IR3502B DATA SHEET XPHASE3TM CONTROL IC DESCRIPTION The IR3502B control IC combined with an XPHASE3TM Phase IC provides a full featured and flexible way to implement a complete VR11.0 and VR11.1 power solution. The IR3502B provides overall system control and interfaces with any number of Phase ICs, each driving and monitoring a single phase. The XPhase3TM architecture results in a power supply that is smaller, less expensive, and easier to design while providing higher efficiency than conventional approaches. FEATURES 1 to X phase operation with matching Phase IC 0.5% overall system set point accuracy Daisy-chain digital phase timing provides accurate phase interleaving without external components Programmable 250kHz to 9MHz clock oscillator frequency provides per phase switching frequency of 250kHz to 1.5MHz Programmable Dynamic VID Slew Rate Programmable VID Offset or No Offset Programmable Load Line Output Impedance High speed error amplifier with wide bandwidth of 30MHz and fast slew rate of 10V/us Programmable constant converter output current limit during soft start Hiccup over current protection with delay during normal operation Central over voltage detection and latch with programmable threshold and communication to phase ICs Over voltage signal output to system with overvoltage detection during powerup and normal operation Load current reporting Single NTC thermistor compensation for correct current reporting, OC Threshold, and Droop Detection and protection of open remote sense line Open control loop protection IC bias linear regulator controller Programmable VRHOT function monitors temperature of power stage through a NTC thermistor Remote sense amplifier with true converter voltage sensing Small thermally enhanced 32L 5mm x 5mm MLPQ package RoHS Compliant ORDERING INFORMATION Device IR3502BMTRPBF * IR3502BMPBF Package 32 Lead MLPQ (5 x 5 mm body) 32 Lead MLPQ (5 x 5 mm body) Order Quantity 3000 per reel 100 piece strips Samples only Page 1 of 38 V3.2 IR3502B APPLICATION CIRCUIT 12V +12V Q2 VCCL CVCCL RVCCLDRV IIN PHSIN PGOOD PHSOUT RMON CLKOUT 25 27 26 CLKOUT PHSIN PHSOUT 28 30 29 IIN VCCL IMON VDAC_BUFF VDRP FB 24 ROSC 23 CSS/DEL 22 21 RVDAC 20 RVSETPT 19 RTCMP3 CVDAC VDAC 18 17 RTCMP1 RTHERM RTCMP2 16 9 ENABLE EAOUT VN VID0 VO VID1 15 8 VID0 VSETPT VID2 14 7 VID1 VDAC IR3502B VID3 VOSEN+ VID2 VID4 VOSEN- 6 SS/DEL 13 5 VID3 VID5 HOTSET VID4 GND ROSC 12 4 VID6 11 VID5 VCCLDRV 32 3 VID7 VRHOT 2 VID6 ENABLE 1 VID7 PGOOD RMON1 VOSEN- 10 CMON 31 IOUT RDRP VRHOT RHOTSET1 RHOTSET3 CHOTSET RFB1 CFB1 EAOUT CEA1 RFB RHOTSET2 CEA REA VOSEN+ VOSEN- Figure 1: IR3502B Application Circuit IR3502B ERROR AMPLIFIER VDAC BUFFER AMPLIFIER EAOUT 1k + FB + VSETPT ISOURCE FAST VDAC VDAC ISINK - IVDAC IOCSET IVSETPT IROSC IROSC RVDAC OCSET ROCSET CURRENT SOURCE GENERATOR ROSC BUFFER AMPLIFIER CVDAC IROSC 0.6V LGND + ROSC ROSC VO REMOTE SENSE AMPLIFIER VOSEN+ + EAOUT SYSTEM SET POINT VOSNSVOLTAGE VOSEN- - Figure 2 –System-set point measurements. Page 2 of 38 V3.2 IR3502B 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. Operating Junction Temperature……………..0 to 150oC Storage Temperature Range………………….-65oC to 150oC ESD Rating………………………………………HBM Class 1C JEDEC Standard MSL Rating………………………………………2 Reflow Temperature…………………………….260oC PIN # PIN NAME VMAX VMIN ISOURCE ISINK 1-8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 VID7-0 ENABLE VRHOT HOTSET VOSENVOSEN+ VO FB EAOUT VDRP VN VDAC_BUFF VSETPT VDAC SS/DEL ROSC/OVP LGND CLKOUT 7.5V 3.5V 7.5V 7.5V 1.0V 7.5V 7.5V 7.5V 7.5V 7.5V 7.5V 3.5V 3.5V 3.5V 7.5V 7.5V n/a 7.5V -0.3V -0.3V -0.3V -0.3V -0.5V -0.5V -0.5V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.3V -0.5V n/a -0.3V 1mA 1mA 1mA 1mA 5mA 5mA 35mA 1mA 35mA 35mA 1mA 1mA 1mA 1mA 1mA 1mA 20mA 100mA 1mA 1mA 50mA 1mA 1mA 1mA 5mA 1mA 5mA 1mA 1mA 35mA 1mA 1mA 1mA 1mA 1mA 100mA 26 27 28 PHSOUT PHSIN VCCL 7.5V 7.5V 7.5V -0.3V -0.3V -0.3V 10mA 1mA 1mA 10mA 1mA 20mA 29 IIN 7.5V -0.3V 1mA 1mA 30 VCCLDRV 10V -0.3V 1mA 50mA 31 PGOOD VCCL + 0.3V -0.3V 1mA 20mA 32 IMON 3.5V -0.3V 25mA 1mA Page 3 of 38 V3.2 IR3502B ELECTRICAL SPECIFICATIONS Unless otherwise specified, these specifications apply over: 8V≤Vin≤16V, VCCL = 6.8V±3.4%, -0.3V ≤ VOSEN- ≤ 0.3V, 0 oC ≤ TJ ≤ 100 oC, 7.75KΩ ≤ ROSC ≤ 50.0 KΩ, CSS/DEL = 0.1F +/-10%. PARAMETER VDAC Reference System Set-Point Accuracy TEST CONDITION MIN VID ≥ 1V 0.8V ≤ VID < 1V 0.5V ≤ VID < 0.8V Include OCSET and VSETPT currents Source & Sink Currents VIDx Input Threshold VIDx Input Bias Current 0V≤V(VIDx)≤2.5V. VIDx OFF State Blanking Delay Measure time till PGOOD drives low Oscillator ROSC Voltage CLKOUT High Voltage I(CLKOUT)= -10 mA, measure V(VCCL) – V(CLKOUT). CLKOUT Low Voltage I(CLKOUT)= 10 mA PHSOUT Frequency ROSC = 50.0 KΩ PHSOUT Frequency ROSC = 24.5 KΩ PHSOUT Frequency ROSC = 7.75 KΩ PHSOUT High Voltage I(PHSOUT)= -1 mA, measure V(VCCL) – V(PHSOUT) PHSOUT Low Voltage I(PHSOUT)= 1 mA PHSIN Threshold Voltage Compare to V(VCCL) VDAC Buffer Amplifier Input Offset Voltage V(VDAC_BUFF) – V(VDAC), 0.5V ≤ V(VDAC) ≤ 1.6V, < 1mA load Source Current 0.5V ≤ V(VDAC) ≤ 1.6V Sink Current 0.5V ≤ V(VDAC) ≤ 1.6V Unity Gain Bandwidth Note 1 Slew Rate Note 1 Thermal Compensation Amplifier Output Offset Voltage 0V ≤ V(IIN) – V(VDAC) ≤ 1.6V, 0.5V ≤ V(VDAC) ≤ 1.6V, Req/R2 = 2 Source Current 0.5V ≤ V(VDAC) ≤ 1.6V Sink Current 0.5V ≤ V(VDAC) ≤ 1.6V Unity Gain Bandwidth Note 1, Req/R2 = 2 Slew Rate Note 1 Current Report Amplifier Output Offset Voltage V(VDRP)–V(VDAC) = 0,225,450,900mV Page 4 of 38 TYP MAX UNIT -0.5 -5 -8 30 500 -1 0.5 44 600 0 1.3 0.5 +5 +8 58 700 1 2.1 % mV mV A mV A s 0.570 0.595 0.620 1 V V 225 450 1.35 250 500 1.50 1 275 550 1.65 1 V kHz kHz MHz V V % 30 50 1 70 -5 0 9 mV 0.3 3.5 0.44 13 3.5 1.5 0.6 20 mA mA MHz V/s -10 0 10 mV 3 0.3 2 8 0.4 4.5 5.5 15 0.5 7 mA mA MHz -15 0 V/s 15 V3.2 mV IR3502B PARAMETER TEST CONDITION Source Current 0.5V ≤ V(IMON) ≤ 0.9V Sink Resistance 0.5V ≤ V(IMON) ≤ 0.9V Unity Gain Bandwidth Note 1 Input Filter Time Constant Max Output Voltage Soft Start and Delay Start Delay (TD1) Soft Start Time (TD2) VID Sample Delay (TD3) PGOOD Delay (TD4 + TD5) OC Delay Time V(VDRP) – V(DACBUFF) = 1.67 mV SS/DEL to FB Input Offset With FB = 0V, adjust V(SS/DEL) until Voltage EAOUT drives high Charge Current Discharge Current Charge/Discharge Current Ratio Charge Voltage Relative to Charge Voltage, SS/DEL rising Delay Comparator Threshold Relative to Charge Voltage, SS/DEL falling Delay Comparator Threshold Delay Comparator Input Filter Delay Comparator Hysteresis VID Sample Delay Comparator Threshold Discharge Comp. Threshold Remote Sense Differential Amplifier Unity Gain Bandwidth Note 1 Input Offset Voltage 0.5V≤ V(VOSEN+) - V(VOSEN-) ≤ 1.6V Sink Current 0.5V≤ V(VOSEN+) - V(VOSEN-) ≤ 1.6V Source Current 0.5V≤ V(VOSEN+) - V(VOSEN-) ≤ 1.6V Slew Rate 0.5V≤ V(VOSEN+) - V(VOSEN-) ≤ 1.6V VOSEN+ Bias Current 0.5 V < V(VOSEN+) < 1.6V VOSEN- Bias Current -0.3V ≤ VOSEN- ≤ 0.3V, All VID Codes High Voltage V(VCCL) – V(VO) Low Voltage V(VCCL)=7V Error Amplifier Input Offset Voltage Measure V(FB) – V(VSETPT). Note 2 FB Bias Current VSETPT Bias Current ROSC= 24.5 KΩ DC Gain Note 1 Bandwidth Note 1 Slew Rate Note 1 Sink Current Source Current Maximum Voltage Measure V(VCCL) – V(EAOUT) Page 5 of 38 MIN 5 5 1.04 TYP 9 10 1 1 1.09 MAX 15 17 1.145 UNIT mA kΩ MHz s V 1.0 0.8 0.3 0.5 75 0.7 2.9 2.2 1.2 1.2 125 1.4 3.5 3.25 3.0 2.3 300 1.9 ms ms ms ms us V 35.0 2.5 10 3.6 50 85 70.0 6.5 16 4.2 125 160 10 2.8 52.5 4.5 12 4.0 80 120 5 30 3.0 60 3.2 A A A/A V mV mV s mV V 150 200 275 mV 3.0 -3 0.4 3 2 6.4 0 1 9 4 1.5 160 2 9.0 3 2 20 8 100 275 2.5 50 MHz mV mA mA V/us uA uA V mV -1 -1 23.00 100 20 7 0.40 5 500 0 0 24.25 110 30 12 0.85 8 780 1 1 25.50 120 40 20 1.00 12 950 mV A A dB MHz V/s mA mA mV V3.2 IR3502B PARAMETER Minimum Voltage Open Voltage Loop Detection Threshold Open Voltage Loop Detection Delay Enable Input VR 11 Threshold Voltage VR 11 Threshold Voltage VR 11 Hysteresis Bias Current Blanking Time TEST CONDITION MIN Measure V(VCCL) - V(EAOUT), Relative to Error Amplifier maximum voltage. Measure PHSOUT pulse numbers from V(EAOUT) = V(VCCL) to PGOOD = low. 125 ENABLE rising ENABLE falling 825 775 25 -5 75 850 800 50 0 250 875 825 75 5 400 mV mV mV -40 -25 2 1.17 4096 2048 1024 -10 mV S V Cycle Cycle Cycle 0V ≤ V(ENABLE) ≤ 3.3V Noise Pulse < 100ns will not register an ENABLE state change. Note 1 Over-Current Comparator Input Offset Voltage 1V ≤ V(IIN) ≤ 3.3V Input Filter Time Constant Over-Current Threshold VDRP-VDAC_BUFF Over-Current Delay Counter ROSC = 7.75 KΩ (PHSOUT=1.5MHz) Over-Current Delay Counter ROSC = 15.0 KΩ (PHSOUT=800kHz) Over-Current Delay Counter ROSC = 50.0 KΩ (PHSOUT=250kHz) Over-Current Limit Amplifier Input Offset Voltage Transconductance Note 1 Sink Current Unity Gain Bandwidth Note 1 Over Voltage Protection (OVP) Comparators Threshold at Power-up Measure at 1.5V VCCLDRV Threshold during Normal Compare to V(VDAC) Operation OVP Release Voltage during Compare to V(VDAC) Normal Operation Threshold during Dynamic VID down Dynamic VID Detect Comparator Threshold Propagation Delay to IIN Measure time from V(VO) > V(VDAC) (250mV overdrive) to V(IIN) transition to > 0.9 * V(VCCL). IIN Pull-up Resistance Propagation Delay to OVP Measure time from V(VO) > V(VDAC) (250mV overdrive) to