SC2422

SC2422A SEMTECH | Alldatasheet

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SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DEVICE (1) PACKAGE TEMP. RANGE (T J) SC2422ACS.TR SO-16 0 - 125°C SC2422A.EVB Evaluation Board

ORDERING INFORMATION

Note: (1) Only available in tape and reel packaging. A reel con- tains 1000 devices.

FEATURES

• Precision, pulse by pulse phase current match- ing
• Active drooping allows for best transient response
• Input Sensing Current mode control
• Programmable DAC step size/offset allows Compliance with VRM9.0, VRM8.3 or VRM8.4
• Externally programmable soft-start
• 5V or 12V input for next generation processors
• 0% minimum duty cycle improves transient re- sponse
• Externally Programmable UVLO with hysteresis
• Cycle by cycle current limiting
• Programmable Internal Oscillator to 1 MHz
• VID IIIII Inhibit (No CPU)

APPLICATIONS

• Intel Advanced Microprocessors
• AMD Athlon TM power supplies
• Servers/Workstations, high density power supplies TYPICAL APPLICATION SCHEMATIC

DESCRIPTION

The SC2422A biphase, current mode controller is de- signed to work with Semtech smart synchronous drivers, such as the SC1205, SC1305 or the SC1405 to provide the DC/DC converter solution for the most demanding Micro-processor applications. Input current rather than output current sensing is used to guarantee precision phase to phase current matching using a single sense resistor on the input power line. Accurate current sharing and pulse by pulse current limit are implemented without the power loss and transient re- sponse degradation associated with output current sense methods. Two phase operation allows significant reduction in input/output ripple while enhancing tran- sient response. The DAC step size and range are programmable with external components thus allowing compliance with new and emerging VID ranges. A novel approach implements active droop, minimizing output capacitor requirements during load transients. This avoids the pitfalls of the passive droop implemen- tation. This feature also allows easy implementation of N+1 redundancy and current sharing among modules. Programmable Under Voltage Lockout assures proper start-up and shutdown by synchronizing the controller to the driver supply. Wide PWM frequency range allows use of low profile, surface mount components. VININPUT Vout VIN Rf Rref Ri SC1305 VDD BOOST DRVH PHASE IN VCC DRVLPGND SC1305 VDD BOOST DRVH PHASE IN VCC DRVLPGND Rsens SC2422A 6 11 OUT2 GND VID3 VID2 VID4 OUT1 FB VID0 ERROUT OC- OC+ VID1 UVLO BGOUT VCC RREF To Processor VID control

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000

ELECTRICAL CHARACTERISTICS

Unless specified: VCC = +5V, TAMB = 25°C, RREF = 11.5kΩ . See Typical Application Circuit Parameter Conditions Min Typ Max Units Chip_Supply IC Supply Voltage 4.5 5 14 V IC Supply Current V CC = 5.0 ~ 12.0V 9 mA Reference Section Bandgap Output C BG = 4.7nF 1.5 V Source Impedance 3 kΩ Supply Rejection V CC = 5.0V ~ 12.0V 2 mV/V VID Step RI = 6.49kΩ , RREF = 11.5kΩ 25 mV Voltage Accuracy -1 1 % Temperature Stability 0°C < T AMB < 70°C 5 % Voltage Accuracy 0°C < T AMB < 70°C +/-1 % Oscillator Section Frequency Range 400 1000 kHz Frequency Accuracy VIN = 12.0V, RREF = 13kΩ or VIN = 5.0V, RREF =11.5kΩ 450 500 550 kHz Temperature Stability 0°C < T AMB < 70°C +/-5 % Voltage Error Amplifier Input Offset Voltage +/-5 mV Input Offset Current 0.1 µA Open Loop Gain 1V < V ERROUT < 4V 90 dB PSRR V CC = 5 - 12V 80 dB Output Sink Current V ERROUT = 1V 2.5 mA Output Source Current V ERROUT = 4V 2 mA Unity Gain Bandwidth I O < 100µA 5 MHz Slew Rate I O < 100µA 10 V/uS Parameter Symbol Maximum Units Input DC Rail Voltage to GND V IN 15 V PGND to GND + 1V Operating Temperature Range T A -20 to 125 °C Junction Temperature T J 0 to 125 °C Thermal Resistance Junction to Case θJC 20 °C/W Thermal Resistance Junction to Ambient θJA 60 °C/W Storage Temperature Range T STG -65 to +150 °C Lead Temperature (Soldering) 10 sec T LEAD 300 °C ABSOLUTE MAXIMUM RATINGS

