IR3505ZMPBF

IR3505Z DATA SHEET XPHASE3TM PHASE IC DESCRIPTION The IR3505Z Phase IC combined with an IR XPhase3TM Control IC provides a full featured and flexible way to implement power solutions for the latest high performance CPUs and ASICs. The “Control” IC provides overall system control and interfaces with any number of “Phase” ICs which each drive and monitor a single phase of a multiphase converter. 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 • • • • • • • • • • • • • 7V/2A gate drivers (4A GATEL sink current) Support converter output voltage up to 5.1 V (Limited to VCCL-1.4V) Support loss-less inductor current sensing Feed-forward voltage mode control Integrated boot-strap synchronous PFET Only four IC related external components per phase 3 wire analog bus connects Control and Phase ICs (VDAC, Error Amp, ISHARE) 3 wire digital bus for accurate daisy-chain phase timing control without external components Debugging function isolates phase IC from the converter Self-calibration of PWM ramp, current sense amplifier, and current share amplifier Single-wire bidirectional average current sharing Small thermally enhanced 16L 3 x 3mm MLPQ package RoHS compliant APPLICATION CIRCUIT Page 1 of 20 March 17, 2009 IR3505Z ORDERING INFORMATION Part Number IR3505ZMTRPBF * IR3505ZMPBF * Samples only Package 16 Lead MLPQ (3 x 3 mm body) 16 Lead MLPQ (3 x 3 mm body) Order Quantity 3000 per reel 100 piece strips ABSOLUTE MAXIMUM RATINGS Stresses beyond those listed below 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…………….. 0oC to 150oC Storage Temperature Range………………….-65oC to 150oC MSL Rating………………………………………2 Reflow Temperature…………………………….260oC PIN # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 PIN NAME ISHARE DACIN LGND PHSIN PHSOUT CLKIN PGND GATEL VCCL BOOST GATEH SW VCC CSIN+ CSINEAIN VMAX 8V 3.3V n/a 8V 8V 8V 0.3V 8V 8V 34V 34V 34V 18V 8V 8V 8V VMIN -0.3V -0.3V n/a -0.3V -0.3V -0.3V -0.3V -0.3V DC, -5V for 100ns -0.3V -0.3V -0.3V DC, -5V for 100ns -0.3V DC, -5V for 100ns -0.3V -0.3V -0.3V -0.3V ISOURCE 1mA 1mA n/a 1mA 2mA 1mA 5A for 100ns, 200mA DC 5A for 100ns, 200mA DC n/a 1A for 100ns, 100mA DC 3A for 100ns, 100mA DC 3A for 100ns, 100mA DC n/a 1mA 1mA 1mA ISINK 1mA 1mA n/a 1mA 2mA 1mA n/a 5A for 100ns, 200mA DC 5A for 100ns, 200mA DC 3A for 100ns, 100mA DC 3A for 100ns, 100mA DC n/a 10mA 1mA 1mA 1mA Note: 1. Maximum GATEH – SW = 8V 2. Maximum BOOST – GATEH = 8V Page 2 of 20 March 17, 2009 IR3505Z RECOMMENDED OPERATING CONDITIONS FOR RELIABLE OPERATION WITH MARGIN 8.0V ≤ VCC ≤ 16V, 4.75V ≤ VCCL ≤ 7.5V, 0.5V ≤ V(DACIN) ≤ 1.6V, 250kHz ≤ CLKIN ≤ 9MHz, 250kHz ≤ PHSIN ≤1.5MHz, 0 oC ≤ TJ ≤ 125 oC ELECTRICAL CHARACTERISTICS The electrical characteristics involve the spread of values guaranteed within the recommended operating conditions. Typical values represent the median values, which are related to 25°C. CGATEH = 3.3nF, CGATEL = 6.8nF (unless otherwise specified). PARAMETER Gate Drivers GATEH Source Resistance GATEH Sink Resistance GATEL Source Resistance GATEL Sink Resistance GATEH Source Current GATEH Sink Current GATEL Source Current GATEL Sink Current GATEH Rise Time GATEH Fall Time GATEL Rise Time GATEL Fall Time GATEL low to GATEH high delay GATEH low to GATEL high delay Disable Pull-Down Resistance Clock CLKIN Threshold CLKIN Bias Current CLKIN Phase Delay PHSIN Threshold PHSOUT Propagation Delay PHSIN Pull-Down Resistance PHSOUT High Voltage PHSOUT Low Voltage TEST CONDITION BOOST – SW = 7V. Note 1 BOOST – SW = 7V. Note 1 VCCL – PGND = 7V. Note 1 VCCL – PGND = 7V. Note 1 BOOST=7V, GATEH=2.5V, SW=0V. BOOST=7V, GATEH=2.5V, SW=0V. VCCL=7V, GATEL=2.5V, PGND=0V. VCCL=7V, GATEL=2.5V, PGND=0V. BOOST – SW = 7V, measure 1V to 4V transition time BOOST - SW = 7V, measure 4V to 1V transition time VCCL – PGND = 7V, Measure 1V to 4V transition time VCCL – PGND = 7V, Measure 4V to 1V transition time BOOST = VCCL = 7V, SW = PGND = 0V, measure time from GATEL falling to 1V to GATEH rising to 1V BOOST = VCCL = 7V, SW = PGND = 0V, measure time from GATEH falling to 1V to GATEL rising to 1V Note 1 MIN TYP 1.0 1.0 1.0 0.4 2.0 2.0 2.0 4.0 5 5 10 5 10 20 MAX 2.5 2.5 2.5 1.0 UNIT Ω Ω Ω Ω A A A A ns ns ns ns ns 10 10 20 10 40 10 20 40 ns 30 80 130 kΩ Compare to V(VCCL) CLKIN = V(VCCL) Measure time from CLKIN1V Compare to V(VCCL) Measure time from CLKIN > (VCCL * 50% ) to PHSOUT > (VCCL *50%). 