V(ROSC/OVP) transition to >1V. OVP High Voltage Measure V(VCCL)-V(ROSC/OVP) OVP Power-up High Voltage ROSC = 7.75 KΩ. Measure V(VCCLDRV)-V(ROSC/OVP) @ 1.5V OVP Power-up High Voltage ROSC = 24.5 KΩ. Measure V(VCCLDRV)-V(ROSC/OVP) @ 1.5V Page 6 of 38 TYP 120 300 MAX 250 600 8 1.07 UNIT mV mV Pulses 1.27 A ns -10 0.50 35 0.75 0 1.00 55 2.00 10 1.75 75 3.00 mV mA/V uA kHz 1.1 105 1.21 125 1.30 145 V mV -13 3 20 mV 1.70 1.73 1.75 V 25 50 75 mV 90 180 nS 5 90 0 .100 0 .240 15 180 1.2 .375 0.2 V3.2 Ω nS V V IR3502B PARAMETER PGOOD Output Output Voltage Leakage Current Under Voltage Threshold-VO decreasing Under Voltage Threshold-VO increasing Under Voltage Threshold Hysteresis VCCL_DRV Activation Threshold Open Sense Line Detection Sense Line Detection Active Comparator Threshold Voltage Sense Line Detection Active Comparator Offset Voltage VOSEN+ Open Sense Line Comparator Threshold VOSEN- Open Sense Line Comparator Threshold Sense Line Detection Source Currents VRHOT Comparator Threshold Voltage HOTSET Bias Current Hysteresis Output Voltage VRHOT Leakage Current VCCL Regulator Amplifier VCCL Output Voltage VCCLDRV Sink Current UVLO Start Threshold UVLO Stop Threshold Hysteresis General VCCL Supply Current TEST CONDITION MIN I(PGOOD) = 4mA V(PGOOD) = 5.5V Reference to VDAC MAX mV A mV 300 10 -350 -300 -250 -290 -240 -190 25 60 95 1 2 3.6 V 150 200 250 mV 30 55 80 mV 87.5 90.0 92.5 % 0.36 0.40 0.44 V 200 500 700 uA 1.584 -1 75 1.600 0 100 150 0 1.616 1 125 400 10 I(PG)=4mA, V(PG)<300mV, V(VCCL)=0 V(VO) < [V(VOSEN+) – V(LGND)] / 2 Compare to V(VCCL) V(VO) = 100mV I(VRHOT) = 30mA V(VRHOT) = 5.5V 7.031 mV mV V A mV mV A 6.568 10 6.12 5.168 0.85 6.8 30 6.392 5.44 0.95 6.664 5.712 1.05 V mA V V V 4 8 12 mA Note 1: Guaranteed by design, but not tested in production Note 2: VDAC Output is trimmed to compensate for Error Amplifier input offsets errors Page 7 of 38 UNIT 150 0 Reference to VDAC Compare to V(VCCL) Compare to V(VCCL) TYP V3.2 IR3502B PIN DESCRIPTION PIN# 1-8 9 PIN SYMBOL VID7-0 ENABLE 10 VRHOT 11 HOTSET 12 13 14 15 16 17 VOSENVOSEN+ VO FB EAOUT VDRP 18 19 20 VN VDAC_BUFF VSETPT 21 VDAC 22 SS/DEL 23 ROSC/OVP 24 25 LGND CLKOUT 26 PHSOUT 27 28 29 PHSIN VCCL IIN 30 VCCLDRV 31 PGOOD 32 IMON Page 8 of 38 PIN DESCRIPTION Inputs to VID D to A Converter. Enable input. A logic low applied to this pin puts the IC into fault mode. Do not float this pin as the logic state will be undefined. Open collector output of the VRHOT comparator which drives low if HOTSET pin voltage is lower than 1.6V. Connect external pull-up. A resistor divider including thermistor senses the temperature, which is used for VRHOT comparator. Remote sense amplifier input. Connect to ground at the load. Remote sense amplifier input. Connect to output at the load. Remote sense amplifier output. Inverting input to the Error Amplifier. Output of the error amplifier. Buffered, scaled and thermally compensated IIN signal. Connect an external RC network to FB to program converter output impedance. Node for DCR thermal compensation network. Buffered VDAC. Error amplifier non-inverting input. Converter output voltage can be decreased from the VDAC voltage with an external resistor connected between VDAC and this pin (there is an internal sink current at this pin). Regulated voltage programmed by the VID inputs. Connect an external RC network to LGND to program dynamic VID slew rate and provide compensation for the internal buffer amplifier. Programs converter startup and over current protection delay timing. It is also used to compensate the constant output current loop during soft start. Connect an external capacitor to LGND to program. Connect a resistor to LGND to program oscillator frequency and OCSET, VSETPT and VDAC bias currents. Oscillator frequency equals switching frequency per phase. The pin voltage is 0.6V during normal operation and higher than 1.6V if an overvoltage condition is detected. Local Ground for internal circuitry and IC substrate connection. Clock output at switching frequency multiplied by phase number. Connect to CLKIN pins of phase ICs. Phase clock output at switching frequency per phase. Connect to PHSIN pin of the first phase IC. Feedback input of phase clock. Connect to PHSOUT pin of the last phase IC. Voltage regulator and IC power input. Connect a decoupling capacitor to LGND. Average current input from the phase IC(s). This pin is also used to communicate over voltage condition to phase ICs. Output of the VCCL regulator error amplifier to control external transistor. The pin senses 12V power supply through a resistor. Open collector output that drives low during startup and under any external fault condition. Indicates converter within regulation. Connect external pull-up. Voltage at IOUT pin will be proportional to load current. V3.2 IR3502B SYSTEM THEORY OF OPERATION System Description The system consists of one control IC and a scalable array of phase converters, each requiring one phase IC. The control IC communicates with the phase ICs using three digital buses, i.e., CLOCK, PHSIN, PHSOUT and three analog buses, i.e., VDAC, EA, IIN. The digital buses are responsible for switching frequency determination and accurate phase timing control without any external component. The analog buses are used for PWM control and current sharing among interleaved phases. The control IC incorporates all the system functions, i.e., VID, CLOCK signals, error amplifier, fault protections, current monitor, etc. The Phase IC implements the functions required by each phase of the converter, i.e., the gate drivers, PWM comparator and latch, over-voltage protection, Phase disable circuit, current sensing and sharing, etc. GATE DRIVE VOLTAGE CONTROL IC VIN PHSOUT PHASE IC CLOCK GENERATOR CLKOUT VCC CLKIN CLK Q VCCH D PHSOUT 1 PHSIN 2 D PHSIN PWM COMPARATOR GATEH RESET U246 DOMINANT COUT VCCL DFFRH GND PWM LATCH GATEL ENABLE + + VID6 BODY BRAKING COMPARATOR VID6 - - PSI LGND PSI - SHARE ADJUST ERROR AMPLIFIER EAOUT ISHARE CURRENT SENSE AMPLIFIER VID6 VID6 - + + - 3K CEA ERROR AMPLIFIER - VDAC + VID6 VID6 + RFB + REA CFB1 FB IROSC RCS PHSOUT RDRP VSETPT IMON PHASE IC VCC CLK Q CLKIN D VDAC 1 2 PHSIN GATEH D PWM COMPARATOR RTHERM RTCMP1 EAIN CLK Q + SW OFF DFFRH VCCL PWM LATCH ENABLE + - VDAC_BUFF + VID6 RTCMP3 - IIN VID6 - RTCMP2 CBST Q R VDRP VN VCCH RESET U248 DOMINANT 3 Thermal Compensation CCS CSIN- DACIN RVSETPT IVSETPT CSIN+ + RFB1 CEA1 - + VOSNS- - VDAC VDRP AMP PGND OFF + RAMP DISCHARGE CLAMP VO VOUT R 3 + VOSNS+ SW OFF - EAIN REMOTE SENSE AMPLIFIER CBST VID6 Q CLK Q RAMP DISCHARGE CLAMP GATEL BODY BRAKING COMPARATOR VID6 PGND OFF - + PSI PSI SHARE ADJUST ERROR AMPLIFIER CURRENT SENSE AMPLIFIER + - VID6 VID6 + CSIN+ VID6 VID6 + + DACIN CCS RCS - - 3K + ISHARE CSIN- Figure 3 System Block Diagram PWM Control Method The PWM block diagram of the XPhase3TM architecture is shown in Figure 3. Feed-forward voltage mode control with trailing edge modulation is used. A high-gain wide-bandwidth voltage type error amplifier in the control IC is used for the voltage control loop. Input voltage is sensed in phase ICs and feed-forward control is realized. The PWM ramp slope will change with the input voltage and automatically compensate for changes in the input voltage. The input voltage can change due to variations in the silver box output voltage or due to the wire and PCB-trace voltage drop related to changes in load current. Frequency and Phase Timing Control The oscillator is located in the control IC and the system clock frequency is programmable from 250kHz to 9MHZ by an external resistor. The control IC system clock signal CLKOUT is connected to CLKIN of all the phase ICs. The phase timing of the phase ICs is controlled by the daisy chain loop, where control IC phase clock output PHSOUT is Page 9 of 38 V3.2 IR3502B connected to the phase clock input PHSIN of the first phase IC, and PHSOUT of the first phase IC is connected to PHSIN of the second phase IC, etc. The PHSOUT of the last phase IC is connected back to PHSIN of the control IC. During power up, the control IC sends out clock signals from both CLKOUT and PHSOUT pins and detects the feedback at PHSIN pin to determine the phase number and monitor any fault in the daisy chain loop. Figure 4 shows the phase timing for a four phase converter. The switching frequency is set by the resistor ROSC. The clock frequency equals the number of phase times the switching frequency. Control IC CLKOUT (Phase IC CLKIN) Control IC PHSOUT (Phase IC1 PHSIN) Phase IC1 PWM Latch SET Phase IC 1 PHSOUT (Phase IC2 PHSIN) Phase IC 2 PHSOUT (Phase IC3 PHSIN) Phase IC 3 PHSOUT (Phase IC4 PHSIN) Phase IC4 PHSOUT (Control IC PHSIN) Figure 4 Four Phase Oscillator Waveforms PWM Operation The PWM comparator is located in the phase IC. With the PHSIN voltage high, upon receiving the falling edge of a clock pulse, the PWM latch is set. The PWMRMP voltage begins to increase; the low side driver is turned off, and the high side driver is turned on after the non-overlap time. When the PWMRMP voltage exceeds the error amplifier’s output voltage, the PWM latch is reset. This turns off the high side driver and then turns on the low side driver after the non-overlap time. Along with that, it activates the ramp discharge clamp, which quickly discharges