Page 1
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
1
The SC1144 is patent pending
Pentium is a registered trademark of Intel Corporation
BLOCK DIAGRAM
PIN CONFIGURATION
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
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DEVICE
(1)
PACKAGE TEMP. (TJ)
SC1144ABCSW SO-24 0 - 85°C
ORDERING INFORMATION
Note:
(1) Add suffix ‘TR’ for tape and reel.
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.
(24-Pin SOIC)
Top View
Page 2
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
2
The SC1144 is patent pending
ELECTRICAL CHARACTERISTICS
Unless otherwise noted: TA = 25°C, V
CC 5V
= 5V, V
CC 12V
= 12V, 4-Phase operation.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range V
CC12V
10.0 12.0 14.0 V
UVLO Range V
CC5V
3.9 V
UVLO Hystersis V
CC5V
50 mV
UVLO Range V
CC12V
9.0 V
UVLO Hystersis V
CC12V
100 mV
Supply Voltage Range V
CC5V
4.5 5.0 5.5 V
Supply Current V
CC12V
DRV Outputs open 12 20 mA
Supply Current V
CC5V
V
OUT
= 2.00V, I
O
= 0 40 mA
Reference Current Pin Voltage V
REF
Iref = 250µA 2.05 V
Vid0-4 Clock Select & Divide V
INL
Logic Low 0.8 V
Select Logic Threshold V
INH
Logic High 2 V
Vid0-4 Clock Select & Divide I
INL
Vid0-4=0V -20 µA
Select Input Bias Current I
INH
Vid0-4=4.5V +50 µA
Enable Pin V
INL
.8 V
V
INH
2V
DRV0-3 Output Voltage V
OL
I
sink
= 1mA .3 V
V
OH
I
source
=1ma,OUTV=V
cc12
V
CC12
-1
V
DRV0-3 Source Current I
SRC
V
OUT
= 2.00V 20 mA
DRV0-3 Sink Current I
SNK
V
OUT
= 2.00V 40 mA
ABSOLUTE MAXIMUM RATINGS
Parameter Symbol Limits Units
V
CC5V
to GND V
cc5v
-0.3 to + 12 V
FBG to GND FBG ± 1 V
V
CC12V
to GND V
cc12v
-0.3 to +20 V
Operating Temperature Range T
A
0 to +70 °C
Junction Temperature Range T
J
0 to +125 °C
Storage Temperature Range T
STG
-55 to +150 °C
Thermal Resistance Junction to Case
θ
JC
25 °C/W
Thermal Resistance Junction to Ambient
θ
JA
80 °C/W
Lead Temperature (Soldering) 10 sec T
LEAD
300 °C
Page 3
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
3
The SC1144 is patent pending
ELECTRICAL CHARACTERISTICS (Cont.)
Unless otherwise noted: TA = 25°C, V
CC5V
= 5V, V
CC12V
= 12V, 4-Phase operation.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Bgout Voltage V
Bgout
Vid = 00000 2.05 V
Bgout Impedance R
O_Bg
3
K
Ω
External Clock Freq. Range F
ext_CK
.80 8.0 8.5 MHz
Oscillator Frequency Accuracy F
OSC
Iref = 250µA 7.2 8.0 8.8 MHz
Internal Clock Freq. Range F
int_CK
.80 8.0 8.5 MHz
Match DRV0-3
∆
D
Duty cycle deviation from Avg. -1 +1 %
PWM Off Time Toff 25 %
Drive Voltage Range OutV Output Freq. = 2MHz/Phase
V
O
= 2.000V
51012 V
Overcurrent Comparator,
Comparator, Common Mode
Range
OCC_CMR 3 15 V
OC+I/P bias Current IB_OC+ Vin = 5V,Roc+<20Kohm +75 185 +250
µ
Α
OC-I/P bias Current IB_OC- Vin = 5V,Roc-<20Kohm +75 125 +250
µ
Α
Input Offset Voltage VOS_OCC Vin = 5V 10 mV
Feedback Input Impedance Ri_FB V
O
= 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
V
OUT
VID 0-4 = 0000-1111
V
CC5V
= 5.0V
-1 +1 %
Load Regulation V
O
= 2.000V
I
O
= 3A - 20A
.025 .05 %/A
Line Regulation V
CC5V
= 5V, VO = 2.000V
V
IN
= 4-6V, (vin separated from
Vcc5v) I
O
= 5A , Clk = external
.15
%/V
O
OUT
I
V
∆
∆
IN
OUT
V
V
∆
∆
Page 4
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
4
The SC1144 is patent pending
NOTE:
(1) All logic inputs and outputs are open collector TTL compatible.