10pF @125 oC 40 -0.5 40 35 4 30 45 0.0 75 50 15 100 0.6 0.4 57 0.5 125 55 35 170 % µA ns % ns kΩ V I(PHSOUT) = -10mA, measure VCCL – PHSOUT I(PHSOUT) = 10mA 1 1 V Page 3 of 20 March 17, 2009 IR3505Z PARAMETER PWM Comparator PWM Ramp Slope Input Offset Voltage EAIN Bias Current Minimum Pulse Width Minimum GATEH Turn-off Time Current Sense Amplifier CSIN+/- Bias Current CSIN+/- Bias Current Mismatch Input Offset Voltage Gain Unity Gain Bandwidth Slew Rate Differential Input Range Differential Input Range Common Mode Input Range Rout at TJ = 25 oC Rout at TJ = 125 oC ISHARE Source Current ISHARE Sink Current Share Adjust Amplifier Input Offset Voltage Differential Input Range Gain Unity Gain Bandwidth PWM Ramp Floor Voltage Maximum PWM Ramp Floor Voltage Minimum PWM Ramp Floor Voltage Body Brake Comparator Threshold Voltage with EAIN falling. Threshold Voltage with EAIN rising. Hysteresis Propagation Delay Vin=12V Note 1 0 ≤ EAIN ≤ 3V Note 1 TEST CONDITION MIN TYP MAX UNIT mV/ %DC mV µA ns nS nA nA mV V/V MHz V/µs mV mV V kΩ kΩ mA mA mV V V/V kHz mV mV 120 180 240 mV -220 -160 -100 42 -5 -5 20 -200 -50 -1 30 4.8 52.5 0 -0.3 65 80 0 0 57 5 5 75 160 200 50 1 Note 1 CSIN+ = CSIN- = DACIN. Measure input referred offset from DACIN 0.5V ≤ V(DACIN) < 1.6V C(ISHARE)=10pF. Measure at ISHARE. Note 1 0.8V ≤ V(DACIN) ≤ 1.6V, Note 1 0.5V ≤ V(DACIN) < 0.8V, Note 1 Note 1 Note 1 32.5 6.8 6 35 8.8 -10 -5 0 2.3 3.6 0.500 0.500 -3 -1 4 4 -116 3.0 4.7 1.6 1.4 0 5.0 8.5 0 50 50 Note2 3.7 5.4 2.9 2.9 3 1 6 17 +116 Note 1 Note 1 CSIN+ = CSIN- = DACIN. Note 1 Note 1 ISHARE unconnected Measured Relative to DACIN ISHARE = DACIN - 200mV Measured relative to FLOOR with ISHARE unconnected ISHARE = DACIN + 200mV Measured relative to FLOOR with ISHARE unconnected Measured relative to PWM Ramp Floor Voltage Measured relative to PWM Ramp Floor Voltage VCCL = 5V. Measure time from EAIN < V(DACIN) (200mV overdrive) to GATEL transition to < 4V. -300 -200 70 40 -200 -100 105 65 -110 -10 130 90 mV mV mV ns Page 4 of 20 March 17, 2009 IR3505Z PARAMETER OVP Comparator OVP Threshold TEST CONDITION MIN -1.0 15 TYP -0.8 40 MAX -0.4 70 UNIT V nS Step V(ISHARE) up until GATEL drives high. Compare to V(VCCL) Propagation Delay V(VCCL)=5V, Step V(ISHARE) up from V(DACIN) to V(VCCL). Measure time to V(GATEL)>4V. Synchronous Rectification Disable Comparator Threshold Voltage The ratio of V(CSIN-) / V(DACIN), below which V(GATEL) is always low. Negative Current Comparator Input Offset Voltage Note 1 Propagation Delay Time Apply step voltage to V(CSIN+) – V(CSIN-). Measure time to V(GATEL)< 1V. Bootstrap Diode Forward Voltage I(BOOST) = 30mA, VCCL=6.5V Debug Comparator Threshold Voltage Compare to V(VCCL) General VCC Supply Current VCCL Supply Current BOOST Supply Current 4.75V ≤ V(BOOST)-V(SW) ≤ 8V DACIN Bias Current SW Floating Voltage Measured in the application 66 75 86 % -16 100 0 200 16 400 mV nS 180 -250 1.1 3.1 1.2 -1.5 260 -150 3.0 6.7 3.5 -0.75 0.3 480 -50 6.1 12.1 5.8 1 mV mV mA mA mA µA V Note 1: Guaranteed by design, but not tested in production Note 2: VCCL-0.5V or VCC – 2.5V, whichever is lower Page 5 of 20 March 17, 2009 IR3505Z PIN DESCRIPTION PIN# 1 PIN SYMBOL ISHARE PIN DESCRIPTION Output of the Current Sense Amplifier is connected to this pin through a 3kΩ resistor. Voltage on this pin is equal to V(DACIN) + 32.5 [V(CSIN+) – V(CSIN-)]. Connecting all ISHARE pins together