Datasheet SC1144 Datasheet (SEMTECH)

查询SC1144供应商

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

Preliminary - August 24, 1999

TEL:[phone] FAX:[phone] 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
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.

®

ll and beyond. Utilizing a novel and

PIN CONFIGURATION

SC1144

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

SC1144ABCSW SO-24 0 - 85°C
Note:

(1) Add suffix ‘TR’ for tape and reel.

BLOCK DIAGRAM

(1)

PACKAGE TEMP. (TJ)

Top View

(24-Pin SOIC)

The SC1144 is patent pending

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Pentium is a registered trademark of Intel Corporation

1

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

Preliminary - August 24, 1999

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Limits Units

V

to GND V

CC5V

cc5v

FBG to GND FBG ± 1 V

-0.3 to + 12 V

to GND V

V

CC12V

Operating Temperature Range T
Junction Temperature Range T
Storage Temperature Range T
Thermal Resistance Junction to Case

Thermal Resistance Junction to Ambient
Lead Temperature (Soldering) 10 sec T

cc12v

STG

θ

JC

θ

JA

LEAD

A

J

-0.3 to +20 V
0 to +70 °C

0 to +125 °C

-55 to +150 °C
25 °C/W

80 °C/W

300 °C

ELECTRICAL CHARACTERISTICS

Unless otherwise noted: TA = 25°C, V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage Range V
UVLO Range V
UVLO Hystersis V
UVLO Range V
UVLO Hystersis V
Supply Voltage Range V
Supply Current V
Supply Current V
Reference Current Pin Voltage V
Vid0-4 Clock Select & Divide V
Select Logic Threshold V
Vid0-4 Clock Select & Divide I
Select Input Bias Current I
Enable Pin V

DRV0-3 Output Voltage V

CC 5V

CC12V

CC5V

CC5V

CC12V

CC12V

CC5V

CC12V

CC5V

REF

INL

INH

INL

INH

INL

V

INH

OL

V

OH

= 5V, V

= 12V, 4-Phase operation.

CC 12V

10.0 12.0 14.0 V

3.9 V
50 mV

9.0 V

100 mV

4.5 5.0 5.5 V

DRV Outputs open 12 20 mA

V

= 2.00V, I

OUT

= 0 40 mA

O

Iref = 250µA 2.05 V

Logic Low 0.8 V
Logic High 2 V
Vid0-4=0V -20 µA

Vid0-4=4.5V +50 µA

.8 V

2V

I

= 1mA .3 V

sink

I

=1ma,OUTV=V

source

cc12

V

CC12

-1

V

DRV0-3 Source Current I
DRV0-3 Sink Current I

The SC1144 is patent pending

SRC

SNK

V

= 2.00V 20 mA

OUT

V

= 2.00V 40 mA

OUT

2

© 1999 SEMTECH CORP. 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, V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

CC5V

= 5V, V

= 12V, 4-Phase operation.

CC12V

Bgout Voltage V
Bgout Impedance R
External Clock Freq. Range F
Oscillator Frequency Accuracy F
Internal Clock Freq. Range F
Match DRV0-3

Bgout

O_Bg

ext_CK

OSC

int_CK

∆

D

Duty cycle deviation from Avg. -1 +1 %

Vid = 00000 2.05 V

3

K

.80 8.0 8.5 MHz

Iref = 250µA 7.2 8.0 8.8 MHz

.80 8.0 8.5 MHz

PWM Off Time Toff 25 %
Drive Voltage Range OutV Output Freq. = 2MHz/Phase

= 2.000V

V

O

Overcurrent Comparator,

OCC_CMR 3 15 V

51012 V

Comparator, Common Mode
Range

OC+I/P bias Current IB_OC+ Vin = 5V,Roc+<20Kohm +75 185 +250
OC-I/P bias Current IB_OC- Vin = 5V,Roc-<20Kohm +75 125 +250

