Semtech SC2603SKTRT Schematic [ru]

POWER MANAGEMENT

R2

R3

L1

Q1

D1

C2

C1

R4

VIN

VOUT

GND

D2

optional

U2

SC2603

VIN

5

EN/SS

3

FB

1

GND

2

CS

6

Gate

4

R1

C4

Enable

C3

R5

C5

(open collector)

Open Drain with < 100Ω
pull down impedance

SC2603

Simple PWM Boost Controller

Description

The SC2603 is a versatile, low-cost, voltage-mode PWM
controller designed for 16V input DC/DC power supply
applications. A simple, fixed-voltage boost regulator can
be implemented using the SC2603 with a minimum of
external components. The small device footprint
allows for compact circuit design.

SC2603 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 SC2603 operates at a fixed frequency of 200kHz,
providing an optimum compromise between efficiency,
external component size, and cost.

Typical Application Circuit

Features

u Low cost / small size
u Switch mode efficiency up to 95%
u 1% reference voltage accuracy
u Over-current protection
u 800mA output drive
u 5V to 16V input power source
u No need for external compensation network
u SOT23-6 is fully WEEE and RoHS compliant

Applications

u Portable Devices
u Flat Panel TV
u TV Set Top Box
u Auxiliary Supplies
u Peripheral Card Supplies
u Industrial Power Supplies
u High Density DC/DC Conversion

Revision: Nov 14, 2006

1

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SC2603

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POWER MANAGEMENT

Absolute Maximum Ratings

Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.

Note:
(1) Mounting pad has to be larger than one square inch on two sided printed circuit board with minimum 1 ounce copper
(2) Human model.

Electrical Characteristics

VIN= 12V; VO = 25V; TA = TJ = -40°C to 125°C unless otherwise specified.

2 2005 Semtech Corp.

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2

1

3

FB

GND

EN/SS

4

6

CS

5

VIN

GATE

SOT23-6

VIN

FB

Gate

CS

UVLO

GND

PWM

EN/SS

70mV

Current
Limit

VIN

UV

S

Q

R

OSCILLATOROSCILLATOR

1.25V
REF

1.25V
REF

25K

SC2603

Pin Configuration

Pin Descriptions

Ordering Information

Top View

Note:
(1) Only available in tape and reel packaging. A reel
contains 3000 devices.

(2) Lead free product. This product is fully WEEE and
RoHS compliant

Block Diagram

 2005 Semtech Corp.

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POWER MANAGEMENT











−= 1

25.1

21

OUT

V

RR

VOUT

R2

R1

FB

1

SC2603

SC2603

Theory of Operation

The SC2603 is a versatile, low-cost, voltage-mode PWM
controller designed for DC/DC power supply applications.
In normal condition, the SC2603 operats at a fixed
200KHz. One exception is that when the FB pin voltage
drops to one half, the frequency will be shifted to one
fouth of 200KHz.

SC2603 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.

Application Information

Soft-Start

Soft-start prevents a DC-DC converter from drawing
excessive current from the power source during start up.
If the soft-start time is made sufficiently long, then the
output will enter regulation without overshoot. An external
capacitor is connected from the EN/SS pin to the ground.
After the part’s input voltage surpasses the UVLO, the
EN/SS pin is allowed to charge its capacitor with 60µA.
When 100mV is reached at the EN/SS pin, the internal
comp node is at 0.4V. The SC2603 will start switching,
and the converter output comes into regulation. Because
the FB pin voltage follows EN/SS pin voltage, finally, the
EN/SS pin voltage will be clamped at 1.25V same as the
refernece voltage.

Setting the Output Voltage

An external resistive divider R1 and R2 with its center
tap tied to the FB pin sets the output voltage.

Under Voltage Lockout

The under voltage lockout circuit of the SC2603 assures
that the gate driver output remains in the off state when­ever the supply voltage drops below set parameters. Lock­out occurs if VIN falls below 3.8V. Normal operation re­sumes once V

rises above 4.2V.

IN

4 2005 Semtech Corp.

