1 A Synchronous Switching Regulator
June 28, 2000
SC1409
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1409 is a versatile, voltage-mode switching
regulator designed for use in battery operated power
supply applications. A simple, fixed-voltage buck regu-
lator can be implemented using the SC1409 with a
minimum of external components. Internal MOSFETs
and control circuitry minimize board space and design
time. The small device footprint allows for compact
circuit design.
SC1409 features include a temperature compensated
voltage reference, triangle wave oscillator, hiccup
mode current limit, an internally compensated error
amplifier, overcurrent temperature protection, soft
start, and under voltage lock out.
The SC1409 operates at a selectable, fixed frequency
of 300kHz or 500kHz, or can be synchronized to an
external clock within this range, providing an optimum
compromise between efficiency, external component
size, and cost.
FEATURES
•=
Internal MOSFETs
•=
Excellent efficiency >88%
•=
1% Voltage accuracy
•=
Built-in over current protection
•=
1A Output current
•=
5µA Standby current
•=
Industrial temperature range
•=
300kHz/500kHz selectable frequency
APPLICATIONS
•=
Handheld equipment
•=
PDA power supplies
•=
Notebook I/O power supplies
•=
Peripheral card supplies
•=
High density DC/DC conversion
ORDERING INFORMATION
DEVICE
(1)
PACKAGE
SO-8
SC1409ISTR
Note:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
APPLICATION CIRCUIT
Vin=5V
R1
OPEN
U1
1
2
Vout
3.45V
3.30V
3.10V
2.90V
2.80V
2.50V
1.50V
R3
1.87k
1.74k
1.58k
1.40k
1.33k
1.07k
249
R4
1.00k
1.00k
1.00k
1.00k
1.00k
1.00k
1.00k
C6
0.1uF
SYNC/FSET
EN/SS
AGND
FB
SC1409IS
ISET
VIN
8
7
6
L1
5
R2
100uH
Vout
3
4
+
C1
47uF/16V
C3
0.033uF
PHASE
PGND
+
C2
47uF/16V
R4
1
© 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 A Synchronous Switching Regulator
June 28, 2000
SC1409
ABSOLUTE MAXIMUM RATINGS
Parameter
Supply Voltage
Ground Differential
Input Voltage
Operating Ambient Temperature Range
Operating Junction Temperature Range
Storage Temperature
Lead Temperature (Soldering) 10 seconds
Thermal Resistance, Junction to Ambient
Thermal Resistance, Junction to Case
ESD Rating (Human Body Model)
Symbol
V
CC
P
GND
to GND
V
IN
T
A
T
J
T
STG
T
L
θ=
JA
θ=
JC
ESD
Maximum
-0.3 to +7
±1
-0.3 to +7
-40 to +85
-40 to +125
-60 to +150
300
165
40
2
Units
V
V
V
°C
°C
°C
°C
°C/W
°C/W
kV
ELECTRICAL CHARACTERISTICS
Unless specified; T
A
= 25°C, V
IN
= 5V, V
O
= 1.8V. Output current = 1A. Per typical application circuit.
Values in
bold
apply over full operating temperature range.
Parameter
Reference
Symbol
V
REF
I
FB
I
Q
I
Q
REG
LOAD
REG
LINE
OSC
δ
max
I
O
Conditions
Min
1.191
1.179
Typ
1.203
Max
1.215
1.227
Units
V
Feedback Bias Current
Quiescent Current
10.0
Current into V
CC
pin
Io=0mA
Enable = 0V
2.0
50.0
4.0
15
nA
mA
Shutdown Quiescent Current
5.0
10
uA
Regulation Load
Regulation Line
Oscillator Frequency
Max Duty Cycle
Output Current Limit
Soft start charging current
EN/SS Shutdown Threshold
UVLO Trip point
RDS(ON)
I
O
= 100mA to 1A
FSET=Vin
FSET=GND
425
255
90
1.5
0.5
1.0
0.5
%
%
kHz
kHz
%
A
500
300
95
575
345
32
1.0
Vin Increasing
Vin decreasing
R
DS(ON)
Top side PFET
4.5
4.1
250
375
525
Bottom side NFET
175
250
350
uA
V
V
V
mΩ
mΩ
2
© 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 A Synchronous Switching Regulator
June 28, 2000
SC1409
BLOCK DIAGRAM
VIN
OC_DET
4.5V
S
-
1:800
I
+
R
Q
ISET
EN/SS
-
+
S
Q
2I
UV LOCKOUT
1.5V
R
+
-
PHASE
AGND
R
Q
S
THERMAL
SHUTDOWN
SHOOT THRU
CONTROL
OSCILLATOR
SYNC/FSET
VREF
SOFT
START
ERROR
AMP
R
Q
-
+
+
-
S
60nS DELAY
FB
PGND
PIN CONFIGURATION
Top View
PIN DESCRIPTION
Pin #
1
Pin Name
SYNC/FSET
Pin Function
Sets frequency, allows synchronization.
