SC2443 Dual-Phase Single or Two Output Synchronous Step-Down Controller POWER MANAGEMENT Features Description u Wide input voltage range: 4.7V to 16V u 0.5V feedback voltage for low-voltage outputs u Programmable frequency up to 1 MHz per phase u 2-Phase synchronous continuous conduction mode for high efficiency step-down converters u Out-of-phase operation for low input current ripples u Output source and sink currents u Fixed frequency peak current-mode control u 75mV/-110mV maximum current sense voltage u Inductor DCR current-sensing for low-cost applications u Dual outputs or 2-phase single output operation u Excellent current sharing between individual phases u Individual soft-start, overload shutdown and enable u External reference input for DDR applications u External synchronization u Industrial temperature range u 4mm X 4mm X1mm 24-lead MLPQ package The SC2443 is a high-frequency dual synchronous step-down switching power supply controller. It provides out-of-phase high-current output gate drives to all N-channel MOSFET power stages. The SC2443 operates in synchronous continuous-conduction mode. Both phases are capable of maintaining regulation with sourcing or sinking load currents, making the SC2443 suitable for generating both VDDQ and the tracking VTT for DDR applications. Applications Individual soft-start and overload shutdown timer is included in each step-down controller. The SC2443 implements hiccup overload protection. In single output current share configuration, the master timer controls the soft-start and overload shutdown functions of both controllers. The SC2443 employs fixed frequency peak current-mode control for the ease of frequency compensation and fast transient response. The dual-phase step-down controllers of the SC2443 can be used to produce two individually controlled and regulated outputs or a single output with shared current in each phase. The Step-down controllers operate from an input of at least 4.7V and are capable of regulating outputs as low as 0.5V u Telecommunication power supplies u DDR memory power supplies u Graphic power supplies u Servers and base stations Typical Application Circuit VIN 3 15 4 14 5 VOUT2 13 IN2- 6 19 GDH1 20 BST1 22 23 24 21 SS1/EN1 CS1+ CS1- ROSC COMP1 IN1- GDL1 PVCC SYNC PGND SC2443 AGND GDL2 REF GDH2 REFIN AVCC 16 IN1- SS2/EN2 2 CS2+ AVCC BST2 1 VOUT1 BST2 18 17 16 VIN 15 14 13 12 11 10 9 7 12 SS2/EN2 11 REFIN CS2+ GDH2 IN1- 17 CS2- GDL2 REF 18 IN2- AGND VP1 U1 8 20 21 19 GDH1 BST1 22 CS1+ SS1/EN1 23 CS1- ROSC PGND SC2443 7 6 SYNC CS2- 5 GDL1 VIN VOUT1 IN1- PVCC 10 4 COMP1 9 3 IN1- IN2- 2 COMP2 1 8 IN1- 24 VP1 U1 VIN VOUT1 VP1 VIN COMP2 VIN VOUT1 VP1 VIN VIN IN2- Dual Independent Outputs Aug. 2008 Single Output With Current Sharing 1 SC2443 Pin Configuration Ordering Information Top View IN1- GDH1 BST1 SS1/EN1 CS1+ CS1- ROSC 24 19 18 1 GDL1 COMP1 PVCC SYNC PGND AGND GDL2 REF GDH2 REFIN 6 13 7 Device Package SC2443MLTRT (1,2) 24-lead 4mm X 4mm X 1mm MLPQ SC2443EVB Evaluation Board Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Available in lead-free package only. Device is WEEE and RoHS compliant. BST2 12 AVCC SS2/EN2 CS2+ CS2- IN2- COMP2 (24-lead 4mm X 4mm X 1mm MLPQ) θJA = 29°C/W Marking Information Marking for the 4 X 4mm MLPQ-24 package: SC2443 Absolute Maximum Ratings Recommended Operating Conditions AVCC, PVCC Voltage …………………………… -0.3 to 20V VBST1, VBST2 Voltage ……………………………… -0.3 to 32V ……………………………… - 0.3 to 40V (for <10ns @ freq. < 500kHz) Input Voltage Range ………………………… 4.75V to 16V Thermal Information Junction to Ambient(1) …………………………… 29°C/W -0.3 to 6V Maximum Junction Temperature ……………………… 150°C IN1-, IN2-, REF Voltage ………………… -0.3 to AVCC+ 0.3V Storage Temperature ………………………… -65 to +150°C SS1/EN1, SS2/EN2, SYNC Voltage ……………… REFIN , COMP1, COMP2 Voltage ………… -0.3 to AVCC+ 0.3V CS1+, CS1-, CS2+, CS2- Voltage ………… -0.3 to AVCC+ 0.3V PGND to AGND ……………………………………… ± 0.3V Peak IR Reflow Temperature …………………………… 260°C Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not recommended. NOTES(1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. (2) This device is ESD sensitive. Use of standard ESD handing precautions is required Electrical Characteristics Unless otherwise specified: AVCC = PVCC = 12V, VBST1 = VBST2 = 12V, SYNC = 0V, -40°C < TA = TJ < 85°C, ROSC =51.1kW. Parameter Symbol Conditions Min Typ Max Units AVCC Start Threshold AVCCTH AVCC rising 4.5 4.7 V AVCC Start Hysteresis AVCCHYST 170 AVCC Operating Current ICC 12 AVCC Quiescent Current in UVLO Iq Undervoltage