SC4502EVB [SEMTECH]
1.4Amp, 2MHz Step-Up Switching Regulator with Soft-Start; 1.4Amp ， 2MHz降压型开关调节器具有软启动
| 型号： | SC4502EVB |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | 1.4Amp, 2MHz Step-Up Switching Regulator with Soft-Start |
| 文件： | 总19页 (文件大小：407K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC4502/SC4502H
1.4Amp, 2MHz Step-Up Switching
Regulator with Soft-Start
POWER MANAGEMENT
Features
Description
The SC4502/SC4502H is a high-frequency current-mode Low saturation voltage switch: 210mV
step-up switching regulator with an integrated 1.4A
(250mV for the SC4502H)
power transistor. Its high switching frequency (program- Constant switching frequency current-mode control
mable up to 2MHz) allows the use of tiny surface-mount Programmable switching frequency up to 2MHz
external passive components. Programmable soft-start Soft-Start function
eliminates high inrush current during start-up. The inter- Input voltage ranges from 1.4V to 16V
nal switch is rated at 32V (40V for the SC4502H) mak- Output voltage up to 32V (40V for the SC4502H)
ing the converter suitable for high voltage applications Low shutdown current
such as Boost, SEPIC and Flyback.
Adjustable undervoltage lockout threshold
Small low-profile thermally enhanced lead free
package. This product is fully WEEE and RoHS
compliant.
The operating frequency of the SC4502/SC4502H can
be set with an external resistor. The ability to set the
operating frequency gives the SC4502/SC4502H design
flexibilities. A dedicated COMP pin allows optimization of
the loop response. The SC4502/SC4502H is available
in thermally enhanced 10-pin MLPD package.
Applications
Flat screen LCD bias supplies
TFT bias supplies
XDSL power supplies
Medical equipment
Digital video cameras
Portables devices
White LED power supplies
Typical Application Circuit
D1
L1
VIN
5V
VOUT
12V
10BQ015
Efficiency
R1
8
6,7
SW
FB
866K
95
IN
SHDN
SC4502
10.5 H, 700KHz
H, 1.4MHz
5.3µ
3
µ
2
1
OFF ON
90
85
80
75
70
65
60
55
50
C2
C1
2.2µF
10µF
10
SS
GND
4,5
COMP
ROSC
R2
R3
C4
100K
C3
9
C6
47nF
H, 2MHz
3.3µ
R4
All Capacitors are Ceramic.
VIN = 5V
VOUT = 12V
f (MHz) R3 (KΩ) R4 (KΩ) C4 (pF) C6 (pF)
L1 (µH)
0.0
0.1
0.2
0.3
0.4
0.5
0.7
1.4
2
33.2
59.0
73.2
23.7
9.53
5.36
1500
560
-
-
10.5 (Falco D08019)
5.3 (Sumida CDRH5D28)
3.3 (Coilcraft DO1813P)
Load Current (A)
330
22
Figure 1(b). Efficiencies of 5V to 12V Boost Converters at
700KHz, 1.4MHz and 2MHz.
Figure 1(a). 5V to 12V Boost Converter.
Revision: July 25, 2005
1
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SC4502/SC4502H
POWER MANAGEMENT
Absolute Maximum Rating
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.
Parameter
Symbol
VIN
Typ
-0.3 to 16
-0.3 to 32
-0.3 to 40
-0.3 to 2.5
-0.3 to VIN + 1
-40 to +85
40
Units
V
Supply Voltage
SW Voltage
VSW
VSW
VFB
V
SW Voltage (SC4502H)
FB Voltages
V
V
SHDN Voltage
VSHDN
TA
V
Operating Temperature Range
Thermal Resistance Junction to Ambient (MLPD-10)
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering)10 sec
ESD Rating (Human Body Model)
°C
°C/W
°C
°C
°C
V
θJA
TJ
160
TSTG
TLEAD
ESD
-65 to +150
260
2000
Electrical Characteristics
Electrical Characteristics
Unless other specified: VIN = 2V, SHDN = 1.5V, ROSC = 7.68kΩ, -40°C < TA = TJ < 85°C
Parameter
Test Conditions
Min
Typ
Max
1.4
Unit
Minimum Operating Voltage
Maximum Operating Voltage
1.3
V
V
16
TA = 25°C
1.224
1.217
1.242
1.260
1.267
V
Feedback Voltage
-40°C < TA < 85°C
1.5V < VIN < 16V
V
Feedback Voltage Line Regulation
FB Pin Bias Current
0.01
40
60
49
5
%
80
nA
µΩ−1
dB
µA
µA
mA
µA
MHz
%
Error Amplifier Transconductance
Error Amplifier Open-Loop Gain
COMP Source Current
V
V
FB = 1.1V
FB = 1.4V
COMP Sink Current
5
VIN Quiescent Supply Current
VIN Supply Current in Shutdown
Switching Frequency
VSHDN = 1.5V, VCOMP = 0 ( Not Switching )
VSHDN = 0
1.1
10
1.5
90
1.6
18
1.3
85
1.7
Maximum Duty Cycle
Minimum Duty Cycle
0
%
Switch Current Limit
1.4
2
A
Switch Saturation Voltage
ISW = 1.3A
ISW = 1.3A
2
210
250
340
390
mV
mV
Switch Saturation Voltage (SC4502H)
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SC4502/SC4502H
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless other specified: VIN = 2V, SHDN = 1.5V, ROSC = 7.68kΩ, -40°C < TA = TJ < 85°C
Parameter
Test Conditions
Min
Typ
0.01
1.1
-4.6
0
Max
1
Unit
mA
V
Switch Leakage Current
Shutdown Threshold Voltage
VSW = 5V
1.02
1.18
VSHDN = 1.2V
VSHDN = 0
µA
µA
µA
°C
Shutdown Pin Current
0.1
Soft-Start Charging Current
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
VSS = 0.3V
1.5
160
10
°C
Pin Configurations
Ordering Information
Device(1)(2)
SC4502MLTRT
SC4502HMLTRT
SC4502EVB
Package
MLPD-10
MLPD-10
Temp. Range( TA)
-40 to 85°C
TOP VIEW
-40 to 85°C
Evaluation Board
Evaluation Board
SC4502HEVB
Notes:
(1) Only available in tape and reel packaging. A reel
contains 3000 devices for MLP package.
