SC2420ISWTR [SEMTECH]
Switching Controller, Voltage-mode, 2A, 1000kHz Switching Freq-Max, PDSO28, SOIC-28;
| 型号： | SC2420ISWTR |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | Switching Controller, Voltage-mode, 2A, 1000kHz Switching Freq-Max, PDSO28, SOIC-28 开关 光电二极管 |
| 文件： | 总17页 (文件大小：919K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC2420
BI-Phase/Dual Controller
POWER MANAGEMENT
ꢀeatures
Description
The SC2420 can be configured as a dual converter or a
bi-phase converter for high current applications. The part
is designed for point of use power supplies with 10-14V
nominal backplane power sources. The power dissipa-
tion is controlled using a novel low voltage supply tech-
nique, allowing high speed and integration, with the high
drive currents to ensure low MOSꢀET switching loss. The
synchronous buck configuration also allows converter
sinking current from load without losing output regula-
tion.
u Selectable dual output or bi-phase operation
u Direct drive for N-channel MOSꢀETs
u Undervoltage lockout
u Source and sink current
u Soft start
u ꢀast transient response
u Max duty cycle 45%
u Output over voltage protection
u Thermal shut down
The use of high speed switching circuits allows very nar-
row PWM outputs allowing up to 10:1 voltage ratios.
Single pin compensation for each channel simplifies de-
velopment as well as reducing external pin count.
Applications
u DDR memory power supplies
u Point of use power supplies
Capable of driving MOSꢀETs via external driver transis-
tors for phase currents beyond 20A.
Typical Application Circuit
1
www.semtech.com
Revision 1, August 2001
SC2420
POWER MANAGEMENT
Absolute Maximum Ratings
Parameter
Symbol
VIN
Maximum
Units
V
Supply Voltage
16
Voltage on BST Pins
VBST
24
V
Oscillator Frequency
2
MHz
°C/W
°C/W
°C/W
°C
VCC
8
25
Thermal Resistance Junction to Case
Thermal Resistance Junction to Ambient
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering) 10 seconds
θJC
θJA
80
TA
-40 to +85
-55 to +150
300
TSTG
TLEAD
°C
°C
Note:
(1) Maximum frequency and maximum supply voltage could cause excessive dissipation in the part.
Electrical Characteristics
Unless specified: VIN = 12V; TA = 25°C.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage, VIN
Supply Current
10
14
40
V
mA
V
ENABLE = 0
30
5.8
400
Under Voltage Lock Out
UVLO Hysteresis
Voltage Regulator
Pre Regulator Voltage
Bgout Voltage
mV
6
7
V
V
CLOAD = 4.7nF
0.99
1
3
5
1.01
Bgout Impedance
REGDRV Pin Sink Current
Error Amp
KΩ
mA
IREGDRV
Input Offset Voltage
10
mV
KΩ
A/V
Input Impedance
5
Linear Transconductance
Internal Oscillator
.002
Frequency
R
REF = 30K
1
MHz
kHz
V
Frequency
RREF = 60K
VIN = 12V
2
500
1.5
Ramp Valley to Peak
2001 Semtech Corp.
www.semtech.com
SC2420
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: VIN = 12V; TA = 25°C.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
High Side Gate Drive
Max Duty Cycle
Peak Source
45
1
%
A
CLOAD = 10nF
CLOAD = 10nF
Peak Sink
1
A
Low Side Gate Drive
Peak Source
CLOAD = 10nF
CLOAD = 10nF
2
2
A
A
Peak Sink
Sync Drive Timing
Minimum Non-overlap
PWM Match
CLOAD = 1nF Fet Drive < 1V
40
ns
%
50% Duty cycle, FOSC = 1 MHz
-1
1
Logic Input Pins
Input Bias Current
Logic Threshold
VIN_LOGIC = 0 - 5V
-10
10
µA
V
0.8
FB2 Disable Threshold
Over Current Protection
OC+ I/P Bias Current
OC- I/P Bias Current
Over Voltage Protection
OVP Threshold
VCC - 0.7V
V
VIN = 12V
400
50
µA
µA
@ Trip voltage
40
60
120
150
%
Thermal Shut Down
°C
Note:
