SC4812EVB [SEMTECH]
Current Mode PWM Controller with Integrated Start-up Circuit and Op Amp; 电流模式PWM控制器，集成启动电路和运算放大器
| 型号： | SC4812EVB |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | Current Mode PWM Controller with Integrated Start-up Circuit and Op Amp |
| 文件： | 总15页 (文件大小：208K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC4812
Current Mode PWM Controller with
Integrated Start-up Circuit and Op Amp
POWER MANAGEMENT
Description
Features
The SC4812 is a highly integrated current mode PWM
controller designed for isolated or non-isolated dc-dc con-
verters in telecommunication and data communication
applications. It minimizes the amount of external discrete
components needed and leads to substantial cost and
space saving converter designs.
Wide input range 12V to 90V
High-voltage start-up circuit
Current mode control
Transconductance error amplifier
Leading-edge blanking
Cycle by cycle current limit
Programmable external soft-start
Thermal shutdown
The circuitry of the SC4812 includes an integrated high
voltage start-up circuit suitable for telecom/industrial
voltage applications. It is disabled during regular opera-
tion and improves efficiency. Current mode control with
leading-edge blanking simplifies control loop design and
internal ramp compensation circuit stabilizes the current
loop when operating above 50% duty cycle. Internal er-
ror amplifier could be used for non-isolated applications.
SO-8 package. Fully WEEE and RoHS compliant
Applications
IP phones, PoE
Telecom isolated converters
Off-line isolated power supplies
Instrumentation power supplies
Battery chargers
Typical Application Circuit
D1
Vin
Vout
T1
C1
C2
R1
C4
C3
R2
U1
Q1
R5
2
7
FB
OUT
CS
SC4812
3
5
6
COMP
C5
R4
4
R3
SS/SHDN
GND
C6
Revision: February 6, 2007
1
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SC4812
POWER MANAGEMENT
Pin Configuration
Ordering Information
Part Number
SC4812STRT(1)(2)
SC4812EVB
Top Mark
Package
TOP VIEW
SC4812
SO-8
Evaluation Board
VIN
VCC
OUT
GND
CS
Notes:
FB
COMP
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2) Lead free product. This product is fully WEEE and RoHS
compliant.
SS/SHDN
(SO - 8 PIN)
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. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device
reliability.
Parameter
Symbol
Maximum
Units
Input Voltage
VIN
VCC
ICC
-0.5 to 100
-0.5 to 18
20
V
V
Supply Voltage
Supply Current
mA
V
FB, COMP, CS, and SS/SHDN to GND
OUT Peak Current
-0.5 to 7
±1
A
Continuous Power Dissipation
Junction Temperature Range
Thermal Resistance (1)
PD
TJ
Internally limited
-40 to +150
105
W
°C
°C/W
θ
JA
Storage Temperature Range
TSTG
-65 to +150
+300
°C
°C
Lead Temperature (Soldering) 10 Sec.
Note:
TLEAD
(1) Mounted to 3” x 4.5”, 4 layer FR4 PCB in still air per JESD51 standards.
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Electrical Characteristics
Unless specified: VCC = 12V, a 10uF capacitor connects V to GND, VCS = 0, VIN = 48V, a 0.1uF capacitor connects SS/SHDN to GND, OUT = open
circuit, FB = GND, TA = TJ = -40 to +125ºC. Typical valuesCaCre at TA = 25ºC
Parameter
Test Conditions
Min
Typ
Max
Unit
Startup/Winding Regulator
VIN Input Voltage Range
VIN Supply Current
12
90
V
VIN = 90V, VCC open, driver switching
5
7.5
mA
VIN = 90V, VCC open, VFB = 3V,
driver not switching
3.5
5
mA
VIN Supply Current after Startup
VIN Shutdown Current
VCC Output Voltage
VIN = 90V
VIN = 90V, VSS/SHDN = 0
50
250
7.4
20
100
380
8
µA
µA
V
Power from VIN
6.8
12
VCC Current Limit
10% below no load VCC output voltage
mA
VCC Supply
VCC Turn-on Voltage
Hysteresis
6
6.5
1
6.7
1.4
V
V
0.8
Operating Current
VCC Zener Shunt Voltage
Error Amplifier
3
7.5
mA
V
ICC = 10mA
15.25
16.25
17.25
Feedback Input Voltage
Feedback Input Voltage Regulation
Input Bias Current
close loop
2.44
2.50
2.56
2.575
0.8
V
V
VCC = 8V to 14V
2.425
0.5
1000
110
110
60
µA
Amplifier Transconductance
Amplifier Source Current
Amplifier Sink Current