(2) Lead free product. This product is fully WEEE and
RoHS compliant.
(10 Pin - MLPD, 3 x 3mm)
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SC4502/SC4502H
POWER MANAGEMENT
Pin Descriptions
Pin
Pin Name
Pin Function
1
COMP
The output of the internal transconductance error amplifier. This pin is used for loop compensation.
The inverting input of the error amplifier. Tie to an external resistive divider to set the output voltage.
2
FB
Shutdown Pin. The accurate 1.1V shutdown threshold and the 4.6uA shutdown pin current
hysteresis allow the user to set the undervoltage lockout threshold and hysteresis for the switching
regulator. Pulling this pin below 0.1V causes the converter to shut down to low quiescent current.
Tie this pin to IN if the UVLO and the shutdown features are not used. This pin should not be left
floating.
3
SHDN
4,5
6,7
GND
SW
Ground. Tie both pins to the ground plane. Pins 4 and 5 are not internally connected.
Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode.
8
9
IN
Power Supply Pin. Bypassed with capacitors close to the pin.
A resistor from this pin to the ground sets the switching frequency.
ROSC
Soft-Start Pin. A capacitor from this pin to the ground lengthens the start-up time and reduces start-
up current.
10
SS
Exposed Pad The exposed pad must be soldered to the ground plane on the PCB for good thermal conduction.
Block Diagram
IN
8
SW SW
6
7
4.6µA
SHDN
3
+
INTERNAL
SUPPLY
CMP
REG
-
1.1V
ENABLE
CLK
VOLTAGE
REFERENCE
THERMAL
SHUTDOWN
1.242V
+
-
R
S
FB
2
COMP
1
EA
-
+
Q
PWM
REG
1.5µA
SS
10
+
I-LIMIT
ILIM
-
REG_GOOD
ENABLE
R
SENSE
+
ISEN
-
+
+
Σ
CLK
SLOPE COMP
4
5
ROSC
9
OSCILLATOR
GND GND
Figure 2. SC4502/SC4502H Block Diagram.
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SC4502/SC4502H
POWER MANAGEMENT
Typical Characteristics
Switching Frequency
vs Temperature
Feedback Voltage vs Temperature
ROSC vs Switching Frequency
1.7
1.6
1.5
1.4
1.3
1.3
1.25
1.2
100
10
1
ROSC = 7.68KΩ
VIN = 2V
25ºC
VIN = 12V
V
IN = 2V
1.15
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Temperature (ºC)
Temperature (ºC)
Frequency (MHz)
Switch Saturation Voltage
vs Switch Current
Switch Saturation Voltage
vs Switch Current
Minimum VIN vs Temperature
500
400
300
200
100
0
500
400
300
200
100
0
1.5
1.4
1.3
1.2
1.1
1
SC4502H
SC4502
85ºC
25ºC
85ºC
25ºC
0
0.5
1
1.5
2
0
0.5
1
1.5
2
-50 -25
0
25
50
75 100 125
Switch Current (A)
Switch Current (A)
Temperature (ºC)
VIN Current in Shutdown
vs Input Voltage
Shutdown Threshold
vs Temperature
VIN Quiescent Current vs Temperature
1.3
50
40
30
20
10
0
1.20
1.15
1.10
1.05
1.00
Not Switching
VIN = 2V
1.2
VIN = 16V
-40ºC
125ºC
1.1
1
VIN = 2V
0.9
0.8
VSHDN = 0
-50 -25
0
25
50
75
100 125
0
5
10
15
20
-50 -25
0
25
50
75
100 125
Temperature (ºC)
Input Voltage (V)
Temperature (ºC)
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SC4502/SC4502H
POWER MANAGEMENT
Typical Characteristics
Shutdown Pin Current
vs Temperature
VIN Current vs SHDN Pin Voltage
VIN Current vs SHDN Pin Voltage
1.2
-3
-4
-5
-6
0.1
0.08
0.06
0.04
0.02
0
VIN = 2V
VIN = 2V
VSHDN = 1.25V
1
0.8
0.6
0.4
0.2
0
125ºC
25ºC
VIN = 2V
VIN = 12V
125ºC
-40ºC
-40ºC
0
0.5
1
1.5
0
0.2
0.4
0.6
0.8
1
1.2
-50
-25
0
25
50
75
100 125
SHDN Voltage (V)
SHDN Voltage (V)
Temperature (ºC)
Switch Current Limit
vs Temperature
Soft-Start Charging Current
vs Temperature
Transconductance vs Temperature
80
2
1.8
1.6
1.4
1.2
1
2.4
2.2
2
VSS = 0.3V
VIN = 2V
70
60
50
40
30
1.8
1.6
-50
-25
0
25
50
75
100 125
-50
-25
0
25
50
75
100
-50 -25
0
25
50
75
100 125
Temperature (ºC)
Temperature (ºC)
Temperature (ºC)
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SC4502/SC4502H
POWER MANAGEMENT
Operation
Applications Information
The SC4502/SC4502H is a programmable constant-
frequency peak current-mode step-up switching regulator
