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PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1144 is a high performance, multi-phase (PWM) controller designed for high power microprocessors requiring ultra fast transient response, such as (R) the Pentium ll and beyond. Utilizing a novel and unique design, the controller distributes the output load across (up to) four converter channels by digitally phase shifting the PWM outputs. This approach greatly reduces the stress and heat on the output stage components while lowering input ripple current by as much as 80%. Accurate current sharing among the four phases is achieved by precision design techniques and trimming of critical elements. The high speed transconductance error amplifier is externally initialized using a soft-start capacitor allowing the controller to "wake-up" without overshoot, thus protecting the low voltage microprocessor loads. The output drive voltage to the power MOSFETs is programmable to minimize switching losses in the drive circuitry. The floating feedback ground allows remote sense capability. The output voltage is digitally programmable by means of a 5 bit DAC. A single resistor programs the master clock frequency (8MHz max) or the controller may be synchronized using an external oscillator. The number of operating phases is programmed independently of the external clock. The parts features under-voltage lock-out with hysteresis and overcurrent protection.
FEATURES * Allows use of small surface mount components * Ultra fast transient recovery time * Wide, High frequency operating range * Selectable 2, 3, 4 phase operation * Floating feedback ground for remote sensing * Precision load current sharing * Selectable internal or external clock * Soft start, Over current protection * 5-bit DAC programmable output * programmable clock, 200Khz-2Mhz per phase APPLICATIONS * High end servers and workstations * High current/Ultra-fast transient microprocessors * Voltage Regulator Modules ORDERING INFORMATION
DEVICE
(1)
PACKAGE SO-24
TEMP. (TJ) 0 - 85C
SC1144ABCSW
Note: (1) Add suffix `TR' for tape and reel.
BLOCK DIAGRAM
PIN CONFIGURATION
Top View
(24-Pin SOIC)
The SC1144 is patent pending
Pentium is a registered trademark of Intel Corporation
1
(c) 1999 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
ABSOLUTE MAXIMUM RATINGS
Parameter VCC5V to GND FBG to GND VCC12V to GND Operating Temperature Range Junction Temperature Range Storage Temperature Range Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Lead Temperature (Soldering) 10 sec Symbol Vcc5v FBG Vcc12v TA TJ TSTG JC JA TLEAD Limits -0.3 to + 12 1 -0.3 to +20 0 to +70 0 to +125 -55 to +150 25 80 300 Units V V V C C C C/W C/W C
ELECTRICAL CHARACTERISTICS
Unless otherwise noted: TA = 25C, VCC 5V = 5V, VCC 12V = 12V, 4-Phase operation. PARAMETER Supply Voltage Range UVLO Range UVLO Hystersis UVLO Range UVLO Hystersis Supply Voltage Range Supply Current Supply Current Reference Current Pin Voltage Vid0-4 Clock Select & Divide Select Logic Threshold Vid0-4 Clock Select & Divide Select Input Bias Current Enable Pin SYMBOL VCC12V VCC5V VCC5V VCC12V VCC12V VCC5V VCC12V VCC5V VREF VINL VINH IINL IINH VINL VINH DRV0-3 Output Voltage VOL VOH DRV0-3 Source Current DRV0-3 Sink Current ISRC ISNK Isink = 1mA Isource=1ma,OUTV=Vcc12 VOUT = 2.00V VOUT = 2.00V VCC12 -1 20 40 2 .3 DRV Outputs open VOUT = 2.00V, IO = 0 Iref = 250A Logic Low Logic High Vid0-4=0V Vid0-4=4.5V 2 -20 +50 .8 2.05 0.8 4.5 CONDITIONS MIN 10.0 TYP 12.0 3.9 50 9.0 100 5.0 12 5.5 20 40 MAX 14.0 UNITS V V mV V mV V mA mA V V V A A V V V V mA mA
The SC1144 is patent pending
2 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
ELECTRICAL CHARACTERISTICS (Cont.)