FSET = V
IN
, f = 500kHz
FSET = GND, f = 300kHz
Enable and Soft Start pin.
Analog ground.
Output voltage feedback.
Device power ground.
Power output to the inductor.
Input voltage.
Current limit programming input.
SYNC/FSET
EN/SS
AGND
FB
1
2
3
4
8
7
6
5
ISET
VIN
PHASE
PGND
2
3
4
5
6
7
8
EN/SS
AGND
FB
PGND
PHASE
VIN
ISET
(8 LEAD SOIC)
3
© 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 A Synchronous Switching Regulator
June 28, 2000
50
Phase
40
30
Gain (dB)
20
Gain
10
0
-10
100E+0
0
-45
-90
100E+6
-0.6%
0.0
0.2
0.4
Io (A)
0.6
0.8
SC1409
180
135
90
45
0.0%
Load Reg (%)
-0.2%
Phase (deg)
-0.4%
10E+3
Frequency (Hz)
1E+6
1.0
Error Amplifier, Gain and Phase
Load Regulation Characteristic
0.4%
Vo=3.3V
Io=0.2A
Ta=25
o
C
Efficiency (%)
90%
25 mOhm
0.2%
Line Regulation (%)
80%
0.0%
-0.2%
70%
-0.4%
3.3V; f=300kHz
3.3V; f=500kHz
2.5V; f=300kHz
2.5V; f=500kHz
-0.6%
4.4
4.6
4.8
5.0
Vin (V)
5.2
5.4
5.6
60%
0.0
0.2
0.4
Io(A)
0.6
0.8
1.0
Typical Line Regulation
Efficiency
1.0
Output Voltage - Normalized (V)
0.8
0.6
0.4
0.2
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
EN/SS Voltage (V)
Soft Start control of Vout
Ripple; Vo=3.3V; Io=1A; f=300kHz
4
© 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
1 A Synchronous Switching Regulator
June 28, 2000
8.0
7.0
Quiescent Current (mA)
6.0
5.0
4.0
3.0
2.0
1.0
0.0
-50
-25
0
25
50
75
100
Temperature (
o
C)
8.0
7.0
6.0
Shutdown Quiescent (uA)
SC1409
550
500
Frequency (KHz)
450
400
100
98
96
94
Frequency (FSET=V
IN
)
5.0
4.0
3.0
Max Duty Cycle
350
300
92
90
Quiescent Current
2.0
1.0
0.0
125
Frequency (FSET=GND)
250
-50
-25
0
25
50
o
75
100
88
125
Temperature ( C)
Quiescent current vs temperature
0.45
0.40
Frequency and max. duty cycle vs temperature
4.5
P-Channel (Topside)
0.35
0.30
R
DS(ON)
(
Ω
)
0.25
0.20
0.15
0.10
V
IN
(V)
4.4
4.3
4.2
4.1
4.0
V
IN
Increasing
N-Channel (Bottomside)
0.05
0.00
3.9
V
IN
Decreasing
-50
-25
0
25
50
o
75
100
125
-50
-25
0
25
50
o
75
100
125
Temperature ( C)
Temperature ( C)
FET R
DS(ON)
vs temperature
50
45
40
Soft Start Current (uA)
35
30
25
20
15
10
5
0
UVLO trip point vs temperature
1.206
1.204
Reference Voltage (V)
1.202
1.200
1.198
1.196
-50
-25
0
25
50
o
75
100
125
-50
-25
0
25
50
o
75
100
125
Temperature ( C)
Temperature ( C)
Soft start current vs temperature
Reference voltage vs temperature
Duty Cycle (%)
Shutdown Quiescent Current
5
© 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
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