1 IR3897 PQFN 4x5mm IR IR3897MPBF 36 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 37 Vin=12 V C6 0.1uF Cin = 3 X 10uF Cvin 1.0uF Enable U1 Enable S_Ctrl 2.2uF Vin PVin Lo SW PGood PGood R6 IR3897 Vref Gnd 60.4 K N/S (optional) R5 3.32k PGnd C3 8.2nF Comp C5 0.1uF C4 3.3nF R4 100 Fb Rt/Sync Rt R7 3.32k Vsns Vp C7 10nF R8 1k Vo=0.6V 0.82uH RPG 49.9k 1k C1 0. 1 uF Boot Vcc/LDO_out CVcc VDDQ=1.2V IR3897 Co=4X47uF R3 1.6k C2 150pF Figure 30: Application Circuit for a 12V to 0.6V, 4A, VTT rail Vin=1.2V C6 0.1uF Cin = 3 X 22uF Enable U1 Ext VCC 2.2uF CVcc Vin Enable S_Ctrl PVin Boot C1 0. 1 uF Lo Vcc/LDO_out SW RPG 49.9k PGood Vin=1.2V PGood R6 1k 1k R8 C7 10nF Rt 39.2 K Vo=0.6V 0.36uH IR3897 Vsns Vp N/S (optional) R5 5.62k Fb Rt/Sync Vref Gnd R7 5.62k PGnd Comp C3 5.6nF R3 4.64k C2 110pF Figure 31: Application Circuit for a 1.2V to 0.6V, 4A, VTT rail 37 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 C5 0.1uF C4 2.2nF R4 182 Co=5X22uF PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 38 - IR3897 TYPICAL OPERATING WAVEFORMS Vin = 12V, Vo = 1.2V, Iout = 0‐4A, Room Temperature, No Air Flow Figure 32: Start up at 4A Load, Ch1:Vin, Ch2:Vo, Ch3:PGood, Ch4:Enable Figure 33: Start up at 4A Load, Ch1:Vin, Ch2:Vo, Ch3:PGood, Ch4:Vcc Figure 34: Start up with 1V pre bias, 0A Load, Ch2:Vo Figure 35: Output Voltage Ripple 4A Load, Ch2:Vo Figure 36: Inductor node at 4A Load, Ch2‐LX Figure 37: Short Circuit Recovery, Ch2:Vo, Ch4:Iout(2A/Div) 38 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 39 - IR3897 TYPICAL OPERATING WAVEFORMS Vin = 12V, Vo = 1.2V, Iout = 0‐4A, Room Temperature, No Air Flow Figure 38: Turn on at No Load showing Vcc level, Ch1:Vin, Ch2:Vo, Ch3:Vcc, Ch4:Inductor Current Figure 39: Turn on at Full Load showing Vcc level, Ch1:Vin, Ch2:Vo, Ch3:Vcc, Ch4:Inductor Current 40: Transient Response, 2A to 4A step @2.5A/uSec slew rate, Ch2:Vout, Ch4‐Iout (1A/Div) 39 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 40 - IR3897 TYPICAL OPERATING WAVEFORMS Vin = 12V, Vo = 1.2V, Iout = 0‐4A, Room Temperature, No Air Flow Figure 41: Bode Plot at 4A load shows a bandwidth of 112.6KHz and phase margin of 52.4 degrees Figure 42: Thermal Image of the Board at 4A Load, Test Point 1 is IR3897, Test Point 2 is inductor 40 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 41 - IR3897 TYPICAL OPERATING WAVEFORMS Vin = 12V, Vo = 1.2V, Iout = 0‐4A, Room Temperature, No Air Flow Figure 43: Feed Forward for Vin change from 7 to16V and back to 7V, Ch2:Vo, Ch4:Vin Figure 45: External Frequency Synchronization to 800KHz from free running 600KHz , Ch1:LX, Ch2:Vo,Ch4‐Rt/Sync Figure 47: Voltage Margining using Vref pin Ch2‐Vo,Ch3‐Vref,Ch4‐PGood 41 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 Figure 44: Start/Stop using S‐Ctrl pin, Ch1:Enable, Ch2:Vo, Ch3:pGood, Ch4:S‐Ctrl Figure 46: Over Voltage protection, Ch2‐Vo,Ch3‐PGood 48: Voltage tracking using Vp pin Ch2‐Vo,Ch3‐Vp,Ch4‐PGood PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 42 LAYOUT RECOMMENDATIONS The layout is very important when designing high frequency switching converters. Layout will affect noise pickup and can cause a good design to perform with less than expected results. Make the connections for the power components in the top layer with wide, copper filled areas or polygons. In general, it is desirable to make proper use of power planes and polygons for power distribution and heat dissipation. The inductor, output capacitors and the IR3897 should be as close to each other as possible. This helps to reduce the EMI radiated by the power traces due to the high switching currents through them. Place the input capacitor directly at the PVin pin of IR3897. The feedback part of the system should be kept away from the inductor and other noise sources. IR3897 The critical bypass components such as capacitors for Vin, Vcc and Vref should be close to their respective pins. It is important to place the feedback components including feedback resistors and compensation components close to Fb and Comp pins. In a multilayer PCB use one layer as a power ground plane and have a control circuit ground (analog ground), to which all signals are referenced. The goal is to localize the high current path to a separate loop that does not interfere with the more sensitive analog control function. These two grounds must be connected together on the PC board layout at a single point. It is recommended to place all the compensation parts over the analog ground plane in top layer. The Power QFN is a thermally enhanced package. Based on thermal performance it is