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 ELECTRICAL CHARACTERISTICS (Cont) Unless specified: VCC = +5V, TAMB = 25°C, RREF = 11.5kΩ . PARAMETER CONDITIONS MIN TYP MAX UNITS Current Sense Amplifier Amplifier Gain (V OC- - VOC+ ) < 100mV 26 dB Input Offset Voltage, Input Referred (VOC- - VOC+ ) < 100mV 4 mV CMRR V ICM = 9 ~ 14V @ DC 80 dB PSRR V CC = 9 ~ 14V @ DC 80 dB Input Common Mode Range V CC +/- 0.3 Max Differential Signal/ Current Limit Threshold VOC- - VOC+ 100 mV I-Limit Delay Current limit activation to OUT 1 & OUT 2 switching off 60 ns Protection UVLO Ramp-up Threshold RSOURCE UVLO pin = 20kΩ 1.475 V UVLO Ramp-down Threshold RSOURCE UVLO pin = 20kΩ 1.375 V Outputs (OUT 1, OUT 2) Max Duty Cycle Per phase, F OSC = 500kHz 47 % Duty Match F OSC = 500kHz -.5 .5 % Typical Output Voltage Swing RL = 10kΩ .8 2.5 V RL = 100kΩ .2 3.3 V VID Logic Threshold 0.8 2 V VID Logic Pin Bias Current V IN = 0 12 µA Note: 1. If the VID pins are driven high by an external source (in contrast to being left open), then all VIDs input will need to be externally pulled high. If VIDs are left open, no external pull-up is required. 2. This device is ESD sensitive. Use of standard ESD handling precautions is required.

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 PIN CONFIGURATION Top View (16-Pin SOIC) FUNCTIONAL BLOCK DIAGRAM PIN DESCRIPTION Pin 1: VID4 , MSB Pin 2: VID3 Pin 3: VID2 Pin 4: VID 1 Pin 5: VID0 , LSB Pin 6: ERROUT Error-amplifier output. Pin 7: FB Error-amplifier inverting input. Pin 8: RREF Frequency setting resistor pin. Also pro- grams the DAC current step size. (see application in- formation for programming the frequency) Pin 9: GND Chip ground. Pin 10: UVLO Programmable Under Voltage Lock- Out. This pin may be connected to the MOSFET driver supply through a voltage divider to inhibit the SC2422A until the drivers are on. The UVLO comparator trip point is 1.5V. Pin 11: OC- Input current sense, negative input. This pin is connected to the input supply side of the current sense resistor. Pin 12: OUT2 PWM output for phase 2. Drives exter- nal Power MOSFET driver. Pin 13: OUT1 PWM output for phase 1. Drives exter- nal Power MOSFET driver. Pin 14: OC+ Input current sense positive input. This pin is connected to MOSFET side of the current sense resistor. Pin 15: BGOUT Soft start and reference. Bypass to ground (GSEN) with a .022µF - 0.1µF capacitor to im- plement soft start in conjunction with internal 3KΩ re- sistor. To ensure output voltage accuracy, the maxi- mum current source/sink from this pin should be lim- ited to 0.5 uA. Pin 16: VCC Chip positive supply.

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 OUTPUT VOLTAGE (VRM 9.0) Unless specified: 0 = GND; 1 = High (or Floating). TA = 25°C, VCC = 5V, 2-Phase operation VCCCORE VID4 VID3 VID2 VID1 VID0 (VDC) 1 1 1 1 1 Output Off 11 1 1 0 1 . 1 1 1 1 0 1 1.125 11 1 0 0 1 . 1 5 1 1 0 1 1 1.175 11 0 1 0 1 . 2 1 1 0 0 1 1.225 1 1 0 0 0 1.250 1 0 1 1 1 1.275 10 1 1 0 1 . 3 1 0 1 0 1 1.325 10 1 0 0 1 . 3 5 1 0 0 1 1 1.375 10 0 1 0 1 . 4 1 0 0 0 1 1.425 10 0 0 0 1 . 4 5 0 1 1 1 1 1.475 01 1 1 0 1 . 5 0 1 1 0 1 1.525 01 1 0 0 1 . 5 5 0 1 0 1 1 1.575 01 0 1 0 1 . 6 0 1 0 0 1 1.625 01 0 0 0 1 . 6 5 0 0 1 1 1 1.675 00 1 1 0 1 . 7 0 0 1 0 1 1.725 00 1 0 0 1 . 7 5 0 0 0 1 1 1.775 00 0 1 0 1 . 8 0 0 0 0 1 1.825 00 0 0 0 1 . 8 5