(1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
www.semtech.com
2001 Semtech Corp.
3
SC2420
POWER MANAGEMENT
Pin Configuration
Ordering Information
Part Number(1)
SC2420ISWTR
SC2420EVB
PACKAGE
SO-28
TAMB (TA)
Top View
-40 - +85°C
Evaluation Board
Notes:
(1) Only available in tape and reel packaging. A reel
contains 1000 devices.
(28 Pin SOIC)
Pin Descriptions
Pin
Pin Name
Pin Function
1
2
3
4
FB1
COMP1
NC
Feedback for channel 1.
Compensation for channel 1.
No connection.
BG
1V reference for error amplifiers, 3K source impedance.
Feedback for channel 2.
5
FB2
COMP2
REGDRV
ENABLE
PHASE2
DRVH2
BSTH2
DRVL2
BSTL2
VCC
6
Compensation for channel 2.
7
Regulator drive for external pass transistor.
Enable threshold is 2.05 V, connect to ground to disable.
Phase node input for channel 2.
Gate drive for high side channel 2.
Bootstrap input for high side channel 2.
Gate drive for low side channel 2.
Supply for low side channel 2.
8
9
10
11
12
13
14
15
16
17
18
Pre-regulated IC power supply.
BSTL1
DRVL1
BSTH1
DRVH1
Supply for low side channel 1.
Gate drive for low side channel 1.
Bootstrap input for high side channel 1.
Gate drive for high side channel 1.
4
www.semtech.com
2001 Semtech Corp.
SC2420
POWER MANAGEMENT
Pin Descriptions (Cont.)
Pin
19
20
21
22
23
24
25
26
27
28
Pin Name
PHASE1
PGND
OC+
Pin Function
Phase node input for high side channel 1.
Power ground.
Overcurrent comparator inverting input.
Overcurrent comparator non-inverting input for channel 2.
Overcurrent comparator non-inverting input for channel 1.
No connection.
OC-2
OC-1
NC
CLKOUT
NC
Clock out, logic level drive to provide synchronizing signal for other converters.
No connection.
AGND
RREF
Analog ground.
External reference resistor for internal oscillator and ramp generator.
Block Diagram
www.semtech.com
2001 Semtech Corp.
5
SC2420
POWER MANAGEMENT
Typical Application Schematic
Two Channel Operation
www.semtech.com
2001 Semtech Corp.
6
SC2420
POWER MANAGEMENT
Bill of Material
Two Channel Operation
Item
1
Qty Reference
Part Number/Value
0.47µF, 50V, Cer.
0.33µF, Cer., 1206
22nF, Cer., 1206
0.1µF, Cer., 1206
100pF, Cer., 1206
47pF, Cer., 1206
22µF, 35V, Tant.
680µF, 35V, Alum.
2.2nF, Cer., 1206
1.0nF, Cer., 1206
1.0µF, Cer., 1206
Manufacturer
8
3
2
1
2
1
6
2
2
3
1
C1 - C8
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
2
C9,C24,C25
C10,C11
3
4
C12
5
C13,C14
6
C15
7
C16,C19,C20,C21,C22,C23
C17,C18
8
9
C26,C27
10
11
12
13
14
C28,C29,C50
C30
11 C31,C32,C33,C36,C37,C40,C41,C42,C43,C44,C45 10µF, Cer., 1206
4
4
C34,C35,C38,C39
D1,D2,D5,D6
1500µF, 6.3V, Alum.
1A, 40V, Schottky, MELF,
1N5819M
15
16
2
2
D3,D4
L1,L2
3A, 40V, Schottky, 30BQ040 Any
Inductor, 9 turns
Magnetics:
Kool Mu
P/N: 77206-A7
17
18
4
1
M1,M2,M3,M4
Q1
N-Channel MOSFET,
TO-263AB
Fairchild
P/N: FDB7030BL
80V, 1A, NPN, Med. Pwr.