PIN DESCRIPTION
Pin # Pin Name Pin Function
1V
CC 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.
5R
REF
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.
6VID0
(1)
Programming Input (LSB)
7VID1
(1)
Programming Input
8VID2
(1)
Programming Input
9VID3
(1)
Programming Input
10 VID4
(1)
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 B
GOUT
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 V
CC12V
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.
Page 5
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
5
The SC1144 is patent pending
OUTPUT VOLTAGE
Unless specified: 0 = GND; 1 = Hi gh (or Fl oating).
T
A
= 25°C, V
CC5V
= 5V, V
CC12V
= 12V, 4-Phase operation.
PARAMETER VID
43210
MIN TYP MAX
Output Voltage 01111 1.287 1.300 1.313
01110 1.336 1.350 1.364
01101 1.386 1.400 1.414
01100 1.435 1.450 1.465
01011 1.485 1.500 1.515
01010 1.534 1.550 1.566
01001 1.584 1.600 1.616
01000 1.633 1.650 1.667
00111 1.683 1.700 1.717
00110 1.732 1.750 1.768
00101 1.782 1.800 1.818
00100 1.831 1.850 1.869
00011 1.881 1.900 1.919
00010 1.930 1.950 1.970
00001 1.980 2.000 2.020
00000 2.029 2.050 2.071
11111 1.980 2.000 2.020
11110 2.079 2.100 2.121
11101 2.178 2.200 2.222
11100 2.277 2.300 2.323
11011 2.376 2.400 2.424
11010 2.475 2.500 2.525
11001 2.574 2.600 2.626
11000 2.673 2.700 2.727
10111 2.772 2.800 2.828
10110 2.871 2.900 2.929
10101 2.970 3.000 3.030
10100 3.069 3.100 3.131
10011 3.168 3.200 3.232
10010 3.267 3.300 3.333
10001 3.366 3.400 3.434
10000 3.465 3.500 3.535
Page 6
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
6
The SC1144 is patent pending
TYPICAL APPLICATION CIRCUIT
{Doc} {RevCode}
SC1144 Application Circuit
A
11Wednesday, January 06, 1999
Title
Size Document Number Rev
Date: Sheet
of
VID2
VID1
VID4
VID3
VID0
+5V
VOUT
12V
22u,10V
2k
22u,10V
1u,10V
2.7k
22u,10V
.022
.01u
300k
22u,10V
1u, 16V *3
Ext. Load
1u
1000UF
10
.01
8.2k
.001
.1u 10u
22u,10V
.008
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
22u,10V
2222
22u,10V
22u,10V
20N03
2907
20N03
1u,10V
300nH
300nH
2.2
1u,10V
2907
20N03
1u,10V
20N03
MBRD835
MBRD835
300nH
2907
22u,10V
2222
2.2
2.2
2.2
300nH
2222
MBRD835
MBRD835
2907
2222
1k
12
10k
SC1144-SOIC
12
9
2
3
1
13
7
5
6
11 14
4
10 15
16
17
18
19
20
21
22
23
24
8
OC-
Vid3
Divsel
Clksel
Vcc5V
Comp
Vid1
Rref
Vid0
OC+ FB
Extclk
Vid4 Bgout
FBG
Enable
GND
Drv2
Drv0
Vcc12V
Drv1
Drv3
Outv
Vid2
10
OUTPUT
VOLTAGE
SENSE
Ceramic Surface Mount
(1210) Caps
Iout=0-25Amps
Vout=1.3-3.5Volts
Page 7
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
7
The SC1144 is patent pending
A
SC1144evb1 Evaluation Board
B
11
Wednesday, July 07, 1999
Title
Size Document Number Rev
Date: Sheet
of
vcc5v
EN
VOUT
VID2
vcc5v
VOUT
EN
VID0
VID3
VID1
+5V
VID4
VOUT
12V
2.2
R19
22u,10V
C41
22u,10V
C4
R26
10K
22u,10V
C25
R21
10K
10k
R12
IRF7811
Q8
IRF7811
Q11
J2
osc
1u,16V
C36
22u,10V
C6
R22
10K
1u,10V
C44
51
R13
300nh
L2
2.2
R5
FMMT618Q4
1u,16V
C37
22u,10V
C7
22u,10V
C10
100UF
C28
250
R7
IRF7811
Q5
1u,10V
C45
1u,10V
C46
22u,10V
C5
835L
D3
2.2
R6
1u,10V
C40
51
R16
1u,10V
C47
22u,10V
C12
51
R14
FMMT618Q10
FMMT618Q7
R25
10K
.01u
C27
J1
INPUT
12345
6
FMMT718
Q12
.01u
C31
1000UF
C35
300k
R17
10uf
C30
1u,10V
C42
.1u
C48
4.75k
R18
22u,10V
C3
22u,10V
C15
C33
.01
2.2
R8
8.2k
R10
51
R15
S1
Vout/Clk switch
1234567
8
16151413121110
9
SEL.