the PWMRMP capacitor to the output voltage of share adjust amplifier in phase IC until the next clock pulse. The PWM latch is reset dominant allowing all phases to go to zero duty cycle within a few tens of nanoseconds in response to a load step decrease. Phases can overlap and go up to 100% duty cycle in response to a load step increase with turn-on gated by the clock pulses. An error amplifier output voltage greater than the common mode input range of the PWM comparator results in 100% duty cycle regardless of the voltage of the PWM ramp. This arrangement guarantees the error amplifier is always in control and can demand 0 to 100% duty cycle as required. It also favors response to a load step decrease which is appropriate, given the low output to input voltage ratio of most systems. The inductor current will increase much more rapidly than decrease in response to load transients. The error amplifier is a high speed amplifier with wide bandwidth and fast slew rate incorporated in the control IC. It is not unity gain stable. This control method is designed to provide “single cycle transient response,” where the inductor current changes in response to load transients within a single switching cycle maximizing the effectiveness of the power train and minimizing the output capacitor requirements. An additional advantage of the architecture is that differences in the ground or input voltage at the phases have no effect on operation since the PWM ramps are referenced to VDAC. Figure 5 depicts PWM operating waveforms under various conditions. Page 10 of 38 V3.2 IR3502B PHASE IC CLOCK PULSE EAIN PWMRMP VDAC GATEH GATEL STEADY-STATE OPERATION Body BrakingTM DUTY CYCLE INCREASE DUE TO LOAD INCREASE DUTY CYCLE DECREASE DUE TO VIN INCREASE (FEED-FORWARD) DUTY CYCLE DECREASE DUE TO LOAD DECREASE (BODY BRAKING) OR FAULT (VCCLUV, OCP, VID=11111X) STEADY-STATE OPERATION Figure 5 PWM Operating Waveforms In a conventional synchronous buck converter, the minimum time required to reduce the current in the inductor in response to a load step decrease is; TSLEW L * ( I MAX I MIN ) VO The slew rate of the inductor current can be significantly increased by turning off the synchronous rectifier in response to a load step decrease. The switch node voltage is then forced to decrease until conduction of the synchronous rectifier’s body diode occurs. This increases the voltage across the inductor from Vout to Vout + VBODYDIODE. The minimum time required to reduce the current in the inductor in response to a load transient decrease is now; TSLEW L * ( I MAX I MIN ) VO VBODYDIODE Since the voltage drop in the body diode is often comparable to the output voltage, the inductor current slew rate can be increased significantly. This patented technique is referred to as “body braking” and is accomplished through the “body braking comparator” located in the phase IC. If the error amplifier’s output voltage drops below the output voltage of the share adjust amplifier in the phase IC, this comparator turns off the low side gate driver, enabling the bottom FET body diode to take over. There is 100mV upslope and 200mV down slope hysteresis for the body braking comparator. Lossless Average Inductor Current Sensing Inductor current can be sensed by connecting a series resistor and a capacitor network in parallel with the inductor and measuring the voltage across the capacitor, as shown in Figure 6. The equation of the sensing network is, vC ( s) vL ( s) 1 RL sL iL ( s) 1 sRCS CCS 1 sRCS CCS Usually the resistor Rcs and capacitor Ccs are chosen, such that, the time constant of Rcs and Ccs equals the time constant of the inductor, which is the inductance L over the inductor DCR RL. If the two time constants match, the voltage across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense Page 11 of 38 V3.2 IR3502B resistor with the value of RL was used. The mismatch of the time constants does not affect the measurement of inductor DC current, but affects the AC component of the inductor current. vL iL Current Sense Amp L RL RC CC VO CO vCc CSOUT Figure 6 Inductor Current Sensing and Current Sense Amplifier The advantage of sensing the inductor current versus high side or low side sensing is that actual output current being delivered to the load is obtained rather than peak or sampled information about the switch currents. The output voltage can be positioned to meet a load line based on real time information. Except for a sense resistor in series with the inductor, this is the only sense method that can support a single cycle transient response. Other methods provide no information during either load increase (low side sensing) or load decrease (high side sensing). An additional problem associated with peak or valley current mode control for voltage positioning is that they suffer from peak-to-average errors. These errors will show in many ways but one example is the effect of frequency variation. If the frequency of a particular unit is 10% low, the peak to peak inductor current will be 10% larger and the output impedance of the converter will drop by about 10%. Variations in inductance, current sense amplifier bandwidth, PWM prop delay, any added slope compensation, input voltage, and output voltage are all additional sources of peak-toaverage errors. Current Sense Amplifier A high speed differential current sense amplifier is located in the phase IC, as shown in Figure 6. Its gain is nominally 33 at 25ºC, and the 3850 ppm/ºC increase in inductor DCR should be compensated in the voltage loop feedback path. The current sense amplifier can accept positive differential input up to 50mV and negative up to -10mV before clipping. The output of the current sense amplifier is summed with the VDAC voltage and sent to the control IC and other phases through an on-chip 3KΩ resistor connected to the IIN pin. The IIN pins of all the phases are tied together and the voltage on the share bus represents the average current through all the inductors and is used by the control IC for voltage positioning and current limit protection. The input offset of this amplifier is calibrated to +/- 1mV in order to reduce the current sense error. The input offset voltage is the primary source of error for the current share loop. In order to achieve very small input offset error and superior current sharing performance, the current sense amplifier continuously calibrates itself. This calibration algorithm creates ripple on IIN bus with a frequency of fsw/(32*28) in a multiphase architecture. Average Current Share Loop Current sharing between the phases of the converter is achieved by the average current share loop in each phase IC. The output of the current sense amplifier is compared with average current at the share bus. If current in a phase is smaller than the average current, the share adjust amplifier of the phase will pull down the starting point of the PWM ramp thereby increasing its duty cycle and output current; if current in a phase is larger than the average current, the share adjust amplifier of the phase will pull up the starting point of the PWM ramp thereby decreasing its duty cycle and output current. The current share amplifier is internally compensated; such that, the crossover frequency of the current share loop is much slower than that of the voltage loop and the two loops do not interact. Page 12 of 38 V3.2 IR3502B IR3502B THEORY OF OPERATION Block Diagram The block diagram of the IR3502B is shown in Figure 7. VID Control The control IC allows the processor voltage to be set by a parallel eight bit digital VID bus. The VID codes set the VDAC as shown in Table 1. The VID pins require an external bias voltage and should not be floated. The VID input comparators monitor the VID pins and control the Digital-to-Analog Converter (DAC), whose output is sent to the VDAC buffer amplifier. The output of the buffer amplifier is the VDAC pin. The VDAC voltage, input offsets of error amplifier and remote sense differential amplifier are post-package trimmed to achieve 0.5% system set-point accuracy for VID range between 1V to 1.6V. A set-point accuracy of ±5mV and ±8mV is achieved for VID ranges of 0.8V-1V and 0.5V-0.8V respectively. The actual VDAC voltage does not determine the system accuracy, which has a wider tolerance. The IR3502B can accept changes in the VID code while operating and vary the VDAC voltage accordingly. The slew rate of the voltage at the VDAC pin can be adjusted by an external capacitor between VDAC pin and LGND pin. A resistor connected in series with this capacitor is required to compensate the VDAC buffer amplifier. Digital VID transitions result in a smooth analog transition of the VDAC voltage and converter output voltage minimizing inrush currents in the input and output capacitors and overshoot of the output voltage. Adaptive Voltage Positioning Adaptive voltage positioning is needed to optimize the output voltage deviations during load transients and the power dissipation of the load at heavy load. The circuitry related to voltage positioning is shown in Figure 8. The output voltage is set by the reference voltage VSETPT at the positive input to the error amplifier. This reference voltage can be programmed to have a constant DC offset below the VDAC