SOT-223
BCP56CT
19
20
21
22
23
24
2
2
4
1
2
1
R1,R3
R4,R6
R2,R5,R7,R11
R8
2.2, 5%, 1206
4.7, 5%, 1206
1.0, 5%, 1206
56k, 5%, 1206
2.2k, 5%, 1206
Any
Any
Any
Any
Any
Any
R9,R10
R12
Chip resistor,
0.005, 1W, 1%, 2512
www.semtech.com
2001 Semtech Corp.
7
SC2420
POWER MANAGEMENT
Bill of Material (Cont.)
Two Channel Operation (Cont.)
Item
25
26
27
28
29
30
31
32
33
34
35
Qty Reference
Part Number/Value
2.2, 1/4W, 5%, 1210
Chip resistor, 0, 1206
1.00k, 1%, 1206
249, 1%, 1206
Manufacturer
4
0
2
1
1
2
1
1
1
1
1
R13,R14,R15,R16
Any
Any
Any
Any
Any
Any
Any
Any
Any
Any
R17*, R31*
R20,R21
R22
R23
1.5k, 1%, 1206
R26,R27
R28
2.0k, 5%, 1206
10, 5%, 1206
R34
5.1k, 5%, 1206
R36
40.2k, 1%, 1206
10.0k, 1%, 1206
R37
SC2420
Bi-Phase/Dual Controller,
SO-28W
Semtech Corp.
P/N: SC2420ISW
805-498-2111
Notes:
1. * Indicates optional parts.
2. Some parts are selected due to availability or lead time, and are not optimized.
www.semtech.com
2001 Semtech Corp.
8
SC2420
POWER MANAGEMENT
Electrical Characteristic Curves
Phase Node Waveform
of the Two Channel Evaluation Circuit
(Vin = 12V, 2.5V output source 10A,
1.25V output sink 10A)
Ch2: Phase node of 1.25V channel
Ch3: Phase node of 2.5V channel
Gate Drive Waveform
of the Two Channel Evaluation Circuit
(Vin = 12V, 2.5V output source 10A,
1.25V output sink 10A)
Ch2: Bottom Gate of 2.5V channel
Ch3: Top Gate of 2.5V channel
Gate Drive Waveform
of the Two Channel Evaluation Circuit
(Vin = 12V, 2.5V output source 10A,
1.25V output sink 10A)
Ch2: Bottom Gate of 1.25V channel
Ch3: Top Gate of 1.25V channel
www.semtech.com
2001 Semtech Corp.
9
SC2420
POWER MANAGEMENT
Applications Information
THEORY Oꢀ OPERATION
ꢀeed ꢀorward
The SC2420 employs a voltage mode control with feed The SC2420 incorporates a voltage feed forward scheme
forward to provide fast output response to load and line to improve line transient immunity when changes in the
transients.
input voltage occur. As the input voltage changes, the
ramp valley to peak voltage of the internal oscillator fol-
The SC2420 has two outputs, which can be used to gen- lows this change instantly. As a result the output voltage
erate two separate supply voltages or can be combined will have minimum disturbance due to the input line
in bi-phase operation to generate one single supply volt- change.
age. The internal reference is trimmed to 1V with +/-1%
accuracy, and the outputs voltages can be adjusted by Bias Generation
two external resistors. In bi-phase operation, the dual
switching regulators are operated 180° out of phase. A 6-7 Volt supply voltage is required to power up the
Load current sharing between phases is normally re- SC2420. This voltage could be provided by an external
quired, and this can be achieved by using precise feed- power supply or derived from VIN through and external
back voltage divider resistors (typically 0.1%) to match pass transistor.