R11
22u,10V
C43
2.2
R20
2.2
R3
835L
D2
22u,10V
C22
22u,10V
C8
FMMT718
Q6
835L
D4
.1u
C32
300nh
L4
1u,10V
C2
300nh
L3
SC1144ABCSW
U1
12
9
231
13
756
11 14410 15
16
17
18
19
20
21
22
23
24
8
OC-
Vid3
Divsel
Clksel
Vcc5v
Comp
Vid1
Rref
Vid0
OC+ FB
Extclk
Vid4 Bgout
FBG
Enable
GND
Drv2
Drv0
Vcc12v
Drv1
Drv3
Outv
Vid2
10
R9
1u,16V
C38
300nh
L1
835L
D1
10
R2
1u,10V
C34
IRF7811
Q2
U2
PentiumII
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
A32
A33
A34
A35
A36
A37
A38
A39
A40
A41
A42
A43
A44
A45
A46
A47
A48
A49
A50
A51
A52
A53
A54
A55
A56
A57
A58
A59
A60
A61
A62
A63
A64
A65
A66
A67
A68
A69
A70
A71
A72
A73
A74
A75
A76
A77
A78
A79
A80
A81
A82
A83
A84
A85
A86
A87
A88
A89
A90
A91
A92
A93
A94
A95
A96
A97
A98
A99
A100
A101
A102
A103
A104
A105
A106
A107
A108
A109
A110
A111
A112
A113
A114
A115
A116
A117
A118
A119
A120
A121
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
B32
B33
B34
B35
B36
B37
B38
B39
B40
B41
B42
B43
B44
B45
B46
B47
B48
B49
B50
B51
B52
B53
B54
B55
B56
B57
B58
B59
B60
B61
B62
B63
B64
B65
B66
B67
B68
B69
B70
B71
B72
B73
B74
B75
B76
B77
B78
B79
B80
B81
B82
B83
B84
B85
B86
B87
B88
B89
B90
B91
B92
B93
B94
B95
B96
B97
B98
B99
B100
B101
B102
B103
B104
B105
B106
B107
B108
B109
B110
B111
B112
B113
B114
B115
B116
B117
B118
B119
B120
B121
VCC_VTT
GND
VCC_VTT
IERR#
A20M#
GND
FERR#
IGNNE#
TDI
GND
TDO
PWRGOOD
TESTHI
GND
THERMTRIP#
Reserved
$PIN16
GND
$PIN18
$PIN19
$PIN20
GND
$PIN22
$PIN23
$PIN24
GND
$PIN26
$PIN27
$PIN28
GND
$PIN30
$PIN31
$PIN32
GND
$PIN34
$PIN35
$PIN36
GND
$PIN38
$PIN39
$PIN40
GND
$PIN42
$PIN43
$PIN44
GND
$PIN46
$PIN47
$PIN48
GND
$PIN50
$PIN51
$PIN52
GND
$PIN54
$PIN55
$PIN56
GND
$PIN58
$PIN59
$PIN60
GND
$PIN62
$PIN63
$PIN64
GND
$PIN66
$PIN67
$PIN68
GND
$PIN70
$PIN71
$PIN72
GND
$PIN74
$PIN75
$PIN76
GND
$PIN78
$PIN79
$PIN80
GND
$PIN82
$PIN83
$PIN84
GND
$PIN86
$PIN87
$PIN88
GND
$PIN90
$PIN91
$PIN92
GND
$PIN94
$PIN95
$PIN96
GND
$PIN98
$PIN99
$PIN100
GND
$PIN102
$PIN103
$PIN104
GND
$PIN106
$PIN107
$PIN108
GND
$PIN110
$PIN111
$PIN112
GND
$PIN114
$PIN115
$PIN116
GND
VID[2]
VID[1]
VID[4]
$PIN121
$PIN122
$PIN123
$PIN124
VCC_VTT
$PIN126
$PIN127
$PIN128
VCC_VTT
$PIN130
$PIN131
$PIN132
VCC_CORE
$PIN134
$PIN135
$PIN136
VCC_CORE
$PIN138
$PIN139
$PIN140
$PIN141
$PIN142
$PIN143
$PIN144
VCC_CORE
$PIN146
$PIN147
$PIN148
VCC_CORE
$PIN150
$PIN151
$PIN152
VCC_CORE
$PIN154
$PIN155
$PIN156
VCC_CORE
$PIN158
$PIN159
$PIN160
$PIN161
$PIN162
$PIN163
$PIN164
VCC_CORE
$PIN166
$PIN167
$PIN168
VCC_CORE
$PIN170
$PIN171
$PIN172
VCC_CORE
$PIN174
$PIN175
$PIN176
VCC_CORE
$PIN178
$PIN179
$PIN180
$PIN181
$PIN182
$PIN183
$PIN184
VCC_CORE
$PIN186
$PIN187
$PIN188
VCC_CORE
$PIN190
$PIN191
$PIN192
VCC_CORE
$PIN194
$PIN195
$PIN196
VCC_CORE
$PIN198
$PIN199
$PIN200
$PIN201