Lockout AVCC = AVCCTH - 0.2V mV 16 1.7 mA mA Channel 1 Error Amplifier Non-inverting Input Voltage VIN1+ Non-inverting Input Voltage VIN1+ Non-inverting Input Line Regulation 0°C < TA = TJ < 70°C 0.49 0.5 0.51 V 0.4925 0.5 0.5075 V 0.02 %/V AVCCTH < AVCC < 15V Input Offset Voltage 1 mV Inverting Input Bias Current IIN1- -0.1 Amplifier Transconductance GM1 260 µW-1 Amplifier Open Loop Gain AOL1 65 dB 5 MHz VCS1+=VCS1- = 0, VSS1 Rising 2.2 V Amplifier Output Sink Current VIN1- = 1V, VCOMP1 = 2.5V 16 µA Amplifier Output Source Current VIN1- = 0V, VCOMP1 = 2.5V 12 µA Amplifier Unity Gain Bandwidth COMP1 Switching Threshold -0.25 µA 3 SC2443 Electrical Characteristics (continued) Parameter Symbol Conditions Min Typ Max Units Channel 2 Error Amplifier Input Common-mode Range(1) 0 3 V Inverting Input Voltage Range 0 AVCC V (1) Input Offset Voltage 1.5 mV Non-inverting Input Bias Current IIN2+ -150 -380 nA Inverting Input Bias Current IIN2- -100 -250 nA Inverting Input Voltage for 2 phases Single Output Operation 2.5 V Amplifier Transconductance GM2 260 µW-1 Amplifier Open Loop Gain AOL2 65 dB 5 MHz VCS2+=VCS2- = 0, VSS2 Rising 2.2 V Amplifier Output Sink Current VCOMP2 = 2.5V 16 µA Amplifier Output Source Current VCOMP2 = 2.5V 12 µA Amplifier Unity Gain Bandwidth COMP2 Switching Threshold Oscillator fCH1, fCH2 Channel Frequency 450 500 550 kHz Synchronizing Frequency 2.1fCH kHz SYNC Input High Voltage 1.5 V (1) SYNC Input Low Voltage 0.5 Channel Maximum Duty Cycle DMAX1, DMAX2 Channel Minimum Duty Cycle DMIN1, DMIN2 88 V % 0 % AVCC-1 V Current Limit Comparator Input Common Mode Range 0 Cycle by cycle Peak Currentr Limit VILIM1+ , VILIM2+ VCS1- = VCS2- = 0.5V, Sourcing 60 75 90 mV Valley Current Overload Shutdown Threshold VILIM1- , VILIM2- VCS1- = VCS2- = 0.5V, Sinking -85 -110 -130 mV Positive Current sense Input Bias Current ICS1+ , ICS2+ VCS1+ = VCS1- = 0 VCS2+ = VCS2- = 0 -0.7 -2 µA Negative Current sense Input Bias Current ICS1- , ICS2- VCS1+ = VCS1- = 0 VCS2+ = VCS2- = 0 -0.7 -2 µA SC2443 Electrical Characteristics (continued) Parameter Symbol Conditions Min Typ Max Units Gate Drivers High side Gate Driver Peak Source Current VBST1, VBST2 = 12V 1.5 A High side Gate Driver Peak Sink Current VBST1, VBST2 = 12V 1 A Low side Gate Driver Peak Source Current AVCC = PVCC = 12V 1.5 A Low side Gate Driver Peak Sink Current AVCC = PVCC = 12V 1 A Gate Drive Rise Time CL = 2200pF 20 ns Gate Drive Fall Time CL = 2200pF 20 ns Low side Gate Driver to High side Gate Driver Non-overlapping delay CL = 0 90 ns High side Gate Driver to Low side Gate Driver Non-overlapping delay CL = 0 90 ns TA = 25°C 150 ns VSS1 = VSS2 = 1.5V 2 µA VSS1 and VSS2 Rising 3.2 V Overload IN1- Threshold VSS1 = 3.8V, VIN1- falling 0.75VREF V Overload IN2- Threshold VSS2 = 3.8V, VIN2- falling 0.72 X V ISS1 _DIS , ISS2_DIS VSS1 = VSS2 = 3.8V 1.4 µA VSSRCV1 , VSSRCV2 VSS1 and VSS2 Falling Minimum On Time Soft Start, Overload Latchoff and Enable Soft Start Charging Current ISS1 , ISS2 Overload Enabling Soft Start Voltage Soft Start Discharge Current Overload Recovery Soft Start Voltage Gate Driver Disable SS/EN Voltage 0.3 0.5 0.7 0.9 Gate Driver Enable SS/EN Voltage 0.7 V V 1.2 1.5 V 500 510 mV Internal 0.5V Reference Buffer Output Voltage Load Regulation VREF IREF = -1mA 0 < IREF <-5mA 490 0.05 %/mA Notes: (1) Guaranteed by design. SC2443 Typical Characteristics AVCC operation current vs. Temperature UVLO Threshold vs. Temperature 4.54 AVCC UVLO(V) 4.53 4.52 4.51 4.50 4.49 -40 25 12.9 AVCC Current in UVLO(mA) AVCC operation Current(mA) 4.55 12.8 12.7 12.6 12.5 12.4 12.3 12.2 12.1 12 85 1.80 1.75 1.70 1.65 1.60 25 85 -40 COMP Sink/Source current vs. Temperature 501.5 500.5 500.0 499.5 499.0 85 85 E/A GM vs. Temperature 20 290 15 280 SINK 10 E/A GM(uW-1) VREF(mV) 501.0 COMP SINK/SOURCE Current(uA) 502.0 25 Temperature (OC) Temperature (OC) VREF vs. Temperature 25 1.85 1.55 -40 Temperature (OC) -40 AVCC current in UVLO vs. Temperature 5 0 -5 SOURCE -10 270 260 250 240 230 -15 220 -40 25 85 -40 25 85 Temperature (OC) Temperature (OC) COMP switching Threshold vs. Temperature Switching Frequency setting vs. Temperature Cycle by Cycle OCP threshold vs. Temperature 512 Switching Frequency(KHz) COMP Switching Threshold(V) 2.35 2.30 2.25 2.20 2.15 2.10 2.05 -40 25 510 508 506 504 502 500 498 496 85 ROSC = 51.1KW -40 Temperature (OC) SS/EN Threshold for Gate Driver Enable / Disable vs. Temperature 3.17 3.16 3.15 3.14 3.13 3.12 3.11 3.10 Temperature (OC) 74.5 74.0 73.5 73.0 72.5 72.0 71.5 71.0 -40 85 1.30 1.25 