SEMTECH SC2443EVB

SC2443
Dual-Phase Single or Two Output
Synchronous Step-Down Controller
POWER MANAGEMENT
Features
Description
u Wide input voltage range: 4.7V to 16V
u 0.5V feedback voltage for low-voltage outputs
u Programmable frequency up to 1 MHz per phase
u 2-Phase synchronous continuous conduction mode for
high efficiency step-down converters
u Out-of-phase operation for low input current ripples
u Output source and sink currents
u Fixed frequency peak current-mode control
u 75mV/-110mV maximum current sense voltage
u Inductor DCR current-sensing for low-cost applications
u Dual outputs or 2-phase single output operation
u Excellent current sharing between individual phases
u Individual soft-start, overload shutdown and enable
u External reference input for DDR applications
u External synchronization
u Industrial temperature range
u 4mm X 4mm X1mm 24-lead MLPQ package
The SC2443 is a high-frequency dual synchronous step-down
switching power supply controller. It provides out-of-phase
high-current output gate drives to all N-channel MOSFET power
stages. The SC2443 operates in synchronous continuous-conduction mode. Both phases are capable of maintaining regulation with sourcing or sinking load currents, making the SC2443
suitable for generating both VDDQ and the tracking VTT for
DDR applications.
Applications
Individual soft-start and overload shutdown timer is included
in each step-down controller. The SC2443 implements hiccup
overload protection. In single output current share configuration, the master timer controls the soft-start and overload shutdown functions of both controllers.
The SC2443 employs fixed frequency peak current-mode control for the ease of frequency compensation and fast transient
response.
The dual-phase step-down controllers of the SC2443 can be
used to produce two individually controlled and regulated outputs or a single output with shared current in each phase. The
Step-down controllers operate from an input of at least 4.7V
and are capable of regulating outputs as low as 0.5V
u Telecommunication power supplies
u DDR memory power supplies
u Graphic power supplies
u Servers and base stations
Typical Application Circuit
VIN
3
15
4
14
5
VOUT2
13
IN2-
6
19
GDH1
20
BST1
22
23
24
21
SS1/EN1
CS1+
CS1-
ROSC
COMP1
IN1-
GDL1
PVCC
SYNC
PGND
SC2443
AGND
GDL2
REF
GDH2
REFIN
AVCC
16
IN1-
SS2/EN2
2
CS2+
AVCC
BST2
1
VOUT1
BST2
18
17
16
VIN
15
14
13
12
11
10
9
7
12
SS2/EN2
11
REFIN
CS2+
GDH2
IN1-
17
CS2-
GDL2
REF
18
IN2-
AGND
VP1
U1
8
20
21
19
GDH1
BST1
22
CS1+
SS1/EN1
23
CS1-
ROSC
PGND
SC2443
7
6
SYNC
CS2-
5
GDL1
VIN
VOUT1
IN1-
PVCC
10
4
COMP1
9
3
IN1-
IN2-
2
COMP2
1
8
IN1-
24
VP1
U1
VIN
VOUT1 VP1
VIN
COMP2
VIN
VOUT1 VP1
VIN
VIN
IN2-
Dual Independent Outputs
Aug. 2008
Single Output With Current Sharing
1
SC2443
Pin Configuration
Ordering Information
Top View
IN1-
GDH1
BST1
SS1/EN1
CS1+
CS1-
ROSC
24
19
18
1
GDL1
COMP1
PVCC
SYNC
PGND
AGND
GDL2
REF
GDH2
REFIN
6
13
7
Device
Package
SC2443MLTRT (1,2)
24-lead 4mm X 4mm X 1mm MLPQ
SC2443EVB
Evaluation Board
Notes:
(1) Available in tape and reel only. A reel contains 3,000 devices.
(2) Available in lead-free package only. Device is WEEE and RoHS
compliant.
BST2
12
AVCC
SS2/EN2
CS2+
CS2-
IN2-
COMP2
(24-lead 4mm X 4mm X 1mm MLPQ)
θJA = 29°C/W
Marking Information
Marking for the 4 X 4mm MLPQ-24 package:
SC2443
Absolute Maximum Ratings
Recommended Operating Conditions
AVCC, PVCC Voltage ……………………………
-0.3 to 20V
VBST1, VBST2 Voltage ………………………………
-0.3 to 32V
……………………………… - 0.3 to 40V
(for <10ns @ freq. < 500kHz)
Input Voltage Range …………………………
4.75V to 16V
Thermal Information
Junction to Ambient(1) ……………………………
29°C/W
-0.3 to 6V
Maximum Junction Temperature ……………………… 150°C
IN1-, IN2-, REF Voltage ………………… -0.3 to AVCC+ 0.3V
Storage Temperature ………………………… -65 to +150°C
SS1/EN1, SS2/EN2, SYNC Voltage ………………
REFIN , COMP1, COMP2 Voltage ………… -0.3 to AVCC+ 0.3V
CS1+, CS1-, CS2+, CS2- Voltage ………… -0.3 to AVCC+ 0.3V
PGND to AGND ………………………………………
± 0.3V
Peak IR Reflow Temperature …………………………… 260°C
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not recommended.