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POWER MANAGEMENT

PEAKS

ImVR /70=

V

IN

V

OUT

I

OUT

I

IN

t0

t1

t2 t3

t4

Application Information

Over Current Protection

The over-current protection is implemented by a sensing
resistor and an internal current-limit comparator with a
threshold of 70mV. If the switching current through the
sensing resistor causing voltage to drop at the CS pin
reachs 70mV, the SC2603 will immediately turn the gate
pulse off to limit the current through the power switch.
The figure below shows over-current waveforms. At t1,
the input current IIN begins to increase as the load I
builds up until it hits the OCP threshold at t2. At t2, V
begins to drop as I

starts increasing toward t3 while V

OUT

and IIN remain the same. At t3, there two events are
happening. 1) V

is at half of its regulating voltage. At

OUT

this point, the internal oscillator runs into frequency shift
mode and shifts the frequency to one fourth of the oper­ating frequency. 2) The diode starts conducting current
without limit causing V
Finally, V

and V

IN

OUT

to fall due to supply current limit.

IN

both drops to zero and I

becomes the

IN

input supply current limit.

OUT

OUT

SC2603

IN

A RC filter at the CS pin is necessary to filter out noise to
ensure accurate sensing.
The value of the sensing resistor can be caculated by
the following equation:

Where I
MOSFET.

is the input peak current through the power

PEAK

 2005 Semtech Corp.

Over Current Waveforms

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Applications Information

Layout Guidelines

SC2603

Careful attention to layout requirements are necessary
for successful implementation of the SC2603 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 output Capacitor(s) (Cout), the
FET (Q1), the current sensing resistor, 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.

5) The SC2603 is best placed over an isolated ground
plane area. The soft-start capacitor, the VIN decoupling
capacitor, and the current sensing filter capacitor should
also connected to this ground pad area. 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
the output capacitor. If this is not possible, the GND pin
may be connected to the ground path between the Out­put Capacitor and the Cin, Q1, D1 loop. Under no cir­cumstances should GND be returned to a ground inside
the Cin, Q1, D1 loop.

6) Input voltage of the SC2603 should be supplied from

the power rail through a 2.2~10Ω resistor, the V

should be decoupled directly to GND by a 0.1µF~1µf
ceramic capacitor, trace lengths should be as short as
possible.

7) An RC low pass filter is required to filter out leading
edge current spikes on the current sensing resistor. The
filter capacitor needs to be very close to the CS and
GND to reduce noise pickup.

IN

pin

3) The connection between the junction of Q1, D1 and
the output capacitor should be a wide trace or copper
region. It should be as short as practical. Since this con­nection has fast voltage transitions, keeping this con­nection short will minimize EMI.

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.

6 2005 Semtech Corp.

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POWER MANAGEMENT

Vout

12VIN

+

Cout

2.2

0.1uF

Q1

0.1uF

D1

SC2603

GND

1

VIN

5

3

CS

6

Gate

2

FB

4

Rb

Ra

Rs

EN/SS

20uH

Cin

Heavy lines indicate the critical loop carrying high pulsating current.
The inductance of this loop needs to be minimized.

Applications Information (Cont.)

Layout diagram for the SC2603

SC2603

 2005 Semtech Corp.

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POWER MANAGEMENT

R2

34K

R4

1.78K

L1

18uH

Q1

AO4442

D1

3A, 40V

C2

330u/35V

C1

470u

R5

1K

VIN = 12V

VOUT=25V

U2

SC2603

VIN

5

EN/SS

3

FB1GND

2

CS

6

Gate

4

C11

1u

R1

2.2

C4

0.1u

Enable

C3

1u

R6

20m

C5

120p

(open drain)

R2

34K

R4

1.78K

L1

18uH

Q1

AO4442

D1

3A, 40V

C2

330u/35V

C1

470u

R5

1K

VIN = 12V

VOUT=25V

U2

SC2603

VIN

5

EN/SS

3

FB1GND

2

CS

6

Gate

4

C11

1u

R1

2.2

C4

0.1u

Enable

C3

1u

R6

20m

C5

120p

(open drain)