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 +5V EN EN EN VCORE VIN VIN Vin+5V local gnd +5V TTIB1106-450 R13 C22 C15 10u,CER C31 10u,CER C29 10u,CER C24 10u,CER C23 10u,CER C20 10u,CER C19 10u,CER C17 10u,CER C28 10u,CER C16 R11 10k C25 100pf R10 100k R14 11.5k GFB70N03 FDB7030BL INPUT 1u,16V 1uf 1uf 10u,CER 10u,CER 10uf C26 R17 6.49k 10u,CER Vout/Clk switch R15 2.2 C30 .01 R18 820uf,16V C12 820uf,16V LL42 LL42 R19 26.1k R20 10k FDB7030BL TTIB1106-450 820uf,16V C14 .01 R22 2.2 C32 .01 C27 .01 R21 2.2 GFB70N03 820uf,OS C33 820uf,16V 820uf,16V C35 820uf,16V C10 820uf,16V C34 R30 1uf C13 .005 R31 open R33 36k 10nf C11 SC2422A 6 11 OUT2 GND VID3 VID2 VID4 OUT1 FB VID0 ERROUT OC- OC+ VID1 UVLO BGOUT VCC RREF C18 10uf R32 75k 41.2 C21 .005 2.2 SC1205S CO BSTTG DRNVS EN BG GND SC1205S CO BSTTG DRNVS EN BG GND R99 open C99 ENABLE Place jumper for EN control of SC1205's * Droop=95mv at 1.6V and 35A load, with above values. Change R10 to change droop. Large changes may affect DC offsets. R19 controls output offset, set for VID=01010=1.600V Cut at X and install R99 to enable Driver side UVLO X Figure 1: SC2422A SCHEMATIC WITH +5V INPUT FOR THE AMD ATHLON TM PROCESSOR TO OPERATE FROM +12V: R3=20.5 R6=open R11=2.7K R14=12.40K R17=7.50K R19=31.6K R30=20.5 R32=120K R33=22K C25=150pf C99=1nf

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 Programming the DAC Step Size The SC2422A allows programming the output voltage and the DAC step size by selecting external resistors. The DAC current step size, for one MSB is: where R REF is the resistor from RREF pin to Ground. The DAC MSB voltage step size is calculated as fol- lows: VDAC_MSB = IDAC_MSB * RI or Note that changing RREF affects both frequency and DAC step size. RI must be proportionally adjusted to keep the same step size at different frequencies. The advantage of this method is that all new VID specifica- tions can be accommodated by modifying external components while maintaining the required precision without the need for converter redesign. Programming the DAC Offset Voltage Kirchoff’s current law can be applied to the error ampli- fier’s Inverting node (see figure 2) to calculate R OS, the DAC offset setting resistor. The output Offset at zero DAC current (VID=00000), is set as follows: Where V EO is the error amplifier output voltage and as a first approximation is equal to 1.75V. Where VBG = Precision Reference Voltage = 1.50V. The value of ROS can be fine trimmed using a poten- tiometer connected from the FB pin to ground. Programming the Dynamic (Active) Droop The SC2422A employs a novel approach to active drooping for optimum transient response. The output voltage is regulated as a function of output current. At zero current the output is regulated to the upper limit of the output voltage specification. As the load is in- creased, the output “droops” towards the lower limit. This makes optimum use of the output voltage error band, yielding minimum output capacitor size and cost. Active drooping, does not compromise the converter response time as does passive droop techniques. The active droop also allows for an accurate Inter-Module current sharing scheme, where multiple DC/DC con- verters are required to share the current required by a DC bus. As one module supplies more current, that modules output voltage ”droops”, allowing other mod- ules to provide the balance of the required current.Any changes in the output voltage is instantaneously re- flected to the error amplifier, which has a high Slew Rate and wide Gain-Bandwidth product to recover the output voltage to its nominal level with minimal delay. The droop is adjusted by setting the feedback resistor, Rf. While the optimum value of R F may be derived ex- perimentally, the following equation can provide the droop at a given output current: The Gain of the current amplifier is set to 20 (26dB), while R S is the input sense resistor. The effective inductance of the sense resistor must be minimized to achieve accurate correlation between the above equation and actual droop achieved. This is be- cause the inductive spike, which may also be caused by layout inductance's, will alter the PWM comparator trip point. The value of R F may have to be adjusted to compensate for such parasitic effects. Since Rf also sets the DC gain of the system, changing the value of Rf affects the offset voltage, which is set via Ros. The value of Ros can be modified to achieve exact offset after the droop resistor has been chosen.It must be noted that the Current Amplifier gain is quite precise, with greater than 80dB of Common Mode Re- jection Ratio (CMRR). Thus the droop’s accuracy is limited primarily by external components tolerances and the external parasitic effects. Loop Gain Considerations The Modulator gain in Input Current Mode control is equal to: RAMP IN MOD V VK = L VVXGXTXRV3.0V OIN CAOSCSENSERAMP −+= R R VV I REF BG LSB_DAC ∗= REF BG MSB_DAC R VI = F BGEO I BGO BG OS R VV R VV VR −+−= RF OUTSICA DROOP I*R*R*GV = VV MSB_DAC LSB_DAC =