Open Loop Voltage Gain
PWM Comparator
µmho
µA
µA
dB
Slope Compensation
Oscillator
28
mV/µS
Clock Frequency Range
Max Duty Cycle
235
75
260
80
285
85
kHz
%
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: VCC = 12V, a 10uF capacitor connects V to GND, VCS = 0, VIN = 48V, a 0.1uF capacitor connects SS/SHDN to GND, OUT = open
circuit, FB = GND, TA = TJ = -40 to +125ºC. Typical valuesCaCre at TA = 25ºC
Parameter
Test Conditions
Min
Typ
Max
Units
Current Limit
CS Threshold Voltage
CS Input Bias Current
Propagation Delay to Gate
CS Blanking Time
Soft Start
419
-1
465
510
1
mV
µA
nS
nS
0 ≤ VCS ≤ 2V
70
70
SS Source Current
SS Sink Current
VSS/SHDN = 0
4
6
8
µA
1
mA
Shutdown Threshold
VSS/SHDN falling
VSS/SHDN rising
0.25
0.61
0.5
0.7
0.6
0.8
V
Output
Peak Source Current
Peak Sink Current
Rise Time
570
1000
45
mA
mA
nS
CL = 1nF
CL = 1nF
Fall Time
35
nS
Thermal Shutdown
Thermal Shutdown Temperature
Thermal Hysteresis
150
25
°C
°C
Note:
(1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Pin Descriptions
Pin #
Pin Name
Pin Function
High voltage startup input. Connect directly to an input voltage between 12 to 90V. Connects
internally to a high voltage linear regulator that generates VCC during startup.
1
VIN
Feedback input to the internal transconductance error amplifier. VFB sensed the regulated
output voltage through an external resistor divider.
2
3
FB
Internal transconductance error amplifier output. Compensation network of the overall loop is
placed between this pin and GND.
COMP
Soft start timing capacitor connection. Ramp time to full current limit is approximately TBD
ms/nF. This pin is also the reference voltage output. Bypass with a minimum 10nF capacitor
to GND. The device goes into shutdown when VSS_SHDN is pulled below 0.25V.
4
5
SS/SHDN
CS
Current sense input. Turns power switch off if V rises above 465mV for cycle-by-cycle
current limiting. CS is also the feedback for the CcSurrent mode controller. CS is connected to
the PWM comparator through a leading edge blanking circuit.
6
7
GND
OUT
Ground.
Gate drive. Drives a high voltage external N-channel power MOSFET.
Supply voltage. Provides power for entire IC. VCC is regulated from VIN during startup. Bypass
VCC with a 10uF tantalum capacitor in parallel with 0.1uF ceramic capacitor to GND.
8
VCC
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SC4812
POWER MANAGEMENT
Block Diagram
7.4V
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Application Information
Introduction
The SC4812 is a 8 pin peak current mode controlled
PWM controller for isolated or non-isolated DC-DC
switching power supplies. It features an internal startup
regulator, programmable external soft start and
programmable cycle -by-cycle current limit It operates in
a fixed frequency at 260KHz.
RS = 0.465V/(1.2xILIM_PRI
)
where, ILIM_PRI is the maximum peak primary-side current.
When VCS > 465mV, the power MOSFET turns off after
70nS propagation delay from the switch current reaches
the trip point to the driver.
The SC4812 can be applied in a flyback or forward
topology with the input voltage ranging from 36V to 75V.
PWM Comparator and Slope Compensation
The SC4812 runs fixed 260 KHz frequency by an internal
oscillator. At the beginning of each switching cycle, the
OUT pin switches the MOSFET on. the OUT pin switches
off after the 80% maximum duty cycle has been reached,
regardless of the feedback.
Since an artificial slope is required for current-mode
operation when duty cycle is larger than 50%, the SC4812
uses an internal ramp generator for slope compensation.
The internal ramp signal is reset at the beginning of each
Startup Regulator
The internal startup regulator of the SC4812 makes its
initial startup without a lossy startup resistor or external
startup circuitry to save cost and board space. As input
voltage exceeds 12V, it provides regulated 7.4V to VCC
which is with the maximum turn-on voltage 6.7V.