NOTES(1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
(2) This device is ESD sensitive. Use of standard ESD handing precautions is required
Electrical Characteristics
Unless otherwise specified: AVCC = PVCC = 12V, VBST1 = VBST2 = 12V, SYNC = 0V, -40°C < TA = TJ < 85°C, ROSC =51.1kW.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
AVCC Start Threshold
AVCCTH
AVCC rising
4.5
4.7
V
AVCC Start Hysteresis
AVCCHYST
170
AVCC Operating Current
ICC
12
AVCC Quiescent Current in UVLO
Iq
Undervoltage Lockout
AVCC = AVCCTH - 0.2V
mV
16
1.7
mA
mA
Channel 1 Error Amplifier
Non-inverting Input Voltage
VIN1+
Non-inverting Input Voltage
VIN1+
Non-inverting Input Line Regulation
0°C < TA = TJ < 70°C
0.49
0.5
0.51
V
0.4925
0.5
0.5075
V
0.02
%/V
AVCCTH < AVCC < 15V
Input Offset Voltage
1
mV
Inverting Input Bias Current
IIN1-
-0.1
Amplifier Transconductance
GM1
260
µW-1
Amplifier Open Loop Gain
AOL1
65
dB
5
MHz
VCS1+=VCS1- = 0, VSS1 Rising
2.2
V
Amplifier Output Sink Current
VIN1- = 1V, VCOMP1 = 2.5V
16
µA
Amplifier Output Source Current
VIN1- = 0V, VCOMP1 = 2.5V
12
µA
Amplifier Unity Gain Bandwidth
COMP1 Switching Threshold
-0.25
µA
3
SC2443
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Channel 2 Error Amplifier
Input Common-mode Range(1)
0
3
V
Inverting Input Voltage Range
0
AVCC
V
(1)
Input Offset Voltage
1.5
mV
Non-inverting Input Bias Current
IIN2+
-150
-380
nA
Inverting Input Bias Current
IIN2-
-100
-250
nA
Inverting Input Voltage for 2 phases
Single Output Operation
2.5
V
Amplifier Transconductance
GM2
260
µW-1
Amplifier Open Loop Gain
AOL2
65
dB
5
MHz
VCS2+=VCS2- = 0, VSS2 Rising
2.2
V
Amplifier Output Sink Current
VCOMP2 = 2.5V
16
µA
Amplifier Output Source Current
VCOMP2 = 2.5V
12
µA
Amplifier Unity Gain Bandwidth
COMP2 Switching Threshold
Oscillator
fCH1, fCH2
Channel Frequency
450
500
550
kHz
Synchronizing Frequency
2.1fCH
kHz
SYNC Input High Voltage
1.5
V
(1)
SYNC Input Low Voltage
0.5
Channel Maximum Duty Cycle
DMAX1, DMAX2
Channel Minimum Duty Cycle
DMIN1, DMIN2
88
V
%
0
%
AVCC-1
V
Current Limit Comparator
Input Common Mode Range
0
Cycle by cycle Peak Currentr Limit
VILIM1+ , VILIM2+
VCS1- = VCS2- = 0.5V, Sourcing
60
75
90
mV
Valley Current Overload Shutdown
Threshold
VILIM1- , VILIM2-
VCS1- = VCS2- = 0.5V, Sinking
-85
-110
-130
mV
Positive Current sense
Input Bias Current
ICS1+ , ICS2+
VCS1+ = VCS1- = 0
VCS2+ = VCS2- = 0
-0.7
-2
µA
Negative Current sense
Input Bias Current
ICS1- , ICS2-
VCS1+ = VCS1- = 0
VCS2+ = VCS2- = 0
-0.7
-2
µA
SC2443
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Gate Drivers
High side Gate Driver
Peak Source Current
VBST1, VBST2 = 12V
1.5
A
High side Gate Driver
Peak Sink Current
VBST1, VBST2 = 12V
1
A
Low side Gate Driver
Peak Source Current
AVCC = PVCC = 12V
1.5
A
Low side Gate Driver
Peak Sink Current
AVCC = PVCC = 12V
1
A
Gate Drive Rise Time
CL = 2200pF
20
ns
Gate Drive Fall Time
CL = 2200pF
20
ns
Low side Gate Driver to High side
Gate Driver Non-overlapping delay
CL = 0
90
ns
High side Gate Driver to Low side
Gate Driver Non-overlapping delay
CL = 0
90
ns
TA = 25°C
150
ns
VSS1 = VSS2 = 1.5V
2
µA
VSS1 and VSS2 Rising
3.2
V
Overload IN1- Threshold
VSS1 = 3.8V, VIN1- falling
0.75VREF
V
Overload IN2- Threshold
VSS2 = 3.8V, VIN2- falling
0.72 X
V
ISS1 _DIS , ISS2_DIS
VSS1 = VSS2 = 3.8V
1.4
µA
VSSRCV1 ,
VSSRCV2
VSS1 and VSS2 Falling
Minimum On Time
Soft Start, Overload Latchoff and Enable
Soft Start Charging Current
ISS1 , ISS2
Overload Enabling Soft Start Voltage
Soft Start Discharge Current
Overload Recovery Soft Start Voltage
Gate Driver Disable SS/EN Voltage
0.3
0.5
0.7
0.9
Gate Driver Enable SS/EN Voltage
0.7
V
V
1.2
1.5
V
500
510
mV
Internal 0.5V Reference Buffer
Output Voltage
Load Regulation
VREF
IREF = -1mA
0 < IREF <-5mA
490
0.05
%/mA
Notes:
(1) Guaranteed by design.
SC2443
Typical Characteristics
AVCC operation current vs.
Temperature
UVLO Threshold vs. Temperature
4.54
AVCC UVLO(V)
4.53
4.52
4.51
4.50
4.49
-40
25
12.9
AVCC Current in UVLO(mA)
AVCC operation Current(mA)
4.55
12.8
12.7
12.6
12.5
12.4
12.3
12.2
12.1
12
85
1.80
1.75
1.70
1.65
1.60
25
85
-40
COMP Sink/Source current vs.
Temperature
501.5
500.5
500.0
499.5
499.0
85
85
E/A GM vs. Temperature
20
290
15
280
SINK
10
E/A GM(uW-1)
VREF(mV)
501.0
COMP SINK/SOURCE Current(uA)
502.0
25
Temperature (OC)
Temperature (OC)
VREF vs. Temperature
25
1.85
1.55
-40
Temperature (OC)
-40
AVCC current in UVLO vs.
Temperature
5
0
-5
SOURCE
-10
270
260
250
240
230
-15
220
-40
25
85
-40
25
85
Temperature (OC)
Temperature (OC)
COMP switching Threshold vs.