1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 0.80 Enable Disable -40 25 Temperature (OC) 85 25 Temperature (OC) 85 SS/EN Threshold for Overload Hiccup Recovery vs. Temperature SS/EN Threshold Voltage(V) SS/EN Threshold Voltage(V) SS/EN Threshold Voltage(V) 3.18 25 85 75.0 Temperature (OC) SS/EN Threshold for Overload Hiccup vs. Temperature -40 25 Cycle by Cycle OCP Threshols(mV) Temperature (OC) 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 -40 25 Temperature (OC) 85 SC2443 Typical Application Circuit Performance Circuit Conditions : Single output current share configuration as shown in page 15 Releasing SS/EN pin from GND Releasing SS/EN pin from GND Soft Start VIN 5V/DIV VIN 5V/DIV EN1/SS1 2V/DIV COMP1 1V/DIV COMP1 1V/DIV EN1/SS1 2V/DIV EN1/SS1 2V/DIV VIN 2V/DIV VOUT 1V/DIV 10ms/DIV GDL1 5V/DIV VOUT 1V/DIV VOUT 1V/DIV Shuting down _ VIN ramp down VIN 2V/DIV VIN 5V/DIV EN1/SS1 2V/DIV EN1/SS1 2V/DIV GDL1 10V/DIV GDL1 10V/DIV VOUT 1V/DIV VOUT 1V/DIV 10ms/DIV 10ms/DIV Pulling SS/EN pin to GND Gate Wavefroms GDH1 GDL1 10V/DIV GDH2 GDL2 10V/DIV 1ms/DIV 400us/DIV 1us/DIV Output Ripple _ IOUT = 40A Transient Response _ 10A ~ 30A OCP Trip _ IOUT = 56A SS1/EN1 2V/DIV GDH1 GDH2 10V/DIV VOUT 50mV/DIV GDH1 20V/DIV GDL1 10V/DIV VOUT 20mV/DIV VOUT 0.5V/DIV 1us/DIV OCP Recovery to 30A loading 200us/DIV 400us/DIV Efficiency (12VIN to 1VOUT) EFF (%) 90 80 SS1/EN1 2V/DIV 70 GDH1 20V/DIV GDL1 10V/DIV 60 50 40 VOUT 0.5V/DIV 20ms/DIV 30 1 5 10 15 20 25 30 35 40 IOUT(A) SC2443 Typical Application Circuit Performance Circuit Conditions : Dual independent outputs configuration as shown in page 17 Soft Start (VOUT2) Soft Start (VOUT1) Soft Start (Both outputs) SS1/EN1 2V/DIV COMP1 EN1/SS1 2V/DIV VIN 2V/DIV VOUT1 1V/DIV 10ms/DIV COMP2 1V/DIV EN2/SS2 2V/DIV VOUT1 0.5V/DIV VIN 2V/DIV SS2/EN2 2V/DIV VOUT2 2V/DIV VOUT2 2V/DIV 10ms/DIV Output Ripple (VOUT1_20A) Gate waveforms (VOUT1_2 = 20A) GDH1 GDL1 10V/DIV Output Ripple (VOUT2_20A) GDH2 GDL2 10V/DIV GDH1 GDL1 10V/DIV GDH2 GDL2 10V/DIV VOUT2 50mV/DIV VOUT1 50mV/DIV 1us/DIV 1us/DIV Transient Response (VOUT2 _ 2A ~ 17A) OCP Trip (VOUT1 = 30A) 1us/DIV Transient Response (VOUT1 _ 2A ~ 17A) 20ms/DIV SS1/EN1 2V/DIV VOUT2 50mV/DIV VOUT1 50mV/DIV GDH1 GDL1 20V/DIV VOUT1 0.5V/DIV 200us/DIV OCP Trip (VOUT2 = 28A) 200us/DIV EFF (%) 400us/DIV Combined Efficiency (12VIN to 1VOUT & 2.5VOUT) 95 90 SS2/EN2 2V/DIV 85 GDH2 20V/DIV GDL2 10V/DIV 80 75 VOUT2 1V/DIV 70 400us/DIV 1 5 10 15 20 IOUT(A) SC2443 Pin Descriptions Pin # Pin Name Pin Function 1 IN1- 2 COMP1 3 SYNC Edge-triggered Synchronization Input. When not synchronized, tie this pin to a voltage above 1.5V or the ground. An external clock (frequency > frequency set with ROSC) at this pin synchronizes the controllers. 4 AGND Analog Signal Ground 5 REF Buffered Output of the Internal 0.5V Reference. The non-inverting input of the error amplifier for the step-down converter 1 is internally connected to this pin 6 REFIN An external Reference voltage is applied to this pin.The non-inverting input of the error amplifier for the step-down converter 2 is internally connected to this pin. 7 COMP2 8 IN2- Inverting Input of the Error Amplifier for the Step-down Controller 2. Tie to AVCC for two-phase single output applications. 9 CS2- The Inverting Input of the Current-sense Amplifier/Comparator for the Controller 2. 10 CS2+ The Non-inverting Input of the Current-sense Amplifier/Comparator for the Controller 2. 11 SS2/EN2 12 AVCC Power Supply Voltage for the Analog Portion of the Controllers. 13 BST2 Bootstrapped Supply for the High-side Gate Drive 2. 14 GDH2 Gate Drive Output for the High-side N-channel MOSFET of Output 2. 15 GDL2 Gate Drive Output for the Low-side N-channel MOSFET of Output 2. 16 PGND Ground Supply for All the Gate drivers. 17 PVCC Power Supply Voltage for Low-side MOSFET Drivers. 18 GDL1 Gate Drive Output for the Low-side N-channel MOSFET of Output 1. 19 GDH1 Gate Drive Output for the High-side N-channel MOSFET of Output 1. 20 BST1 Bootstrapped Supply for the High-side Gate Drive 1. 21 SS1/EN1 22 CS1+ The Non-inverting Input of the Current-sense Amplifier/Comparator for the Controller 1. 