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 Where: RS = Input current sense resistor TOSC = Oscillator period GCA = Current Amplifier Gain 0.3V is the ramp added for slope compensation when the output current is near zero. The DC loop gain is the product of the modulator gain and the error amplifier gain and is calculated as follows: Refer to Application note AN00-1 for detailed treatment of frequency compensation component selection as well as programming the SC2422A. The application note is available on the Semtech website or by contacting the factory. Programming the Under Voltage Lockout The SC2422A may be operated from any supply in +5V to +12V range. A pin has been dedicated to externally selecting the voltage at which the SC2422A outputs are active. A good typical turn-on threshold value is 4.5V for a +5V input supply and 9V for a +12V supply. A voltage divider connected to the UVLO pin selects this threshold. The UVLO comparator trip point is approximately 1.475V. Sufficient hysterisis is provided to ensure proper DC/DC converter shutdown. The UVLO setting should consider external MOSFET driver’s UVLO threshold. Ideally, the external MOSFET driver should turn on before the SC2422 controller and turn off before the controller. This assures the converter output will rise and fall slowly using the soft start feature and that the output voltage will not go negative at turn- off. PCB layout Care must be excercised when laying out the PC board for SC2422 or other input current mode DC/DC convert- ers. SInce the current is delivered and sensed in pulse packets, the inductance of the current carrying traces and thus their length must be minimized. Ceramic by- pass capacitors must be located near the sense resistor. For a detailed treatment and circuit parasitic models, consult application note: AN00-7:“Component Selection and PC Board layout IRAMP FIN LOOP R*V R*VG = Considerations in Input Current Mode DC/DC Con- verters”. This application note is available by con- tacting the factory. Remote Sensing Capability The SC2422 has a single ground for error amplifier and DAC reference and for the internal biasing of the chip. Since the chip uses approximately 10ma of qui- escent current, the ground pin may be connected to a remote location without fear of ground loops. When used as a microprocessor power supply, connecting the ground pin directly to the ground plane may result in undesirable voltage drops in the plane at high out- put current. This is not entirely predictable since the error amplifier is correcting for the DC error with ref- erence with the ground plane and not the processor “feedback ground”. Thus any voltage difference be- tween the two ground will result in a DC error. This error will obviously consume valuable static error band tolerance. To avoid this DC error, the SC2422 ground pin (pin 9) can be connected to a copper “Island”, to which Rref (frequency setting resistor) and Ros (offset setting resistor) will also be con- nected. This “Island” in turn will only be connected to the “Processor Feedback” ground via a trace. While the trace may be long, it should not be routed through or near the switching sections or noisy components. This method of remote sensing will alleviate the need for a differential amplifier to sense the output voltage/ output return pair and the design effort and costs as- sociated with it. SC2422A Evaluation Board The SC2422A based DC/DC converter utilizes the SC1205 High Speed MOSFET drivers to achieve VRM 9.0 output Voltage Specifications. SC2422A Evaluation Board Schematic (Figure 1) shows the circuit for a 40A, BiPhase DC/DC converter. The Evaluation board is available by contacting the fac- tory or Semtech website at WWW.Semtech.com.

SC2422ABIPHASE CURRENT MODE CONTROLLER © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 PRELIMINARY - August 7, 2000 OUTLINE DRAWING SO-16 LAND PATTERN SO-16 Jedec MS-012AC ECN00-1242