Temperature
Switching Frequency setting vs.
Temperature
Cycle by Cycle OCP threshold vs.
Temperature
512
Switching Frequency(KHz)
COMP Switching Threshold(V)
2.35
2.30
2.25
2.20
2.15
2.10
2.05
-40
25
510
508
506
504
502
500
498
496
85
ROSC = 51.1KW
-40
Temperature (OC)
SS/EN Threshold for Gate Driver
Enable / Disable vs. Temperature
3.17
3.16
3.15
3.14
3.13
3.12
3.11
3.10
Temperature (OC)
74.5
74.0
73.5
73.0
72.5
72.0
71.5
71.0
-40
85
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
Enable
Disable
-40
25
Temperature (OC)
85
25
Temperature (OC)
85
SS/EN Threshold for Overload
Hiccup Recovery vs. Temperature
SS/EN Threshold Voltage(V)
SS/EN Threshold Voltage(V)
SS/EN Threshold Voltage(V)
3.18
25
85
75.0
Temperature (OC)
SS/EN Threshold for Overload Hiccup vs.
Temperature
-40
25
Cycle by Cycle OCP Threshols(mV)
Temperature (OC)
0.58
0.56
0.54
0.52
0.50
0.48
0.46
0.44
0.42
-40
25
Temperature (OC)
85
SC2443
Typical Application Circuit Performance
Circuit Conditions : Single output current share configuration as shown in page 15
Releasing SS/EN pin from GND
Releasing SS/EN pin from GND
Soft Start
VIN
5V/DIV
VIN
5V/DIV
EN1/SS1
2V/DIV
COMP1
1V/DIV
COMP1
1V/DIV
EN1/SS1
2V/DIV
EN1/SS1
2V/DIV
VIN
2V/DIV
VOUT
1V/DIV
10ms/DIV
GDL1
5V/DIV
VOUT
1V/DIV
VOUT
1V/DIV
Shuting down _ VIN ramp down
VIN
2V/DIV
VIN
5V/DIV
EN1/SS1
2V/DIV
EN1/SS1
2V/DIV
GDL1
10V/DIV
GDL1
10V/DIV
VOUT
1V/DIV
VOUT
1V/DIV
10ms/DIV
10ms/DIV
Pulling SS/EN pin to GND
Gate Wavefroms
GDH1
GDL1
10V/DIV
GDH2
GDL2
10V/DIV
1ms/DIV
400us/DIV
1us/DIV
Output Ripple _ IOUT = 40A
Transient Response _ 10A ~ 30A
OCP Trip _ IOUT = 56A
SS1/EN1
2V/DIV
GDH1
GDH2
10V/DIV
VOUT
50mV/DIV
GDH1
20V/DIV
GDL1
10V/DIV
VOUT
20mV/DIV
VOUT
0.5V/DIV
1us/DIV
OCP Recovery to 30A loading
200us/DIV
400us/DIV
Efficiency (12VIN to 1VOUT)
EFF (%)
90
80
SS1/EN1
2V/DIV
70
GDH1
20V/DIV
GDL1
10V/DIV
60
50
40
VOUT
0.5V/DIV
20ms/DIV
30
1
5
10
15
20
25
30
35
40 IOUT(A)
SC2443
Typical Application Circuit Performance
Circuit Conditions : Dual independent outputs configuration as shown in page 17
Soft Start (VOUT2)
Soft Start (VOUT1)
Soft Start (Both outputs)
SS1/EN1
2V/DIV
COMP1
EN1/SS1
2V/DIV
VIN
2V/DIV
VOUT1
1V/DIV
10ms/DIV
COMP2
1V/DIV
EN2/SS2
2V/DIV
VOUT1
0.5V/DIV
VIN
2V/DIV
SS2/EN2
2V/DIV
VOUT2
2V/DIV
VOUT2
2V/DIV
10ms/DIV
Output Ripple (VOUT1_20A)
Gate waveforms (VOUT1_2 = 20A)
GDH1
GDL1
10V/DIV
Output Ripple (VOUT2_20A)
GDH2
GDL2
10V/DIV
GDH1
GDL1
10V/DIV
GDH2
GDL2
10V/DIV
VOUT2
50mV/DIV
VOUT1
50mV/DIV
1us/DIV
1us/DIV
Transient Response (VOUT2 _ 2A ~ 17A)
OCP Trip (VOUT1 = 30A)
1us/DIV
Transient Response (VOUT1 _ 2A ~ 17A)
20ms/DIV
SS1/EN1
2V/DIV
VOUT2
50mV/DIV
VOUT1
50mV/DIV
GDH1
GDL1
20V/DIV
VOUT1
0.5V/DIV
200us/DIV
OCP Trip (VOUT2 = 28A)
200us/DIV
EFF (%)
400us/DIV
Combined Efficiency (12VIN to 1VOUT & 2.5VOUT)
95
90
SS2/EN2
2V/DIV
85
GDH2
20V/DIV
GDL2
10V/DIV
80
75
VOUT2
1V/DIV
70
400us/DIV
1
5
10
15
20
IOUT(A)
SC2443
Pin Descriptions
Pin #
Pin Name
Pin Function
1
IN1-
2
COMP1
3
SYNC
Edge-triggered Synchronization Input. When not synchronized, tie this pin to a voltage above 1.5V
or the ground. An external clock (frequency > frequency set with ROSC) at this pin synchronizes the
controllers.
4
AGND
Analog Signal Ground
5
REF
Buffered Output of the Internal 0.5V Reference. The non-inverting input of the error amplifier for the
step-down converter 1 is internally connected to this pin
6
REFIN
An external Reference voltage is applied to this pin.The non-inverting input of the error amplifier for
the step-down converter 2 is internally connected to this pin.
7
COMP2
8
IN2-
Inverting Input of the Error Amplifier for the Step-down Controller 2. Tie to AVCC for two-phase single
output applications.