recommended to use at least a 4‐layers PCB. To effectively remove heat from the device the exposed pad should be connected to the ground plane using vias. Figures 46a‐d illustrates the implementation of the layout guidelines outlined above, on the IRDC3897 4‐ layer demo board. Enough copper & minimum ground length path between Input and Output All bypass caps should be placed as close as possible to their connecting pins Compensation parts should be placed as close as possible to the Comp pin SW node copper is kept only at the top layer to minimize the switching noise Resistor Rt and Vref decoupling cap should be placed as close as possible to their pins Figure 49a: IRDC3897 Demo board Layout Considerations – Top Layer 42 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 43 - Single point connection between AGND & PGND, should be close to the SupIRBuck kept away from noise sources IR3897 Feedback and Vsns trace routing should be kept away from noise sources Figure 49b: IRDC3897 Demo board Layout Considerations – Bottom Layer Analog Ground plane Power Ground plane Figure 49c: IRDC3897 Demo board Layout Considerations – Mid Layer 1 Figure 49d: IRDC3897 Demo board Layout Considerations – Mid Layer 2 43 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 44 PCB METAL AND COMPONENT PLACEMENT Evaluations have shown that the best overall performance is achieved using the substrate/PCB layout as shown in following figures. PQFN devices should be placed to an accuracy of 0.050mm on both X and Y axes. Self‐centering behavior is highly dependent on solders and processes, and experiments should be run to confirm the limits of self‐centering on specific processes. For further information, please refer to “SupIRBuck™ Multi‐Chip Module (MCM) Power Quad Flat No‐Lead (PQFN) Board Mounting Application Note.” (AN1132) Figure 50: PCB Metal Pad Spacing (all dimensions in mm) * Contact International Rectifier to receive an electronic PCB Library file in your preferred format 44 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 IR3897 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 45 - IR3897 SOLDER RESIST IR recommends that the larger Power or Land Area pads are Solder Mask Defined (SMD.) This allows the underlying Copper traces to be as large as possible, which helps in terms of current carrying capability and device cooling capability. When using SMD pads, the underlying copper traces should be at least 0.05mm larger (on each edge) than the Solder Mask window, in order to accommodate any layer to layer misalignment. (i.e. 0.1mm in X & Y.) However, for the smaller Signal type leads around the edge of the device, IR recommends that these are Non Solder Mask Defined or Copper Defined. When using NSMD pads, the Solder Resist Window should be larger than the Copper Pad by at least 0.025mm on each edge, (i.e. 0.05mm in X&Y,) in order to accommodate any layer to layer misalignment. Ensure that the solder resist in‐between the smaller signal lead areas are at least 0.15mm wide, due to the high x/y aspect ratio of the solder mask strip. Figure 51: Solder resist * Contact International Rectifier to receive an electronic PCB Library file in your preferred format 45 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 46 - IR3897 STENCIL DESIGN Stencils for PQFN can be used with thicknesses of 0.100‐0.250mm (0.004‐0.010"). Stencils thinner than 0.100mm are unsuitable because they deposit insufficient solder paste to make good solder joints with the ground pad; high reductions sometimes create similar problems. Stencils in the range of 0.125mm‐0.200mm (0.005‐0.008"), with suitable reductions, give the best results. Evaluations have shown that the best overall performance is achieved using the stencil design shown in following figure. This design is for a stencil thickness of 0.127mm (0.005"). The reduction should be adjusted for stencils of other thicknesses. Figure 52: Stencil Pad Spacing (all dimensions in mm) * Contact International Rectifier to receive an electronic PCB Library file in your preferred format 46 JANUARY 18, 2013 |DATA SHEET | Rev 3.5 PD‐97663 4A Highly Integrated SupIRBuckTM Single‐Input Voltage, Synchronous Buck Regulator - 47 - IR3897 MARKING INFORMATION Figure 53: Marking Information PACKAGE INFORMATION Figure 54: Package Dimensions IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 This product has been designed and qualified for the Industrial market Visit us at www.irf.com for sales contact information Data and specifications subject to change without notice.9/11 47 JANUARY 18, 2013 |DATA SHEET | Rev 3.5