Unless otherwise noted: TA = 25C, VCC5V = 5V, VCC12V = 12V, 4-Phase operation. PARAMETER Bgout Voltage Bgout Impedance External Clock Freq. Range Oscillator Frequency Accuracy Internal Clock Freq. Range Match DRV0-3 PWM Off Time Drive Voltage Range Overcurrent Comparator, Comparator, Common Mode Range OC+I/P bias Current OC-I/P bias Current Input Offset Voltage Feedback Input Impedance Maximum Duty Cycle Mimimum Duty Cycle SYMBOL VBgout RO_Bg Fext_CK FOSC Fint_CK D Toff OutV OCC_CMR Output Freq. = 2MHz/Phase VO = 2.000V 5 3 Duty cycle deviation from Avg. Iref = 250A .80 7.2 .80 -1 25 10 12 15 CONDITIONS Vid = 00000 MIN TYP 2.05 3 8.0 8.0 8.0 8.5 8.8 8.5 +1 MAX UNITS V K MHz MHz MHz % % V V
IB_OC+ IB_OCVOS_OCC Ri_FB Dmax Dmin
Vin = 5V,Roc+<20Kohm Vin = 5V,Roc-<20Kohm Vin = 5V VO = 2.00V FB=0V FB=4.0V
+75 +75
185 125 10 12 75 0
+250 +250
mV % %
CONVERTER SPECIFICATIONS, Reference Application Circuit Output Accuracy Over Set Range Load Regulation VOUT
VOUT IO VOUT VIN
VID 0-4 = 0000-1111 VCC5V = 5.0V VO = 2.000V IO = 3A - 20A VCC5V = 5V, VO = 2.000V VIN = 4-6V, (vin separated from Vcc5v) IO = 5A , Clk = external
-1 .025
+1 .05
% %/A
Line Regulation
%/V .15
The SC1144 is patent pending
3 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
PIN DESCRIPTION
Pin # 1 2 3 4 VCC 5V Divsel Clksel Extclk Pin Name Pin Function Supply voltage input (5V nominal) Connect to Gnd for four phase operation and to logic High for three Phase operation. Clock Select: Logic high selects internal clock. Logic low selects external clock. External Clock Input. The output frequency is determined by (Clock Input Freq.)/4. Output freq.= (Clock Input)/4. Pull up to Vcc5v to select internal clock. Connects to external reference resistor. Sets the operating frequency of the internal clock and the ramp time for the PWM. Reference voltage at this pin is 2.05V. Trimmed to set 250A at 8MHz.
(1) (1) (1) (1) (1)
5
RREF
6 7 8 9 10 11 12 13
VID0 VID1 VID2 VID3
Programming Input (LSB) Programming Input Programming Input Programming Input Programming Input (MSB) Over current comparator. Non-Inverting input. Over current comparator. Inverting input. Compensation Pin. Compensation is acheived by connecting a capacitor in series with a resistor between this pin and FBG. A 300k ohm resistor must also be directly connected between this pin and FBG. Feedback input connected to supply output. Bandgap Reference Output. Output resistance=3kohm. Must be bypassed with 4.7nf -100nf capacitor to FBG. This capacitor programs the soft start time. Feedback Ground. This pin must be connected to return side of output caps. This pin is floating, (within one diode drop of GND pin). Connects to 5V to enable. Connect to GND to disable entire device. Ground Pin Phase 2 output Phase 0 output Supply voltage for the FET Drivers/DRV0-3 Phase 1 output Phase 3 output Sets the maximum DRV0-3 drive voltage in order to reduce switching losses in the external MOSFETs.
VID4 OC+ OC-
COMP
14 15
FB BGOUT
16 17 18 19 20 21 22 23 24
FBG ENABLE GND DRV2 DRV0 VCC12V DRV1 DRV3 OutV
NOTE: (1) All logic inputs and outputs are open collector TTL compatible.