23 CS1- The Inverting Input of the Current-sense Amplifier/Comparator for the Controller 1 24 ROSC An external resistor connected from this pin to GND sets the oscillator frequency THPAD Solder to the Analog ground plane of the PCB. Inverting Input of the Error Amplifier for the Step-down Controller 1. The Error Amplifier Output for Step-down Controller 1. The Error Amplifier Output for Step-down Controller 2. An external capacitor tied to this pin sets (i) the soft-start time (ii) output overload latch off time for step-down converter 2. Pulling this pin below 0.7V shuts off the gate drivers for the second controller. Leave open for two-phase single output applications. An external capacitor tied to this pin sets (i) the soft-start time (ii) output overload latch off time for buck converter 1. Pulling this pin below 0.7V shuts off the gate drivers for the first controller. SC2443 Block Diagram SYNC 3 CLK2 OSCILLATOR ROSC 24 COMP1 2 IN11 EA1 + + - 0.5V UVLO 4.3/4.5V BST1 R S GDH1 19 Q Non-Overlapping Conduction Control UVLO 0.75 VREF Soft-Start And Overload Hiccup Control + + + ISEN - 6 +ILIM+ - 110mV REFIN/IN2+ 6 PWM + SLOPE COMP 75mV COMP2 7 IN28 CLK1 AVCC 12 20 REF/IN1+ 5 CS1+ 22 CS123 REFERENCE ILIM- OL PVCC 17 GDL1 18 PGND 16 DSBL SS1/EN1 21 OCN + EA2 + + - AGND 4 0.72 VREFOUT SC2443 Block Diagram (Channel 1 PWM Control Only) Figure 1. SC2443 Block Diagram 10 SC2443 Applications Information Description The SC2443 is a constant frequency 2-phase current-mode step-down PWM switching controller driving all N-channel MOSFET. The two channels of the controller operate at 180 degrees out-of-phase from each other. Since input currents are interleaved in a two-phase converter, input ripple current is lower and smaller input capacitor can be used for filtering. Also, with lower inductor current and smaller inductor ripple current per phase, overall I2R losses are reduced. The supply voltages for the high-side gate drivers are obtained from two diode-capacitor bootstrap circuits. If the bootstrap capacitor is charged from VCC, the highside gate drive voltage swing will be from approximately 2VCC to the ground. The power dissipated in the highside gate driver is not higher with higher voltage swing because the gate-source voltage of the high-side MOSFET still swing from zero to VCC. The outputs of the low-side gate drivers swing from VCC to ground. The SC2443 operates in synchronous continuousconduction mode. It can be configured either as two independent step-down controllers producing two separate outputs or as a dual-phase single-output controller by tying the IN2- pin to VCC. In single output operation, the channel one error amplifier controls both channels and the channel two error amplifier is disabled. Soft-start and overload hiccup of both channels is synchronized to channel one. The SC2443 has internal ramp-compensation to prevent sub-harmonic oscillation when operating above 50% duty cycle. There is enough ramp internally for a sensed voltage ripple between 1/4 to 1/3 of the full-scale sensed voltage limit of 75mV. The maximum sensed voltage limit is unaffected by the compensating ramp. Frequency Setting and Synchronization The internal oscillator of the SC2443 runs at twice the phase frequency. The free-running frequency of the oscillator can be programmed with an external resistor from the ROSC pin to ground. The step-down controllers are capable of operating up to 1 MHz. It is necessary to consider the operating duty-ratio before deciding the switching frequency. See Applications Information section for more details. When synchronized externally, the applied clock frequency should be twice the desired phase frequency. The synchronizing clock frequency should also be between 2 - 2.6 times the set free-running channel frequency. Control Loop The SC2443 uses peak current-mode control for fast transient response, ease of compensation and current sharing in single output operation. The low-side MOSFET of each channel is turned off at the falling-edge of the phase timing clock. After a brief non-overlapping time interval of 90ns, the high-side MOSFET is turned on. The phase inductor current ramps up. When the sensed inductor current reaches the threshold determined by the error amplifier output and compensation ramp, the high-side MOSFET is turned off. After a non-overlapping conduction time of 90ns, the low-side MOSFET is turned on. Current-Sensing There are two ways to sense the inductor current for current-mode control with the SC2443. Since the peak inductor current corresponds to 75mV of sensed voltage (CS+ - CS-), resistor current sensing can be used at the output without resulting in excessive power dissipation. Although accurate and far easier to lay out than high-side resistor sensing, a pair of precision sense resistors adds cost to the converter. With proper RC filter, Inductor DCR sensing can also be used for SC2443 