by connecting RSETPT between VDAC and VSETPT. The IVSETPT is controlled by the ROSC. The average load current information for all the phases is fed back to the control IC through the IIN pin. As shown in Figure 8, this information is thermally compensated with some gain by a set of buffer and thermal compensation amplifiers to generate the voltage at the VDRP pin. The VDRP pin is connected to the FB pin through the resistor RDRP. Since the error amplifier will force the loop to maintain FB to be equal to the VDAC reference voltage, an additional current will flow into the FB pin equal to (VDRP-VDAC) / RDRP. When the load current increases, the VDRP voltage increases accordingly. More current flows through the feedback resistor RFB and causes the output to have more droop. The positioning voltage can be programmed by the resistor RDRP so that the droop impedance produces the desired converter output impedance. The offset and slope of the converter output impedance are referenced to and therefore independent of the VDAC voltage. Inductor DCR Temperature Compensation A negative temperature coefficient (NTC) thermistor should be used for inductor DCR temperature compensation. The thermistor and tuning resistor network connected between the VN and VDRP pins provides a single NTC thermal compensation. The thermistor should be placed close to the power stage to accurately reflect the thermal performance of the inductor DCR. The resistor in series with the thermistor is used to reduce the nonlinearity of the thermistor. Remote Voltage Sensing VOSEN+ and VOSEN- are used for remote sensing and connected directly to the load. The remote sense differential amplifier with high speed, low input offset and low input bias current ensures accurate voltage sensing and fast transient response. There is finite input current at both pins VOSEN+ and VOSEN- due to the internal resistor of the differential amplifier. This limits the size of the resistors that can be used in series with these pins for acceptable regulation of the output voltage. Page 13 of 38 V3.2 IR3502B VCCLDRV 400K ENABLE COMPARATOR OC after VRRDY DISABLE VID FAULT POWER OK LATCH SS RESET 8-Pulse Delay + 0.2V 1.08V VCCL OPEN SENSE LINE OPEN DAISY CHAIN OPEN VOLTAGE LOOP + - VID1 VID0 VID0 200K 200K VID SAMPLE DELAY COMPARATOR VID0 VDAC OV FAULT 3V S OVER 130mV VOLTAGE 3mV COMPARATOR DETECTION SOFT START CLAMP F_VDAC 1.6V VDAC VO PHSIN DYNAMIC VID DETECT COMPARATOR S SET 60mV 50mV VDAC BUFFER AMPLIFIER + ISOURCE 25k OPEN SENSE LINE DETECT COMPARATORS ISINK DETECTION PULSE + - IROSC VCCL OPEN SENSE LINE DETECT COMPARATORS 6.1V - + ROSC/OVP VDAC VDAC VO VCCL - - OV@START VOSEN+ VOSEN- IVOSEN+ IVOSENVIDSEL IVOSEN- RESET - VCCLDRV ROSC BUFFER AMPLIFIER CURRENT SOURCE GENERATOR 25k + 0.6V + 200mV 0.4V OPEN SENSE LINE + Figure 7 Block Diagram Page 14 of 38 OV FAULT LATCH OV@START 25k - OV@OPERATION LGND R UV POWER-UP OV 1.21V COMPARATOR OV FAULT + VO IROSC VCCLDRV-0.2V Q VCCL UVLO DOMINANT REMOTE SENSE AMPLIFIER FB ISETPT - - PHSIN OPEN DAISY FAULT CHAIN EAOUT ERROR AMPLIFIER + PHSOUT IMON 0 VSETPT + CLKOUT 1.03 OV@OPERATION 25k CLKOUT PHSOUT VDRP IO IROSC 315mV 275mV + - Hold Last VID Q + FAULT LATCH1 VID0 + DISABLE PULSE VCCL UVLO VDRP CURRENT REPORT AMP 1.4V IDCHGDIS 4.5uA R THERMAL COMP 200K DAC_BUF FAULT LATCH1 Q S SET DOMINANT DYNAMIC VID1 VIDSEL R INTERNAL VID 0.6V 200K VOSEN- FAULT LATCH2 - VID1 - VID2 DAC_BUF OC LIMIT AMPLIFIER + + VID2 DAC_BUFF VN - VID3 DAC_BUF VDAC BUFFER AMP - + VID3 VID5 DIGITAL VID4 TO ANALOG CONVERTER VBOOT VID3 VBOOT (1.1V) VID2 100K VDRP SET DOMINANT S 1.3uS VID VIDSEL BLANKING FAULT VBOOT LATCH IIN - VID4 VID6 Q VDAC 200K R - VID4 VID7 SET DOMINANT VDRP + VID5 VID7 VID INPUT VID6 COMPARATORS (1/8 SHOWN) VID5 VID6 VCCL UVLO Q 1.17V VID FAULT LATCH R OV@OPERATION + + + EAOUT S OC LIMIT COMPARATOR - SS/DEL VID7 VCCL OV@START UV CLEARED FAULT LATCH2 PHSOUT - VCCL UVLO OC DELAY COUNTER + VCCL OUTPUT COMPARATOR 6.45V 5.45V VRHOT + + 6.8V HOTSET - R IROSC OC - SET DOMINANT - + 4.0V 1.6V 1.5V SS RESET R DISCHARGE COMPARATOR Q + VCCL - 80mV 120mV VCCL REGULATOR AMPLIFIER SS RESET S Q RESET DOMINANT UV VRHOT COMPARATOR S VID FAULT LATCH VCCL UVLO OC before VRRDY + VCCLDRV PGOOD FAULT LATCH1 FAULT LATCH2 OV FAULT - 250nS BLANKING DELAY COMPARATOR + INTEL 850mV 800mV SS CLEARED FAULT LATCH1 + ENABLE - V3.2 VOSEN- IR3502B TABLE 1 VR11 VID TABLE (PART1) Hex (VID7:VID0) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F Page 15 of 38 Dec (VID7:VID0) 00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000 00001001 00001010 00001011 00001100 00001101 00001110 00001111 00010000 00010001 00010010 00010011 00010100 00010101 00010110 00010111 00011000 00011001 00011010 00011011 00011100 00011101 00011110 00011111 00100000 00100001 00100010 00100011 00100100 00100101 00100110 00100111 00101000 00101001 00101010 00101011 00101100 00101101 00101110 00101111 00110000 00110001 00110010 00110011 00110100 00110101 00110110 00110111 00111000 00111001 00111010 00111011 00111100 00111101 00111110 00111111 Voltage Fault Fault 1.60000 1.59375 1.58750 1.58125 1.57500 1.56875 1.56250 1.55625 1.55000 1.54375 1.53750 1.53125 1.52500 1.51875 1.51250 1.50625 1.50000 1.49375 1.48750 1.48125 1.47500 1.46875 1.46250 1.45625 1.45000 1.44375 1.43750 1.43125 1.42500 1.41875 1.41250 1.40625 1.40000 1.39375 1.38750 1.38125 1.37500 1.36875 1.36250 1.35625 1.35000 1.34375 1.33750 1.33125 1.32500 1.31875 1.31250 1.30625 1.30000 1.29375 1.28750 1.28125 1.27500 1.26875 1.26250 1.25625 1.25000 1.24375 1.23750 1.23125 1.22500 1.21875 Hex (VID7:VID0) 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F 60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F Dec (VID7:VID0) 01000000 01000001 01000010 01000011 01000100 01000101 01000110 01000111 01001000 01001001 01001010 01001011 01001100 01001101 01001110 01001111 01010000 01010001 01010010 01010011 01010100 01010101 01010110 01010111 01011000 01011001 01011010 01011011 01011100 01011101 01011110 01011111 01100000 01100001 01100010 01100011 01100100 01100101 01100110 01100111 01101000 01101001 01101010 01101011 01101100 01101101 01101110 01101111 01110000 01110001 01110010 01110011 01110100 01110101 01110110 01110111 01111000 01111001 01111010 01111011 01111100 01111101 01111110 01111111 Voltage 1.21250 1.20625 1.20000 1.19375 1.18750 1.18125 1.17500 1.16875 1.16250 1.15625 1.15000 1.14375 1.13750 1.13125 1.12500 1.11875 1.11250 1.10625 1.10000 1.09375 1.08750 1.08125 1.07500 1.06875 1.06250 1.05625 1.05000 1.04375 1.03750 1.03125 1.02500 1.01875 1.01250 1.00625 1.00000 0.99375 0.98750 0.98125 0.97500 0.96875 0.96250 0.95625 0.95000 0.94375 0.93750 0.93125 0.92500 0.91875 0.91250 0.90625 0.90000 0.89375 0.88750 0.88125 0.87500 0.86875 0.86250 0.85625 0.85000 0.84375 0.83750 0.83125 0.82500 0.81875 V3.2 IR3502B TABLE 1 VR11 VID TABLE (PART 2) Hex (VID7:VID0) 80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F 90 91 92 93 94 95 96 97 98 99 9A 9B 9C 9D 9E 9F A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF Page 16 of 38 Dec (VID7:VID0) 10000000 10000001 10000010 10000011 10000100 10000101 10000110 10000111 10001000 10001001 10001010 10001011 10001100 10001101 10001110 10001111 10010000 10010001 10010010 10010011 10010100 10010101 10010110 10010111 10011000 10011001 10011010 10011011 10011100 10011101 10011110 10011111 10100000 10100001 10100010 10100011 10100100 10100101 10100110 10100111 10101000 10101001 10101010 10101011 10101100 10101101 10101110 10101111 10110000 10110001 10110010 10110011 10110100 10110101 10110110 10110111 10111000 10111001 10111010 10111011 10111100 10111101 10111110 10111111 Voltage 0.81250 0.80625 0.80000 0.79375 0.78750 0.78125 0.77500 0.76875 0.76250 0.75625 0.75000 0.74375 0.73750 0.73125 0.72500 0.71875 0.71250 0.70625 0.70000 0.69375 0.68750 0.68125 0.67500 0.66875 0.66250 0.65625 0.65000 0.64375 0.63750 0.63125 0.62500 0.61875 0.61250 0.60625 0.60000 0.59375 0.58750 0.58125 0.57500 0.56875 0.56250 0.55625 0.55000 0.54375 0.53750 0.53125 0.52500 0.51875 0.51250 0.50625 0.50000 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a Hex (VID7:VID0) C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 CA CB CC CD CE CF D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 DA DB DC DD DE DF E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF Dec (VID7:VID0) 11000000 11000001 11000010 11000011 11000100 11000101 11000110 11000111 11001000 11001001 11001010 11001011 11001100 11001101 11001110 11001111 11010000 11010001 11010010 11010011 11010100 11010101 11010110 11010111 11011000 11011001 11011010 11011011 11011100 11011101 11011110 11011111 11100000 11100001 11100010 11100011 11100100 11100101 11100110 11100111 11101000 11101001 11101010 11101011 11101100 11101101 11101110 11101111 11110000 11110001 11110010 11110011 11110100 11110101 11110110 11110111 11111000 11111001 11111010 11111011 11111100 11111101 11111110 11111111 Voltage n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a FAULT FAULT V3.2 IR3502B Control IC VSETPT Error Amplifier + EAOUT Phase IC + FB VDAC RFB 3k RDRP VDAC 100k 200k CSIN+ IOUT - CSIN- Current Sense Amplifier VDAC IIN VDAC Buffer + - Thermal Comp Amplifier + RTCMP1 RTHERM VDRP RTCMP2 - Phase IC VN + CSIN+ IOUT DAC_BUFF 3k RTCMP3 VO Remote Sense Amplifier + - VDAC - CSIN- Current