The SC1144 is patent pending
4 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
OUTPUT VOLTAGE
Unless specified: 0 = GND; 1 = High (or Floating). TA = 25C, VCC5V = 5V, VCC12V = 12V, 4-Phase operation.
PARAMETER Output Voltage
VID 43210 01111 01110 01101 01100 01011 01010 01001 01000 00111 00110 00101 00100 00011 00010 00001 00000 11111 11110 11101 11100 11011 11010 11001 11000 10111 10110 10101 10100 10011 10010 10001 10000
MIN 1.287 1.336 1.386 1.435 1.485 1.534 1.584 1.633 1.683 1.732 1.782 1.831 1.881 1.930 1.980 2.029 1.980 2.079 2.178 2.277 2.376 2.475 2.574 2.673 2.772 2.871 2.970 3.069 3.168 3.267 3.366 3.465
TYP 1.300 1.350 1.400 1.450 1.500 1.550 1.600 1.650 1.700 1.750 1.800 1.850 1.900 1.950 2.000 2.050 2.000 2.100 2.200 2.300 2.400 2.500 2.600 2.700 2.800 2.900 3.000 3.100 3.200 3.300 3.400 3.500
MAX 1.313 1.364 1.414 1.465 1.515 1.566 1.616 1.667 1.717 1.768 1.818 1.869 1.919 1.970 2.020 2.071 2.020 2.121 2.222 2.323 2.424 2.525 2.626 2.727 2.828 2.929 3.030 3.131 3.232 3.333 3.434 3.535
The SC1144 is patent pending
5 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
12V
The SC1144 is patent pending
.008 1u, 16V *3 1k 2.2 300nH 10 1 Vcc5V 22u,10V 23 1u,10V 22u,10V 10k 3 Clksel 2222 4 Extclk 2.2 300nH 2907 22u,10V 19 1u,10V 22u,10V 18 2222 8 Vid2 Enable 2.2 2907 1u 10 Vid4 14 2222 12 OCComp 2k 8.2k .01u 12 300k .022 Ext. Load 13 2.2 2907 MBRD835 300nH 22u,10V Bgout 15 1u,10V 22u,10V 20N03 22u,10V 22u,10V MBRD835 22u,10V 16 17 20N03 22u,10V MBRD835 22u,10V 20 Vcc12V 21 20N03 VOUT 22u,10V Drv1 22 22u,10V MBRD835 22u,10V Outv 24 2907 2222 20N03 2 Divsel Drv3 5 Rref Drv0 6 Vid0 SC1144-SOIC Drv2 Vid1 GND 7 300nH 22u,10V 9 Vid3 FBG 11 OC+ FB
+5V
10
2.7k
.01
.001
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
OUTPUT VOLTAGE SENSE
Vout=1.3-3.5Volts Iout=0-25Amps
Title SC1144 Application Circuit Size A Date: Document Number {Doc} Wednesday, January 06, 1999 Sheet 1 of 1 Rev {RevCode}
Ceramic Surface Mount (1210) Caps
(c) 1999 SEMTECH CORP.
