600kHz/1MHz/200kHz
Step-Down DC/DC Converter
POWER MANAGEMENT
Description
The SC2612 is a voltage mode switcher designed for low
cost, “point of use” voltage conversion. SC2612 is avail-
able with fixed switching frequencies of 200kHz
(SC2612C), 600kHz (SC2612A) and 1MHz (SC2612B).
The SC2612 has soft start and enable functions and is
short circuit protected. The output of the switcher may
be set anywhere between 0.8V and 75% of Vin. Short
circuit protection is disabled during start-up to allow the
output capacitors time to fully charge.
SC2612A/B/C
PRELIMINARY
Features
Operating frequency of 200kHz, 600kHz or 1MHz
Input supply of 3V to 15V
0.5A Drive current for up to 10A output
Output voltages down to 0.8V
Overcurrent protection and soft start
SO-8 or MSOP-8 packages
Applications
Graphics IC Power supplies
Embedded, low cost, high efficiency converters
Typical Application Circuit
12V IN
3.3V IN
R1
C10
C1
C2
U2
4
1
2
C5
C7
C9
R9
R10
5
VCC
BST
8
7
6
3
Q3
C3
R6
R2
R3
Q2
L1
1.5V OUT
COMP DH
SS/EN
GND
DL
FB
SC2612
Revision 1, September 2002
1
www.semtech.com
SC2612A/B/C
POWER MANAGEMENT
Absolute Maximum Ratings
Parameter
Input Supply Voltage
Boost Pin Voltage
DL to GND
(2)
, DH to GND
(2)
Operating Ambient Temperature Range
Operating Junction Temperature
Storage Temperature
Lead Temperature (Soldering) 10s
Thermal Resistance Junction to Ambient
Thermal Resistance Junction to Case
(3)
PRELIMINARY
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.
Symbol
V
CC
V
BST
V
DLO
, V
DHI
T
A
T
J
T
STG
T
LEAD
θ
JA
θ
JC
Maximum
15
20
-1 to +20
0 to 70
125
-65 to 150
300
Units
V
V
V
°C
°C
°C
°C
°C/W
°C/W
Electrical Characteristics
Unless specified: V
CC
= 3V to 12V; V
FB
= V
O
; BST = Vcc+5V; T
A
= 0 to 70°C
Parameter
VCC Supply Voltage
VCC Quiescent Current
BST Supply Voltage
BST Quiescent Current
VCC Under Voltage Lockout
BST Under Voltage Lockout
Output Voltage
Overcurrent trip voltage
Load Regulation
Line Regulation
Oscillator Frequency
Symbol
V
CC
I
QVCC
V
BST
I
QBST
UV
VCC
UV
BST
V
OS
V
ITS
Conditions
Min
3.0
Typ
Max
15
Units
V
mA
V
mA
V
V
mV
V
%
%
V
CC
= 5.0V, V
BST
= 12.0V, SS/EN = 0V
11
V
CC
= 5.0V, V
BST
= 12.0V, SS/EN = 0V
2.3
7.0
I
O
= 500mA; V
FB
= V
OS
780
0.4
I
O
= 0.2A to 4A
5
10
20
3
2.6
8.0
800
2.9
9.0
820
0.7
1
±0.5
f
OSC
S C 2612A
S C 2612B
S C 2612C
480
800
160
80
70
0.3
600
1000
200
720
1200
240
%
kHz
Oscillator Max Duty Cycle
δ
MAX
S C 2612A , S C 2612C
S C 2612B
SS/EN Shutdown Voltage
SS/EN Charge current
Peak DH Sink/Source Current
Peak DL Sink/Source Current
V
SS
I
SS
Vss = 0.8V
BST - DH = 4.5V,
BST - DL = 4.5V,
DH - GND = 3.3V
DH - GND = 1.5V
DL - GND = 3.3V
DL - GND = 1.5V
0.8
25
V
µA
A
mA
A
mA
0.5
50
0.5
50
2002 Semtech Corp.
2
www.semtech.com
SC2612A/B/C
POWER MANAGEMENT
Electrical Characteristics
Unless specified: V
CC
= 3V to 12V; V
FB
= V
O
; BST = Vcc+5V; T
A
= 0 to 70°C
PRELIMINARY
Parameter
Error Amplifier Transconductance
Error Amplifier Gain
Error Amplifier Source/Sink Current
Modulator Gain
Dead Time
Symbol
Conditions
Min
Typ
0.8
Max
Units
mS
dB
µA
dB
ns
g
m
A
EA
R
COMP
= open
45
±60
A
M
V
C C
= 5V
19
50
Notes:
(1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
(2) See Gate Resistor selection recommendations
(3) 1 square inch of FR4, double sided, 1oz. minimum copper weight.