Sense Amplifier VOSEN+ VOSEN- Figure 8 Adaptive voltage positioning with thermal compensation. Start-up Sequence The IR3502B has a programmable soft-start function to limit the surge current during the converter start-up. A capacitor connected between the SS/DEL and LGND pins controls soft start timing, over-current protection delay and hiccup mode timing. A charge current of 52.5uA and discharge current of 4uA control the up slope and down slope of the voltage at the SS/DEL pin respectively. Figure 9 depicts start-up sequence of converter with VR 11.1 VID. If there is no fault, as the ENABLE is asserted, the SS/DEL pin will start charging. The error amplifier output EAOUT is clamped low until SS/DEL reaches 1.4V. The error amplifier will then regulate the converter’s output voltage to match the SS/DEL voltage less the 1.4V offset until the converter output reaches the 1.1V boot voltage. The SS/DEL voltage continues to increase until it rises above the 3.0V threshold of VID delay comparator. The VID set inputs are then activated and VDAC pin transitions to the level determined by the VID inputs. The SS/DEL voltage continues to increase until it rises above 3.92V and allows the PGOOD signal to be asserted. SS/DEL finally settles at 4.0V, indicating the end of the soft start. The remote sense amplifier has a very low operating range of 50 mV in order to achieve a smooth soft start of output voltage without bump. The VCCL under voltage lock-out, VID fault modes, over current, as well as a low signal on the ENABLE input immediately sets the fault latch, which causes the EAOUT pin to drive low turning off the phase IC drivers. The PGOOD pin also drives low and SS/DEL begin to discharge until the voltage reaches 0.2V. If the fault has cleared the fault latch will be reset by the discharge comparator allowing a normal soft start to occur. Other fault conditions, such as over voltage, open sense lines, open loop monitor, and open daisy chain, set different fault latches, which start discharging SS/DEL, pull down EAOUT voltage and drive PGOOD low. However, the latches can only be reset by cycling VCCL power. Page 17 of 38 V3.2 IR3502B VCC (12V) ENABLE VID 1.1V VDAC 4.0V 3.92V 3V 1.4V SS/DEL EAOUT VOUT VRRDY SOFT START TIME (TD2) START DELAY (TD1) VID SAMPLE TIME (TD3) VRRDY DELAY TIME (TD4+TD5) TD4 NORMAL OPERATION TD5 Figure 9 Start-up sequence of converter with boot voltage Current Monitor (IMON) The control IC generates a current monitor signal IMON using the VDRP voltage and the VDAC reference, as shown in Figure 10. This voltage is thermally compensated for the inductor DCR variation. The voltage at this pin reports the average load current information without being referenced to VDAC. The slope of the IMON signal with respect to the load current can be adjusted with the resistors RTCMP2 and RTCMP3. The IMON signal is clamped at 1.03V in order to facilitate direct interfacing with the CPU. Control IC VDAC Buffer + VDAC - 100k 200k - DAC_BUFF VDRP Buffer IIN + Thermal Comp Amplifier From Phase ICs RTCMP1 RTHERM + VDRP RTCMP2 VN RTCMP3 DAC_BUFF 200k 200k - 200k VDRP + 1.03 IMON 0 200k VOSEN- Figure 10 Current report signal (IMON) implementation Page 18 of 38 V3.2 IR3502B Constant Over-Current Control during Soft Start The over current limit is fixed by 1.17V above the VDAC. If the VDRP pin voltage, which is proportional to the average current plus VDAC voltage, exceeds (VDAC+1.17V) during soft start, the constant over-current control is activated. Figure 11 shows the constant over-current control with delay during soft start. The delay time is set by the ROSC resistor, which sets the number of switching cycles for the delay counter. The delay is required since overcurrent conditions can occur as part of normal operation due to inrush current. If an over-current occurs during soft start (before PGOOD is asserted), the SS/DEL voltage is regulated by the over current amplifier to limit the output current below the threshold set by OC limit voltage. If the over-current condition persists after delay time is reached, the fault latch will be set pulling the error amplifier’s output low and inhibiting switching in the phase ICs. The SS/DEL capacitor will discharge until it reaches 0.2V and the fault latch is reset allowing a normal soft start to occur. If an over-current condition is again encountered during the soft start cycle, the constant over-current control actions will repeat and the converter will be in hiccup mode. The delay time is controlled by a counter which is triggered by clock. The counter values vary with switching frequency per phase in order to have a similar delay time for different switching frequencies. ENABLE INTERNAL OC DELAY SS/DEL 4.0V 3.92V 3.88V 1.1V EA VOUT VRRDY OCP THRESHOLD =VDAC_BUFF+1.17V IOUT START-UP WITH OUTPUT SHORTED HICCUP OVER-CURRENT PROTECTION (OUTPUT SHORTED) NORMAL START-UP OCP DELAY OVER-CURRENT NORMAL NORMAL PROTECTION START-UP OPERATION POWER-DOWN (OUTPUT SHORTED) (OUTPUT NORMAL OPERATION SHORTED) Figure 11 Constant over-current control waveforms during and after soft start. Over-Current Hiccup Protection after Soft Start The over current limit is fixed at 1.17V above the VDAC. Figure 11 shows the constant over-current control with delay after PGOOD is asserted. The delay is required since over-current conditions can occur as part of normal operation due to load transients or VID transitions. If the VDRP pin voltage, which is proportional to the average current plus VDAC voltage, exceeds (VDAC+1.17V) after PGOOD is asserted, it will initiate the discharge of the capacitor at SS/DEL. The magnitude of the discharge current is proportional to the voltage difference between VDRP and (VDAC+1.17V) and has a maximum nominal value of 55uA. If the over-current condition persists long enough for the SS/DEL capacitor to discharge below the 120mV offset of the delay comparator, the fault latch will be set pulling the error amplifier’s output low and inhibiting switching in the phase ICs and de-asserting the PGOOD signal. The output current is not controlled during the delay time. The SS/DEL capacitor will discharge until it reaches 200 mV and the fault latch is reset allowing a normal soft Page 19 of 38 V3.2 IR3502B start to occur. If an over-current condition is again encountered during the soft start cycle, the over-current action will repeat and the converter will be in hiccup mode. Linear Regulator Output (VCCL) The IR3502B has a built-in linear regulator controller, and only an external NPN transistor is needed to create a linear regulator. The voltage of VCCL is fixed at 6.8V with the feedback resistive divider internal to the IC. The regulator output powers the gate drivers of the phase ICs and circuits in the control IC, and the voltage is usually programmed to optimize the converter efficiency. The linear regulator can be compensated by a 4.7uF capacitor at the VCCL pin. As with any linear regulator, due to stability reasons, there is an upper limit to the maximum value of capacitor that can be used at this pin and it’s a function of the number of phases used in the multiphase architecture and their switching frequency. Figure 12 shows the stability plots for the linear regulator with 5 phases switching at 750 kHz. VCCL Under Voltage Lockout (UVLO) The IR3502B has no under voltage lockout for converter input voltage (VCC), but monitors the VCCL voltage instead, which is used for the gate drivers of phase ICs and circuits in control IC and phase ICs. During power up, the fault latch will be reset if VCCL is above 94% of 6.8V. If VCCL voltage drops below 80% of 6.8V, the fault latch will be set. Figure 12 VCCL regulator stability with 5 phases and PHSOUT equals 750 kHz. Over Voltage Protection (OVP) Output over-voltage happens during normal operation if a high side MOSFET short occurs or if output voltage is out of regulation. The over-voltage protection comparator monitors VO pin voltage. If VO pin voltage exceeds VDAC by 130mV after SS, as shown in Figure 13, IR3502B raises ROSC/OVP pin voltage above to V(VCCL) - 1V, which sends over voltage signal to system. During startup, the threshold is 130 mV above last VID and reverts back to VBOOT+130mV during boot mode. The ROSC/OVP pin can also be connected to a thyrister in a crowbar circuit, which pulls the converter input low in over voltage conditions. The over voltage condition also sets the over voltage fault latch, which pulls error amplifier output low to turn off the converter output. At the same time IIN pin (IIN of phase ICs) is pulled up to VCCL to communicate the over voltage condition to phase ICs, as shown in Figure 13. In each phase IC, the OVP circuit overrides the normal PWM operation and will fully turn-on the low side MOSFET within approximately 150ns. The low side MOSFET will remain on until IIN pin voltage drops below V(VCCL) - 800mV, which signals the end of over voltage condition. An over voltage fault condition is latched in the IR3502B and can only be cleared by cycling power to the IR3502B VCCL. Page 20 of 38 V3.2 IR3502B OUTPUT VOLTAGE (VO) OVP THRESHOLD 130mV VCCL-800 mV IIN (ISHARE) GATEH (PHASE IC) GATEL (PHASE IC) FAULT LATCH ERROR AMPLIFIER OUTPUT (EAOUT) VDAC NORMAL OPERATION OVP CONDITION AFTER OVP Figure 13 