individual phase output voltage. In addition, small droop-
ing resistors ( could be PCB traces) are employed at the REGDRV is the control signal to the base of the pass
output of each phase to enhance phase current balance. transistor that will regulate VCC. The voltage at the VCC
PWM Control
pin is compared to the internal voltage reference, and
the REGDRV pin can sink up to 5mA current to the volt-
Changes on the output voltages are fed to the inverting age at the VCC pin.
input of the Error Amplifiers, by the ꢀB1 and ꢀB2 pins,
and compared with the internal 1V reference. The com-
Enable
pensation to the transconductance amplifier is achieved
by connecting a capacitor in series with a resistor from
the COMP1 and COMP2 pins to AGND respectively. The
error signal from the error amplifier is compared to the
saw tooth waveform by the PWM comparator, and
matched timing signal is generated to control the upper
and lower gate drives of the two phases. A single Ramp
signal is used to generate the control signals for both of
the phases, hence the maximum duty cycle is less than
50%.
If the ENABLE pin is connected to logic high, the SC2420
is enabled, while connecting it to ground will put the de-
vice into disabled mode.
Under Voltage Lockout
Under Voltage Lockout (UVLO) circuitry senses VCC
through a voltage divider. If this signal falls below 5.8V,
with a typical hysteresis of 400mV, the BG pin is pulled
low by an internal transistor causing the lower
MOSFET gate to be on and the upper MOSFET gate
off for both phases.
Oscillator ꢀrequency Selection
The sawtooth signal is generated by charging an internal
capacitor with a current source. The charge current is Over Voltage Crowbar Protection
set by an external resistor connected from the RREꢀ pin
to AGND. The oscillator frequency and the external resis-
tance follow linear relationship.
The SC2420 provides OVP protection for each output
individually. Once the converter output voltage exceeds
120% nominal output voltage, the lower MOSꢀET gates
are latched on and the upper MOSꢀET gates are latched
off. The latch is then reset once the OVP condition is
removed.
www.semtech.com
2001 Semtech Corp.
10
SC2420
POWER MANAGEMENT
Applications Information
Gate Drive
Soft Start
The SC2420 integrates high current gate drives for fast
switching of large MOSꢀETs. The high-side gates can be
switched with peak currents of 1 Amp, while the larger
low-side gates can be switched with peak currents of 2
Amps. A cross conduction prevention circuitry ensures a
non-overlapping operation between the upper and lower
MOSꢀETs. This prevents false current limit tripping and
provides higher efficiency.
An external capacitor at the BG pin is used to set up the
Soft Start duration. The capacitor value, in conjunction
with the internal 3K resistor at the BG pin, control the
duration to bring up the bandgap to its final level. As the
BG capacitor is being charged through the internal resis-
tor, the PWM pulse opens slowly until the bandgap is
charged completely. This controlled start up of the PWM
prevents unnecessary component stress and noise gen-
eration during initial start up.
R2
R1
0
Gpwm
Error-Amp
L
Verror
Duty
-
Over Current Protection
+
R
C
Rc
Co
+
-
+
-
Ro
Vin
Vbg
The SC2420 current limit provides protection during an
over current condition. A sense resistor or PCB trace
can be used to sense the input supply current.
0
0
0
0
ꢀig. 1 SC2420 control model.
SC2420 Control Loop Design
The over current protection trip point is determined by
the voltage drop across the sense resistor. Once this
voltage exceeds the product of 50µA and the threshold
setting resistance (R26, R27 of evaluation circuit), OCP
protection circuit will be triggered. Due to component and
layout parasitics, filtering might be necessary across the
OC+ and OC- pins. It is recommended to use a 200ns
time constant for the RC filter (R26, C13). To clean up
the phase node ringing, one usually has to put a ceramic
capacitor close to the top ꢀET drain to the power ground.
Too much capacitance will bypass the top ꢀET current
from the sensing resistor, and too little the capacitance
will not be able to clean up the phase node ringing for full
load operation.
The control model of SC2420 can be depicted in ꢀig. 1.
This model can also be used in a Pspice kind of simulator
to generate loop gain Bode plots. The bandgap refer-
ence is 1V and trimmed to +/-1% accuracy. The desired
output voltage can be achieved by setting the resistive
divider network, R1 and R2.
