SEMTECH SC1101 Technical data

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VOLTAGE MODE PWM CONTROLLER

February 29, 2000

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DESCRIPTION

The SC1101 is a versatile, low-cost, voltage-mode
PWM controller designed for use in single ended DC/
DC power supply applications. A simple, fixed-voltage
buck regulator can be implemented using the SC1101
with a minimum of external components. Internal level
shift and drive circuitry eliminates the need for an ex­pensive p-channel, high-side switch. The small device
footprint allows for compact circuit design.

SC1101 features include a temperature compensated
voltage reference, triangle wave oscillator, current limit
comparator, frequency shift over-current protection,
and an internally compensated error amplifier. Pulse by
pulse current limiting is implemented by sensing the
differential voltage across an external resistor, or an
appropriately sized PC board trace.

The SC1101 operates at a fixed frequency of 200kHz,
providing an optimum compromise between efficiency,
external component size, and cost.

SC1101

FEATURES

•

Low cost / small size

•

Switch mode efficiency (90%)

•

1% reference voltage accuracy

•

Over current protection

•

500mA output drive

•

SO-8 package

APPLICATIONS

•

Pentium® P55 Core Supply

•

Low Cost Microprocessor Supplies

•

Peripheral Card Supplies

•

Industrial Power Supplies

•

High Density DC/DC Conversion

ORDERING INFORMATION

DEVICE

SC1101CS SO-8 0° to 125°C

(1)

PACKAGE TEMP RANGE (TJ)

PIN CONFIGURATION

Top View

1

Vcc

s(+)

2
3
4

Cs(-)

GND

(8 LEAD PLASTIC SOIC)

8
7
6
5

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

BLOCK DIAGRAM

GND

FB
BST

DH

Pentium is a registered trademark of Intel Corporation

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

1

VOLTAGE MODE PWM CONTROLLER

February 29, 2000

PIN DESCRIPTION

Pin # Pin Name Pin Function

1V
2C
3C
4P

CC

s(-)

s(+)

GND

5 DH High Side Driver Output

Device Input Voltage
Current Sense Input (Negative)
Current Sense Input (Positive)
Device Power Ground

SC1101

6 BST High Side Driver V

(Boost)

CC

7 FB Error Amplifier Input (-)
8 GND Small Signal Ground

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Maximum Units

Input Voltage V
Ground Differential P

Boost Input Voltage BST to GND -0.3 to +15 V
Operating Temperature T
Storage Temperature T
Lead Temperature (Soldering) 10 seconds T
Thermal Resistance, Junction to Ambient
Thermal Resistance, Junction to Case

to GND -0.3 to +7 V

CC

to GND ± 1 V

GND

A

J

L

θ JA

θ JC

0 to +70 °C

-45 to +125 °C
300 °C
165 °C/W

40 °C/W

2

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

ELECTRICAL CHARACTERISTICS

VOLTAGE MODE PWM CONTROLLER

SC1101

VCC = 4.75V to 5.25V; GND = P

= 0V; VO = 3.3V; TA = 25°C; BST = 12V; Output current = 2A.

GND

Per test circuit, unless otherwise specified.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Reference V

REF

1.238 1.250 1.263 V

Over Temp 1.225 1.250 1.275 V
Feedback Bias Current I
Quiescent Current I
Regulation Load REG
Regulation Line REG

FB

Q

LOAD

LINE

Current into VCC pin 5.0 8.0 mA

IO=1A to 12A 0.5 1.0 %

2.0 8.0 uA

0.5 %
Current Limit Threshold CLT CS(+) to CS(-) 60 70 80 mV
Oscillator Frequency OSC 180 200 220 kHz
Oscillator Frequency Shift OFS V

FB

< V

/2 50 kHz

REF

Max Duty Cycle d.c. 90 95 %
DH Sink/Source Current I

UVLO Threshold V

O

UVLO

V

- VDH = 4.5V

BST

- V

(V

DH

PGND

= 2V)

500 mA

3.8 V

TEST CIRCUIT

J1 J2

+5V

+

C3

1500uF

C2

1500uF

+

C4

1500uF

C1

0.1uF

J3

J4

+12V

R2

+

10

VOUT R3 R4

3.45 174 100

BUK556

R5

1.00k

PSR16C30CT

D1

Q1

3.30 165 100

3.10 147 100

2.90 133 100

2.80 124 100

2.50 100 100
20

1.50

100

C11

0.1uF

2.32k

R6

C10

0.1uF

L1

4uH

U1

1

VCC

2

CS(-)

3

CS(+)
PGND4DH

SC1101CS

GND

BST

R1
5mOhm

FB

C6
1500uF

+

C5
1500uF

8
7
6
5

+

+

C7
1500uF

C8
1500uF

+

C9

0.1uF

R3
See Table

R4
See Table

VOUT=1.25*(R3+R4)/R4

VOUT

3

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

VOLTAGE MODE PWM CONTROLLER

SC1101

40

35

30

25

20

15

Gain (dB)

10

5

0

-5

-10

100.0E+0 1.0E+3 10.0E+3 100.0E+3 1.0E+6 10.0E+6

Gain
Phase

Frequency (Hz)

Fig.1: Error Amplifier, Gain and Phase

180

135

90

45

0

-45

0.05

0.04

0.03

0.02

Phase (deg)

0.01

Voltage change (V)

0

normalized to 0 at Io=2A

-0.01

-0.02

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Output Current ( Amps)

Fig.2: Load Regulation Characteristic

100%

95%

90%

85%

Efficiency

80%

75%

3.50V Set

3.00V Set

2.40V Set

2.00V Set

Fig.3: Ripple; Vo=2.90V; Io=10A

70%

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Output Curre nt (Amps)

Fig.4: Efficiency

4

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

VOLTAGE MODE PWM CONTROLLER

SC1101

LAYOUT GUIDELINES

Careful attention to layout requirements are necessary
for successful implementation of the SC1101 PWM con­troller. High currents switching at 200kHz are present in
the application and their effect on ground plane voltage
differentials must be understood and minimized.