Over-voltage protection during normal operation 12V VCC VCCL+0.7V VCCL+0.7V 12V VCCLDRV 1.8V OUTPUT VOLTAGE (VOSEN+) VCCL UVLO ROSC/OVP 1.6V Figure 14 Over-voltage protection during power-up. Page 21 of 38 V3.2 IR3502B 12V VCCL+0.7V VCC VCCL+0.7V VCCLDRV 1.8V OUTPUT VOLTAGE (VOSEN+) 1.73V VCCL UVLO ROSC/OVP 1.6V Figure 15 Over-voltage protection with pre-charging converter output Vo > 1.73V 12V VCC VCCL+0.7V VCCL+0.7V VCCLDRV OUTPUT VOLTAGE (VOSEN+) 1.73V VID + 0.13V VCCL UVLO VCCL - 1V ROSC/OVP 0.6V 3.92V (4V-0.08V) SS/DEL Figure 16 Over-voltage protection with pre-charging converter output VID + 0.13V <Vo < 1.73V Page 22 of 38 V3.2 IR3502B In the event of a high side MOSFET short before power up, the OVP flag is activated with as little supply voltage as possible, as shown in Figure 14. The VOSEN+ pin is compared against a fixed voltage of 1.73V (typical) for OVP conditions at power-up. The ROSC/OVP pin will be pulled higher than 1.6V with VCCLDRV voltage as low as 1.8V. An external MOSFET or comparator should be used to disable the silver box, activate a crowbar, or turn off the supply source. The 1.8V threshold is used to prevent false over-voltage triggering caused by pre-charging of output capacitors. Pre-charging of converter may trigger OVP. If the converter output is pre-charged above 1.73V as shown in Figure 15, ROSC/OVP pin voltage will be higher than 1.6V when VCCLDRV voltage reaches 1.8V. ROSC/OVP pin voltage will be VCCLDRV-1V and rise with VCCLDRV voltage until VCCL is above UVLO threshold, after which ROSC/OVP pin voltage will be VCCL-1V. The converter cannot start unless the over voltage condition stops and VCCL is cycled. If the converter output is pre-charged 130mV above VDAC but lower than 1.73V, as shown in Figure 16, the converter will soft start until SS/DEL voltage is above 3.92V (4.0V-0.08V). Then, over voltage comparator is activated and fault latch is set. VID (FAST VDAC) VDAC OV THRESHOLD 1.73V VDAC + 130mV OUTPUT VOLTAGE (VO) VDAC 50mV 50mV NORMAL OPERATION VID DOWN LOW VID VID UP NORMAL OPERATION Figure 17 Over-voltage protection during dynamic VID During dynamic VID down, OVP may be triggered when output voltage can not follow VDAC voltage change at light load with large output capacitance. Therefore, over-voltage threshold is raised to 1.73V from VDAC+130mV whenever dynamic VID is detected and the difference between output voltage and VDAC is more than 50mV, as shown in Figure 19. The over-voltage threshold is changed back to VDAC+130mV if the difference is smaller than 50mV. VID Fault Codes VID codes of 0000000X and 1111111X for VR11 will set the fault latch and disable the error amplifier. A 1.3us delay is provided to prevent a fault condition from occurring during Dynamic VID changes. A VID FAULT condition is latched with boot voltage and can only be cleared by cycling power to VCCL or re-issuing ENABLE. Voltage Regulator Ready (PGOOD) The PGOOD pin is an open-collector output and should be pulled up to a voltage source through a resistor. After the soft start completion cycle, the PGOOD remains high until the output voltage is in regulation and SS/DEL is above 3.92V. The PGOOD pin becomes low if the fault latch, over voltage latch, open sense line latch, or open daisy chain Page 23 of 38 V3.2 IR3502B is set. A high level at the PGOOD pin indicates that the converter is in operation and has no fault. The PGOOD stays high as long as the output voltage is within 300 mV of the programmed VID. During start-up, it is pulled low with an input voltage as low as 2 V. It stays low until the startup sequence has completed, and the output voltage has moved to the programmed VID. Open Voltage Loop Detection The output voltage range of error amplifier is detected all the time to ensure the voltage loop is in regulation. If any fault condition forces the error amplifier output above VCCL-1.08V for 8 switching cycles, the fault latch is set. The fault latch can only be cleared by cycling power to VCCL. Open Remote Sense Line Protection If either remote sense line VOSEN+ or VOSEN- or both are open, the output of remote sense amplifier (VO) drops. The IR3502B monitors VO pin voltage continuously. If VO voltage is lower than 200 mV, two separate pulse currents are applied to VOSEN+ and VOSEN- pins respectively to check if the sense lines are open. If VOSEN+ is open, a voltage higher than 90% of V(VCCL) will be present at VOSEN+ pin and the output of open line detect comparator will be high. If VOSEN- is open, a voltage higher than 700mV will be present at VOSEN- pin and the output of open-line-detect comparator will be high. The open sense line fault latch is set, which pulls error amplifier output low immediately and shut down the converter. The SS/DEL voltage is discharged and the fault latch can only be reset by cycling VCCL power. During dynamic VID down, OVP may be triggered when output voltage can not follow VDAC voltage change at light load with large output capacitance. Therefore, over-voltage threshold is raised to 1.73V from VDAC+130mV whenever dynamic VID is detected and the difference between output voltage and VDAC is more than 50mV, as shown in Figure 17. The over-voltage threshold is changed back to VDAC+130mV if the difference is smaller than 50mV. Open Daisy Chain Protection IR3502B checks the daisy chain every time it powers up. It starts a daisy chain pulse on the PHSOUT pin and detects the feedback at PHSIN pin. If no pulse comes back after 32 CLKOUT pulses, the pulse is restarted again. If the pulse fails to come back the second time, the open daisy chain fault is registered, and SS/DEL is not allowed to charge. The fault latch can only be reset by cycling the power to VCCL. After powering up, the IR3502B monitors PHSIN pin for a phase input pulse equal or less than the number of phases detected. If PHSIN pulse does not return within the number of phases in the converter, another pulse is started on PHSOUT pin. If the second started PHSOUT pulse does not return on PHSIN, an open daisy chain fault is registered. Enable Input The ENABLE pin below 0.8V sets the Fault Latch and a voltage above 0.85V enables the soft start of the converter. Thermal Monitoring (VRHOT) A resistor divider including a thermistor at HOTSET pin sets the VRHOT threshold. The thermistor is usually placed at the temperature sensitive region of the converter, and is linearized by a series resistor. The IR3502B compare HOTSET pin voltage with a reference voltage of 1.6V. The VRHOT pin is an open-collector output and should be pulled up to a voltage source through a resistor. If the thermal trip point is reached the VRHOT output drives low. The hysteresis of the VRHOT comparator helps eliminate toggling of VRHOT output. The overall system must be considered when designing for OVP. In many cases the over-current protection of the AC-DC or DC-DC converter supplying the multiphase converter will be triggered and provide effective protection without damage as long as all PCB traces and components are sized to handle the worst-case maximum current. If this is not possible, a fuse can be added in the input supply to the multiphase converter. Page 24 of 38 V3.2 IR3502B Phase Number Determination After a daisy chain pulse is started, the IR3502B checks the timing of the input pulse at PHSIN pin to determine the phase number. This information is used to have symmetrical phase delay between phase switching without the need of any external component. Single Phase Operation In an architecture where only a single phase is needed the switching frequency is determined by the clock frequency. CURRENT SHARE LOOP COMPENSATION The internal compensation of current share loop ensures that crossover frequency of the current share loop is at least one decade lower than that of the voltage loop so that the interaction between the two loops is eliminated. The crossover frequency of current share loop is approximately 8 kHz. Fault Operation Table The Fault Table below describes the different faults that can occur and how IR3502A would react to protect the supply and the load from possible damage. The fault types that can occur are listed in row 1. Row 2 has the method that a fault is cleared. The first 5 faults are latched in the UV fault latch and the VCCL power has to be recycled by switching off the input and switching it back on for the converter to work again. The rest of the faults (except for UVLO Vout) are latched in the SS fault latch and does not need to recycle the VCCL power in order to resume normal operation once the fault condition clears. Most of the faults disable the error amplifier (EA) and discharge the soft start capacitor. All the faults flag PGOOD. PGOOD returns back to high when the faults are cleared. The delay row shows reaction time after detecting a fault condition. Delays are provided to minimize the possibility of nuisance faults. Fault Type Open Daisy Fault Clearing Method Error Amp Disabled ROSC/OVP & IIN drive high until OV clears SS/DEL Discharge Flags PGood Delay? Open Control Loop Open Sense Line Over Voltage VID Disable Recycle VCCL VCCL UVLO OC Before Start-up OC After Start-up Resume Normal Operation when Condition Clears Yes No VOUT UVLO No Yes No Yes No Yes 32 Clock Pulses Page 25 of 38 8 PHSOUT Pulses No