creates a share bus which provides an indication of the average current being supplied by all the phases. The signal is used by the Control IC for voltage positioning and over-current protection. OVP mode is initiated if the voltage on this pin rises above V(VCCL)- 0.8V. Reference voltage input from the Control IC. The Current Sense signal and PWM ramp is referenced to the voltage on this pin. Ground for internal IC circuits. IC substrate is connected to this pin. Phase clock input. Phase clock output. Clock input. Return for low side driver and reference for GATEH non-overlap comparator. Low-side driver output and input to GATEH non-overlap comparator. Supply for low-side driver. Internal bootstrap synchronous PFET is connected from this pin to the BOOST pin. Supply for high-side driver. Internal bootstrap synchronous PFET is connected between this pin and the VCCL pin. High-side driver output and input to GATEL non-overlap comparator. Return for high-side driver and reference for GATEL non-overlap comparator. Supply for internal IC circuits. Non-Inverting input to the current sense amplifier, and input to debug comparator. Inverting input to the current sense amplifier, and input to synchronous rectification disable comparator. PWM comparator input from the error amplifier output of Control IC. Body Braking mode is initiated if the voltage on this pin is less than V(DACIN). 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 DACIN LGND PHSIN PHSOUT CLKIN PGND GATEL VCCL BOOST GATEH SW VCC CSIN+ CSINEAIN Page 6 of 20 March 17, 2009 IR3505Z SYSTEM THEORY OF OPERATION PWM Control Method The PWM block diagram of the XPhaseTM architecture is shown in Figure 1. 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. GATE DRIVE VOLTAGE VIN PHSOUT CONTROL IC CLOCK GENERATOR CLKOUT PHASE IC CLKIN CLK Q D 1 2 1 RESET DOMINANT D R Q 4 5 VCC VCCH GATEH SW COUT CBST PHSOUT PHSIN PHSIN VOSNS+ VOUT PWM COMPARATOR EAIN 2 + CLK Q 3 VCCL GND GATEL PGND VOSNS- PWM LATCH VID6 VO LDO AMPLIFIER VDAC LGND ERROR AMPLIFIER + + 2 1 2 + 3 + REMOTE SENSE AMPLIFIER ENABLE RAMP DISCHARGE CLAMP BODY BRAKING COMPARATOR + - + EAOUT RCOMP CCOMP1 CCOMP RFB1 RFB 3K + CFB FB RVSETPT DACIN PHSOUT RDRP RDRP1 IVSETPT IROSC + VDRP AMP VSETPT VDRP CDRP PHASE IC CLKIN CLK Q D IIN 1 PHSIN PWM COMPARATOR EAIN ENABLE RESET DOMINANT D R Q 4 5 CLK Q PWM LATCH VID6 + RAMP DISCHARGE CLAMP BODY BRAKING COMPARATOR + - SHARE ADJUST ERROR AMPLIFIER ISHARE 3K VID6 VID6 + - CURRENT SENSE AMPLIFIER CSIN+ + + VID6 VID6 + DACIN Figure 1 PWM Block Diagram 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 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. and 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 2 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. Page 7 of 20 - VID6 VID6 + + - - - ISHARE + VDAC - + - - SHARE ADJUST ERROR AMPLIFIER VID6 VID6 + - CURRENT SENSE AMPLIFIER CSIN+ CCS RCS CSIN- VCC VCCH GATEH SW VCCL GATEL PGND CBST CCS RCS CSIN- March 17, 2009 IR3505Z 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 2 Four Phase Oscillator Waveforms PWM Operation The PWM comparator is located in the phase IC. Upon receiving the falling edge of a clock pulse, the PWM latch is set; the PWM ramp 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 PWM ramp voltage exceeds the error amplifier’s output voltage the PWM latch is reset. This turns off the high side driver, turns on the low side driver after the non-overlap time, and activates the ramp discharge clamp. The clamp drives the PWM ramp voltage to the level set by the share adjust amplifier 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. An additional advantage of this PWM modulator is that differences in ground or input voltage at the phases have no effect on operation since the PWM ramps are referenced to VDAC. Figure 3 depicts PWM operating waveforms under various conditions. Page 8 of 20 March 17, 2009 IR3505Z PHASE IC CLOCK PULSE EAIN PWMRMP VDAC GATEH GATEL STEADY-STATE OPERATION 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 3 PWM Operating Waveforms Body BrakingTM 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. 