Preliminary - August 24, 1999
1u,10V
1000UF
TYPICAL APPLICATION CIRCUIT
.1u
10u
VID0
VID1
VID2
VID3
VID4
6
652 MITCHELL ROAD NEWBURY PARK CA 91320
SC1144
B120 B119 B118 B117 B116 B115 B114 B113 B112 B111 B110 B109 B108 B107 B106 B105 B104 B103 B102 B101 B100 B99 B98 B97 B96 B95 B94 B93 B92 B91 B90 B89 B88 B87 B86 B85 B84 B83 B82 B81 B80 B79 B78 B77 B76 B75 B74 B73 B72 B71 B70 B69 B68 B67 B66 B65 B64 B63 B62 B61 B60 B59 B58 B57 B56 B55 B54 B53 B52 B51 B50 B49 B48 B47 B46 B45 B44 B43 B42 B41 B40 B39 B38 B37 B36 B35 B34 B33 B32 B31 B30 B29 B28 B27 B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 VOUT
VID[0] VID[3] $PIN238 VCC_L2 $PIN236 $PIN235 $PIN234 VCC_L2 $PIN232 $PIN231 $PIN230 VCC5 $PIN228 $PIN227 $PIN226 VCC_CORE $PIN224 $PIN223 $PIN222 $PIN221 $PIN220 $PIN219 $PIN218 VCC_CORE $PIN216 $PIN215 $PIN214 VCC_CORE $PIN212 $PIN211 $PIN210 VCC_CORE $PIN208 $PIN207 $PIN206 VCC_CORE $PIN204 $PIN203 $PIN202 $PIN201 $PIN200 $PIN199 $PIN198 VCC_CORE $PIN196 $PIN195 $PIN194 VCC_CORE $PIN192 $PIN191 $PIN190 VCC_CORE $PIN188 $PIN187 $PIN186 VCC_CORE $PIN184 $PIN183 $PIN182 $PIN181 $PIN180 $PIN179 $PIN178 VCC_CORE $PIN176 $PIN175 $PIN174 VCC_CORE $PIN172 $PIN171 $PIN170 VCC_CORE $PIN168 $PIN167 $PIN166 VCC_CORE $PIN164 $PIN163 $PIN162 $PIN161 $PIN160 $PIN159 $PIN158 VCC_CORE $PIN156 $PIN155 $PIN154 VCC_CORE $PIN152 $PIN151 $PIN150 VCC_CORE $PIN148 $PIN147 $PIN146 VCC_CORE $PIN144 $PIN143 $PIN142 $PIN141 $PIN140 $PIN139 $PIN138 VCC_CORE $PIN136 $PIN135 $PIN134 VCC_CORE $PIN132 $PIN131 $PIN130 VCC_VTT $PIN128 $PIN127 $PIN126 VCC_VTT $PIN124 $PIN123 $PIN122 $PIN121
VID[1] VID[2] GND $PIN116 $PIN115 $PIN114 GND $PIN112 $PIN111 $PIN110 GND $PIN108 $PIN107 $PIN106 GND $PIN104 $PIN103 $PIN102 GND $PIN100 $PIN99 $PIN98 GND $PIN96 $PIN95 $PIN94 GND $PIN92 $PIN91 $PIN90 GND $PIN88 $PIN87 $PIN86 GND $PIN84 $PIN83 $PIN82 GND $PIN80 $PIN79 $PIN78 GND $PIN76 $PIN75 $PIN74 GND $PIN72 $PIN71 $PIN70 GND $PIN68 $PIN67 $PIN66 GND $PIN64 $PIN63 $PIN62 GND $PIN60 $PIN59 $PIN58 GND $PIN56 $PIN55 $PIN54 GND $PIN52 $PIN51 $PIN50 GND $PIN48 $PIN47 $PIN46 GND $PIN44 $PIN43 $PIN42 GND $PIN40 $PIN39 $PIN38 GND $PIN36 $PIN35 $PIN34 GND $PIN32 $PIN31 $PIN30 GND $PIN28 $PIN27 $PIN26 GND $PIN24 $PIN23 $PIN22 GND $PIN20 $PIN19 $PIN18 GND $PIN16 Reserved THERMTRIP# GND TESTHI PWRGOOD TDO GND TDI IGNNE# FERR# GND A20M# IERR# VCC_VTT GND VCC_VTT
A120 A119 A118 A117 A116 A115 A114 A113 A112 A111 A110 A109 A108 A107 A106 A105 A104 A103 A102 A101 A100 A99 A98 A97 A96 A95 A94 A93 A92 A91 A90 A89 A88 A87 A86 A85 A84 A83 A82 A81 A80 A79 A78 A77 A76 A75 A74 A73 A72 A71 A70 A69 A68 A67 A66 A65 A64 A63 A62 A61 A60 A59 A58 A57 A56 A55 A54 A53 A52 A51 A50 A49 A48 A47 A46 A45 A44 A43 A42 A41 A40 A39 A38 A37 A36 A35 A34 A33 A32 A31 A30 A29 A28 A27 A26 A25 A24 A23 A22 A21 A20 A19 A18 A17 A16 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1
(c) 1999 SEMTECH CORP.