with an integrated power transistor. As shown in the block
diagram in Figure 2, the power transistor is turned on at
the trailing edge of the clock. Switch current is sensed
with an integrated sense resistor. The sensed current
signal is summed with the slope-compensating ramp
before compared to the output of the error amplifier EA.
The PWM comparator trip point determines the switch
turn-on pulse width. The current-limit comparator ILIM
turns off the power switch when the switch current
exceeds the 2A current-limit threshold. ILIM therefore
provides cycle-by-cycle current limit. Current-limit is not
affected by slope compensation because the current limit
comparator ILIM is not in the PWM signal path.
Setting the Output Voltage
An external resistive divider R1 and R2 with its center tap
tied to the FB pin (Figure 3) sets the output voltage.
VOUT
1.242V
R1 = R2
−1
(1)
VOUT
SC4502/SC4502H
FB
R1
40nA
2
R2
Figure 3. The Output Voltage is set with a Resistive Divider
Current-mode switching regulators utiilize a dual-loop
feedback control system. In the SC4502/SC4502H the
amplifier output COMP controls the peak inductor current.
This is the inner current loop. The double reactive poles
of the output LC filter are reduced to a single real pole by
the inner current loop, easing loop compensation. Fast
transient response can be obtained with a simple Type-2
compensation network. In the outer loop, the error amplifier
regulates the output voltage.
The input bias current of the error amplifier will introduce
an error of:
∆VOUT 40nA
(
R1//R2
)
100
=
%
(2)
VOUT
1.242V
The percentage error of a VOUT = 5V converter with R1 =
100KΩ and R2 = 301KΩ is
The switching frequency of the SC4502/SC4502H can
be programmed up to 2MHz with an external resistor
from the ROSC pin to the ground. For converters requiring
extremely low or high duty cycles, the operating frequency
can be lowered to maintain the necessary minimum on
time or the minimum off time.
∆VOUT
VOUT
40nA
(
100KΩ // 301KΩ
)
100
=
= 0.24%
1.242V
Operating Frequency and Efficiency
Switching frequency of SC4502/SC4502H is set with
an external resistor from the ROSC pin to the ground. A
graph showing the relationship between ROSC and
switching frequency is given in the “Typical
Characteristics”.
The SC4502/SC4502H requires a minimum input of 1.4V
to operate. A voltage higher than 1.1V at the shutdown
pin enables the internal linear regulator REG in the
SC4502/SC4502H. After VREG becomes valid, the soft-
start capacitor is charged with a 1.5µA current source. A
PNP transistor clamps the output of the error amplifier
as the soft-start capacitor voltage rises. Since the COMP
voltage controls the peak inductor current, the inductor
current is ramped gradually during soft-start, preventing
high input start-up current. Under fault conditions
(VIN<1.4V or over temperature) or when the shutdown
pin is pulled below 1.1V, the soft-start capacitor is
discharged to ground. Pulling the shutdown pin below 0.1V
reduces the total supply current to 10µA.
High frequency operation reduces the size of passive
components but switching losses are higher. The efficiencies
of 5V to 12V converters operating at 700KHz, 1.4MHz
and 2MHz are plotted in Figure 1(b) for SC4502.
Duty Cycle
The duty cycle D of a boost converter in continuous
conduction mode is:
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
V
It is worth noting that IOUTMAX is directly proportional to the
IN
1−
VOUT + VD
D =
V
IN
ratio of
. Equation (4) over-estimates the maximum
VCESAT
1−
(3)
VOUT
VOUT + VD
output current at high frequencies (>1MHz) since
switching losses are neglected in its derivation.
Nevertheless it is a useful first-order approximation.
where VCESAT is the switch saturation voltage and VD is the
voltage drop across the rectifying diode.