9
CS2-
The Inverting Input of the Current-sense Amplifier/Comparator for the Controller 2.
10
CS2+
The Non-inverting Input of the Current-sense Amplifier/Comparator for the Controller 2.
11
SS2/EN2
12
AVCC
Power Supply Voltage for the Analog Portion of the Controllers.
13
BST2
Bootstrapped Supply for the High-side Gate Drive 2.
14
GDH2
Gate Drive Output for the High-side N-channel MOSFET of Output 2.
15
GDL2
Gate Drive Output for the Low-side N-channel MOSFET of Output 2.
16
PGND
Ground Supply for All the Gate drivers.
17
PVCC
Power Supply Voltage for Low-side MOSFET Drivers.
18
GDL1
Gate Drive Output for the Low-side N-channel MOSFET of Output 1.
19
GDH1
Gate Drive Output for the High-side N-channel MOSFET of Output 1.
20
BST1
Bootstrapped Supply for the High-side Gate Drive 1.
21
SS1/EN1
22
CS1+
The Non-inverting Input of the Current-sense Amplifier/Comparator for the Controller 1.
23
CS1-
The Inverting Input of the Current-sense Amplifier/Comparator for the Controller 1
24
ROSC
An external resistor connected from this pin to GND sets the oscillator frequency
THPAD
Solder to the Analog ground plane of the PCB.
Inverting Input of the Error Amplifier for the Step-down Controller 1.
The Error Amplifier Output for Step-down Controller 1.
The Error Amplifier Output for Step-down Controller 2.
An external capacitor tied to this pin sets (i) the soft-start time (ii) output overload latch off time for
step-down converter 2. Pulling this pin below 0.7V shuts off the gate drivers for the second controller.
Leave open for two-phase single output applications.
An external capacitor tied to this pin sets (i) the soft-start time (ii) output overload latch off time for
buck converter 1. Pulling this pin below 0.7V shuts off the gate drivers for the first controller.
SC2443
Block Diagram
SYNC
3
CLK2
OSCILLATOR
ROSC
24
COMP1
2
IN11
EA1
+
+
-
0.5V
UVLO
4.3/4.5V
BST1
R
S
GDH1
19
Q
Non-Overlapping
Conduction
Control
UVLO
0.75 VREF
Soft-Start And
Overload
Hiccup
Control
+ +
+
ISEN
-
6
+ILIM+
-
110mV
REFIN/IN2+
6
PWM
+
SLOPE
COMP
75mV
COMP2
7
IN28
CLK1
AVCC
12
20
REF/IN1+
5
CS1+
22
CS123
REFERENCE
ILIM-
OL
PVCC
17
GDL1
18
PGND
16
DSBL
SS1/EN1
21
OCN
+
EA2
+
+
-
AGND
4
0.72 VREFOUT
SC2443 Block Diagram (Channel 1 PWM Control Only)
Figure 1. SC2443 Block Diagram
10
SC2443
Applications Information
Description
The SC2443 is a constant frequency 2-phase current-mode
step-down PWM switching controller driving all N-channel
MOSFET. The two channels of the controller operate at
180 degrees out-of-phase from each other. Since input
currents are interleaved in a two-phase converter, input
ripple current is lower and smaller input capacitor can
be used for filtering. Also, with lower inductor current
and smaller inductor ripple current per phase, overall I2R
losses are reduced.
The supply voltages for the high-side gate drivers are
obtained from two diode-capacitor bootstrap circuits. If
the bootstrap capacitor is charged from VCC, the highside gate drive voltage swing will be from approximately
2VCC to the ground. The power dissipated in the highside gate driver is not higher with higher voltage swing
because the gate-source voltage of the high-side MOSFET
still swing from zero to VCC. The outputs of the low-side
gate drivers swing from VCC to ground.
The SC2443 operates in synchronous continuousconduction mode. It can be configured either as two
independent step-down controllers producing two
separate outputs or as a dual-phase single-output
controller by tying the IN2- pin to VCC. In single output
operation, the channel one error amplifier controls both
channels and the channel two error amplifier is disabled.
Soft-start and overload hiccup of both channels is
synchronized to channel one.
The SC2443 has internal ramp-compensation to prevent
sub-harmonic oscillation when operating above 50%
duty cycle. There is enough ramp internally for a sensed
voltage ripple between 1/4 to 1/3 of the full-scale sensed
voltage limit of 75mV. The maximum sensed voltage limit
is unaffected by the compensating ramp.
Frequency Setting and Synchronization
The internal oscillator of the SC2443 runs at twice the
phase frequency. The free-running frequency of the
oscillator can be programmed with an external resistor
from the ROSC pin to ground. The step-down controllers
are capable of operating up to 1 MHz. It is necessary to
consider the operating duty-ratio before deciding the
switching frequency. See Applications Information section
for more details.
When synchronized externally, the applied clock frequency
should be twice the desired phase frequency. The
synchronizing clock frequency should also be between 2
- 2.6 times the set free-running channel frequency.
Control Loop
The SC2443 uses peak current-mode control for fast
transient response, ease of compensation and current
sharing in single output operation. The low-side MOSFET
of each channel is turned off at the falling-edge of the
phase timing clock. After a brief non-overlapping time
interval of 90ns, the high-side MOSFET is turned on.
The phase inductor current ramps up. When the sensed
inductor current reaches the threshold determined by
the error amplifier output and compensation ramp, the
high-side MOSFET is turned off. After a non-overlapping
conduction time of 90ns, the low-side MOSFET is turned
on.
Current-Sensing
There are two ways to sense the inductor current for
current-mode control with the SC2443. Since the peak
inductor current corresponds to 75mV of sensed voltage
(CS+ - CS-), resistor current sensing can be used at the
output without resulting in excessive power dissipation.
Although accurate and far easier to lay out than high-side
resistor sensing, a pair of precision sense resistors adds
cost to the converter.