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 4. 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 so 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 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. Page 9 of 20 March 17, 2009 IR3505Z vL iL L RCS Current Sense Amp RL CCS c VO CO CSOUT Figure 4 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-to-average errors. Current Sense Amplifier A high speed differential current sense amplifier is located in the phase IC, as shown in Figure 5. Its gain is nominally 32.5 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 DAC voltage and sent to the control IC and other phases through an on-chip 3KΩ resistor connected to the ISHARE pin. The ISHARE 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 ISHARE bus with a frequency of fsw/(32*28) in a multiphase architecture. Average Current Share Loop Current sharing between 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 the 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 so 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 10 of 20 March 17, 2009 IR3505Z IR3505Z THEORY OF OPERATION Block Diagram The Block diagram of the IR3505Z is shown in Figure 5, and specific features are discussed in the following sections. CLKIN PHSIN 100% DUTY LATCH PWMQ PWM_CLK PWM_CLK CLK Q D CLK Q D PHSOUT GATEH DRIVER BOOST GATEH PWM LATCH D Q PWM_CLK CLK Q RESET DOMINANT R PWMQ PWM COMPARATOR EAIN + GATEH NONOVERLAP LATCH Q S GATEH NONOVERLAP COMPARATOR + SW RMPOUT PHSIN PWM RESET VCC VCC CALIBRATION DACIN-SHARE_ADJ PWM RAMP GENERATOR VCCL SET R DOMINANT GATEL NONOVERLAP LATCH Q S 1V GATEL NONOVERLAP COMPARATOR 1V + - BODY BRAKING 100mV COMPARATOR 200mV + SET R DOMINANT DACIN + SHARE_ADJ VCCL OVP COMPARATOR - NEGATIVE CURRENT LATCH GATEL DRIVER VCCL GATEL PGND 0.8V ISHARE DEBUG OFF (LOW=OPEN) SHARE ADJUST AMPLIFIER 3K + - CALIBRATION DACIN (CLKIN PHSIN IF 1-PHASE) LGND IROSC Tri-State Gate Drivers The gate drivers can deliver up to 2A peak current (4A sink current for bottom driver). An adaptive non-overlap circuit monitors the voltage on the GATEH and GATEL pins to prevent MOSFET shoot-through current while minimizing body diode conduction. The non-overlap latch is added to eliminate the error triggering caused by the switching noise. An enable signal is provided by the control IC to the phase IC without the addition of a dedicated signal line. The error amplifier output of the control IC drives low in response to any fault condition such as VCCL under voltage or output overload. The IR3505Z Body BrakingTM comparator detects this and drives bottom gate output low. This tri-state operation prevents negative inductor current and negative output voltage during powerdown. A synchronous rectification disable comparator is used to detect converter CSIN- pin voltage, which represents local converter output voltage. If the voltage is below 75% of VDAC and negative current is detected, GATEL drives low, which disables synchronous rectification and eliminates negative current during power-up. The gate drivers pull low if the supply voltages are below the normal operating range. An 80kΩ resistor is connected across the GATEH/GATEL and PGND pins to prevent the GATEH/GATEL voltage from rising due to leakage or other causes under these conditions. Page 11 of 20 + Q RESET DOMINANT R S SYNCHRONOUS RECTIFICATION DISABLE COMPARATOR + NEGATIVE CURRENT COMPARATOR - CURRENT SENSE AMPLIFIER - CSAOUT + CSINCSIN+ DEBUG COMPARATOR + + + IROSC DACIN X33 + X 0.75 CALIBRATION 0.2V Figure 5 Block diagram March 17, 2009 IR3505Z Over Voltage Protection (OVP) The IR3505Z includes over-voltage