The SC1144 is patent pending
1 2 3 4 5 6
EVALUATION BOARD SCHEMATIC
Preliminary - August 24, 1999
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
652 MITCHELL ROAD NEWBURY PARK CA 91320
SC1144
7
9 10 11 12 13 14 15 16 B121 VCC_L2 A121 VID[4] VID1 VID2 VID3 VID4 .01u C31 .1u C32 8.2k R10 SC1144ABCSW U1 12 OCComp 11 10 9 8 7 6 Vid4 Vid3 Vid2 Vid1 Vid0 OC+ Drv2 GND Enable Bgout FBG FB SEL. R11 250 R7 2.2 R20 C27 300k R17 VOUT .01 .1u R18 10k R12 C49 4.75k .01u C33 C34 22u,10V C25 R13 R14 R15 R16 51 51 51 51 1u,10V 22u,10V C22 10 Q10 Q9 R9 Q12 FMMT718 835L D4 300nh L4 22u,10V C17 22u,10V C15 2.2 Q11 835L D3 IRF7811 22u,10V C12 300nh L3 22u,10V C10 22u,10V C8 13 FMMT618 R8 14 15 C44 C43 1u,10V 22u,10V 16 FMMT718 2.2 Q8 835L D2 IRF7811 22u,10V C7 300nh L2 22u,10V C6 18 17 EN Q7 FMMT618 R6
J1
INPUT
12V
1u,10V 1u,10V 1u,10V C35
C47 C46 C45
S1
8 7 6 5 4 3 2 1
VID0 Vout/Clk switch 19 Q6 C42 C41 1u,10V 22u,10V
1000UF 100UF 100UF
EN
C29
10K
C48
C28
R22
vcc5v
.1u 10uf
+5V
C30
J2
4 3 Extclk Clksel Vcc12v Drv1 21 22 Q4 FMMT618 R5 2.2 Q5 VOUT 22u,10V C5 IRF7811
osc
5 Rref Drv0 20 FMMT718
10 R2
10K 10K 10K Divsel Drv3
R21R25R26
Q3 835L D1
vcc5v 1
Vcc5v Long PCB Trace Outv 24 3.24k R4 FMMT618 Q1 R3 2.2 FMMT718 Q2 IRF7811 300nh L1
2 23 22u,10V C4
C40 C39 1u,10V 22u,10V
*
C50 1u,10V C2
22u,10V C3
470uF,opt.