With proper RC filter, Inductor DCR sensing can also be
used for SC2443 resulting in low cost and without extra
power dissipation.
Error Amplifiers
In closed loop operation, the error amplifier output ranges
from 1.1V to 3.5V. The upper output operating range
of either error amplifier is reserved for positive currentsense voltage (CS+ - CS-) and corresponds to positive
(sourcing) output current. If the amplifier swings to its
lower operating range, the amplifier will still modulate the
high-side gate drive duty-ratio. However the peak currentsense voltage (hence the peak inductor current) will be
limited to a negative value. The error amplifier output
is about 2.2V when the peak sense-voltage is zero. The
built-in offset in the current sense amplifier together with
synchronous continuous-conduction mode of operation
allows the SC2443 to regulate the output irrespective of
the direction of the load current.
11
SC2443
Applications Information (continued)
The non-inverting input of the first feedback amplifier is
tied to the internal 0.5V voltage reference. Both the noninverting and the inverting inputs of the second error
amplifier are brought out as device pins so that the output
of the second converter can be made to track the output
of the first channel. For example in DDR applications,
Channel 1 can be used to generate VDDQ (2.5V) from
the input (5V or 12V) and channel 2 is used to produce a
tracking VTT (1.25V) with VDDQ being its input.
Current-Limit
The maximum current sense voltage of +75mV is the
cycle-by-cycle peak current limit when the load is
drawing current from the converter. There is no cycle-bycycle current limiting when the inductor current flows in
the negative direction. However once the valley of the
current sense voltage exceeds -110mV, the corresponding
channel will undergo shutdown and restart (hiccup).
Soft-Start and Overload Protection
The undervoltage lockout circuit discharges the SS/EN
capacitors. After VCC rises above 4.5V, the SS/EN capacitors
are slowly charged by internal 2mA current source. With
internal PNP transistors, the SS/EN voltages clamp the error
amplifier outputs. When the error amplifier output rises
to 2.2V, the high-side MOSFET starts to switch. As the SS/
EN capacitor continues to be charged, the COMP voltage
follows. The converter gradually delivers increasing power
to the output. The inductor current follows the COMP
voltage envelope until the output goes into regulation.
The SS/EN clamp on COMP is then released.
After the SS/EN capacitor is charged above 3.2V (high
enough for the error amplifier to provide full load current),
the overload detection circuit is activated. If the output
voltage falls below 70% of its set value or the valley
current-sense voltage exceeds -110mV, an overload latch
will be set and both the top and the bottom MOSFETs will
be turned off. The SS/EN capacitor is slowly discharged
with an internal 1.4mA current sink. The overload latch
is reset when the SS/EN capacitor is discharged below
0.5V. The SS/EN capacitor is then recharged with the 2uA
current source and the converter undergoes soft-start.
If overload persists, the SC2443 will undergo repetitive
shutdown and restart.
If the output is short-circuited, the inductor current will
not increase indefinitely between the time the inductor
current reaching its current limit and the instant the
converter shuts down. This is due to cycle skipping(a
consequence of inductor current sense) reduces the
actual operating frequency.
The SS/EN pin can also be used as the enable input for that
channel. Both the high-side and the low-side MOSFETs
will be turned off if the SS/EN pin is pulled below 0.7V.
Operating Frequency (fs)
The switching frequency in the SC2443 is userprogrammable. The advantages of using constant
frequency operation are simple passive component
selection and ease of feedback compensation. Before
setting the operating frequency, the following trade-offs
should be considered.
1) Passive component size
2) Circuitry efficiency
3) EMI condition
4) Minimum switch on time and
5) Maximum duty ratio
For a given output power, the sizes of the passive
components are inversely proportional to the switching
frequency, whereas MOSFET and Diodes switching losses
are proportional to the operating frequency. Other
issues such as heat dissipation, packaging and the cost
issues are also to be considered. The frequency bands
for signal transmission should be avoided because of EM
interference.
Minimum Switch On Time Consideration
In the SC2443 the falling edge of the clock turns on the
top MOSFET. The inductor current and the sensed voltage
ramp up. After the sensed voltage crosses a threshold
determined by the error amplifier output, the top MOSFET
is turned off. The propagation delay time from the turnon of the controlling FET to its turn-off is the minimum
switch on time. The SC2443 has a minimum on time of
about 150ns at room temperature. This is the shortest on
interval of the controlling FET. The controller either does
not turn on the top MOSFET at all or turns it on for at least
150ns.
For a synchronous step-down converter, the operating
duty cycle is VO / VIN . So the required on time for the
top MOSFET is VO / (VIN × FS ) . If the frequency is set
such that the required pulse width is less than 150ns,
then the converter will start skipping cycles. Due to
minimum on time limitation, simultaneously operating at
12
SC2443
Applications Information (continued)
very high switching frequency and very short duty cycle
is not practical. If the voltage conversion ratio VO / VIN
and hence the required duty cycle is higher, the switching
frequency can be increased to reduce the sizes of passive
components.
There will not be enough modulation headroom if the
on time is simply made equal to the minimum on time
of the SC2443. For ease of control, we recommend the
required pulse width to be at least 1.5 times the minimum
on time.
Setting the Switching Frequency
The switching frequency is set with an external resistor
connected from Pin 24 to ground. The set frequency is
inversely proportional to the resistor value (Figure 2).
Figure 2. Free running frequency vs. ROSC.
800
700
fs (kHz)
600
PC Board Layout Issues
Circuit board layout is very important for the proper
operation of high frequency switching power converters.
A power ground plane is required to reduce ground
bounces. The following are suggested for proper layout:
Power Stage
1) Separate the power ground from the signal ground. In
the SC2443, the power ground PGND should be tied to
the source terminal of lower MOSFETs. The signal ground
AGND should be tied to the negative terminal of the
output capacitor.