protection that turns on the low side MOSFET to protect the load in the event of a shorted high-side MOSFET, converter out of regulation, or connection of the converter output to an excessive output voltage. As shown in Figure 6, if ISHARE pin voltage is above V(VCCL) – 0.8V, which represents over-voltage condition detected by control IC, the over-voltage latch is set. GATEL drives high and GATEH drives low. The OVP circuit overrides the normal PWM operation and within approximately 150ns will fully turn-on the low side MOSFET, which remains ON until ISHARE drops below V(VCCL) – 0.8V when over voltage ends. The over voltage fault is latched in control IC and can only be reset by cycling the power to control IC. The error amplifier output (EAIN) is pulled down by control IC and will remain low. The lower MOSFETs alone can not clamp the output voltage however an SCR or N-MOSFET could be triggered with the OVP output to prevent processor damage. OUTPUT VOLTAGE (VO) OVP THRESHOLD VCCL-800 mV ISHARE(IIN) GATEH GATEL FAULT LATCH (CONTROL IC) ERROR AMPLIFIER INPUT (EAIN) VDAC NORMAL OPERATION OVP CONDITION AFTER OVP Figure 6 - Over-voltage protection waveforms Page 12 of 20 March 17, 2009 IR3505Z PWM Ramp Every time the phase IC is powered up PWM ramp magnitude is calibrated to generate a 50 mV/% ramp for a VCC=12V. For example, for a 15% duty ratio the ramp amplitude is 750mV for VCC=12V. Feed-forward control is achieved because the PWM ramp varies with VCC voltage proportionally after calibration. In response to a load step-up the error amplifier can demand 100 % duty cycle. In order to avoid pulse skipping under this scenario and allow the BOOST cap to replenish, a minimum off time is allowed in this mode of operation. As shown in Figure 6, 100 % duty is detected by comparing the PWM latch output (PWMQ) and its input clock (PWM_CLK). If the PWMQ is high when the PWM_CLK is asserted the TopFET turnoff is initiated. The TopFET is again turned on once the RMPOUT drops within 200 mV of the VDAC. NORMAL OPERATION 100 % DUTY OPERATION CLKIN PHSIN (2 Phase Design) EAIN RMPOUT VDAC VDAC+200mV PWMQ 80ns Figure 7: PWM Operation during normal and 100 % duty mode. Debugging Mode If CSIN+ pin is pulled up to VCCL voltage, IR3505Z enters into debugging mode. Both drivers are pulled low and ISHARE output is disconnected from the current share bus, which isolates this phase IC from other phases. However, the phase timing from PHSIN to PHSOUT does not change. Emulated Bootstrap Diode IR3505Z integrates a PFET to emulate the bootstrap diode. An external bootstrap diode connected from VCCL pin to BOOST pin can be added to reduce the drop across the PFET but is not needed in most applications. Page 13 of 20 March 17, 2009 IR3505Z Applications information IR3505Z EXTERNAL COMPONENTS Inductor Current Sensing Capacitor CCS and Resistor RCS The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor RCS and capacitor CCS in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage across the capacitor CCS represents the inductor current. If the two time constants are not the same, the AC component of the capacitor voltage is different from that of the real inductor current. The time constant mismatch does not affect the average current sharing among the multiple phases, but does effect the current signal ISHARE as well as the output voltage during the load current transient if adaptive voltage positioning is adopted. Measure the inductance L and the inductor DC resistance RL. Pre-select the capacitor CCS and calculate RCS as follows. L RL (1) RCS = C CS Bootstrap Capacitor CBST Depending on the duty cycle and gate drive current of the phase IC, a capacitor in the range of 0.1uF to 1uF is needed for the bootstrap circuit. Decoupling Capacitors for Phase IC A 0.1uF-1uF decoupling capacitor is required at the VCCL pin. 