No 1.3us Blank Time 250 ns Blank Time No PHSOUT Pulses. Count Programmed by ROSC value SS/DEL Discharge Threshold V3.2 No IR3502B DESIGN PROCEDURES - IR3502B AND IR3507 CHIPSET IR3502B EXTERNAL COMPONENTS Oscillator Resistor Rosc The oscillator of IR3502B generates square-wave pulses to synchronize the phase ICs. The switching frequency of the each phase converter equals the PHSOUT frequency, which is set by the external resistor ROSC according to the curve in Figure 18. The CLKOUT frequency equals the switching frequency multiplied by the phase number. The Rosc sets the reference current used for no load offset which is given by Figure 19 and equals: ISETPT 0.595 Rosc (1) Soft Start Capacitor CSS/DEL The soft start capacitor CSS/DEL programs five different time parameters. They include soft start delay time, soft start time, VID sample delay time, VR ready delay time and over-current fault latch delay time after VR ready. For the converter using VID with boot voltage, the SS/DEL pin voltage controls the slew rate of the converter output voltage, as shown in Figure 9. After the ENABLE pin voltage rises above 0.85V, there is a soft-start delay time TD1, after which the error amplifier output is released to allow the soft start of output voltage. The soft start time TD2 represents the time during which converter voltage rises from zero to 1.1V. The VID sample delay time (TD3) is the time period when VID stays at boot voltage of 1.1V. VID rise or fall time (TD4) is the time when VID changes from boot voltage to the final voltage. The VR ready delay time (TD5) is the time period from VR reaching the final voltage to the VR ready signal being issued, which is determined by the delay comparator threshold. CSS/DEL = 0.1uF meets all the specifications of TD1 to TD5, which are determined by (2) to (6) respectively. TD3 TD 4 TD5 Page 26 of 38 TD1 C SS / DEL *1.4 C SS / DEL *1.4 I CHG 52.5 *10 6 TD 2 C SS / DEL *1.1 C SS / DEL *1.1 I CHG 52.5 *10 6 (2) (3) C SS / DEL * (3 1.4 1.1) C SS / DEL * 0.7 I CHG 52.5 * 10 6 C SS / DEL * V DAC 1.1 I CHG (4) C SS / DEL * V DAC 1.1 (5) 52.5 *10 6 C C SS / DEL * (3.92 3) * 0.92 TD 4 SS / DEL 6 TD 4 I CHG 52.5 * 10 (6) V3.2 IR3502B CSS / DEL TD 2 * I CHG TD 2 * 52.5 *106 VO VO (7) The soft start delay time (TD1) and VR ready delay time (TD3) are determined by (8) to (9) respectively. *1.4 CSS / DEL *1.4 C TD1 SS / DEL I CHG 52.5 *106 TD3 C SS / DEL * (4.0 VO ) C SS / DEL * (4.0 VO ) I CHG 52.5 *10 6 (8) (9) Once CSS/DEL is chosen, the minimum over-current fault latch delay time tOCDEL is fixed and can be quantified as t OCDEL C SS / DEL * 0.12 C SS / DEL * 0.12 I DISCHG 55 * 10 6 (10) VDAC Slew Rate Programming Capacitor CVDAC and Resistor RVDAC The slew rate of VDAC slope SRDOWN can be programmed by the external capacitor CVDAC as defined in (11), where ISINK is the sink current of VDAC pin. The slew rate of VDAC up-slope is the same as that of down-slope. The resistor RVDAC is used to compensate VDAC circuit and can be calculated as follows CVDAC RVDAC I SINK 44 *10 6 SR DOWN SR DOWN (11) 1 2 900kHz CVDAC (12) Current Report Gain and Thermal Compensation Intel VR11.1 specifications require IMON to report the core maximum load current of the CPU be reported as 1 V nominal. The core maximum current can be different for different platforms. The IMON tuning resistors can therefore be adjusted and thermally compensated to adjust the load current gain with respect to the IMON. The expressions that govern the relationship between load current, IMON, and VDRP at room temperature are given by 1 R L _ room Gcs VDRP VDAC 3 n ( RTCMP2) II ( RTCMP1 RTHERM _ room) 1 Io RTCMP3 (13) 1 R L _ room G cs ( RTCMP2) II ( RTCMP1 RTHERM _ room) (14) 1 IMON Io 3 n RTCMP3 The change in inductor DCR with temperature is compensated by an equivalent variation in the RTHERM. The following equations derive the RTCMP1 and RTCMP2 if RTCMP3 and the thermistor (RTHERM and βTHERM) are fixed. RL _ MAX RL _ room [1 3850 *10 6 (TL _ MAX Troom )] K THERM _ room Page 27 of 38 1V I o max , K c _ room ( RL _ room Gcs ) n , K c _ t max (15) ( RL _ max Gcs ) (16) n V3.2 IR3502B 3 K THERM _ room 1 RTCMP3 Rt _ room K c _ room 3 K THERM _ room Rt _ t max 1 RTCMP3 K c _ t max (17) (18) RTHERM t max RTHERM room e BTH RTHERM room CTH RTHERM room RTHERM t max RTCMP1 BTH 1 1 273 Tmax 273 Troom THERM RTHERM (19) (20) t max RTHERM room RTHERM t max 1 1 R R t _ t max t _ room (21) BTH 2 4 CTH (22) 2 RTCMP 2 (23) 1 1 1 R R RTCMP 1 t _ t max t _ t max Droop Resistor The inductor DC resistance is utilized to sense the inductor current. The copper wire of inductor has a constant temperature coefficient of 3850 ppm/°C, and therefore the maximum inductor DCR can be calculated from (15), where RL_tmax and RL_room are the inductor DCR at maximum temperature Tmax and room temperature Troom. respectively. After the thermal compensation is achieved using the procedure given above, the droop resistance can be calculated using the following equation. R DRP 1 R FB GCS R L _ ROOM 3 Ro n R 1 t _ room RTCMP3 (24) Over-current Threshold Once the current report gain and the thermal compensation are calculated the OCP threshold is calculated using the following expression. I OCP (25) 1.17 1 R L _ room Gcs 3 n ( RTCMP2) II ( RTCMP1 RTHERM _ room) 1 RTCMP3 No Load Output Voltage Setting Resistor RVSETPT, A resistor between VSETPT pin and VDAC is used to create output voltage offset VO_NLOFST, which is the difference between VDAC voltage and output voltage at no load condition. RVSETPT is determined by (26), where IVSETPT is the current flowing out of VSETPT pin as shown in Figure 19. RVSETPT Page 28 of 38 VO _ NLOFST (26) IVSETPT V3.2 IR3502B Thermistor RHOTSET3 and Over Temperature Setting Resistors RHOTSET1 and RHOTSET2 The threshold voltage of VRHOT comparator is fixed at 1.6V, and a negative temperature coefficient (NTC) thermistor RHOTSET3 is required to sense the temperature of the power stage. If we pre-select RHOTSET3, the NTC thermistor resistance at allowed maximum temperature TMAX is calculated from (27). RTMAX RHOTSET 3 * EXP[ BHOTSET 3 * ( 1 TL _ MAX 1 T_ ROOM )] (27) Select the series resistor RHOTSET2 to linearize the NTC thermistor, which has non-linear characteristics in the operational temperature range. Then calculate RHOTSET1 corresponding to the allowed maximum temperature TMAX from (28). R HOTSET 1 ( RTMAX R HOTSET 2 ) * (VCCL 1.6) 1. 6 (28) VCCL Capacitor CVCCL The capacitor is selected based on the stability requirement of the linear regulator and the load current to be driven. The linear regulator supplies the bias and gate drive current of the phase ICs. A 4.7uF normally ensures stable VCCL performance for Intel VR11.1 applications. VCCL Regulator Drive Resistor RVCCLDRV The drive resistor is primarily dependent on the load current requirement of the linear regulator and the minimum input voltage requirements. The following equation gives an estimate of the average load current of the switching phase ICs. I drive _ avg (Q gb Q gt ) f sw 10 mA n (29) Qgb and Qgt are the gate charge of the top and bottom FET. For a minimum input voltage and a maximum VCCL, the maximum RVCCLDRV required to use the full pull-down current of the VCCL driver is given by RVCCLDRV V I (min) 0.7 6.8V I drive _ avg / min (30) Due to limited pull down capability of the VCCLDRV pin, make sure the following condition is satisfied. VI (max) 0.7 6.8V 10 mA RVCCLDRV (31) In the above equation, VI( min) and VI( max) is the minimum and maximum anticipated input voltage. If the above condition is not satisfied there is a need to use a device with higher βmin or Darlington configuration can be used instead of a single NPN transistor. Current Monitor Filter A filter is added to isolate the CPU from rapid changes in the load current and trigger false response. A filter with 300 us time constant provides adequate delay for Intel VR11.1 response. A 1k resistor between IMON and local ground helps equalize the source and sink current of the IMON pin. Page 29 of 38 V3.2 IR3502B DESIGN EXAMPLE – HIGH FREQUENCY CONVERTER (FIG. 20) SPECIFICATIONS Input Voltage: VI=12 V DAC Voltage: VDAC=1.2 V No Load Output Voltage Offset: VO_NLOFST=10 mV Continuous Output Current: IOTDC=110 A Maximum DC Output Current: IOMAX=140 A Current Report Gain =0.95 V represents IOMAX Output Impedance: RO=0.8 mΩ Soft Start Delay Time: TD1=0-5ms Soft Start Time: TD2=0.05ms-10ms VID Sample Delay Time: TD3=0.05-3ms VID Rise Time: TD4=0-3.5ms VR Ready Delay Time: TD5=0.05ms-3ms Maximum Over Current Delay Time: tOCDEL<2.5ms Dynamic VID Up-Slope Slew Rate: SRup=10mV/us Over Temperature Threshold: TMAX=100 ºC POWER STAGE Phase Number: n=5 Switching Frequency: fSW = 700 kHz Output Inductors: L=70 nH, RL=0.35 mΩ (Including solder resistance) Output Capacitors: Ceramic: C=22uF, Number Nc=50 SP: C=220uF, Number Nsp=2 IR3502B EXTERNAL COMPONENTS Oscillator Resistor Rosc Once the switching frequency is chosen, ROSC can be determined from the curve in Figure 18 of this data sheet. For a switching frequency of 700kHz per phase, choose ROSC = 17.4 kΩ. The reference current is given by 30uA. Soft Start Capacitor CSS/DEL Determine the soft start capacitor to meet the specifications of the delay time. Choose CSS/DEL=0.1uF. The soft start delay time is C SS / DEL * 1.4 0.1 * 10 6 * 1.4 2.67 mS I CHG 52.5 * 10 6 TD1 The soft start time is TD 2 C SS / DEL *1.1 0.1*10 6 *1.1 2.1mS I CHG 52.5 *10 6 The VID sample delay time is TD3 C SS / DEL * (3.2 1.4 1.1) 0.1*10 6 * 0.7 1.33mS I CHG 52.5 *10 6 VID rise time is Page 30 of 38 V3.2 IR3502B TD 4 C SS / DEL * V DAC 1.1 I CHG The VR ready delay time is TD 5 0.1*10 6 * 1.3 1.1 52.5 *10 6 0.38mS C SS / DEL * (3.92 3) 0.1 * 10 6 * 0.92 TD 4 TD 4 1.37 mS I CHG 52.5 * 10 6 Minimum over current fault latch delay time is t OCDEL C SS / DEL * 0.12 0.1 * 10 6 * 0.12 0.21ms I OCDISCHG 55 * 10 6 VDAC Slew Rate Programming Capacitor CVDAC and Resistor RVDAC Calculate the VDAC down-slope slew-rate programming capacitor from the required down-slope slew rate. The up-slope slew rate is the same as the down-slope slew rate. CVDAC I SINK 44 * 10 6 4.4nF SR DOWN 10 * 10 3 / 10 6 A 3.3 nF capacitor can be used. A series resistor is used to stabilize the VDAC buffer. RVDAC 1 53 A 50 Ω resistor is selected. 