resulting in low cost and without extra power dissipation. Error Amplifiers In closed loop operation, the error amplifier output ranges from 1.1V to 3.5V. The upper output operating range of either error amplifier is reserved for positive currentsense voltage (CS+ - CS-) and corresponds to positive (sourcing) output current. If the amplifier swings to its lower operating range, the amplifier will still modulate the high-side gate drive duty-ratio. However the peak currentsense voltage (hence the peak inductor current) will be limited to a negative value. The error amplifier output is about 2.2V when the peak sense-voltage is zero. The built-in offset in the current sense amplifier together with synchronous continuous-conduction mode of operation allows the SC2443 to regulate the output irrespective of the direction of the load current. 11 SC2443 Applications Information (continued) The non-inverting input of the first feedback amplifier is tied to the internal 0.5V voltage reference. Both the noninverting and the inverting inputs of the second error amplifier are brought out as device pins so that the output of the second converter can be made to track the output of the first channel. For example in DDR applications, Channel 1 can be used to generate VDDQ (2.5V) from the input (5V or 12V) and channel 2 is used to produce a tracking VTT (1.25V) with VDDQ being its input. Current-Limit The maximum current sense voltage of +75mV is the cycle-by-cycle peak current limit when the load is drawing current from the converter. There is no cycle-bycycle current limiting when the inductor current flows in the negative direction. However once the valley of the current sense voltage exceeds -110mV, the corresponding channel will undergo shutdown and restart (hiccup). Soft-Start and Overload Protection The undervoltage lockout circuit discharges the SS/EN capacitors. After VCC rises above 4.5V, the SS/EN capacitors are slowly charged by internal 2mA current source. With internal PNP transistors, the SS/EN voltages clamp the error amplifier outputs. When the error amplifier output rises to 2.2V, the high-side MOSFET starts to switch. As the SS/ EN capacitor continues to be charged, the COMP voltage follows. The converter gradually delivers increasing power to the output. The inductor current follows the COMP voltage envelope until the output goes into regulation. The SS/EN clamp on COMP is then released. After the SS/EN capacitor is charged above 3.2V (high enough for the error amplifier to provide full load current), the overload detection circuit is activated. If the output voltage falls below 70% of its set value or the valley current-sense voltage exceeds -110mV, an overload latch will be set and both the top and the bottom MOSFETs will be turned off. The SS/EN capacitor is slowly discharged with an internal 1.4mA current sink. The overload latch is reset when the SS/EN capacitor is discharged below 0.5V. The SS/EN capacitor is then recharged with the 2uA current source and the converter undergoes soft-start. If overload persists, the SC2443 will undergo repetitive shutdown and restart. If the output is short-circuited, the inductor current will not increase indefinitely between the time the inductor current reaching its current limit and the instant the converter shuts down. This is due to cycle skipping(a consequence of inductor current sense) reduces the actual operating frequency. The SS/EN pin can also be used as the enable input for that channel. Both the high-side and the low-side MOSFETs will be turned off if the SS/EN pin is pulled below 0.7V. Operating Frequency (fs) The switching frequency in the SC2443 is userprogrammable. The advantages of using constant frequency operation are simple passive component selection and ease of feedback compensation. Before setting the operating frequency, the following trade-offs should be considered. 