2) Minimize the size of high pulse current loop. Keep the
top MOSFET, bottom MOSFET and the input capacitors
within a small area with short and wide traces. In addition
to the aluminum energy storage capacitors, add multilayer ceramic (MLC) capacitors from the input to the
power ground to improve high frequency bypass.
3) Reduce high frequency voltage ringing. Widen and
shorten the drain and source traces of the MOSFET to
reduce stray inductances. Add a small RC snubber if
necessary to reduce the high frequency ringing at the
phase node. Sometimes slowing down the gate drive
signal also helps in reducing the high frequency ringing
at the phase node.
500
400
300
200
100
0
0
50
100
150
200
250
Rosc (k Ohm)
Setting the Output Voltage
The non-inverting input of the channel-one error amplifier
is internally tied the 0.5V voltage reference output (Pin 5).
The non-inverting input of the channel-two error amplifier
is brought out as a device pin (Pin 6) to which the user can
connect Pin 5 or an external voltage reference. A simple
voltage divider (Ro1 at top and Ro2 at bottom) sets the
converter output voltage. The voltage feedback gain
h=0.5/Vo is related to the divider resistors value as
h
R o2 =
R o1.
1- h
4) Shorten the gate driver path. Integrity of the gate drive
(voltage level, leading and falling edges) is important for
circuit operation and efficiency. Short and wide gate drive
traces reduce trace inductances. Bond wire inductance is
about 2~3nH. If the length of the PCB trace from the gate
driver to the MOSFET gate is 1 inch, the trace inductance
will be about 25nH. If the gate drive current is 2A with
10ns rise and falling times, the voltage drops across
the bond wire and the PCB trace will be 0.6V and 5V
respectively. This may slow down the switching transient
of the MOSFET. These inductances may also ring with the
gate capacitance.
5) Put the decoupling capacitor for the gate drive power
supplies (BST and PVCC) close to the IC and power
ground.
Control Section
6) The frequency-setting resistor Rosc should be placed
close to Pin 3. Trace length from this resistor to the analog
13
SC2443
Applications Information (continued)
ground should be minimized.
7) Solder the bias decoupling capacitor right across the
AVCC and analog ground AGND.
8) Place the inductor DCR sense components away from
the power circuit and close to the corresponding CS+
and CS- pins. Use X7R type ceramic capacitor for the DCR
sense capacitor because of their temperature stability.
9) Use an isolated local ground plane underneath the
controller and tie it to the negative side of output capacitor
bank.
10) Comp pin is sensitive to noise. Place compensation
network components away from noise signal (i.e. gate
driver signals, phase node) and close to corresponding
Comp pin .
14
SC2443
Evaluation Application Circuit _ Single Output, Current share configuration
C12
R9
1
R5
124K
CS1- CS1+
C7
22nF
GDL1
PVCC
PGND
R1
17
C9
1uF
R10
R7
16
R11
18
15
0R
0R
2R2
0R
D1
1N4148
1uF
IPD09N03LA
C4
IPD06N03LA
D2
1N4148
Q1
Q2
Q4
Q5
C1
C10
Q3
12VIN
C3
R3
1R
C8
2.2nF
L1
R2
10K
C6
22pF
R6
10R
1.5uH/1.8mR
C5
100nF
R4
N.P.
R8
560R
1.5uH/1.8mR
C21
100nF
R15
1.05K
C14
C15
C16
C17
C19
1VOUT/40A
C18
10uF/6.3V
IN1-
N.P.
R16
10R
1500uF/6.3V/FL
C22
R14
N.P.
R20
1K
1500uF/6.3V/FL
R13
22pF
C11
1R
L2
R12
10K
CS1+
CS1-
C2
12VIN
Q6
C24
R19
560R
1500uF/6.3V/FL
1uF
IPD09N03LA
C20
IPD06N03LA
2.2nF
10uF/6.3V
14
13
0R
270uF/16V/OSCON
SC2443
GDL2
GDH2
BST2
R17
12VIN
270uF/16V/OSCON
U1
IN1COMP1
SYNC
AGND
REF
REFIN
10R
IPD06N03LA
2
IN1-
47K
3
C23
100nF
6
5
4
C13
N.P
0R
R21
10uF/16V
270uF/16V/OSCON
IPD06N03LA
C25
1uF
10uF/16V
330pF
R18
20
BST1
19
GDH1
AVCC
12
CS2+
10
SS2/EN2
11
21
SS1/EN1
22
CS1+
CS29
23
CS1IN28
24
ROSC
COMP2
7
15
SC2443
Evaluation Board Bill of Materials
Single Output Current Share Configuration
Item
Reference
Quantity
Description
Package
Part
Vendor
1
C1,C10
2
16V X5R ceramic capacitor
1206
10uF
Murata
2
C2,C3,C11
3
16V Aluminum solid capacitor _SEPC series
8 X 9mm
270uF
Sanyo
3
C4,C9,C20,C25
4
16V X5R ceramic capacitor
0603
1uF
Murata
4
C5,C21,C23
3
16V X7R ceramic capacitor
0603
100nF
Panasonic
5
C6,C22
2
25V X7R ceramic capacitor
0603
22pF
Panasonic
6
C7
1
16V X7R ceramic capacitor
0603
22nF
Panasonic
7
C8,C24
2
25V X7R ceramic capacitor
0603
2.2nF
Panasonic
8
C12
1
25V X7R ceramic capacitor
0603
330pF
Panasonic
9
C14,C19
2
6.3V X7R ceramic capacitor
1206
10uF
Murata
10
C15,C16,C17
3
6.3V Aluminum capacitor _ FL series
8 X 11.5mm
1000uF
Panasonic
11
D1,D2
2
Small signal diode
SMD
1N4148
Any
12
L1,L2
2
SMD inductor
12.5 X 12.5 X
10mm
1.5uH/1.8mR
TRIO
13
Q1,Q4
2
30V N Channel MOSFET
D-pack
IPD09N03LA
Infineon
14
Q2,Q3,Q5,Q6
4
30V N Channel MOSFET
D-pack
IPD06N03LA
Infineon
15
R1,R7,R11,
R17,R18
5
5% SMD resistor
0603
0R
Any
16
R2,R12
2
5% SMD resistor
0603
10K
Any
17
R3,R13
2
5% SMD resistor
0603
1R
Any
18
R5
1
1% SMD resistor
0603
124K
Any
19
R6,R16.R21
3
1% SMD resistor
0603
10R
Any
20
R8,R19
2
1% SMD resistor
0603
560R
Any
21
R9
1
5% SMD resistor
0603
47K
Any
22
R10
1
5% SMD resistor
0603
2R2
Any
23
R15
1
1% SMD resistor
0603
1.05K
Any
24
R20
1
1% SMD resistor
0603
1K
Any
25
U1
1
Dual phase Sync. step down controller
MLPQ-24
SC2443
SEMTECH
16
SC2443
Evaluation Application Circuit_ Dual Independant Outputs
1N11
R6
124K
CS1- CS1+
C7
GDL1
PVCC
PGND
18
17
16
15
14
R12
2R2
R8
0R
R1
0R
C13
1uF
R13
0R
D1
1N4148
C4
1uF
Q2
IPD06N03LA
D2
1N4148
C18
1uF
Q1
Q4
Q3
N.P.
