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
®
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
TEMP. (TJ)
SO-24
0 - 85°C
SC1144ABCSW
Note:
(1) Add suffix ‘TR’ for tape and reel.
BLOCK DIAGRAM
PIN CONFIGURATION
Top View
(24-Pin SOIC)
The SC1144 is patent pending
© 1999 SEMTECH CORP.
Pentium is a registered trademark of Intel Corporation
1
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Limits
Units
VCC5V to GND
Vcc5v
-0.3 to + 12
V
FBG to GND
FBG
±1
V
VCC12V to GND
Vcc12v
-0.3 to +20
V
Operating Temperature Range
TA
0 to +70
°C
Junction Temperature Range
TJ
0 to +125
°C
Storage Temperature Range
TSTG
-55 to +150
°C
Thermal Resistance Junction to Case
θJC
25
°C/W
Thermal Resistance Junction to Ambient
θJA
80
°C/W
TLEAD
300
°C
Lead Temperature (Soldering) 10 sec
ELECTRICAL CHARACTERISTICS
Unless otherwise noted: TA = 25°C, VCC 5V = 5V, VCC 12V = 12V, 4-Phase operation.
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
10.0
12.0
14.0
V
Supply Voltage Range
VCC12V
UVLO Range
VCC5V
3.9
V
UVLO Hystersis
VCC5V
50
mV
UVLO Range
VCC12V
9.0
V
UVLO Hystersis
VCC12V
100
mV
Supply Voltage Range
VCC5V
Supply Current
VCC12V
DRV Outputs open
Supply Current
VCC5V
VOUT = 2.00V, IO = 0
Reference Current Pin Voltage
VREF
Iref = 250µA
Vid0-4 Clock Select & Divide
VINL
Logic Low
Select Logic Threshold
VINH
Logic High
Vid0-4 Clock Select & Divide
IINL
Vid0-4=0V
-20
µA
Select Input Bias Current
IINH
Vid0-4=4.5V
+50
µA
Enable Pin
VINL
.8
V
4.5
VINH
5.0
5.5
V
12
20
mA
40
mA
2.05
V
0.8
2
V
V
2
V
VOL
Isink = 1mA
VOH
Isource=1ma,OUTV=Vcc12
DRV0-3 Source Current
ISRC
VOUT = 2.00V
20
mA
DRV0-3 Sink Current
ISNK
VOUT = 2.00V
40
mA
DRV0-3 Output Voltage
The SC1144 is patent pending
© 1999 SEMTECH CORP.
.3
V
V
VCC12
-1
2
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
ELECTRICAL CHARACTERISTICS (Cont.)
Unless otherwise noted: TA = 25°C, VCC5V = 5V, VCC12V = 12V, 4-Phase operation.
PARAMETER
SYMBOL
CONDITIONS
Bgout Voltage
VBgout
Vid = 00000
Bgout Impedance
RO_Bg
External Clock Freq. Range
Fext_CK
Oscillator Frequency Accuracy
FOSC
Internal Clock Freq. Range
Fint_CK
Match DRV0-3
∆D
PWM Off Time
Toff
Drive Voltage Range
OutV
Overcurrent Comparator,
Comparator, Common Mode
Range
Iref = 250µA
Duty cycle deviation from Avg.
MIN
TYP
MAX UNITS
2.05
V
3
KΩ
.80
8.0
8.5
MHz
7.2
8.0
8.8
MHz
.80
8.0
8.5
MHz
+1
%
-1
25
Output Freq. = 2MHz/Phase
VO = 2.000V
OCC_CMR
5
10
3
%
12
V
15
V
OC+I/P bias Current
IB_OC+
Vin = 5V,Roc+<20Kohm
+75
185
+250
µΑ
OC-I/P bias Current
IB_OC-
Vin = 5V,Roc-<20Kohm
+75
125
+250
µΑ
Input Offset Voltage
VOS_OCC
Vin = 5V
10
mV
Feedback Input Impedance
Ri_FB
VO = 2.00V
12
ΚΩ
Maximum Duty Cycle
Dmax
FB=0V
75
%
Mimimum Duty Cycle
Dmin
FB=4.0V
0
%
CONVERTER SPECIFICATIONS, Reference Application Circuit
Output Accuracy Over Set
Range
VOUT
VID 0-4 = 0000-1111
VCC5V = 5.0V
Load Regulation
∆VOUT
∆IO
VO = 2.000V
IO = 3A - 20A
Line Regulation
∆VOUT
∆VIN
VCC5V = 5V, VO = 2.000V
VIN = 4-6V, (vin separated from
Vcc5v) IO = 5A , Clk = external
The SC1144 is patent pending
© 1999 SEMTECH CORP.