2002 Semtech Corp.
3
www.semtech.com
SC2612A/B/C
POWER MANAGEMENT
Pin Configuration
TOP VIEW
COMP
SS/EN
FB
VCC
1
2
3
4
8
7
6
5
BST
DH
DL
GND
PRELIMINARY
Ordering Information
Part Numbers
(1)
Frequency
600kHz
1MHz
200kHz
600kHz
1MHz
200kHz
P ackag e
MSOP-8
SC2612AMSTR
SC2612BMSTR
SC2612CMSTR
SC2612ASTR
SC2612BSTR
SC2612CSTR
SO-8
(SO-8 or MSOP-8)
Pin Descriptions
Pin #
1
2
3
4
5
6
7
8
Pin Name
COMP
SS/EN
FB
VCC
GND
DL
DH
BST
Note:
(1) Only available in tape and reel packaging. A reel contains
2500 devices.
Pin Function
Output of the Switcher section voltage error amplifier.
Soft start and enable pin, controls the switcher output voltage ramp rate.
Switcher section feeedback input.
Chip Supply Input Voltage.
Analog and Power Ground, connect directly to ground plane, see layout guidelines.
Switcher Low side FET drive output.
Switcher High side FET drive output.
Supply voltage for FET drives.
Block Diagram
VCC
VREF
R
+
R
-
LEVEL SHIFT AND
HIGH SIDE DRIVE
UVLO
UVLO
&
REF
BST
DH
SHDN
+
R
Q
SHOOT-THRU
CONTROL
FB
COMP
-
-
+
VREF
25uA
OSCILLATOR
S
R
Q
S
SYNCHRONOUS
MOSFET DRIVE
DL
GND
SS/EN
-
+
+
-
100mV
SSOVER
2002 Semtech Corp.
4
www.semtech.com
SC2612A/B/C
POWER MANAGEMENT
Theory of Operation
The SC2612 is a step down DC/DC controller designed
for minimum cost and size without sacrificing accuracy
and protection. Overcurrent protection is implemented
by a simple undervoltage detection scheme and is dis-
abled until soft start has been completed to eliminate
false trips due to output capacitor charging. The SS/EN
pin is held low, as are the DH and DL pins, until the
undervoltage lockout points are exceeded. Once the VCC
and BST pins both rise above their undervoltage lockout
points, the SS capacitor begins to charge, controlling the
duty cycle of the switcher, and therefore slowly ramping
up the switcher output voltage. Once the SS capacitor is
charged, the current limit circuitry is enabled. If a short
circuit is applied , the output will be pulled down below
it’s trip point and shut down. The device may be restarted
by either cycling power, or momentarily pulling SS/EN low.
PRELIMINARY
Component Selection
OUTPUT INDUCTOR - A good starting point for output
filter component selection is to choose an inductor value
that will give an inductor ripple current of approximately
20% of max. output current.
Inductor ripple current is given by:-
V
V
O
⋅
1
−
O
V
IN
=
L
⋅
f
OSC
I
L RIPPLE
So choose inductor value from:-
V
5
⋅
V
O
⋅
1
−
O
V
IN
L
=
I
O
⋅
f
OSC
CAPACITOR(S)
OUTPUT CAPACITOR(S) - The output capacitors should
be selected to meet output ripple and transient response
criteria. Output ripple voltage is caused by the inductor
ripple current flowing in the output capacitor’s ESR (There
is also a component due to the inductor ripple current
charging and discharging the output capacitor itself, but
this component is usually small and can often be ignored).
Given a maximum output voltage ripple requirement, ESR
is given by:-
V
V
O
⋅
V
RIPPLE
⋅
1
−
O
V
IN
<
L
⋅
f
OSC
R
ESR
Output voltage transient excursions are a function of load
current transient levels, input and output voltages and
inductor and capacitor values.
Capacitance and R
ESR
values to meet a required tran-
sient condition can be calculated from:-
R
ESR
<
V
T
I
T
2
L
⋅
I
T
C
>
2
⋅
V
T
⋅
V
A
where
V
A
=
V
IN
−
V
O
for negative transients (load applicatio n)
and
V
A
=
V
O
for positive transients (load release)
values for positive and negative transients must be cal-
culated seperately and the worst case value chosen. For
Capacitor values, the calculated value should be doubled
to allow for duty cycle limitation and voltage drop issues.
2002 Semtech Corp.
5
www.semtech.com
FPGA/CPLD
京公网安备 11010802033920号
EEWORLD