Q6
N.P.
C1
C14
C2
R3
1R
12VIN
C3
R2
15K
R4
N.P.
C5
100nF
L1
2.2uH/2mR
C6 27pF
R7
0R
R9
N.P.
R18
0R
C8
C21
C9
C10
2200uF/6.3V/FL
C22
2200uF/6.3V/FL
C23
1VOUT/20A
C11
IN1-
R5
1.05K
R10
1K
R22
1K
R17
4.12K
2.5VOUT/20A
C24
10uF/6.3V
R21
N.P.
1800uF/6.3V/FL
R16
N.P.
C19
100nF
L2
2.2uH/2mR
C20 N.P.
R14
20K
CS1+
C12
CS12.2nF
C15
12VIN
R15
1R
C25
2.2nF
1800uF/6.3V/FL
Q5
IPD06N03LA
10uF/6.3V
R19
0R
1500uF/16V/FL
13
12VIN
IPD09N03LA
GDL2
GDH2
BST2
R23
10R
N.P.
SC2443
C29
IPD09N03LA
10uF/16V
22uF/10V/X7R
22uF/10V/X7R
C30
1uF
1500uF/16V/FL
U1
IN1COMP1
SYNC
AGND
REF
REFIN
C28
20
10uF/16V
2
3
4
5
6
R20
100K
C27
470pF
22nF
SYNC
N.P.
C17
R25
0R
C26
100nF
19
GDH1
AVCC
12
R11
47K
C16
470pF
R24
0R
CS2+
10
BST1
SS2/EN2
11
21
SS1/EN1
22
CS1+
CS29
23
CS1IN28
24
ROSC
COMP2
7
17
N.P.
22nF
SC2443
Evaluation Board Bill of Materials
Dual Independent Output Configuration
Item
Reference
Quantity
Description
Package
Part
Vendor
1
C1,C4
2
16V X5R ceramic capacitor
1206
10uF
Murata
2
C2,C15
2
16V Aluminum capacitor _FL series
10 X 20mm
1500uF
Panasonic
3
C4,C13,C18,
C30
4
16V X5R ceramic capacitor
0603
1uF
Murata
4
C5,C19,C26
3
16V X7R ceramic capacitor
0603
100nF
Panasonic
5
C6
1
25V X7R ceramic capacitor
0603
27pF
Panasonic
6
C7,C29
2
16V X7R ceramic capacitor
0603
22nF
Panasonic
7
C8,C11
2
6.3V X7R ceramic capacitor
1206
10uF
Murata
8
C9,C10
2
6.3V Aluminum capacitor _ FL series
10 X 16mm
1800uF
Panasonic
9
C12,C25
2
25V X7R ceramic capacitor
0603
2.2nF
Panasonic
10
C16,C27
2
25V X7R ceramic capacitor
0603
470pF
Panasonic
11
C21,C24
2
10V X7R ceramic capacitor
1206
10uF
Murata
12
C22,C23
2
6.3V Aluminum capacitor _ FL series
10 X 20mm
2200uF
Panasonic
13
D1,D2
2
Small signal diode
SMD
1N4148
Any
14
L1,L2
2
Through hole inductor
2.2uH/2mR
Any
15
Q1,Q4
2
30V N Channel MOSFET
D-pack
IPD09N03LA
Infineon
16
Q2,Q5
2
30V N Channel MOSFET
D-pack
IPD06N03LA
Infineon
17
R1,R7,R11,R13,
R18,R19,R24
R25
8
5% SMD resistor
0603
0R
Any
18
R2
1
5% SMD resistor
0603
15K
Any
19
R3,R15
2
5% SMD resistor
0603
1R
Any
20
R5
1
1% SMD resistor
0603
1.05K
Any
21
R6
1
1% SMD resistor
0603
124K
Any
22
R10,R22
2
1% SMD resistor
0603
1K
Any
23
R11
1
5% SMD resistor
0603
47K
Any
24
R12
1
5% SMD resistor
0603
2R2
Any
25
R14
1
5% SMD resistor
0603
20K
Any
26
R17
1
1% SMD resistor
0603
4.12K
Any
27
R20
1
5% SMD resistor
0603
100K
Any
28
R23
1
5% SMD resistor
0603
10R
Any
29
U1
1
Dual phase Sync. step down controller
MLPQ-24
SC2443
SEMTECH
18
SC2443
5
1N11
R6
102K
U1
CS1- CS1+
C7
4
GDL1
PVCC
PGND
GDL2
GDH2
18
17
16
15
14
R12
2R2
R8
0R
R1
0R
C13
1uF
R13
0R
D1
1N4148
C4
1uF
D2
1N4148
C18
1uF
Q1
3
FDS6982
Q2
FDS6982
C1
C2
12VIN
12VIN
C14
C15
R3
1R
R4
N.P.