Soft-Start/Shutdown and VCC Lockout
During power startup, the output voltage has to ramp up
in a controlled manner to avoid overshoot. The SC4812
internal non-inverting terminal to the error amplifier is
connected to the soft-start pin, which forces the internal
2.5V reference to gradually ramp up during power
startup. In a non-isolated application, as the internal error
amplifier is used, output voltage of a converter ramps
up with close loop startup fashion smoothly. In case of
an isolated application in which the internal error amplifier
may not be used, isolated voltage feedback is through
an opto-coupler and connected to the COMP pin. During
power startup, the COMP pin will follow the soft-start pin
voltage through an internal diode.
Soft-start operation begins when SS/SHDN ramps above
0.7V. When soft-start completed, SS/SHDN is regulated
to 2.50V, the internal voltage reference. Pull SS/SHDN
below 0.5V to disable the controller.
Undervoltage lockout shuts down the controller when VCC
is less than 5.5V. The internal startup regulator and the
reference remain on during shutdown.
cycle and slews at 26mV/µS.
The PWM comparator compares the instantaneous
primary peak current to the feedback error signal through
the opto-coupler, the internal offset and slope
compensation and determine when to turn off the
MOSFET. In steady state operation, the MOSFET turns
off when:
I
LIM_PRI · RS > VOPTO – VOFFSET - VSLOPE
where ILIM_PRI is the current on the primary side through
the MOSFET. VOFFSET is 1.5V internal offset voltage and
VSLOPE is the artificial ramp starting at with slew rate 26mV/
µS.
When selecting an inductor in a forward-converter or
magnetizing inductance in a flyback-converter, the
following condition must be met to avoid control-loop sub-
harmonic oscillations:
NS K ×RS × VO
×
= 26mV /µS
Current-Sense
NP
L
The function of the CS pin is to limit the peak current
through the MOSFET. Current is sensed at CS as a voltage
across a sense resistor between the source of the
MOSFET and GND. An RC filter is recommended to
connect CS to the sense resistor to reduce effect of the
MOSFET turn-on leading edge spike and noise. Select
the current-sense resistor with the following equation:
where K = 0.5 TO 1, AND NS and NP are the turns of the
main transformer on secondary and primary side
respectively. L is the output inductor on secondary side
in a forward-converter or magnetizing inductance on
secondary side in a flyback-converter.
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Applications Information (Cont.)
PCB Layout Guideline
6) The feed back connection between the error ampli-
fier and the FB pin should be kept as short as possible,
and the GND connections should be to the quiet GND
used for the SC4812.
7) If an opto-coupler is used for isolation, quiet primary
and secondary ground planes should be used. The same
precautions should be followed for the primary GND plane
as mentioned in item 5. For the secondary GND plane,
the GND plane method mentioned in item 4 should be
followed.
8) All the noise sensitive components such as VCC by-
pass capacitor, COMP resistor/capacitor network, cur-
rent sensing circuitry and feedback circuitry should be
connected as close as possible to the SC4812. The GND
return should be connected to the quiet SC4812 GND
plane.
9) The connection from the OUT of the SC4812 should
be minimized to avoid any stray inductance. If the layout
can not be optimized due to constraints, a small Schottky
diode may be connected from the OUT pin to the ground
directly at the IC. This will clamp excessive negative volt-
ages at the IC.
PCB layout is very critical, and the following should be
considered to insure proper operation of the SC4812.
High switching currents are present in applications and
their effect on ground plane must be understood and
minimized.
1) The high power parts of the circuit should be placed
on a board first. A ground plane should be used. Isolated
or semi-isolated areas of the ground plane may be delib-
erately introduced to constrain ground currents to par-
ticular areas, for example the input capacitor and the
main switch FET ground.
2) The loop formed by the Input Capacitor(s) (Cin), the
main transformer and the main switch FET must be kept
as small as possible. This loop contains all the high fast
transient switching current. Connections should be as
wide and as short as possible to minimize loop induc-
tance. Minimizing this loop area will a) reduce EMI, b)
lower ground injection currents, resulting in electrically
“cleaner” grounds for the rest of the system and c)
minimize source ringing, resulting in more reliable gate
switching signals.
3) The connection between FETs and the main trans-
former 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 cur-
rents are supplied by Cout only. Connections between
Cout and the load must be short, wide copper areas to
minimize inductance and resistance.
5) A 0.1uF to 1uF ceramic capacitor should be directly
connected between VCC and GND and a 1uF to 4.7uF.