1). The high power parts of the circuit should be laid out
first. A ground plane should be used, the number and
position of ground plane interruptions should be such as
to not unnecessarily compromise ground plane integrity.
Isolated or semi-isolated areas of the ground plane may
be deliberately introduced to constrain ground currents
to particular areas, for example the input capacitor and
bottom Schottky ground.

2). The loop formed by the Input Capacitor(s) (Cin), the
Top FET (Q1) and the Schottky (D1) must be kept as
small as possible. This loop contains all the high current,
fast transition switching. Connections should be as wide
and as short as possible to minimize loop inductance.
Minimizing this loop area will reduce EMI, lower ground
injection currents, resulting in electrically “cleaner”
grounds for the rest of the system and minimize source
ringing, resulting in more reliable gate switching signals.

3). The connection between the junction of Q1, D1 and
the output inductor should be a wide trace or copper re­gion. It should be as short as practical. Since this con-

nection has fast voltage transitions, keeping this connec­tion short will minimize EMI. The connection between the
output inductor and the sense resistor should be a wide
trace or copper area, there are no fast voltage or current
transitions in this connection and length is not so impor­tant, however adding unnecessary impedance will re­duce efficiency.

4) The Output Capacitor(s) (Cout) should be located as
close to the load as possible, fast transient load currents
are supplied by Cout only, and connections between
Cout and the load must be short, wide copper areas to
minimize inductance and resistance.

5) The SC1101 is best placed over an isolated ground
plane area. GND and PGND should be returned to this
isolated ground. This isolated ground area should be
connected to the main ground by a trace that runs from
the GND pin to the ground side of (one of) the output ca­pacitor(s). If this is not possible, the GND pin may be
connected to the ground path between the Output Ca­pacitor(s) and the Cin, Q1, D1 loop. Under no circum­stances should GND be returned to a ground inside the
Cin, Q1, D1 loop.

6) Vcc for the SC1101 should be supplied from the 5V
supply through a 10Ω resistor, the Vcc pin should be de­coupled directly to GND by a 0.1µF ceramic capacitor,
trace lengths should be as short as possible.

10

0.1uF

SC1101CS

1
2
3

0.1uF

GND

VCC
CS(-)
CS(+)
PGND4DH

BST

Heavy lines indicate
high current paths.

Fig. 5 Layout diagram for the SC1101

Cin

5V

2.32k

+

1.00kQ1

4uH

5mOhm

+

Cout

Vout

12V IN

8
7

FB

6
5

Rb

D1

Ra

5

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

VOLTAGE MODE PWM CONTROLLER

SC1101

7) The Current Sense resistor and the divider across it
should form as small a loop as possible, the traces run­ning back to CS(+) and CS(-) on the SC1101 should run
parallel and close to each other. The 0.1µF capacitor
should be mounted as close to the CS(+) and CS(-) pins
as possible.

8) To minimize noise pickup at the sensitive FB pin, the
feedback resistors should both be close to the SC1101
with the bottom resistor (Rb) returned to ground at the
GND pin.

TYPICAL APPLICATIONS

Q1

J1

+3.3V

1

+

C3

220uF

C2

220uF

+

C1

0.1uF

J3

GND

1

J4

+12V

1

IRL2203S

L1

D1
32CTQ030S

Under Voltage Lockout

The under voltage lockout circuit of the SC1101 assures
that the high-side MOSFET driver outputs remain in the
off state whenever the supply voltage drops below set
parameters. Lockout occurs if V
mal operation resumes once V

R1
6mOhm

+

C4

220uF

220uF

C6

0.1uF

+

C5

falls below 3.8V. Nor-

CC

rises above 3.8V.

CC

VOUT

R2
24

C7
R4
124

0.01uF

J2
1

J5
1

R5

J6

+5V

1

R3
10

1k

C2-C7 - AVX: TPSE227M010S0100
Q1, D1 - International Rectifier
L1- Coilcraft: DO5022P-392HC

C9

0.1uF

Fig. 6: GTL+ 3.3V to 1.5V 8A Application

C10

0.1uF

R6
1k

SC1101CS

1

VCC

2

CS(-)

3

CS(+)
PGND4DH

U1

GND

FB

BST

Cx

0.01

8
7
6
5

C8

0.1uF

6

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

TYPICAL APPLICATIONS (cont.)

VOLTAGE MODE PWM CONTROLLER

SC1101

D2
LL42

+5V

+

C3

220uF

C2

220uF

+

C4

220uF

0.1uF

C1

GND

C2-C7 - AVX: TPSE227M01S0100
Q1, D1 - International Rectifier
L1 - Coilcraft: DO5022P-392HC

C8

0.1uF

Q1
IRL2203S

+

R3
10

R5
1k

R6
1k

C9

0.1uF

C10

0.1uF

L1

D1
32CTQ030

SC1101CS

1

VCC

2

CS(-)

3

CS(+)
PGND4DH

R1

0.012

+

C5

220uF

U1

GND

BST

Cx

0.01

8
7

FB

6
5

C6

220uF

C7

0.1uF

+

+3.3V

R2
205

R4
124

Fig. 7: 5V to 3.3V 8A Application with flying capacitor boost

7

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

February 29, 2000

OUTLINE DRAWING

VOLTAGE MODE PWM CONTROLLER

JEDEC

REF: MS-012AA

SC1101

LAND PATTERN SO-8

ECN00-900

8

© 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320