Using VCESAT = 0.3V, VD = 0.5V and ILIM = 1.4A in (3) and
(4), the maximum output currents for three VIN and VOUT
combinations are shown in Table 1.
Maximum Output Current
In a boost switching regulator the inductor is connected to
the input. The DC inductor current is the input current.
When the power switch is turned on, the inductor current
flows through the switch. When the power switch is off,
the inductor current flows through the rectifying diode to
the output. The maximum output current is the average
diode current. The diode current waveform is trapezoidal
with pulse width (1 – D)T (Figure 4). The output current
available from a boost converter therefore depends on
the converter operating duty cycle. The power switch
current in the SC4502/SC4502H is internally limited to
2A. This is also the maximum inductor or the input current.
By estimating the conduction losses in both the switch
and the rectifying diode, an expression of the maximum
available output current of a boost converter can be
derived as follows:
D
VIN ( V )
2.5
VOUT ( V )
IOUTMAX ( A )
0.25
12
5
0.820
0.423
0.615
3.3
0.80
5
12
0.53
Table 1. Calculated Maximum Output Current [ Equation (4)]
Considerations for High Frequency Operation
The operating duty cycle of a boost converter decreases
as VIN approaches VOUT. The PWM modulating ramp in a
current-mode switching regulator is the sensed current
signal. This current ramp is absent unless the switch is
turned on. The intersection of this ramp with the output
of the voltage feedback error amplifier determines the
switch pulse width. The propagation delay time required
to immediately turn off the switch after it is turned on is
the minimum switch on time. Regulator closed-loop
measurement shows that the SC4502/SC4502H has a
minimum on time of about 150ns at room temperature.
The power switch in the SC4502/SC4502H is either not
turned on at all or on for at least 150ns. If the required
switch on time is shorter than the minimum on time, the
regulator will either skip cycles or it will start to jitter.
ILIM
V
D
45
VD − D VD − VCESAT
( )
−
IN
IOUTMAX
=
1−
(4)
VOUT
V
IN
where ILIM is the switch current limit.
I
IN
Inductor Current
Switch Current
Diode Current
ON
OFF
ON
Example: Determine the maximum operating frequency
of a Li-ion cell to 5V converter using the SC4502.
Assuming that VD=0.5V, VCESAT=0.3V and VIN=2.6V - 4.2V,
the minimum duty ratio can be found using (3).
DT
(1-D)T
ON
I
OUT
ON
OFF
OFF
ON
4.2
1−
5 + 0.5
DMIN
=
= 0.25
0.3
5 + 0.5
Figure 4. Current Waveforms in a Boost Regulator
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
operating in continuous-conduction mode is
V −V
The absolute maximum operating frequency of the
D
(
)
DMIN
0.25
IN
CESAT
∆IL =
(5)
=
= 1.67MHz
. The
converter is therefore
f L
150ns 150ns
where f is the switching frequency and L is the inductance.
Substituting (3) into (5) and neglecting VCESAT
actual operating frequency needs to be lower to allow
for modulating headroom.
,
The power transistor inside the SC4502/SC4502H is
turned off every switching cycle for an interval determined
by the discharge time of the oscillator ramp plus the
propagation delay of the power switch. This minimum off
time limits the maximum duty cycle of the regulator at a
given switching frequency. A boost converter with high
V
V
IN
IN
∆IL =
1−
(6)
f L
VOUT + VD
In peak current-mode control, the slope of the modulating
(sensed switch current) ramp should be steep enough to
lessen jittery tendency but not so steep that large flux
swing decreases efficiency. Inductor ripple current DIL
VOUT
ratio requires long switch on time and high duty cycle.
V
In
between 25%-40% of the peak inductor current limit is a
good compromise. Inductors so chosen are optimized in
size and DCR. Setting ∆IL = 0.3•(1.4A) = 0.42A, VD=0.5V
in (6),
If the required duty cycle is higher than the attainable
maximum, the converter will operate in dropout. (Dropout
is the condition in which the regulator cannot attain its
set output voltage below current limit.)
V
V
V
V
IN
IN
IN
IN
L =
1 −
=
1 −
(7)
The minimum off times of closed-loop boost converters set
to various output voltages were measured by lowering their
input voltages until dropout occurs. It was found that the
minimum off time of the SC4502/SC4502H ranged from
80ns to 110ns at room temperature.
f ∆IL
VOUT + VD
0.42A f
VOUT + 0.5V
where L is in µH and f is in MHz.
Equation (6) shows that for a given VOUT, ∆IL is the highest
VOUT + VD
(
)
V =
when
. If VIN varies over a wide range, then
Beware of dropout while operating at very low input
voltages (1.5V-2V) with off time approaching 110ns.
Shorten the PCB trace between the power source and
the device input pin, as line drop may be a significant
percentage of the input voltage. A regulator in dropout
may appear as if it is in current limit. The cycle-by-cycle
current limit of the SC4502/SC4502H is duty-cycle and
input voltage invariant and is typically 2A. If the switch
current limit is not at least 1.4A, then the converter is
likely in dropout. The switching frequency should then be
lowered to improve controllability.
IN
2
choose L based on the nominal input voltage.