Open Drain with < 100Ω
pull down impedance

SEMTECHSOT23-6SC2603U1116

20mR6115

6031KR5114

6031.78KR4113

6030R3112

60334KR2111

6032.2R1110

Alpha & OmegaAO4442Q119

COOPER18uHL118

1N5819D117

8051uC1116

603120pC515

6030.1uC414

6031uFC313

SANYO330u/AlumC212

SANYO470u/AlumC111

VendorfootprintPartReferenceQuantityItem

SEMTECHSOT23-6SC2603U1116

20mR6115

6031KR5114

6031.78KR4113

6030R3112

60334KR2111

6032.2R1110

Alpha & OmegaAO4442Q119

COOPER18uHL118

1N5819D117

8051uC1116

603120pC515

6030.1uC414

6031uFC313

SANYO330u/AlumC212

SANYO470u/AlumC111

VendorfootprintPartReferenceQuantityItem

Applications Circuit

12V to 25V @ 1A boost converter

SC2603

Bill of Material

8 2005 Semtech Corp.

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POWER MANAGEMENT

-10

-5

0

5

10

15

20

25

30

35

40

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

Frequency (Hz)

Gain (dB)

-45

0

45

90

135

180

Phase (deg)

Gain
Phase

23.000

23.500

24.000

24.500

25.000

25.500

26.000

4 6 8 10 12 14 16

Input Voltage - (V )

Output Voltage - (V)

23

23.5

24

24.5

25

25.5

26

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Output Current - (A)

Output Voltage - (V)

80

82

84

86

88

90

92

94

96

98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Output Current - (A)

Efficiency - (%)

24.2

24.4

24.6

24.8

25

25.2

25.4

25.6

0 0.5 1 1.5 2 2.5 3

Output Current - (A)

Output Voltage - (A)

Typical Characteristics

SC2603

Error Amplifier: Gain and Phase

Efficiency (VIN = 12V, VO = 25V)

Load Regulation (V

= 12V, VO = 25V)

IN

Line Regulation (VO = 25V, IO = 1A)

OCP (VIN = 12V, VO = 25V)

 2005 Semtech Corp.

Frequency Shift (V

9

vs. FSW)

FB

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POWER MANAGEMENT

1.22

1.225

1.23

1.235

1.24

1.245

1.25

1.255

1.26

-50 -25 0 25 50 75 100 125 150

TEMPERATURE

(

o

C

)

REFERENCE VOLTAGE

(

V

)

180

185

190

195

200

205

210

-50 -25 0 25 50 7 5 100 125 150

TEM PERATURE (OC)

OSCILLATOR FREQUENCY

(kHz)

4. 05

4. 08

4. 10

4. 13

4. 15

4. 18

4. 20

4. 23

4. 25

4. 28

4. 30

-50 - 25 0 25 5 0 7 5 100 12 5 1 50

TEMPERA T U R E (OC)

UVLO THRESHOLD (V)

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

-50 0 50 100 15 0

TEM P E R ATURE (OC)

UVLO HYSTERESIS (V)

68

69

70

71

72

73

74

75

-50 -25 0 25 50 75 100 125 150

TEMPERATURE (OC)

CURRENT LIMIT THRESHOLD (mV)

Typical Characteristics

SC2603

Reference Voltage vs Temperature

VIN=12V

VIN=5V

Oscillator Frequency vs Temperature

UVLO Hysteresis vs Temperature

Current Limit Threshold vs Temperature

UVLO Threshold vs Temperature

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POWER MANAGEMENT

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L

(L1)

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C

H

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INCHES

DIMENSIONS

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bbb

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01

N

DIM

c

e

e1

L

E1

E

D

A1
A2

b

A

MIN

MILLIMETERS

MAX MIN NOM MAX

PLANE

D

DATUMS AND TO BE DETERMINED AT DATUM PLANE

CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).

DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS3.
OR GATE BURRS.

NOTES:

1.

2. -A-

-B-

-H-

SIDE VIEW

THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.

NOTES:

1.

DIMENSIONS

INCHES

Y

Z

DIM

G
P
X

C

MILLIMETERS

P

(C)

Z

Y

G

.043
.141

.055

(.098)

.037
.024

1.40

(2.50)

0.95

0.60

1.10

3.60

X

DIMENSIONS

INCHES

Y
Z

DIM

G

P
X

C

MILLIMETERS

Outline Drawing - SOT23-6

SC2603

Land Pattern - SOT23-6

Contact Information

 2005 Semtech Corp.

Phone: [phone] FAX [phone]

Power Management Products Division

200 Flynn Road, Camarillo, CA 93012

Semtech Corporation

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