C5
100nF/X7R
L1
1.9uH/3.9mR
R2
4.87K
C6 27pF
2
R7
10R
R9
604R
R18
10R
R21
604R
C8
C21
C9
C10
1000uF/6.3V/FL
C22
N.P
C23
Title
C11
C24
N.P
R16
N.P.
C19
100nF/X7R
L2
1.9uH/3.9mR
C20 18pF
R14
4.87K
CS1+
C12
CS12.2nF
R15
1R
C25
2.2nF
N.P
R19
0R
1000uF/6.3V/FL
13
VIN
10uF/6.3V
BST2
R23
10R
680uF/16V/FL
C29
680uF/16V/FL
C28
N.P
C30
1uF
10uF/16V
COMP1
IN1-
22nF
SYNC
2
SYNC
AGND
GDH1
AVCC
20
19
SS2/EN2
REF
REFIN
R20
47K
C27
470pF
SC2443
21
11
3
SS1/EN1
CS2+
4
22
10
5
6
CS1+
CS2-
C17
N.P.
R25
0R
C26
100nF
CS1IN2-
9
R11
47K
C16
470pF
R24
0R
24
23
COMP2
7
BST1
12
ROSC
8
D
C
B
A
Evaluation Application Circuit_ Dual Independant Outputs (Lower power application)
1.5VOUT
IN1-
R5
2.05K
R10
1K
1.8VOUT
R17
2.61K
R22
1K
1
19
N.P.
22nF
10uF/16V
10uF/6.3V/X7R
SC2443
Evaluation Board Bill of Materials
Dual Independent Output Configuration
Item
Reference
Quantity
Description
Package
Part
Vendor
1
C1,C14
2
16V X5R ceramic capacitor
1206
10uF
Murata
2
C2,C15
2
16V Aluminum capacitor _FL series
10 X 12.5mm
680uF
Panasonic
3
C4,C13,C18,
C30
4
16V X5R ceramic capacitor
0603
1uF
Murata
4
C5,C19,C26
3
16V X7R ceramic capacitor
0603
100nF
Panasonic
5
C6
1
25V X7R ceramic capacitor
0603
27pF
Panasonic
6
C7,C29
2
16V X7R ceramic capacitor
0603
22nF
Panasonic
7
C8,C21
2
6.3V X7R ceramic capacitor
1206
10uF
Murata
8
C9,C22
2
6.3V Aluminum capacitor _ FL series
10 X 12.5mm
1000uF
Panasonic
9
C12,C25
2
25V X7R ceramic capacitor
0603
2.2nF
Panasonic
10
C16,C27
2
25V X7R ceramic capacitor
0603
470pF
Panasonic
11
C20
1
25V X7R ceramic capacitor
0603
18pF
Murata
12
D1,D2
2
Small signal diode
SMD
1N4148
Any
13
L1,L2
2
Through hole inductor
1.9uH/3.9mR
Any
14
Q1,Q2
2
30V N Channel MOSFET
SO-8
FDS6982
Fairchild
15
R1,R8,R13,
R19,R24,R25
6
5% SMD resistor
0603
0R
Any
16
R2,R14
2
5% SMD resistor
0603
4.87K
Any
17
R3,R15
2
5% SMD resistor
0603
1R
Any
18
R5
1
1% SMD resistor
0603
2.05K
Any
19
R6
1
1% SMD resistor
0603
102K
Any
20
R7,R18,R23
3
5% SMD resistor
0603
10R
Any
21
R9,R21
2
5% SMD resistor
0603
604R
Any
22
R10,R22
2
1% SMD resistor
0603
1K
Any
23
R11,R20
2
5% SMD resistor
0603
47K
Any
24
R12
1
5% SMD resistor
0603
2R2
Any
25
R17
1
1% SMD resistor
0603
2.61K
Any
26
U1
1
Dual phase Sync. step down controller
MLPQ-24
SC2443
SEMTECH
20
SC2443
Outline Drawing - MLPQ-24
A
D
DIMENSIONS
INCHES
MILLIMETERS
DIM
MIN NOM MAX MIN NOM MAX
B
PIN 1
INDICATOR
(LASER MARK)
A
A1
A2
b
D
D1
E
E1
e
L
N
aaa
bbb
E
A2
A
.031 .035 .039
.000 .001 .002
- (.008) .007 .010 .012
.152 .157 .163
.100 .106 .110
.152 .157 .163
.100 .106 .110
.020 BSC
.012 .016 .020
24
.004
.004
0.80 0.90 1.00
0.00 0.02 0.05
- (0.20) 0.18 0.25 0.30
3.85 4.00 4.15
2.55 2.70 2.80
3.85 4.00 4.15
2.55 2.70 2.80
0.50 BSC
0.30 0.40 0.50
24
0.10
0.10
SEATING
PLANE
aaa C
A1
C
D1
LxN
E/2
E1
2
1
N
bxN
e
NOTES:
bbb
C A B
D/2
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS.
© Semtech, Inc. All Rights Reserved. An ISO-registered company. Semtech cannot assume responsibility for use of any circuitry other than
circuitry entirely embodied in a Semtech product. No circuit patent licenses are implied. Semtech reserves the right to change the circuitry and
specifications without notice at any time. Trademarks and Copyrights belong to their respective holders.
© 2007 Semtech Corporation
21
SC2443
Land Pattern - MLPQ-24
K
DIMENSIONS
(C)
G
H
Z
DIM
C
G
H
K
P
X
Y
Z
INCHES
(.156)
.122
.106
.106
.020
.010
.033
.189
MILLIMETERS
(3.95)
3.10
2.70
2.70
0.50
0.25
0.85
4.80
X
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. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
22