The saturation current of the inductor should be 20%-
30% higher than the peak current limit (2A). Low-cost
powder iron cores are not suitable for high-frequency
switching power supplies due to their high core losses.
Inductors with ferrite cores should be used.
Input Capacitor
The input current in a boost converter is the inductor
current, which is continuous with low RMS current ripples.
A 2.2µF-4.7µF ceramic input capacitor is adequate for
most applications.
Both the minimum on time and the minimum off time
reduce control range of the PWM regulator. Bench
measurement showed that reduced modulating range
started to be a problem at frequencies over 2MHz. Although
the oscillator is capable of running well above 2MHz,
controllability limits the maximum operating frequency.
Output Capacitor
Both ceramic and low ESR tantalum capacitors can be
used as output filtering capacitors. Multi-layer ceramic
capacitors, due to their extremely low ESR (<5mΩ), are
the best choice. Use ceramic capacitors with stable
Inductor Selection
The inductor ripple current ∆IL of a boost converter
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
temperature and voltage characteristics. One may be Volts higher than the output voltage. For switching
tempted to use Z5U and Y5V ceramic capacitors for regulators operating at low duty cycles (i.e. low output
output filtering because of their high capacitance and voltage to input voltage conversion ratios), it is beneficial
small sizes. However these types of capacitors have high to use rectifying diodes with somewhat higher RMS
temperature and high voltage coefficients. For example, current ratings (thus lower forward voltages). This is
the capacitance of a Z5U capacitor can drop below 60% because the diode conduction interval is much longer
than that of the transistor. Converter efficiency will be
improved if the voltage drop across the diode is lower.
of its room temperature value at –25°C and 90°C. X5R
ceramic capacitors, which have stable temperature and
voltage coefficients, are the preferred type.
The rectifying diodes should be placed close to the SW
pins of the SC4502/SC4502H to minimize ringing due
to trace inductance. Surface-mount equivalents of
1N5817, 1N5819, MBRM120, MBR0520 (ON Semi) and
10BQ015, 10BQ040 (IRF) are all suitable.
The diode current waveform in Figure 4 is discontinuous
with high ripple-content. In a buck converter, the inductor
ripple current ∆IL determines the output ripple voltage.
The output ripple voltage of a boost regulator is however
much higher and is determined by the absolute value of
the inductor current. Decreasing the inductor ripple
current does not appreciably reduce the output ripple
voltage. The current flowing in the output filter capacitor
is the difference between the diode current and the
output current. This capacitor current has a RMS value
of:
Soft-Start
Soft-start prevents a DC-DC converter from drawing
excessive current (equal to the switch current limit) from
the power source during start up. If the soft-start time is
made sufficiently long, then the output will enter regulation
without overshoot. An external capacitor from the SS pin
to the ground and an internal 1.5µA charging current
source set the soft-start time. The soft-start voltage ramp
at the SS pin clamps the error amplifier output. During
regulator start-up, COMP voltage follows the SS voltage.
The converter starts to switch when its COMP voltage
exceeds 0.7V. The peak inductor current is gradually
increased until the converter output comes into regulation.
If the shutdown pin is forced below 1.1V or if a fault
situation is detected, then the soft-start capacitor will
be discharged to ground immediately.
VOUT
IOUT
−1
(8)
V
IN
If a tantalum capacitor is used, then its ripple current rating
in addition to its ESR will need to be considered.
When the switch is turned on, the output capacitor supplies
the load current IOUT (Figure 4). The output ripple voltage
due to charging and discharging of the output capacitor is
therefore:
The SS pin can be left open if soft-start is not required.
Shutdown
IOUT D T
=
∆VOUT
(9)
COUT
The input voltage and shutdown pin voltage must be greater
than 1.4V and 1.1V respectively to enable the SC4502/
SC4502H. Forcing the shutdown pin below 1.1V stops
the SC4502/SC4502H from switching. Pulling this pin
below 0.1V completely shuts off the SC4502/SC4502H.
The total VIN shutdown current decreases to 10µA at 2V.
Figure 5 shows several ways of interfacing the control
logic to the shutdown pin. Beware that the shutdown pin
is a high impedance pin. It should always be driven from
a low-impedance source or tied to a resistive divider.
Floating the shutdown pin will result in undefined voltage.
In Figure 5(c) the shutdown pin is driven from a logic
For most applications, a 10µF - 22µF ceramic capacitor
is sufficient for output filtering. It is worth noting that the
output ripple voltage due to discharging of a 10µF ceramic
capacitor (9) is higher than that due to its ESR.