-1
.025
+1
%
.05
%/A
%/V
.15
3
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
PIN DESCRIPTION
Pin #
Pin Name
Pin Function
1
VCC 5V
Supply voltage input (5V nominal)
2
Divsel
Connect to Gnd for four phase operation and to logic High for three Phase
operation.
3
Clksel
Clock Select: Logic high selects internal clock. Logic low selects external
clock.
4
Extclk
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.
5
RREF
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 250µA at 8MHz.
6
VID0
7
(1)
Programming Input (LSB)
(1)
Programming Input
(1)
Programming Input
(1)
Programming Input
(1)
VID1
8
VID2
9
VID3
10
VID4
Programming Input (MSB)
11
OC+
Over current comparator. Non-Inverting input.
12
OC-
Over current comparator. Inverting input.
13
COMP
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.
14
FB
Feedback input connected to supply output.
15
BGOUT
Bandgap Reference Output. Output resistance=3kohm. Must be bypassed
with 4.7nf -100nf capacitor to FBG. This capacitor programs the soft start
time.
16
FBG
Feedback Ground. This pin must be connected to return side of output
caps. This pin is floating, (within one diode drop of GND pin).
17
ENABLE
Connects to 5V to enable. Connect to GND to disable entire device.
18
GND
Ground Pin
19
DRV2
Phase 2 output
20
DRV0
Phase 0 output
21
VCC12V
Supply voltage for the FET Drivers/DRV0-3
22
DRV1
Phase 1 output
23
DRV3
Phase 3 output
24
OutV
Sets the maximum DRV0-3 drive voltage in order to reduce switching
losses in the external MOSFETs.
NOTE: (1) All logic inputs and outputs are open collector TTL compatible.
The SC1144 is patent pending
© 1999 SEMTECH CORP.
4
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
OUTPUT VOLTAGE
Unless specified: 0 = GND; 1 = High (or Floating).
TA = 25°C, VCC5V = 5V, VCC12V = 12V, 4-Phase operation.
PARAMETER
Output Voltage
The SC1144 is patent pending
© 1999 SEMTECH CORP.
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
TYP
MAX
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
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
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
5
652 MITCHELL ROAD NEWBURY PARK CA 91320
1u,10V
+5V
The SC1144 is patent pending
© 1999 SEMTECH CORP.
.001
10
VID4
.01
9
VID3
2.7k
8
VID2
8.2k
12
11
7
5
4
3
2
VID1
10u
1
6
.1u
10
VID0
1000UF
12V
Drv0
Vcc12V
Drv1
Drv3
Outv
OC-
OC+
Vid4
Vid3
Vid2
Vid1
13
14
15
16
17
18
19
20
21
22
23
24
.01u
Comp
FB
Bgout
FBG
Enable
GND
Vid0 SC1144-SOIC Drv2
Rref
Extclk
Clksel
Divsel
Vcc5V
.008
300k
1u
10
.022
2k
10k
1k
OUTPUT
VOLTAGE
SENSE
2.2
2.2
2.2
Date:
Size
A
Title
2907
2222
20N03
22u,10V
22u,10V
22u,10V
300nH
300nH
300nH
MBRD835
300nH
MBRD835
20N03
MBRD835
20N03
MBRD835
20N03
Wednesday, January 06, 1999
Document Number
{Doc}
SC1144 Application Circuit
Vout=1.3-3.5Volts
Iout=0-25Amps
2.2
1u,10V
2907
2222
1u,10V
2907
2222
1u,10V
2907
2222
12
Sheet
1
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
Ext. Load
VOUT
22u,10V
22u,10V
1u, 16V *3
Ceramic Surface Mount
(1210) Caps
of
1
Rev
{RevCode}
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
TYPICAL APPLICATION CIRCUIT
6
652 MITCHELL ROAD NEWBURY PARK CA 91320
652 MITCHELL ROAD NEWBURY PARK CA 91320
7
B121
1u,10V
8
7
6
5
4
3
2
1
VCC_L2
VID[4]
1u,10V
1u,10V
VID4
VID3
VID2
VID1
EN
C29
100UF
C35
VID0
Vout/Clk switch
A121
9
10
11
12
13
14
15
16
S1
C47 C46 C45
INPUT
1
2
3
4
5
6
1000UF
.01u
C31
SEL.