1) Passive component size 2) Circuitry efficiency 3) EMI condition 4) Minimum switch on time and 5) Maximum duty ratio For a given output power, the sizes of the passive components are inversely proportional to the switching frequency, whereas MOSFET and Diodes switching losses are proportional to the operating frequency. Other issues such as heat dissipation, packaging and the cost issues are also to be considered. The frequency bands for signal transmission should be avoided because of EM interference. Minimum Switch On Time Consideration In the SC2443 the falling edge of the clock turns on the top MOSFET. The inductor current and the sensed voltage ramp up. After the sensed voltage crosses a threshold determined by the error amplifier output, the top MOSFET is turned off. The propagation delay time from the turnon of the controlling FET to its turn-off is the minimum switch on time. The SC2443 has a minimum on time of about 150ns at room temperature. This is the shortest on interval of the controlling FET. The controller either does not turn on the top MOSFET at all or turns it on for at least 150ns. For a synchronous step-down converter, the operating duty cycle is VO / VIN . So the required on time for the top MOSFET is VO / (VIN × FS ) . If the frequency is set such that the required pulse width is less than 150ns, then the converter will start skipping cycles. Due to minimum on time limitation, simultaneously operating at 12 SC2443 Applications Information (continued) very high switching frequency and very short duty cycle is not practical. If the voltage conversion ratio VO / VIN and hence the required duty cycle is higher, the switching frequency can be increased to reduce the sizes of passive components. There will not be enough modulation headroom if the on time is simply made equal to the minimum on time of the SC2443. For ease of control, we recommend the required pulse width to be at least 1.5 times the minimum on time. Setting the Switching Frequency The switching frequency is set with an external resistor connected from Pin 24 to ground. The set frequency is inversely proportional to the resistor value (Figure 2). Figure 2. Free running frequency vs. ROSC. 800 700 fs (kHz) 600 PC Board Layout Issues Circuit board layout is very important for the proper operation of high frequency switching power converters. A power ground plane is required to reduce ground bounces. The following are suggested for proper layout: Power Stage 1) Separate the power ground from the signal ground. In the SC2443, the power ground PGND should be tied to the source terminal of lower MOSFETs. The signal ground AGND should be tied to the negative terminal of the output capacitor. 2) Minimize the size of high pulse current loop. Keep the top MOSFET, bottom MOSFET and the input capacitors within a small area with short and wide traces. In addition to the aluminum energy storage capacitors, add multilayer ceramic (MLC) capacitors from the input to the power ground to improve high frequency bypass. 3) Reduce high frequency voltage ringing. Widen and shorten the drain and source traces of the MOSFET to reduce stray inductances. Add a small RC snubber if necessary to reduce the high frequency ringing at the phase node. Sometimes slowing down the gate drive signal also helps in reducing the high frequency ringing at the phase node. 500 400 300 200 100 0 0 50 100 150 200 250 Rosc (k Ohm) Setting the Output Voltage The non-inverting input of the channel-one error amplifier is internally tied the 0.5V voltage reference output (Pin 5). The non-inverting input of the channel-two error amplifier is brought out as a device pin (Pin 6) to which the user can connect Pin 5 or an external voltage reference. A simple voltage divider (Ro1 at top and Ro2 at bottom) sets the converter output voltage. The voltage feedback gain h=0.5/Vo is related to the divider resistors value as h R o2 = R o1. 1- h 4) Shorten the gate driver path. Integrity of the gate drive (voltage level, leading and falling edges) is important for circuit operation and efficiency. Short and wide gate drive traces reduce trace inductances. Bond wire inductance is about 2~3nH. If the length of the PCB trace from the gate driver to the MOSFET gate is 1 inch, the trace inductance will be about 25nH. If the gate drive current is 2A with 10ns rise and falling times, the voltage drops across the bond wire and the PCB trace will be 0.6V and 5V respectively. This may slow down the switching transient of the MOSFET. These inductances may also ring with the gate capacitance. 5) Put the decoupling capacitor for the gate drive power supplies (BST and PVCC) close to the IC and power ground. Control Section 6) The frequency-setting resistor Rosc should be placed close to Pin 3. Trace length from this resistor to the analog 13 SC2443 Applications Information (continued) ground should be minimized. 7) Solder the bias decoupling capacitor right across the AVCC and analog ground AGND. 8) Place the inductor DCR sense components away from the power circuit and close to the corresponding CS+ and CS- pins. Use X7R type ceramic capacitor for the DCR sense capacitor because of their temperature stability. 