Rectifying Diode
For high efficiency, Schottky barrier diodes should be used
as rectifying diodes for the SC4502/SC4502H. These
diodes should have a RMS current rating between 0.5A
and 1A with a reverse blocking voltage of at least a few
2005 Semtech Corp.
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
IN
IN
SC4502
SC4502
SC4502H
SC4502H
SHDN
SHDN
(a)
(b)
V
IN
IN
IN
SC4502
SC4502H
SC4502
1N4148
SC4502H
SHDN
SHDN
(c)
(d)
Figure 5. Methods of Driving the Shutdown Pin
(a) Directly Driven from a Logic Gate
(b) Driven from an Open-drain N-channel MOSFET or an Open-Collector NPN Transistor (VOL < 0.1V)
(c) Driven from a Logic Gate with VOH > VIN
(d) Combining Shutdown with Programmed UVLO (See Section Below).
gate whose VOH is higher than the supply voltage of the in conjunction with a resistive voltage divider to raise the
SC4502/SC4502H. The diode clamps the maximum UVLO threshold and to add an UVLO hysteresis. Figure 6
shutdown pin voltage to one diode voltage above the shows the scheme. Both VH and VL (the desired upper
input power supply.
and the lower UVLO threshold voltages) are determined
by the 1.1V threshold crossings, VH and VL are therefore:
Programming Undervoltage Lockout
R3
R4
VH = 1+
1.1V
( )
The SC4502/SC4502H has an internal VIN undervoltage
lockout (UVLO) threshold of 1.4V. The transition from idle
to switching is abrupt but there is no hysteresis. If the
input voltage ramp rate is slow and the input bypass is
limited, then sudden turn on of the power transistor will
cause a dip in the line voltage. Switching will stop if VIN
falls below the internal UVLO threshold. The resulting
output voltage rise may be non-monotonic. The 1.1V
disable threshold of the SC4502/SC4502H can be used
(10)
(11)
VL = VH − VHYS = VH −IHYSR3
Re-arranging,
VHYS
R3 =
IHYS
R3
R4 =
VH
1.1V
− 1
(12)
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2005 Semtech Corp.
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
VL = VH − VHYS = 2.75V − 0.69V = 2.06V > 1.4V .
IN
6/8
Frequency Compensation
Figure 7 shows the equivalent circuit of a boost converter
using the SC4502/SC4502H. The output filter capacitor
and the load form an output pole at frequency:
I
HYS
4.6µA
R3
SWITCH CLOSED
WHEN Y = “1”
2 IOUT
2
ωp2
=
=
(13)
VOUT
VOUT C2 ROUT C2
SHDN
3
+
-
Y
ROUT
=
where C2 is the output capacitance and
the equivalent load resistance.
is
IOUT
1.1V
R4
COMPARATOR
SC4502/SC4502H
The zero formed by C2 and its equivalent series resistance
(ESR) is neglected due to low ESR of the ceramic output
capacitor.
Figure 6. Programmable Hysteretic UVLO Circuit
There is also a right half plane (RHP) zero with angular
frequency:
with VL > 1.4V .
ROUT
=
(
1−D 2
L
)
Example: Increase the turn on voltage of a VIN = 3.3V boost
converter from 1.4V to 2.75V.
ωZ2
(14)
Using VH = 2.75V and R4 = 100KΩ in (12),
R3 = 150KΩ .
ωz2 decreases with increasing duty cycle D and increasing
IOUT. Using the 5V to 12V boost regulator (1.4MHz) in
Figure 1(a) as an example,
The resulting UVLO hysteresis is:
5V
0.5A
ROUT
≥
= 10Ω
VHYS = IHYSR3 = 4.6µA • 150KΩ = 0.69V
The turn off voltage is:
I
OUT
V
IN
POWER
STAGE
V
OUT
ESR
C2
R
R1
R2
C5
OUT
FB
-
+
COMP
Gm
R3
C4
1.242V
RO
C6
VOLTAGE
REFERENCE
Figure 7. Simplified Block Diagram of a Boost Converter
12
2005 Semtech Corp.
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SC4502/SC4502H
POWER MANAGEMENT
Applications Information
1
1
ωp1 =
=
ROC4 4.7MΩ • 560pF
5
1−
−1
12 + 0.5
= 380 rads
60Hz
D =
= 0.62
0.3
1−
C4 and R3 also forms a zero with angular frequency:
12 + 0.5
1
1
Therefore
ωz1 =
=
R3C4 59KΩ • 560pF
−1
2
= 30.3 Krads
4.8KHz
−1
ωp2 ≤
= 20Krads
3.18KHz
43.4KHz
(
10Ω) (10µF
)
and
ωz2
The poles p1, p2 and the RHP zero z2 all increase phase
shift in the loop response. For stable operation, the overall
loop gain should cross 0dB with -20dB/decade slope. Due
to the presence of the RHP zero, the crossover frequency
2
10Ω
(
1− 0.62
)
−1
≥
= 272Krads
5.3µH
z2
The spacing between p2 and z2 is the closest when the
converter is delivering the maximum output current from
the lowest VIN. This represents the worst-case
compensation condition. Ignoring C5 and C6 for the
moment, C4 forms a low frequency pole with the
equivalent output resistance RO of the error amplifier:
should not be higher than
. Placing z1 near p2 nulls its
3
effect and maximizes loop bandwidth. Thus
VOUT C2
R3C4 ≈
(15)
2 IOUT(MAX)
AmplifierOpenLoop Gain
Transconductance
49dB
R3 determines the mid-band loop gain of the converter.