µ
µ

Input Offset Voltage VOS_OCC Vin = 5V 10 mV

Ω

Α
Α

Feedback Input Impedance Ri_FB V

= 2.00V 12

O

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

V

OUT

VID 0-4 = 0000-1111

Range
Load Regulation V

Line Regulation V

The SC1144 is patent pending

∆

V

OUT

∆

I

O

∆

V

OUT

∆

V

IN

V

IN

Vcc5v) I

I

= 5V, VO = 2.000V

CC5V

= 4-6V, (vin separated from

O

= 5.0V

V

CC5V

= 2.000V

O

= 3A - 20A

O

= 5A , Clk = external

-1 +1 %

.025 .05 %/A

%/V

.15

3

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

Preliminary - August 24, 1999

PIN DESCRIPTION

Pin # Pin Name Pin Function

SC1144

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
7VID1
8VID2

9VID3

10 VID4

(1)

(1)

(1)

(1)

(1)

Programming Input (LSB)

Programming Input

Programming Input

Programming Input

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.

NOTE:

The SC1144 is patent pending

(1) All logic inputs and outputs are open collector TTL compatible.

4

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 24, 1999

OUTPUT VOLTAGE

Unless specified: 0 = GND; 1 = High (or Floating).
T

= 25°C, V

A

CC5V

= 5V, V

= 12V, 4-Phase operation.

CC12V

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

PARAMETER VID

MIN TYP MAX

43210

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

The SC1144 is patent pending

5

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 24, 1999

TYPICAL APPLICATION CIRCUIT

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

1u, 16V *3

20N03

2222

1k

300nH

2.2

10

2907

22u,10V

MBRD835

22u,10V

1u,10V

22u,10V

10k

22u,10V

20N03

2222

VOUT

2.2

22u,10V

300nH

2907

22u,10V

MBRD835

22u,10V

1u,10V

22u,10V

22u,10V

20N03

2222

22u,10V

300nH

2.2

(1210) Caps
Ceramic Surface Mount

22u,10V

1u,10V

22u,10V

20N03

2222

22u,10V

MBRD835

22u,10V

2907

1u

22u,10V

300nH

2.2

2907

2k

12

MBRD835

Ext. Load

Iout=0-25Amps

Vout=1.3-3.5Volts

OUTPUT

VOLTAGE

SENSE

.022

300k

of

11Wednesday, January 06, 1999

{Doc} {RevCode}

SC1144 Application Circuit

A

Title

Size Document Number Rev

Date: Sheet

13

.01u

Comp

OC-

OC+ FB

12

11 14

8.2k

.001

2.7k
.01

6

12V

The SC1144 is patent pending

+5V

.008

16

17

18

19

20

21

22

23

24

8

VID2

Enable

Vid2

9

VID3

FBG

Vid3

Vid4 Bgout

10 15

VID4

Vcc12V

Extclk

4

Drv0

SC1144-SOIC

Vid0

6

VID0

Vid1

7

VID1

Rref

5

Drv1

Drv3

Outv

Divsel

2

.1u 10u

Clksel

3

Vcc5V

1

10

1000UF

1u,10V

GND

Drv2

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 24, 1999

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

EVALUATION BOARD SCHEMATIC

1u,16V

C38

1u,16V

C37

1u,16V

C36

*

Req'd at Freq.<1MHZ/phase

or for +12V Input

operation

C2

1u,10V

12V

470uF,opt.