9) Use an isolated local ground plane underneath the controller and tie it to the negative side of output capacitor bank. 10) Comp pin is sensitive to noise. Place compensation network components away from noise signal (i.e. gate driver signals, phase node) and close to corresponding Comp pin . 14 SC2443 Evaluation Application Circuit _ Single Output, Current share configuration C12 R9 1 R5 124K CS1- CS1+ C7 22nF GDL1 PVCC PGND R1 17 C9 1uF R10 R7 16 R11 18 15 0R 0R 2R2 0R D1 1N4148 1uF IPD09N03LA C4 IPD06N03LA D2 1N4148 Q1 Q2 Q4 Q5 C1 C10 Q3 12VIN C3 R3 1R C8 2.2nF L1 R2 10K C6 22pF R6 10R 1.5uH/1.8mR C5 100nF R4 N.P. R8 560R 1.5uH/1.8mR C21 100nF R15 1.05K C14 C15 C16 C17 C19 1VOUT/40A C18 10uF/6.3V IN1- N.P. R16 10R 1500uF/6.3V/FL C22 R14 N.P. R20 1K 1500uF/6.3V/FL R13 22pF C11 1R L2 R12 10K CS1+ CS1- C2 12VIN Q6 C24 R19 560R 1500uF/6.3V/FL 1uF IPD09N03LA C20 IPD06N03LA 2.2nF 10uF/6.3V 14 13 0R 270uF/16V/OSCON SC2443 GDL2 GDH2 BST2 R17 12VIN 270uF/16V/OSCON U1 IN1COMP1 SYNC AGND REF REFIN 10R IPD06N03LA 2 IN1- 47K 3 C23 100nF 6 5 4 C13 N.P 0R R21 10uF/16V 270uF/16V/OSCON IPD06N03LA C25 1uF 10uF/16V 330pF R18 20 BST1 19 GDH1 AVCC 12 CS2+ 10 SS2/EN2 11 21 SS1/EN1 22 CS1+ CS29 23 CS1IN28 24 ROSC COMP2 7 15 SC2443 Evaluation Board Bill of Materials Single Output Current Share Configuration Item Reference Quantity Description Package Part Vendor 1 C1,C10 2 16V X5R ceramic capacitor 1206 10uF Murata 2 C2,C3,C11 3 16V Aluminum solid capacitor _SEPC series 8 X 9mm 270uF Sanyo 3 C4,C9,C20,C25 4 16V X5R ceramic capacitor 0603 1uF Murata 4 C5,C21,C23 3 16V X7R ceramic capacitor 0603 100nF Panasonic 5 C6,C22 2 25V X7R ceramic capacitor 0603 22pF Panasonic 6 C7 1 16V X7R ceramic capacitor 0603 22nF Panasonic 7 C8,C24 2 25V X7R ceramic capacitor 0603 2.2nF Panasonic 8 C12 1 25V X7R ceramic capacitor 0603 330pF Panasonic 9 C14,C19 2 6.3V X7R ceramic capacitor 1206 10uF Murata 10 C15,C16,C17 3 6.3V Aluminum capacitor _ FL series 8 X 11.5mm 1000uF Panasonic 11 D1,D2 2 Small signal diode SMD 1N4148 Any 12 L1,L2 2 SMD inductor 12.5 X 12.5 X 10mm 1.5uH/1.8mR TRIO 13 Q1,Q4 2 30V N Channel MOSFET D-pack IPD09N03LA Infineon 14 Q2,Q3,Q5,Q6 4 30V N Channel MOSFET D-pack IPD06N03LA Infineon 15 R1,R7,R11, R17,R18 5 5% SMD resistor 0603 0R Any 16 R2,R12 2 5% SMD resistor 0603 10K Any 17 R3,R13 2 5% SMD resistor 0603 1R Any 18 R5 1 1% SMD resistor 0603 124K Any 19 R6,R16.R21 3 1% SMD resistor 0603 10R Any 20 R8,R19 2 1% SMD resistor 0603 560R Any 21 R9 1 5% SMD resistor 0603 47K Any 22 R10 1 5% SMD resistor 0603 2R2 Any 23 R15 1 1% SMD resistor 0603 1.05K Any 24 R20 1 1% SMD resistor 0603 1K Any 25 U1 1 Dual phase Sync. step down controller MLPQ-24 SC2443 SEMTECH 16 SC2443 Evaluation Application Circuit_ Dual Independant Outputs 1N11 R6 124K CS1- CS1+ C7 GDL1 PVCC PGND 18 17 16 15 14 R12 2R2 R8 0R R1 0R C13 1uF R13 0R D1 1N4148 C4 1uF Q2 IPD06N03LA D2 1N4148 C18 1uF Q1 Q4 Q3 N.P. Q6 N.P. C1 C14 C2 R3 1R 12VIN C3 R2 15K R4 N.P. C5 100nF L1 2.2uH/2mR C6 27pF R7 0R R9 N.P. R18 0R C8 C21 C9 C10 2200uF/6.3V/FL C22 2200uF/6.3V/FL C23 1VOUT/20A C11 IN1- R5 1.05K R10 1K R22 1K R17 4.12K 2.5VOUT/20A C24 10uF/6.3V R21 N.P. 1800uF/6.3V/FL R16 N.P. C19 100nF L2 2.2uH/2mR C20 N.P. R14 20K CS1+ C12 CS12.2nF C15 12VIN R15 1R C25 2.2nF 1800uF/6.3V/FL Q5 IPD06N03LA 10uF/6.3V R19 0R 1500uF/16V/FL 13 12VIN IPD09N03LA GDL2 GDH2 BST2 R23 10R N.P. SC2443 C29 IPD09N03LA 10uF/16V 22uF/10V/X7R 22uF/10V/X7R C30 1uF 1500uF/16V/FL U1 IN1COMP1 SYNC AGND REF REFIN C28 20 10uF/16V 2 3 4 5 6 R20 100K C27 470pF 22nF SYNC N.P. C17 R25 0R C26 100nF 19 GDH1 AVCC 12 R11 47K C16 470pF R24 0R CS2+ 10 BST1 SS2/EN2 11 21 SS1/EN1 22 CS1+ CS29 23 CS1IN28 24 ROSC COMP2 7 17 N.P. 22nF SC2443 Evaluation Board Bill of Materials Dual Independent Output Configuration Item Reference Quantity Description Package Part Vendor 1 C1,C4 2 16V X5R ceramic capacitor 1206 10uF Murata 2 C2,C15 2 16V Aluminum capacitor _FL series 10 X 20mm 1500uF Panasonic 3 C4,C13,C18, C30 4 16V X5R ceramic capacitor 0603 1uF Murata 4 C5,C19,C26 3 16V X7R ceramic capacitor 0603 100nF Panasonic 5 C6 1 25V X7R ceramic capacitor 0603 27pF Panasonic 6 C7,C29 2 16V X7R ceramic capacitor 0603 22nF Panasonic 7 C8,C11 2 6.3V X7R ceramic capacitor 1206 10uF Murata 8 C9,C10 2 6.3V Aluminum capacitor _ FL series 10 X 16mm 1800uF Panasonic 9 C12,C25 2 25V X7R ceramic capacitor 0603 2.2nF Panasonic 10 C16,C27 2 25V X7R ceramic capacitor 0603 470pF Panasonic 11 C21,C24 2 10V X7R ceramic capacitor 1206 10uF Murata 12 C22,C23 2 6.3V