The error amplifier is transconductance type with fixed
gain of:
A
V
.
.
G
0.002
error
The compensation network includes a resistor and a ca-
pacitor in series, which terminates from the output of
the error amplifier to the ground.
Once an over current condition occurs, the lower MOSꢀET
gates are latched on and the upper MOSꢀET gates are
latched off. The latch is then reset at the beginning of
the next clock cycle. The cycle is then reset at the begin-
ning of the next clock setting. The cycle is repeated in-
definitely until the over current condition is removed.
This device uses voltage mode control with input voltage
feed forward. The peak-to-peak ramp voltage is propor-
tional to the input voltage, which results in an excellent
performance to reject input voltage variation. The PWM
gain is inversion of the ramp amplitude, and this gain is
Thermal Shutdown
given by:
In addition to current limit, the SC2420 monitors over
temperature condition. The over temperature detect will
shut down the part if the SC2420 die temperature ex-
ceeds 150°C, and will auto reset once the die tempera-
ture is dropped down.
1
G
pwm
V
ramp
Where the ramp amplitude (peak-to-peak) is 1.5V when
the input voltage is 12V
www.semtech.com
2001 Semtech Corp.
11
SC2420
POWER MANAGEMENT
Typical Characteristics
The total control loop-gain can then be derived as follows: (4) Choose the loop gain cross over frequency (0dB
frequency). It is recommended that the crossover
frequency is always less than one fifth of the switching
.
s.R C
1
1
s.R.C
s.R.C
c
o
frequency or the output ripple frequency in bi-phase mode
operation:
.
.
T(s) T
o
R
R
L
c
2
.
.
.
s L.C
1
1
s. R C
F
c
o
o
sw
R
o
o
F
x_over
5
where:
If the transient specification is not stringent, it is better
to choose a crossover frequency that is less than one
tenth of the switching frequency for good noise immunity.
The resistor in the compensation network can then be
calculated as:
R
2
. .
.
.
G
T
G
V
R
pwm
o
error in
R
R
1
2
The task here is to properly choose the compensation
network for a nicely shaped loop-gain Bode plot. The
following design procedures are recommended to
accomplish the goal:
2
F
F
V
1
esr
x_over
o
.
.
.
R
G
.V .G
F
F
V
pwm in error
o
esr
bg
(1) Calculate the corner frequency of the output filter:
when:
or
<
<
ꢀ
ꢀ
ꢀ
o
esr x_over
1
F
o
. .
.
2 π L C
2
o
F
o
F
V
1
x_over
o
.
.
.
R
(2) Calculate the ESR zero frequency of the output filter
capacitor:
G
.V .G
F
F
o
V
pwm in error
esr
bg
when:
1
F
esr
. .
2 π R
.
C
esr< o< x_over
c
o
F
F
F
(3) Check that the ESR zero frequency is not too high.
(5) The compensation capacitor is determined by choosing
the compensator zero to be about one fifth of the output
filter corner frequency:
F
sw
F
<
ers
5
F
o
F
zero
5
If this condition is not met, the compensation structure
may not provide loop stability. The solution is to add
some electrolytic capacitors to the output capacitor bank
to correct the output filter corner frequency and the ESR
zero frequency. In some cases, the filter inductance may
also need to be adjusted to shift the filter corner
frequency. It is not recommended to use only high
frequency multi-layer ceramic capacitors for output filter.
1
C
2 π
. .R.F
zero
www.semtech.com
2001 Semtech Corp.
12
SC2420
POWER MANAGEMENT
Typical Characteristics
(6) The final step is to generate the Bode plot, either by Step 5. Calculate the compensator C:
using the simulation model in ꢀig. 1 or using the equations
C = 42nF
provided here with Mathcad. The phase margin can then
be checked using the Bode plot. Usually, this design
procedure ensures a healthy phase margin.