2 900kHz CVDAC No Load Output Voltage Setting Resistor RVSETPT From Figure 19, the bias current of VSETPT pin is 30 uA with ROSC=17.4 kΩ. RVSETPT VO _ NLOFST I VSETPT 10 * 10 3 330 30 * 10 6 Current Report Gain and Thermal Compensation The reporting gain specifies the max load current in form of a voltage. For this example, the 140 A represents 0.95 V at IMON. If the thermal effects are neglected (14) can be used to find the reporting gain. However, as the inductor DCR increases with temperature, the thermal compensation string (RTCMP1, RTCMP2, and RTHERM) can be used to compensate this change in DCR. Assuming Troom =25 Deg, Tmax=100 Deg the change in DCR is found our using (15) RL _ MAX 0.35m [1 3850 *10 6 (100 25)] 0.45m Preselect RTCMP3=1 kΩ, and RTHERM_room=10 kΩ with βTHERM=3380K RTCMP1 and RTCMP2 can be found out using (16)-(23) RTCMP1=8.837 kΩ RTCMP2=8.457 kΩ Page 31 of 38 V3.2 IR3502B Droop Resistor Based on the above calculation RDRP can be selected to obtain specific output impedance. Pre-select RFB=1 kΩ and using Ro=0.8 mΩ, Gcs=33.5 along with the converter parameters can be plugged into (24) to find out RDRP. RDRP 1 1k 33.5 0.35m 5.618k 7.5k 1 3 0.8m 5 1k Over Current Threshold The OCP is fixed at 1.17 V above the VDAC voltage. Therefore, it can be determined as follows I OCP 1.17 1 0.35m 33.5 (8.457k ) II (8.837k 10k ) 1 5 1k 3 182 A VCCL Drive Resistor RVCCLDRV The maximum drive current for the linear regulator is dependent on the type of MosFET used. For this example, it’s assumed that IR6622 and IRF6628 are used as the control and sync FET respectively. I drive _ avg (30 .3n 11n) 700 k 10 mA 5 195 mA The minimum input voltage is assumed to be 10.5 V and VCCL is fixed at 6.5V for this design. RVCCLDRV 10.5V 0.7V 6.5V 700 195mA / 30 Choose a transistor with β(min) of 50. The maximum input voltage is assumed 13.5 V, 13.5V 0.7 6.5 9mA 10 mA 700 Thermistor RHOTSET3 and Over Temperature Setting Resistors RHOTSET1 and RHOTSET2 Choose NTC thermistor RHOTSET3=2.2kΩ, which has a constant of BHOTSET3=3520, and the NTC thermistor resistance at the allowed maximum temperature TMAX is, RTMAX R HOTSET 3 * EXP[ B HOTSET 3 * ( 1 TL _ MAX 1 T_ ROOM )] 2.2 * 10 3 * EXP[3520 * ( 1 1 )] 142 273 115 273 25 Select RHOTSET2 = 931Ω to linearize the NTC, which has non-linear characteristics in the operational temperature range. Then calculate RHOTSET1 corresponding to the allowed maximum temperature TMAX. R HOTSET 1 ( RTMAX R HOTSET 2 ) * (VCCL 1.6) (142 931) * (7 1.6) 3.63k , choose RHOTSET1=3.65kΩ. 1. 6 1. 6 Page 32 of 38 V3.2 IR3502B IR3502 Frequency vs. ROSC Resistor 55 50 45 RROSC (KOhm) 40 35 RROSC Nominal Spec 30 25 20 15 10 5 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 Frequency (KHz) Figure 18: Frequency variation with ROSC. I(VSETPT) vs. 1/RROSC 90.0 80.0 70.0 I(VSETPT) (uA) 60.0 I(VSETPT) Min V(ISETPT) Nom V(ISETPT) Max V(ISETPT) 50.0 40.0 30.0 20.0 10.0 0.0 0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 1/RROSC (1/KOhm) Figure 19: ISETPT with ROSC. Page 33 of 38 V3.2 IR3502B LAYOUT GUIDELINES The following layout guidelines are recommended to reduce the parasitic inductance and resistance of the PCB layout, therefore minimizing the noise coupled to the IC. VO VCCL VOSNS + IIN VOSNS – To SYSTEM VID0 VID1 VID2 VID3 VID4 To Phase ICs Analog Ccp1 Rcp Ccp Rhotset1 ENABLE VID5 IMON VID6 VRHOT Rhotset2 HOTSET PGOOD Cfb PHSIN Voltage Remote Sense FB Rfb1 PHSOUT VID7 Rmon1 Rtcmp2 Rdrp EAOUT Rfb CLKOUT VCCLDRV Page 34 of 38 To Rtherm VDRP VN VDAC_BUFF Rtcmp3 Rctmp1 Rsetpt VSETPT VDAC SS/DEL GND ROSC Rosc Css/Del Rvdac Cvdac To Phase ICs Digital Rmon Cmon To Regulator Dedicate at least one middle layer for a ground plane LGND. Connect the ground tab under the control IC to LGND plane through a via. Place VCCL decoupling capacitor VCCL as close as possible to VCCL and LGND pins. Place the following critical components on the same layer as control IC and position them as close as possible to the respective pins, ROSC, RVDAC, CVDAC, and CSS/DEL. Avoid using any via for the connection. Place the compensation components on the same layer as control IC and position them as close as possible to EAOUT, FB, VO and VDRP pins. Avoid using any via for the connection. Use Kelvin connections for the remote voltage sense signals, VOSNS+ and VOSNS-, and avoid crossing over the fast transition nodes, i.e. switching nodes, gate drive signals and bootstrap nodes. Avoid analog control bus signals, VDAC, IIN, and especially EAOUT, crossing over the fast transition nodes. Separate digital bus, CLKOUT, PHSOUT and PHSIN from the analog control bus and other compensation components. Cvccl2 To VCCL To Thermistor LGND PLANE V3.2 IR3502B PCB Metal and Component Placement Lead land width should be equal to nominal part lead width. The minimum lead to lead spacing should be ≥ 0.2mm to prevent shorting. Lead land length should be equal to maximum part lead length + 0.3 mm outboard extension + 0.05mm inboard extension. The outboard extension ensures a large and inspectable toe fillet, and the inboard extension will accommodate any part misalignment and ensure a fillet. Center pad land length and width should be equal to maximum part pad length and width. However, the minimum metal to metal spacing should be ≥ 0.17mm for 2 oz. Copper (≥ 0.1mm for 1 oz. Copper and ≥ 0.23mm for 3 oz. Copper) Four 0.30mm diameter vias shall be placed in the center of the pad land and connected to ground to minimize the noise effect on the IC. No pcb traces should be routed nor vias placed under any of the 4 corners of the IC package. Doing so can cause the IC to rise up from the pcb resulting in poor solder joints to the IC leads. Page 35 of 38 V3.2 IR3502B Solder Resist The solder resist should be pulled away from the metal lead lands by a minimum of 0.06mm. The solder resist mis-alignment is a maximum of 0.05mm and it is recommended that the lead lands are all Non Solder Mask Defined (NSMD). Therefore pulling the S/R 0.06mm will always ensure NSMD pads. The minimum solder resist width is 0.13mm. At the inside corner of the solder resist where the lead land groups meet, it is recommended to provide a fillet so a solder resist width of ≥ 0.17mm remains. The land pad should be Solder Mask Defined (SMD), with a minimum overlap of the solder resist onto the copper of 0.06mm to accommodate solder resist mis-alignment. In 0.5mm pitch cases it is allowable to have the solder resist opening for the land pad to be smaller than the part pad. Ensure that the solder resist in-between the lead lands and the pad land is ≥ 0.15mm due to the high aspect ratio of the solder resist strip separating the lead lands from the pad land. The vias in the land pad should be tented or plugged from bottom boardside with solder resist. Page 36 of 38 V3.2 IR3502B Stencil Design The stencil apertures for the lead lands should be approximately 80% of the area of the lead lands. Reducing the amount of solder deposited will minimize the occurrence of lead shorts. Since for 0.5mm pitch devices the leads are only 0.25mm wide, the stencil apertures should not be made narrower; openings in stencils < 0.25mm wide are difficult to maintain repeatable solder release. The stencil lead land apertures should therefore be shortened in length by 80% and centered on the lead land. The land pad aperture should be striped with 0.25mm wide openings and spaces to deposit approximately 50% area of solder on the center pad. If too much solder is deposited on the center pad the part will float and the lead lands will be open. The maximum length and width of the land pad stencil aperture should be equal to the solder resist opening minus an annular 0.2mm pull back to decrease the incidence of shorting the center land to the lead lands when the part is pushed into the solder paste. Page 37 of 38 V3.2 IR3502B PACKAGE INFORMATION 32L MLPQ (5 x 5 mm Body) – θJA = 24.4oC/W, θJC =0.86 oC/W Data and specifications subject to change without notice. This product has been designed and qualified for the Consumer market. Qualification Standards can be found on IR’s Web site. IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105 TAC Fax: (310) 252-7903 Visit us at www.irf.com for sales contact information. www.irf.com Page 38 of 38 V3.2