Aluminum capacitor _ FL series 10 X 20mm 2200uF Panasonic 13 D1,D2 2 Small signal diode SMD 1N4148 Any 14 L1,L2 2 Through hole inductor 2.2uH/2mR Any 15 Q1,Q4 2 30V N Channel MOSFET D-pack IPD09N03LA Infineon 16 Q2,Q5 2 30V N Channel MOSFET D-pack IPD06N03LA Infineon 17 R1,R7,R11,R13, R18,R19,R24 R25 8 5% SMD resistor 0603 0R Any 18 R2 1 5% SMD resistor 0603 15K Any 19 R3,R15 2 5% SMD resistor 0603 1R Any 20 R5 1 1% SMD resistor 0603 1.05K Any 21 R6 1 1% SMD resistor 0603 124K Any 22 R10,R22 2 1% SMD resistor 0603 1K Any 23 R11 1 5% SMD resistor 0603 47K Any 24 R12 1 5% SMD resistor 0603 2R2 Any 25 R14 1 5% SMD resistor 0603 20K Any 26 R17 1 1% SMD resistor 0603 4.12K Any 27 R20 1 5% SMD resistor 0603 100K Any 28 R23 1 5% SMD resistor 0603 10R Any 29 U1 1 Dual phase Sync. step down controller MLPQ-24 SC2443 SEMTECH 18 SC2443 5 1N11 R6 102K U1 CS1- CS1+ C7 4 GDL1 PVCC PGND GDL2 GDH2 18 17 16 15 14 R12 2R2 R8 0R R1 0R C13 1uF R13 0R D1 1N4148 C4 1uF D2 1N4148 C18 1uF Q1 3 FDS6982 Q2 FDS6982 C1 C2 12VIN 12VIN C14 C15 R3 1R R4 N.P. C5 100nF/X7R L1 1.9uH/3.9mR R2 4.87K C6 27pF 2 R7 10R R9 604R R18 10R R21 604R C8 C21 C9 C10 1000uF/6.3V/FL C22 N.P C23 Title C11 C24 N.P R16 N.P. C19 100nF/X7R L2 1.9uH/3.9mR C20 18pF R14 4.87K CS1+ C12 CS12.2nF R15 1R C25 2.2nF N.P R19 0R 1000uF/6.3V/FL 13 VIN 10uF/6.3V BST2 R23 10R 680uF/16V/FL C29 680uF/16V/FL C28 N.P C30 1uF 10uF/16V COMP1 IN1- 22nF SYNC 2 SYNC AGND GDH1 AVCC 20 19 SS2/EN2 REF REFIN R20 47K C27 470pF SC2443 21 11 3 SS1/EN1 CS2+ 4 22 10 5 6 CS1+ CS2- C17 N.P. R25 0R C26 100nF CS1IN2- 9 R11 47K C16 470pF R24 0R 24 23 COMP2 7 BST1 12 ROSC 8 D C B A Evaluation Application Circuit_ Dual Independant Outputs (Lower power application) 1.5VOUT IN1- R5 2.05K R10 1K 1.8VOUT R17 2.61K R22 1K 1 19 N.P. 22nF 10uF/16V 10uF/6.3V/X7R SC2443 Evaluation Board Bill of Materials Dual Independent Output Configuration Item Reference Quantity Description Package Part Vendor 1 C1,C14 2 16V X5R ceramic capacitor 1206 10uF Murata 2 C2,C15 2 16V Aluminum capacitor _FL series 10 X 12.5mm 680uF Panasonic 3 C4,C13,C18, C30 4 16V X5R ceramic capacitor 0603 1uF Murata 4 C5,C19,C26 3 16V X7R ceramic capacitor 0603 100nF Panasonic 5 C6 1 25V X7R ceramic capacitor 0603 27pF Panasonic 6 C7,C29 2 16V X7R ceramic capacitor 0603 22nF Panasonic 7 C8,C21 2 6.3V X7R ceramic capacitor 1206 10uF Murata 8 C9,C22 2 6.3V Aluminum capacitor _ FL series 10 X 12.5mm 1000uF Panasonic 9 C12,C25 2 25V X7R ceramic capacitor 0603 2.2nF Panasonic 10 C16,C27 2 25V X7R ceramic capacitor 0603 470pF Panasonic 11 C20 1 25V X7R ceramic capacitor 0603 18pF Murata 12 D1,D2 2 Small signal diode SMD 1N4148 Any 13 L1,L2 2 Through hole inductor 1.9uH/3.9mR Any 14 Q1,Q2 2 30V N Channel MOSFET SO-8 FDS6982 Fairchild 15 R1,R8,R13, R19,R24,R25 6 5% SMD resistor 0603 0R Any 16 R2,R14 2 5% SMD resistor 0603 4.87K Any 17 R3,R15 2 5% SMD resistor 0603 1R Any 18 R5 1 1% SMD resistor 0603 2.05K Any 19 R6 1 1% SMD resistor 0603 102K Any 20 R7,R18,R23 3 5% SMD resistor 0603 10R Any 21 R9,R21 2 5% SMD resistor 0603 604R Any 22 R10,R22 2 1% SMD resistor 0603 1K Any 23 R11,R20 2 5% SMD resistor 0603 47K Any 24 R12 1 5% SMD resistor 0603 2R2 Any 25 R17 1 1% SMD resistor 0603 2.61K Any 26 U1 1 Dual phase Sync. step down controller MLPQ-24 SC2443 SEMTECH 20 SC2443 Outline Drawing - MLPQ-24 A D DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX B PIN 1 INDICATOR (LASER MARK) A A1 A2 b D D1 E E1 e L N aaa bbb E A2 A .031 .035 .039 .000 .001 .002 - (.008) .007 .010 .012 .152 .157 .163 .100 .106 .110 .152 .157 .163 .100 .106 .110 .020 BSC .012 .016 .020 24 .004 .004 0.80 0.90 1.00 0.00 0.02 0.05 - (0.20) 0.18 0.25 0.30 3.85 4.00 4.15 2.55 2.70 2.80 3.85 4.00 4.15 2.55 2.70 2.80 0.50 BSC 0.30 0.40 0.50 24 0.10 0.10 SEATING PLANE aaa C A1 C D1 LxN E/2 E1 2 1 N bxN e NOTES: bbb C A B D/2 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. © Semtech, Inc. All Rights Reserved. An ISO-registered company. Semtech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Semtech product. No circuit patent licenses are implied. Semtech reserves the right to change the circuitry and specifications without notice at any time. Trademarks and Copyrights belong to their respective holders. © 2007 Semtech Corporation 21 SC2443 Land Pattern - MLPQ-24 K DIMENSIONS (C) G H Z DIM C G H K P X Y Z INCHES (.156) .122 .106 .106 .020 .010 .033 .189 MILLIMETERS (3.95) 3.10 2.70 2.70 0.50 0.25 0.85 4.80 X P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. 2. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com 22