Increasing R3 increases the mid-band gain and the
crossover frequency. However it reduces the phase
margin. The values of R3 and C4 can be determined
RO =
=
= 4.7MΩ
60µΩ−1
GND
R3
C6
R2
C3
R4
C4
U1
C1
SHDN
L1
R1
C5
C2
D1
VOUT
VIN
Figure 8. Suggested PCB Layout for the SC4502/SC4502H. Notice that there is no
via directly under the device. All vias are 12mil in diameter.
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2005 Semtech Corp.
13
SC4502/SC4502H
POWER MANAGEMENT
Applications Information
empirically by observing the inductor current and the
output voltage during load transient. Compensation is
optimized when the largest R3 and the smallest C4without
producing ringing or excessive overshoot in its inductor
current and output voltage are found. Figures 9(b), 10(c),
11(b) and 11(c) show load transient responses of
empirically optimized DC-DC converters. In a battery-
operated system, compensating for the minimum VIN and
the maximum load step will ensure stable operation over
the entire input voltage range.
The input bypass capacitors should also be placed close
to the input pins. Shortening the trace at the SW node
reduces the parasitic trace inductance. This not only
reduces the EMI but also decreases the sizes of the
switching voltage spikes and glitches.
Figure 8 shows how various external components are
placed around the SC4502/SC4502H. The frequency-
setting resistor should be placed near the ROSC pin with
a short ground trace on the PC board. These precautions
reduce switching noise pickup at the ROSC pin.
C5 adds a feedforward zero to the loop response. In some
cases, it improves the transient speed of the converter.
C6 rolls off the gain at high frequency. This helps to
To achieve a junction to ambient thermal resistance (θJA)
of 40°C/W, the exposed pad of the SC4502/SC4502H
should be properly soldered to a large ground plane. Use
only 12mil diameter vias in the ground plane if necessary.
Avoid using larger vias under the device. Molten solder
may seep through large vias during reflow, resulting in
poor adhesion, poor thermal conductivity and low
reliability.
stabilize the loop. C5 and C6 are often not needed.
Board Layout Considerations
In a step-up switching regulator, the output filter
capacitor, the main power switch and the rectifying diode
carry switched currents with high di/dt. For jitter-free
operation, the size of the loop formed by these
components should be minimized. Since the power switch
is integrated inside the SC4502/SC4502H, grounding
the output filter capacitor next to the SC4502/SC4502H
ground pin minimizes size of the high di/dt current loop.
Typical Application Circuits
D1
L1
VIN
VOUT
5.6µH
3.3V
12V, 0.3A
10BQ015
R1
8
6,7
SW
FB
174K
IN
SHDN
SC4502
3
2
1
OFF ON
C2
10µF
C1
10
SS
GND
4,5
COMP
ROSC
9
2.2µF
R2
R3
20K
40.2K
C3
47nF
R4
C4
9.31K
1.8nF
40µs/div
Upper Trace : Output Voltage, AC Coupled, 1V/div
Lower Trace : Inductor Current, 0.5A/div
L1: Sumida CR43
Figure 9(a). 1.35 MHz All Ceramic Capacitor 3.3V to 12V Boost
Converter.
Figure 9(b). Load Transient Response of the Circuit in Figure
9(a). ILOAD is switched between 0.1A and 0.3A
at 1A/µs.
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SC4502/SC4502H
POWER MANAGEMENT
Typical Application Circuits
Efficiency vs Load Current
95
90
85
80
75
70
65
60
55
50
D1
L1
VOUT
2.6 - 4.2V
1.5MHz
2.5µH
5V, 0.5A
10BQ015
R1
8
IN
SHDN
6,7
SW
FB
301K
VIN = 4.2V
VIN = 3.6V
3
2
OFF ON
1-CELL
C1
C2
SC4502
LI-ION
10µF
2.2µF
10
1
SS
GND
4,5
COMP
ROSC
9
VIN = 2.6V
R2
R3
100K
34.8K
C3
VOUT = 5V
R4
47nF
C4
7.68K
1nF
0.001
0.010
0.100
1.000
L1: Sumida CDRH5D28
Load Current (A)
Figure 10(a). 1.5 MHz All Ceramic Capacitor Single Li-ion Cell
to 5V Boost Converter.
Figure 10(b). Efficiency of the Single Li-ion Cell to 5V Boost
Converter in Figure 10(a).
VIN=2.6V
40µs/div
Upper Trace : Output Voltage, AC Coupled, 0.5V/div
Lower Trace : Inductor Current, 0.5A/div
Figure 10(c). Load Transient Response of the Circuit in Figure .
10(a). ILOAD is switched between 90mA and 0.5A
at 1A/µs.
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SC4502/SC4502H
POWER MANAGEMENT
Typical Application Circuits
4-CELL
3.6 - 6V
VOUT
C6
L1
D1
5V, 0.5A
3.3µH
2.2µF
10BQ015
R1
8
6,7
SW
FB
60.4K
IN
SHDN
SC4502
SS
GND
4,5
3
2
1
OFF ON
C2
C1
2.2µF
10µF
10
COMP
ROSC
L2
R2
R3
3.3µH
20K
35.7K
C6
C3
9
22pF
47nF
R4
C4
7.68K
1.5nF
L1 and L2: Coiltronics DRQ73-3R3
Figure 11(a). 1.5 MHz All Ceramic Capacitor 4-Cell to 5V SEPIC Converter.