The SC4812 is best placed over a quiet ground plane
area. Avoid pulse currents in the Cin and the main switch
FET loop flowing in this area. GND should be returned to
the ground plane close to the package and close to the
ground side of (one of) the VCC supply capacitor(s). Under
no circumstances should GND be returned to a ground
inside the Cin and the main switch FET loop. This can be
achieved by making a star connection between the quiet
GND planes that the SC4812 will be connected to and
the noisy high current GND planes connected to the FETs.
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4812 Evaluation Board - Schematics( Isolated Flyback )
2
3
C
V C
D G N
8
1
6
4
N V I
D S / S S
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4812 Evaluation Board - BOM( Isolated Flyback )
Item
Qty.
Reference
C2,C6
C3,C4
C5
Part/Value Manufacturer Manufacturer P.N.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
2
2
1
1
1
1
1
1
1
1
3
1
1
1
1
1
1
1
1
2
1
2
1
1
1
1
1
1uF/6.3V
470uF/6.3V
Kemet
Sanyo
C0805C105M9PAC3810
6TPB470M
22uF/100V Panasonic-ECG
ECA-2AHG220
C8
C9
C10
C12
C13
C14
C25
10uF/16V
150pF
15nF
TDK
muRata
Panasonic-ECG
Vishay
C3216X7R1C106MT
GRM2165C2A151JA01
ECJ-2VB1H153K
VJ0805Y102KXXAT
VJ0805Y102KXXAT
VJ0805Y104KXXxx
C3216X7R2J222K
1N4148WS-V-GS08
SL43
1nF
1000pF
0.1uF
2.2nF/630V
1N4148WS
SL43
Vishay
Vishay
TDK
Vishay
D1,D3,D6
D2
Vishay
M1
R4
R6
R7
R9
R10
R11
Si3440
330
2.4K
180
3.32K
100
Vishay
Vishay
Vishay
Vishay
SI3440DV-T1-E3
CRCW0805330RFKEA
CRCW08052K40FKEA
CRCW0805180RFKEA
CRCW08053K32FKEA
ERJ-6ENF1000V
CRCW080510K0FK
RL1220S-R50-F
Vishay
Panasonic-ECG
Vishay
10K
0.5
R12,R16
R14
R15,R21
R17
Susumu
2.0K
0
10
Yageo America 9C08052A2001FKHFT
Vishay CRCW08050000ZSTA
Yageo America 9C08052A10R0FKHFT
T1
U1
U2
U3
PA1269
SC4812
PS2521L-1
SC431L
Pulse Eng.
Semtech
NEC
PA1269
SC4812STRT
PS2521L-1
SC431LCSK
Semtech
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4812 Evaluation Board - Schematics( Non-Isolated Flyback )
C
V C
D G N
8
1
6
4
N V I
D S / S S
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4812 Evaluation Board - BOM( Non-Isolated Flyback )
Item Qty.
Reference
C2,C6
C3,C4
C5
Part/Value
1uF/16V
Manufacturer
Panasonic-ECG
Sanyo
Manufacturer P.N.
1
2
2
ECJ-2FB1C105K
6TPB470M
2
1
1
1
2
1
1
1
2
1
1
3
2
2
1
1
470uF/6.3V
22uf/100V
10uF/16V
3
Panasonic-ECG
TDK
ECA-2AHG220
4
C8
C3216X7R1C106MT
ECJ-2VC2A151x
VJ0805Y102KXJPW1BC
VJ0805Y104KXJAC
VJ0805Y473KXJxx
1N4148WS-V-GS08
SL43
5
C9
150pF/100V Panasonic-ECG
6
C12, C13
C14
1nF/16V
0.1uF/16V
47nF/16V
1N4148WS
SL43
Vishay
Vishay
7
8
C16
Vishay
9
D1, D3
D2
Vishay
10
11
12
13
14
15
16
17
Vishay
M1
R4
Si3440
330
Vishay
SI3440DV-T1-E3
CRCW0805330RJNEA
ERJ-6ENF1001V
CRCW0805100RFKxx
ERJ-6BQFR24x
PA1260
Vishay
R9, R13, R14
R10,R17
R12,R16
T1
1.0K
Panasonic-ECG
Vishay
100
0.25
Panasonic-ECG
Pulse
PA1260
SC4812
U1
Semtech
SC4812STRT
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4810B Evaluation Board - Schematics( Forward )
2
3
C
V C
D G N
8
1
6
4
N V I
D S / S S
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
SC4812 Evaluation Board - BOM( Forward )
Item
Qty.