Step 6. Generate Bode plot and check the phase
margin. In this case, the phase margin is about 75°C
An example is given bellow to demonstrate the procedure that ensures the loop stability.
introduced above. The parameters of the power supply
are given as:
V : = 12 • V
IN
VO : = 2.5 • V
IO : = 12 • V
FSW : = 200 • KHz
L : = 3 • µH
CO : = 1680 • µF
RC : = 0.014 • Ω
Vbg : = 1• V
Step 1. Output filter corner frequency:
FO = 2.2 KHz
Step 2. ESR zero frequency:
FESR = 6.8 KHz
Step 3. Check the following condition:
FSW
Fers
<
5
Which is satisfied in this case.
Step 4. Choose crossover frequency and calculate
compensator R:
FX _OVER = 40 KHz
R = 8.4 KΩ
www.semtech.com
2001 Semtech Corp.
13
SC2420
POWER MANAGEMENT
Typical Characteristics
LOOP GAIN CURVES
Loop Gain Mag (dB)
100
50
0
mag(i)
50
3
4
5
6
10
100
1 10
1 10
1 10
1 10
F
i
Loop Gain Phase (Degree)
0
45
phase(i)
90
135
180
3
4
5
6
10
100
1 10
1 10
1 10
1 10
F
i
Layout Guidelines
Good layout is necessary for successful implementa-
tion of the SC2420 bi-phase/dual controller. Important
layout guidelines are listed below.
3). Separate ground planes for analog and power should
be provided. Power current should avoid running over
the analog ground plane. The AGND is star connected to
the PGND at the converter output to provide best pos-
sible ground sense. Refer to the application schematics,
certain components should be connected directly to the
AGND.
1). The high power parts should be laid out first. The para-
sitic inductance of the pulsating power current loop (start
from positive end of the input capacitor, to top MOSꢀET,
then to bottom MOSꢀET back to power ground) must be
minimized. The high frequency input capacitors and top
MOSꢀETs should be close to each other. The freewheel-
ing Schottky diode, the bottom MOSꢀET snubber, and
the bottom MOSꢀET should be placed close to each other.
The MOSꢀET gate drive and current sense loop areas
should be minimized. The gate drive trace should be
short and wide.
4). If a multi-layer PCB is used, power layer and ground
layer are recommended to be adjacent to each other.
Typically the power layer is on the top, followed by the
ground layer. This results in the least parasitic inductance
in the MOSꢀET-capacitor power loop, and reduces the
ringing on the phase node. The rest of the layers could
be used to run DC supply traces and signal traces.
2). The layout of the two phases should be made as sym-
metrical as possible. The SC2420 controller should be
placed in the center of the two phases. Please see evalu-
ation board layout as an example.
www.semtech.com
2001 Semtech Corp.
14
SC2420
POWER MANAGEMENT
Typical Characteristics
PCB Layout (2 Layer)
Component Side (TOP)
Copper (TOP)
www.semtech.com
2001 Semtech Corp.
15
SC2420
POWER MANAGEMENT
Typical Characteristics (Cont.)
PCB Layout (2 Layer)
Copper (BOTTOM)
www.semtech.com
2001 Semtech Corp.
16
SC2420
POWER MANAGEMENT
Outline Drawing - SO-28
Contact Information
Semtech Corporation
Power Management Products Division
652 Mitchell Rd., Newbury Park, CA 91320
Phone: (805)498-2111 ꢀAX (805)498-3804
www.semtech.com
2001 Semtech Corp.
17
相关型号：
SC2420ISWTRT
Switching Controller, Voltage-mode, 2A, 1000kHz Switching Freq-Max, PDSO28, SOIC-28
SEMTECH
SC2422ACS.TR
Switching Controller, Current-mode, 1000kHz Switching Freq-Max, PDSO16, SOIC-16
SEMTECH
SC2422ACS.TRT
Switching Controller, Current-mode, 1000kHz Switching Freq-Max, PDSO16, SOIC-16
SEMTECH
©2020 ICPDF网 联系我们和版权申明