VIN=3.6V
VIN=6V
40µs/div
40µs/div
Upper Trace : Output Voltage, AC Coupled, 0.5V/div
Lower Trace : Input Inductor Current, 0.2A/div
Upper Trace : Output Voltage, AC Coupled, 0.5V/div
Lower Trace : Input Inductor Current, 0.2A/div
Figure 11(b). Load Transient Response of the Circuit in Figure
11(a). ILOAD is switched between 150mA and
450mA at 1A/µs.
Figure 11(c). Load Transient Response of the Circuit in Figure
11(a). ILOAD is switched between 250mA and
700mA at 1A/µs.
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SC4502/SC4502H
POWER MANAGEMENT
Typical Application Circuits
D2
D3
D4
D5
OUT2
23V (10mA)
C5
0.1µF
C6
C7
0.1
C8
0.1 F
µ
µ
F
1 F
µ
L1
D1
3.3V
OUT1
8V (0.4A)
3.3µH
10BQ015
R5
R1
8
6,7
SW
FB
150K
274K
IN
SHDN
SC4502
3
2
1
C2
C1
2.2µF
10µF
C9
10
SS
GND
4,5
COMP
ROSC
9
0.1µF
R6
R2
R3
100K
49.9K
33.2K
C3
47nF
R4
C4
7.68K
1.5nF
D7
D6
OUT3
-8V (10mA)
C10
1µF
L1 : Coiltronics SD18-3R3
D2 - D7 : BAT54S
Figure 12(a). 1.5MHz Triple-Output TFT Power Supply.
C H 4
C H 4
C H 1
C H 1
C H 2
C H 3
C H 2
C H 3
2ms/div
4ms/div
CH1 : OUT1 Voltage, 5V/div
CH2 : OUT2 Voltage, 10V/div
CH3 : OUT3 Voltage, 5V/div
CH4 : SHDN Voltage, 2V/div
CH1 : OUT1 Voltage, 5V/div
CH2 : OUT2 Voltage, 10V/div
CH3 : OUT3 Voltage, 5V/div
CH4 : Input Voltage, 2V/div
Figure 12(c). TFT Power Supply Start-up Transient as the
SHDN Pin is stepped from 0 to 2V.
Figure 12(b). TFT Power Supply VIN Start-up Transient.
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2005 Semtech Corp.
17
SC4502/SC4502H
POWER MANAGEMENT
Typical Application Circuits
Efficiency at 14V input
D1
L1
VIN
14V
VOUT
35V
90
85
80
75
70
65
60
55
50
1.4MHz 6.8µH
SS14
R1
8
6,7
SW
FB
17.4K
IN
SHDN
SC4502H
3
2
1
OFF ON
C2
C1
1.0MHz 10µH
10µF
2.2µF
10
SS
GND
4,5
COMP
ROSC
9
R3
R2
5.11K
649
C3
47nF
R4
C4
1.5nF
0
0.05
0.1
Load (A)
0.15
0.2
Figure 13(a). All Ceramic Capacitor High Voltage Application
Figure 13(b). Efficiency of the All Ceramic Capacitor High
Voltage Application
L1
R4(KΩ)
f
(MHz)
1.0
15.8
10
10uH IHLP-2525BD_01
6.8uH IHLP-2525BD_01
1.4
2005 Semtech Corp.
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SC4502/SC4502H
POWER MANAGEMENT
Outline Drawing - MLPD-10, 3 x 3mm
DIMENSIONS
INCHES MILLIMETERS
A
E
B
E
DIM
A
MIN NOM MAX MIN NOM MAX
-
-
-
-
.031
A1 .000
.039 0.80
.002 0.00
1.00
0.05
-
-
(.008)
-
-
(0.20)
A2
b
.007 .009 .011 0.18 0.23 0.30
.074 .079 .083 1.87 2.02 2.12
.042 .048 .052 1.06 1.21 1.31
.114 .118 .122 2.90 3.00 3.10
C
D
E
PIN 1
INDICATOR
e
.020 BSC
0.50 BSC
(LASER MARK)
L
N
.012 .016 .020 0.30 0.40 0.50
10
.003
.004
10
0.08
0.10
aaa
bbb
A
C
SEATING
PLANE
aaa
C
A1
A2
C
1
2
LxN
D
N
bxN
bbb
e
C
A
B
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS.
Land Pattern - MLPD-10, 3 x 3mm
DIMENSIONS
K
DIM
INCHES
(.112)
.075
MILLIMETERS
(2.85)
1.90
1.40
2.20
0.50
0.30
0.95
3.80
C
G
H
K
P
X
Y
Z
.055
H
G
Y
(C)
Z
.087
.020
.012
.037
X
.150
P
NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
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
2005 Semtech Corp.
19
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