*
Title
Size
B
Req'd at Freq.<1MHZ/phase or for +12V Input operation
Date:
1u,16V C36 1u,16V C37
Document Number
SC1144_EVB
1u,16V C38
SC1144evb1 Evaluation Board
Wednesday, July 07, 1999
Sheet
U2 PentiumII
1
2.2 R19 of
1
Rev A
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
BILL OF MATERIAL Item Qty 1 2 3 4 5 6 7 8 9 10 11 12 13 13A 14 15 16 19 20 21 22 23 24 25 26 27 28 29 30 31 32 11 15 2 2 1 1 1 1 1 4 1 1 4 4 4 4 4 2 6 1 1 1 1 1 4 1 1 4 1 1 1 Reference C2,C34,C36,C37,C38,C40,C42,C44,C45,C46,C47 C3,C4,C5,C6,C7,C8,C10,C12,C15,C17,C22,C25,C39,C41,C 43 C27,C31 C29,C28 C30 C32 C33 C35 C48 D1,D2,D3,D4 J1 J2 L1,L2,L3,L4 L1,L2,L3,L4 Q1,Q4,Q7,Q10 Q2,Q5,Q8,Q11 Q3,Q6,Q9,Q12 R2,R9 R3,R5,R6,R8,R19,R20 R4 R7 R10 R11 R12 R13,R14,R15,R16 R17 R18 R21,R22,R25,R26 S1 U1 U2 Value 1u,10V 22u,10V .01u 100UF, 6.3v 10uf, 6.3v .001 .01u 1000UF, 6.3v .1u 835L INPUT osc 300nH, 8Amp or 450nH, 8Amp 300nH, 6Amp FMMT618 20N03HL FMMT718 10 2.2 680 250 8.2k 2.32k 3k 51, 1/4W, 1206 300k 4.75k 10K Manufacturer
SC1144
AVX (818)883-7606 X7R Murata (512)250-5082 PN #GRM235Y5V226Z010 AVX,Murata,Nichicon Murata,Al. Elec. Murata,Al. Elec. Murata Murata Murata,Al. Elec. Murata,X7R Motorola
Falco (305)662-7276 PN #T025A2 or TO25O2 Steward PN# DI2220V301R-00 Zetex Motorola Zetex Dale,any Dale any any any any any Dale any any any
Vout/Clk switch C&K (800)cal-swch SC1144ABCSW PentiumII conn. Semtech (805)498-2111 Foxconn (714)256-1880
Unless otherwise noted, all resistors are 1/10W, 5%, 0805 and all capacitors are 20%, 50v, 0805.
The SC1144 is patent pending
8 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
THEORY OF OPERATION
FUNCTIONAL DESCRIPTION The SC1144 is a programmable, high performance, multi-phase controller designed for the most demanding DC/DC converter applications in which transient response, space, input ripple current and component form factor and cost are paramount. The SC1144 based dc/dc converter consists of four asynchronous converters. The gate drives to the converters are alternated sequentially by the SC1144 allowing equal sharing of the load current among the stages. The high clock frequency allows for smaller inductor value and miniature surface mount, low inductance output capacitors. Since each stage has 1/4 the output current, the conduction losses in each stage is reduced by a factor of 1/16. Precision active trimming ensures 1% matching of duty cycles among phases, thus ensuring the heat and component stress is shared equally. This allows use of lower cost components in each phase and virtual elimination of heat sinks. time. The ramps are then compared to the error amplifier output at the high speed PWM comparator inputs. The oscilator master clock frequency is programmed as follows: Clock Freq=(8.2K/Rref)*8Mhz
Fig. 1: The four Gate Drives firing 90 out of phase. VOUT = 2.0V, IOUT = 10A ERROR AMPLIFIER At the heart of the controller is an ultra-fast, transconductance error amplifier. Since the output inductor values can be selected to be a minimum, usually less than a micro-Henry, the delays due to inductor ramp time are minimized during transient load recovery. The higher frequency of operation also allows use of much smaller capacitance on the output. This means that the dc/dc converter output capacitors "hold Time" is less. The error amplifier must therefore respond extremely fast "Recover the Fort" after a transient. The SC1144 error amplifier recovers to its normal duty cycle after application of a full load transient within 2 usec maximum, (largely dependant on input and output capacitance) and usually within 1usec. This minimizes undershoot and overshoot during application of a transient. Operation at high frequency minimizes the output inductor thus allowing faster current ramp to the output capacitors. The effective gain of the error amplifier stays constant in both VID ranges, keeping the loop gain constant regardless of output voltage range.