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. Output Voltage Bleed Resistor The floating high side driver draws bias current from the BOOST pin (3.5mA typical). This current flows out of the IR3505Z through the SW pin and will charge up the output capacitor when the control IC is disabled. A bleed resistor connected from the converter output voltage to ground is required to prevent the output voltage from exceeding the control IC Over-Voltage protection threshold. The bleed resistor can be selected using the following equation. RBLEED = VBLEED / (5.8mA x N) (2) Where VBLEED is the maximum desired output voltage pre-bias and N is the number of IR3505Z used in the converter. Optional phases A converter can be designed to support more or less phases. This can be quite useful in situations where the final load current is unknown or where increased load current may be required at some time in the future. Figure 8 provides an application circuit that allows adjustment to the number of phases. By populating zero ohm jumpers, or not; the number of phases can be adjusted by diverting the daisy chain timing from a 3505Z to the next one in sequence. The effect of more or less phases on converter performance can be tested without actually removing a 3505Z or it’s MOSFETs from the printed circuit board through use of a pull-up resistor from VCCL to the CSIN+ pin to enable de-bug mode. Page 14 of 20 March 17, 2009 IR3505Z Three Phase Two Phase Figure 8 – Optional Phase application circuit Page 15 of 20 March 17, 2009 IR3505Z 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. • Dedicate at least one middle layer for a ground plane. • Separate analog bus (EAIN, DACIN, and ISHARE) from digital bus (CLKIN, PHSIN, and PHSOUT) to reduce the noise coupling. • Connect PGND and LGND pins to the ground plane through vias. • Place current sense resistors and capacitors (RCS and CCS) close to phase IC. Use Kelvin connection for the inductor current sense wires, but separate the two wires by ground polygon or route as a differential pair. The wire from the inductor terminal to CSIN- should not cross over the fast transition nodes, i.e. switching nodes, gate drive outputs and bootstrap nodes. • Place the decoupling capacitor CVCCL as close as possible to the VCCL pin. • Place the phase IC as close as possible to the MOSFETs to reduce the parasitic resistance and inductance of the gate drive paths. • Place the input ceramic capacitors close to the drain of top MOSFET and the source of bottom MOSFET. Use a combination of different packages of ceramic capacitors. • There are two switching power loops. One loop includes the input capacitors, top MOSFET, inductor, output capacitors and the load; another loop consists of bottom MOSFET, inductor, output capacitors and the load. Route the switching power paths using wide and short traces or polygons; use multiple vias for connections between layers. Page 16 of 20 March 17, 2009 IR3505Z 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 minimize 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 0.3mm diameter vias shall be placed in the pad land spaced at 0.85mm, and connected to ground to minimize the noise effect on the IC, and to transfer heat to the PCB • 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 17 of 20 March 17, 2009 IR3505Z 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 four vias in the land pad should be tented or plugged from bottom board side with solder resist. Page 18 of 20 March 17, 2009 IR3505Z 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 approximately 70% 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 19 of 20 March 17, 2009 IR3505Z PACKAGE INFORMATION 16L MLPQ (3 x 3 mm Body) – θJA = 38oC/W, θJC = 3oC/W Data and specifications subject to change without notice. This product will be 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 20 of 20 March 17, 2009