Reference
C9
C2, C6
C3, C4
C5, C7
C8
Part/Value
22uf/100V
1uf/6.3V
Manufacturer
Panasonic-ECG
Kemet
Manufacturer P. N.
ECA2AHG220
1
2
1
2
2
2
1
1
1
1
1
1
2
1
1
1
1
1
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
C0805C105M9PAC3810
6TPB470M
3
470uf,/6.3V
1uf/100V
10uf/16V
15nf
Sanyo
4
5
TDK
Panasonic-ECG
Vishay
C3216X7R1C106MT
ECJ2VB1H153K
VJ0805Y102KXXAT
VJ0805Y102KXXAT
C2012X7R1E474K
C3216X7R2J222K
1N4148WS-V-GS08
MBRB2035CT/31
BYM07-200
6
C10
C12
C13
C14
C25
D1, D6
D2
7
1nf
8
1000pf
Vishay
9
0.47uf
TDK
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
2.2nf/630V
1N4148WS
MBRB2035CT
BYM07-200
TDK
Vishay
Vishay
D3
Vishay
D7
MMSZ4699(12V) ON Semiconductor
MMSZ4699T1
L1
4.7uH
FMMT618
SUM27N20-78
0 ohm
Cooper Bussmann
Zetex
HC2LP-4R7
Q1
FMMT618TA
Q2
Vishay
SUM27N20-78-E3
CRCW08050000ZSTA
CRCW08052K40FKEA
ERJ6GEYJ361V
ERJ6ENF1001V
ERJ6ENF1000V
CRCW080510K0FK
ERJ1TRSFR10x
9C08052A10R0FKHFT
ERJ6GEYJ1R0V
ERJ6GEYJ512V
CTX03-14856
R5, R15
R6
Vishay
2.4k ohm
360 ohm
1.0k ohm
100 ohm
10k ohm
0.1 ohm
Vishay
R7
Panasonic-ECG
Panasonic-ECG
Panasonic-ECG
Vishay
R9, R14
R10
R11
R12
R17
R19
R22
T1
Panasonic-ECG
Yageo America
Panasonic-ECG
Panasonic-ECG
10 ohm
1 ohm
5.1k ohm
CTX03-14856 Cooper Bussmann
U1
SC4812
PS2521L-1
SC431
Semtech
NEC
Semtech
SC4812STRT
PS2521L-1-E3-A
SC431CSK-1.TRT
U2
U3
2007 Semtech Corp.
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SC4812
POWER MANAGEMENT
Outline Drawing - SO-8
DIMENSIONS
INCHES MILLIMETERS
A
DIM
A
MIN NOM MAX MIN NOM MAX
D
E
e
-
-
-
-
-
-
-
-
-
-
.053
.069 1.35
.010 0.10
.065 1.25
.020 0.31
.010 0.17
1.75
0.25
1.65
0.51
0.25
N
A1 .004
A2 .049
b
c
D
.012
.007
2X E/2
.189 .193 .197 4.80 4.90 5.00
E1
E1 .150 .154 .157 3.80 3.90 4.00
E
e
.236 BSC
.050 BSC
6.00 BSC
1.27 BSC
1
2
-
-
h
L
.010
.020 0.25
0.50
ccc C
.016 .028 .041 0.40 0.72 1.04
2X N/2 TIPS
(.041)
(1.04)
e/2
L1
N
8
8
B
-
-
01
aaa
bbb
ccc
0°
8°
0°
8°
.004
.010
.008
0.10
0.25
0.20
D
aaa C
h
A2
A
SEATING
PLANE
h
C
A1
H
bxN
bbb
C A-B D
c
GAGE
PLANE
0.25
L
(L1)
01
A
SEE DETAIL
DETAIL A
SIDE VIEW
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H-
3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
4. REFERENCE JEDEC STD MS-012, VARIATION AA.
Land Pattern - SO-8
X
DIMENSIONS
DIM
INCHES
(.205)
.118
MILLIMETERS
(5.20)
3.00
1.27
0.60
2.20
7.40
C
G
P
X
Y
Z
(C)
G
Y
Z
.050
.024
.087
.291
P
NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
2. REFERENCE IPC-SM-782A, RLP NO. 300A.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
2007 Semtech Corp.
15
www.semtech.com
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