Fig. 4: VOUT Ripple, VOUT = 2.0V, IOUT = 30A DECODER/BIAS GENERATOR/PWM CONTROLLER The 8 MHz clock is divided down to 2 MHz for four phase operation by the clock decoder. The start of the output pulses are time shifted 90 degrees by the decoder with respect to each other. The Bias Generator generates the ramps to each phase by a precision trimmed current source and on-chip capacitors. The decoder, which is synchronized to the bias generator via the master clock, phase shifts the ramps and enables the PWM controller sequentially. A resistor from RREF pin to FBG programs the frequency and ramp
The SC1144 is patent pending
9 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999 ERROR AMPLIFIER CONT.
SC1144
application of power, the non-inverting input of the error amplifier is held low for a short time allowing for the decoder and PWM controller to settle. This prevents any harmful output voltage overshoots upon start up or after a converter shut-down (as a result of over-current or the enable pin pulled low). The non-inverting input then ramps up according to the RC time constant allowing gradual rise of output voltage. ISOLATED FEEDBACK GROUND The feedback ground pin on the SC1144, FBG, is isolated from the GND. The maximum voltage between the two pins is set by the ESD diode forward voltage drop. This allows the SC1144 to be configured for remote sensing thus compensating for wiring and connector voltage drops at high currents or during transients. Remote sensing is typically implemented by using differential amplifiers. The use of this feature on the SC1144 eliminates the need for additional components. OVER-CURRENT COMPARATOR The SC1144 has an internal over-current comparator designed to sense current in the input supply path. The comparator inputs have a high common voltage range thus allowing operation under all possible voltage/current combinations. The output of the comparator pulls the BGOUT (soft start) pin low thus disabling the error amplifier and causing the PWM outputs to enter minimum duty cycle mode. SYNCHRONOUS VS. ASYNCHRONOUS MODE The SC1144 can be configured to drive Synchrounous MSOFET drivers, such as the SC1405 for higher efficiency. Refer to SC1405 datasheet for example designs. COMPONENT SELECTION AND LAYOUT CONSIDERATIONS Care must be taken in component selection and PCB layout in high frequency power appliactions. Refer to SC1144EVB user manual for more application information on component selection and layout guidlines as well as example Artwork and Bill of materials.
Fig. 2: Transient response, Top trace, Current sense 8A/div @ 30A/usec. Bottom trace, VOUT.
Fig. 3: Top Trace, Gate drive responding to removal of transient load. Bottom trace, Load current transient 16A/div. BANDGAP REFERENCE/SOFT START The precision internal bandgap reference provides a stable, temperature compensated 2.05 V reference for the error amplifier's non-inverting input, the DACREF for the VID digital to analog converter, the under-voltage lock-out circuitry as well as the reference for the Bias generator current sources. The error amplifiers noninverting input is connected to the bandgap reference through a 3 kohm resistor, which is also externally connected to a soft-start capacitor via the BGOUT pin. Upon
The SC1144 is patent pending
10 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.
PROGRAMMABLE, HIGH PERFORMANCE MULTI-PHASE, PWM CONTROLLER
Preliminary - August 24, 1999
SC1144
An evaluation board is available which may be ordered directly from the factory. SC1144EVB is a DC/DC converter utilizing the SC1144 four-phase controller in an asynchronous appliaction. The SC1144-SYNCH-EVB utilizes SC1405 high speed MOSFET drivers to drive the TOP and Synchronous MOSFETs with enhanced features. The evaluation boards are intended as guidelines for board design, layout and to assess key performance parameters, such as transient response, thermal stress management and input and output ripple considerations. The SC1144EVB includes a SLOT1 connector for Pentium II, a DIP switch for mode/voltage selection as well as qualified selection of components for the SC1144 operation. The SC1144EVB user manual contains useful applications information. Both Evaluation boards may be ordered from our website at www.semtech.com.
OUTLINE DRAWING - SO-24
JEDEC MS-013AD B17104B
The SC1144 is patent pending
11 652 MITCHELL ROAD NEWBURY PARK CA 91320
(c) 1999 SEMTECH CORP.

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