$PIN202
$PIN203
$PIN204
VCC_CORE
$PIN206
$PIN207
$PIN208
VCC_CORE
$PIN210
$PIN211
$PIN212
VCC_CORE
$PIN214
$PIN215
$PIN216
VCC_CORE
$PIN218
$PIN219
$PIN220
$PIN221
$PIN222
$PIN223
$PIN224
VCC_CORE
$PIN226
$PIN227
$PIN228
VCC5
$PIN230
$PIN231
$PIN232
VCC_L2
$PIN234
$PIN235
$PIN236
VCC_L2
$PIN238
VID[3]
VID[0]
VCC_L2
22u,10V
C39
FMMT718
Q9
100UF
C29
22u,10V
C17
3.24k
R4
.1u
C49
470uF,opt.
C50
FMMT718
Q3
FMMT618
Q1
Long PCB Trace
SC1144_EVB
*
*
Req'd at Freq.<1MHZ/phase
or for +12V Input
operation
EVALUATION BOARD SCHEMATIC
Page 8
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
8
The SC1144 is patent pending
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 AVX,Murata,Nichicon
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 Murata,Al. Elec.
9 1 C48 .1u Murata,X7R
10 4 D1,D2,D3,D4 835L Motorola
11 1 J1 INPUT
12 1 J2 osc
13 4 L1,L2,L3,L4 300nH, 8Amp
or 450nH, 8Amp
Falco (305)662-7276
PN #T025A2 or TO25O2
13A 4 L1,L2,L3,L4 300nH, 6Amp Steward
PN# DI2220V301R-00
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 Vout/Clk switch C&K (800)cal-swch
31 1 U1 SC1144ABCSW Semtech (805)498-2111
32 1 U2 PentiumII conn. Foxconn (714)256-1880
Unless otherwise noted, all resistors are 1/10W, 5%, 0805 and all capacitors are 20%, 50v, 0805.
Page 9
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
9
The SC1144 is patent pending
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.
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
R
REF
pin to FBG programs the frequency and ramp
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
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.
THEORY OF OPERATION
Fig. 4: V
OUT
Ripple, V
OUT
= 2.0V, I
OUT
= 30A
Fig. 1: The four Gate Drives firing 90° out of phase.
V
OUT
= 2.0V, I
OUT
= 10A
Page 10
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
10
The SC1144 is patent pending
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 D
ACREF
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 B
GOUT
pin. Upon
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 B
GOUT
(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.
ERROR AMPLIFIER CONT.
Fig. 3: Top Trace, Gate drive responding to removal of
transient load. Bottom trace, Load current transient
16A/div.
Fig. 2: Transient response, Top trace, Current sense
8A/div @ 30A/usec. Bottom trace, V
OUT
.
Page 11
PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER
SC1144
© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
Preliminary - August 24, 1999
11
The SC1144 is patent pending
OUTLINE DRAWING - SO-24
JEDEC MS-013AD
B17104B
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.
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