*

IRF7811

R3

Q1

FMMT618

Long PCB Trace

10

+5V

J1

12345

C50

Q2

R2

C28

C29

C35

22u,10V

300nh

2.2

3.24k

1u,10V
1u,10V
1u,10V

C3

L1

835L

FMMT718

R4

24

Outv

Vcc5v

vcc5v

C30

C48

100UF

100UF

C45
C46
C47

INPUT

6

22u,10V

D1

22u,10V

C39

1u,10V

C40

Q3

23

231

R26
R25
R21

1000UF

10uf

C4

Drv3

Divsel

10K
10K
10K

.1u

22u,10V

C6

22u,10V

D2

22u,10V

C41

1u,10V

C42

Q6

19

vcc5v

VID0

Drv2

Vid0

C7

IRF7811

R6

FMMT618Q7

18

GND

Vid1

756

VID1

Vout/Clk switch

Q8

EN

17

8

VID2

22u,10V

300nh

2.2

10k

Enable

Vid2

C8

L3

FMMT718

R12

16

9

VID3

835L

FBG

Vid3

22u,10V

C5

VOUT

300nh

L2

IRF7811

R5

FMMT618Q4

.1u

C49

22

Drv1

Clksel

8

S1

9

835L

Q5

2.2

FMMT718

20

21

Drv0

Vcc12v

Rref

Extclk

J2

osc

R22

10K

EN

1234567

16151413121110

22u,10V

C10

D3

22u,10V

C43

1u,10V

C44

Q9

VID4

Vid4 Bgout

22u,10V

C12

IRF7811

R8

FMMT618Q10

VOUT

OC+ FB

11 14410 15

22u,10V

C15

300nh

L4

Q11

2.2

10

13

Comp

SC1144ABCSW

OC-

12

250

SEL.

22u,10V

D4

835L

FMMT718

Q12

R9

4.75k

R18

.01u

U1

8.2k

R10

R7

R11

A

2.2

R19

of

11

PentiumII

U2

VCC_VTT

A1

GND

A2

VCC_VTT

A3

IERR#

A4

A20M#

A5

GND

A6

FERR#

A7

IGNNE#

A8

TDI

A9

GND

A10

TDO

A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23

51

R16

51

R15

51

R14

51

R13

22u,10V

C25

22u,10V

C22

C17

1u,10V

C34

C33

.01

300k

R17

C27

R20

.1u

C32

.01u

C31

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

2.2

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

VID[4]

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

GND

TESTHI

$PIN16
$PIN18

$PIN19
$PIN20

$PIN22
$PIN23
$PIN24

$PIN26
$PIN27
$PIN28

$PIN30
$PIN31
$PIN32

$PIN34
$PIN35
$PIN36

$PIN38
$PIN39
$PIN40

$PIN42
$PIN43
$PIN44

$PIN46
$PIN47
$PIN48

$PIN50
$PIN51
$PIN52

$PIN54
$PIN55
$PIN56

$PIN58
$PIN59
$PIN60

$PIN62
$PIN63
$PIN64

$PIN66
$PIN67
$PIN68

$PIN70
$PIN71
$PIN72

$PIN74
$PIN75
$PIN76

$PIN78
$PIN79
$PIN80

$PIN82
$PIN83
$PIN84

$PIN86
$PIN87
$PIN88

$PIN90
$PIN91
$PIN92

$PIN94
$PIN95
$PIN96

$PIN98
$PIN99

$PIN100
$PIN102

$PIN103
$PIN104

$PIN106
$PIN107
$PIN108

$PIN110
$PIN111
$PIN112

$PIN114
$PIN115
$PIN116

VID[2]
VID[1]