R11
250
R7
C30
vcc5v
10K
R22
C48
C28
100UF
.1u
10uf
.1u
C32
osc
J2
12
8.2k
R10
11
10
9
8
7
6
5
4
3
2
vcc5v
1
10K 10K 10K
R21R25R26
10
R2
U1
2.2
R20
Comp
FB
Bgout
FBG
Enable
GND
Drv2
Drv0
Drv1
Drv3
Outv
Vcc12v
SC1144ABCSW
OC-
OC+
Vid4
Vid3
Vid2
Vid1
Vid0
Rref
Extclk
Clksel
Divsel
Vcc5v
Long PCB Trace
13
14
15
16
C27
.01u
17 EN
18
19
20
21
22
23
24
300k
R17
C33
.01
R18
4.75k
VOUT
10k
R12
C49
.1u
3.24k
R4
C34
Q12
1u,10V
R9
10
Q10
Q9
FMMT718
Q7
Q6
FMMT718
2.2
FMMT718
FMMT618 R8
C44 C43
1u,10V 22u,10V
2.2
FMMT618 R6
C42 C41
1u,10V 22u,10V
2.2
C40 C39
1u,10V 22u,10V
2.2
FMMT718
R3
Q4 FMMT618 R5
Q3
FMMT618
Q1
Q11
Q8
Q5
Q2
835L
D4
300nh
L4
IRF7811
835L
D3
300nh
L3
IRF7811
835L
D2
300nh
L2
IRF7811
835L
D1
300nh
L1
IRF7811
VOUT
*
22u,10V
C25
22u,10V
C22
22u,10V
C17
22u,10V
C15
22u,10V
C12
22u,10V
C10
22u,10V
C8
22u,10V
C7
22u,10V
C6
22u,10V
C5
22u,10V
C4
22u,10V
C3
R13
51
1u,10V
C2
470uF,opt.
C50
R14
51
R15
51
R16
51
Date:
B
Size
Title
Wednesday, July 07, 1999
SC1144_EVB
1u,16V
C38
Sheet
1
U2
PentiumII
VOUT
SC1144evb1 Evaluation Board
1u,16V
C37
Document Number
Req'd at Freq.<1MHZ/phase
or for +12V Input
operation
*
1u,16V
C36
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
+5V
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
J1
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
12V
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
© 1999 SEMTECH CORP.
The SC1144 is patent pending
of
2.2
R19
1
Rev
A
EVALUATION BOARD SCHEMATIC
Preliminary - August 24, 1999
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
BILL OF MATERIAL
Item Qty
Reference
Value
Manufacturer
1
11
C2,C34,C36,C37,C38,C40,C42,C44,C45,C46,C47
1u,10V
AVX (818)883-7606
X7R
2
15
C3,C4,C5,C6,C7,C8,C10,C12,C15,C17,C22,C25,C39,C41,C
43
22u,10V
Murata (512)250-5082
PN #GRM235Y5V226Z010
3
2
C27,C31
.01u
4
2
C29,C28
100UF, 6.3v
Murata,Al. Elec.
5
1
C30
10uf, 6.3v
Murata,Al. Elec.
6
1
C32
.001
Murata
7
1
C33
.01u
Murata
8
1
C35
1000UF, 6.3v
9
1
C48
.1u
10
4
D1,D2,D3,D4
11
1
J1
INPUT
12
1
J2
osc
13
4
L1,L2,L3,L4
300nH, 8Amp
or 450nH, 8Amp
13A
4
L1,L2,L3,L4
300nH, 6Amp
14
4
Q1,Q4,Q7,Q10
FMMT618
Zetex
15
4
Q2,Q5,Q8,Q11
20N03HL
Motorola
16
4
Q3,Q6,Q9,Q12
FMMT718
Zetex
19
2
R2,R9
10
Dale,any
20
6
R3,R5,R6,R8,R19,R20
2.2
Dale
21
1
R4
680
any
22
1
R7
250
any
23
1
R10
8.2k
any
24
1
R11
2.32k
any
25
1
R12
3k
any
26
4
R13,R14,R15,R16
51, 1/4W, 1206
Dale
27
1
R17
300k
any
28
1
R18
4.75k
any
29
4
R21,R22,R25,R26
10K
any
30
1
S1
31
1
U1
SC1144ABCSW
Semtech (805)498-2111
32
1
U2
PentiumII conn.
Foxconn (714)256-1880
835L
AVX,Murata,Nichicon
Murata,Al. Elec.
Murata,X7R
Motorola
Falco (305)662-7276
PN #T025A2 or TO25O2
Steward
PN# DI2220V301R-00
Vout/Clk switch C&K (800)cal-swch
Unless otherwise noted, all resistors are 1/10W, 5%, 0805 and all capacitors are 20%, 50v, 0805.
The SC1144 is patent pending
© 1999 SEMTECH CORP.
8
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
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 ¼ 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
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
© 1999 SEMTECH CORP.
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.
9
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
ERROR AMPLIFIER CONT.
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
Fig. 2: Transient response, Top trace, Current sense
8A/div @ 30A/usec. Bottom trace, VOUT.
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
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
© 1999 SEMTECH CORP.
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.
10
652 MITCHELL ROAD NEWBURY PARK CA 91320
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
Preliminary - August 24, 1999
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
© 1999 SEMTECH CORP.
11
652 MITCHELL ROAD NEWBURY PARK CA 91320