PWRGOOD

THERMTRIP#

Reserved

$PIN121

B1

$PIN122

B2

$PIN123

B3

$PIN124

B4

VCC_VTT

B5

$PIN126

B6

$PIN127

B7

$PIN128

B8

VCC_VTT

B9

$PIN130

B10

$PIN131

B11

$PIN132

B12

VCC_CORE

B13

$PIN134

B14

$PIN135

B15

$PIN136

B16

VCC_CORE

B17

$PIN138

B18

$PIN139

B19

$PIN140

B20

$PIN141

B21

$PIN142

B22

$PIN143

B23

$PIN144

B24

VCC_CORE

B25

$PIN146

B26

$PIN147

B27

$PIN148

B28

VCC_CORE

B29

$PIN150

B30

$PIN151

B31

$PIN152

B32

VCC_CORE

B33

$PIN154

B34

$PIN155

B35

$PIN156

B36

VCC_CORE

B37

$PIN158

B38

$PIN159

B39

$PIN160

B40

$PIN161

B41

$PIN162

B42

$PIN163

B43

$PIN164

B44

VCC_CORE

B45

$PIN166

B46

$PIN167

B47

$PIN168

B48

VCC_CORE

B49

$PIN170

B50

$PIN171

B51

$PIN172

B52

VCC_CORE

B53

$PIN174

B54

$PIN175

B55

$PIN176

B56

VCC_CORE

B57

$PIN178

B58

$PIN179

B59

$PIN180

B60

$PIN181

B61

$PIN182

B62

$PIN183

B63

$PIN184

B64

VCC_CORE

B65

$PIN186

B66

$PIN187

B67

$PIN188

B68

VCC_CORE

B69

$PIN190

B70

$PIN191

B71

$PIN192

B72

VCC_CORE

B73

$PIN194

B74

$PIN195

B75

$PIN196

B76

VCC_CORE

B77

$PIN198

B78

$PIN199

B79

$PIN200

B80

$PIN201

B81

$PIN202

B82

$PIN203

B83

$PIN204

B84

VCC_CORE

B85

$PIN206

B86

$PIN207

B87

$PIN208

B88

VCC_CORE

B89

$PIN210

B90

$PIN211

B91

$PIN212

B92

VCC_CORE

B93

$PIN214

B94

$PIN215

B95

$PIN216

B96

VCC_CORE

B97

$PIN218

B98

$PIN219

B99

$PIN220

B100

$PIN221

B101

$PIN222

B102

$PIN223

B103

$PIN224

B104

VCC_CORE

B105

$PIN226

B106

$PIN227

B107

$PIN228

B108

VCC5

B109

$PIN230

B110

$PIN231

B111

$PIN232

B112

VCC_L2

B113

$PIN234

B114

$PIN235

B115

$PIN236

B116

VCC_L2

B117

$PIN238

B118

VID[3]

B119

VID[0]

B120

VCC_L2

B121

VOUT

SC1144evb1 Evaluation Board

SC1144_EVB

B

Title

Size Document Number Rev

Wednesday, July 07, 1999

Date: Sheet

The SC1144 is patent pending

7

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

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 [phone]

X7R

2 15 C3,C4,C5,C6,C7,C8,C10,C12,C15,C17,C22,C25,C39,C41,C

43
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

13A 4 L1,L2,L3,L4 300nH, 6Amp Steward

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

22u,10V Murata [phone]

PN #GRM235Y5V226Z010

Falco [phone]

or 450nH, 8Amp

PN #T025A2 or TO25O2

PN# DI2220V301R-00

SC1144

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 [phone]
32 1 U2 PentiumII conn. Foxconn [phone]

Unless otherwise noted, all resistors are 1/10W, 5%, 0805 and all capacitors are 20%, 50v, 0805.

The SC1144 is patent pending

8

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 24, 1999

THEORY OF OPERATION

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

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.
V

= 2.0V, I

OUT

OUT

= 10A

Fig. 4: V

Ripple, V

OUT

= 2.0V, I

OUT

OUT

= 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

pin to FBG programs the frequency and ramp

R

REF

The SC1144 is patent pending

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

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 24, 1999

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

SC1144

ERROR AMPLIFIER CONT.

Fig. 2: Transient response, Top trace, Current sense
8A/div @ 30A/usec. Bottom trace, V

OUT

.

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

(soft start) pin low thus disabling the

GOUT

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 de-

Fig. 3: Top Trace, Gate drive responding to removal of

signs.
transient load. Bottom trace, Load current transient
16A/div.

COMPONENT SELECTION AND LAYOUT CONSID-

ERATIONS
BANDGAP REFERENCE/SOFT START

Care must be taken in component selection and PCB
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

layout in high frequency power appliactions. Refer to

SC1144EVB user manual for more application informa-

tion on component selection and layout guidlines as

well as example Artwork and Bill of materials.
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

The SC1144 is patent pending

GOUT

pin. Upon

10

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

PROGRAMMABLE, HIGH PERFORMANCE
MULTI-PHASE, PWM CONTROLLER

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.

SC1144

OUTLINE DRAWING - SO-24

JEDEC MS-013AD

B17104B

The SC1144 is patent pending

© 1999 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

11