© Semiconductor Components Industries, LLC, 2008
October, 2008 Rev. 19
1Publication Order Number:
CS51411/D
CS51411, CS51412,
CS51413, CS51414
1.5 A, 260 kHz and 520 kHz,
Low Voltage Buck
Regulators with External
Bias or Synchronization
Capability
The CS5141X products are 1.5 A buck regulator ICs. These devices
are fixedfrequency operating at 260 kHz and 520 kHz. The regulators
use the V2control architecture to provide unmatched transient
response, the best overall regulation and the simplest loop
compensation for today’s highspeed logic. These products
accommodate input voltages from 4.5 V to 40 V.
The CS51411 and CS51413 contain synchronization circuitry. The
CS51412 and CS51414 have the option of powering the controller
from an external 3.3 V to 6.0 V supply in order to improve efficiency,
especially in high input voltage, light load conditions.
The onchip NPN transistor is capable of providing a minimum of
1.5 A of output current, and is biased by an external “boost” capacitor
to ensure saturation, thus minimizing onchip power dissipation.
Protection circuitry includes thermal shutdown, cyclebycycle
current limiting and frequency foldback. The CS51411 and CS51413
are functionally pincompatible with the LT1375. The CS51412 and
CS51414 are functionally pincompatible with the LT1376.
Features
V2 Architecture Provides Ultrafast Transient Response, Improved
Regulation and Simplified Design
2.0% Error Amp Reference Voltage Tolerance
Switch Frequency Decrease of 4:1 in Short Circuit Conditions
Reduces Short Circuit Power Dissipation
BOOST Pin Allows “Bootstrapped” Operation to Maximize
Efficiency
Sync Function for Parallel Supply Operation or Noise Minimization
Shutdown Lead Provides PowerDown Option
85 mA Quiescent Current During PowerDown
Thermal Shutdown
SoftStart
PinCompatible with LT1375 and LT1376
PbFree Packages are Available
5141x = Device Code
x = 1, 2, 3 or 4
A = Assembly Location
L, WL = Wafer Lot
Y, YY = Year
W, WW = Work Week
y = E or G
G=PbFree Package
SOIC8
D SUFFIX
CASE 751
1
8
MARKING DIAGRAMS
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 18 of this data sheet.
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5141x
ALYWy
G
1
8
1
18
18LEAD DFN
MN SUFFIX
CASE 505
CS5141xy
AWLYYWW G
G
118
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2
PIN CONNECTIONS
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
BOOST
VIN
VIN
VIN
Vsw
VSW
VSW
SHDNB
NC
NC
VC
VFB
NC
NC
GND
NC
NC
SYNC
18Lead DFN
SYNCSHDNB
18
GNDVSW
VFB
VIN
VC
BOOST
SHDNBBIAS
18
GNDVSW
VFB
VIN
VC
BOOST
CS51412/4
CS51411/3 CS51411/3
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
BOOST
VIN
VIN
VIN
Vsw
VSW
VSW
BIAS
NC
NC
VC
VFB
NC
NC
GND
NC
NC
SHDNB
18Lead DFN
CS51412/4
PACKAGE PIN DESCRIPTION
SOIC8
Package Pin #
DFN18
Package Pin # Pin Symbol Function
1 1 BOOST The BOOST pin provides additional drive voltage to the onchip NPN
power transistor. The resulting decrease in switch on voltage increases
efficiency.
22, 3, 4 VIN This pin is the main power input to the IC.
35, 6, 7 VSW This is the connection to the emitter of the onchip NPN power transistor
and serves as the switch output to the inductor. This pin may be
subjected to negative voltages during switch offtime. A catch diode is
required to clamp the pin voltage in normal operation. This node can
stand 1.0 V for less than 50 ns during switch node flyback.
4
(CS51412/CS51414)
8 BIAS The BIAS pin connects to the onchip power rail and allows the IC to run
most of its internal circuitry from the regulated output or another low
voltage supply to improve efficiency. The BIAS pin is left floating if this
feature is not used.
5
(CS51411/CS51413) 10 SYNC
This pin provides the synchronization input.
5
(CS51412/CS51414)
4
(CS51411/CS51413)
10
(CS51412/CS51414)
8
(CS51411/CS51413)
SHDNB Shutdown_bar input. This is an activelow logical input, TTL compatible,
with an internal pullup current source. The IC goes into sleep mode,
drawing less than 85 mA when the pin voltage is pulled below 1.0 V. This
pin may be left floating in applications where a shutdown function is not
required.
6 13 GND Power return connection for the IC.
7 16 VFB The FB pin provides input to the inverting input of the error amplifier. If
VFB is lower than 0.29 V, the oscillator frequency is divided by four, and
current limit folds back to about 1 A. These features protect the IC under
severe overcurrent or short circuit conditions.
8 17 VCThe VC pin provides a connection point to the output of the error
amplifier and input to the PWM comparator. Driving of this pin should be
avoided because onchip test circuitry becomes active whenever
current exceeding 0.5 mA is forced into the IC.
9, 11, 12, 14, 15, 18 NC No Connection
CS51411, CS51412, CS51413, CS51414
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PRODUCT SELECTION GUIDE
Part Number Frequency Temperature Range Bias/Sync
CS51411E 260 kHz 40°C to 85°C Sync
CS51411G 260 kHz 0°C to 70°C Sync
CS51412E 260 kHz 40°C to 85°C Bias
CS51412G 260 kHz 0°C to 70°C Bias
CS51413E 520 kHz 40°C to 85°C Sync
CS51413G 520 kHz 0°C to 70°C Sync
CS51414E 520 kHz 40°C to 85°C Bias
CS51414G 520 kHz 0°C to 70°C Bias
SYNC
VFB
VSW
2
GND
SHDNB CS51411/3
1N4148
3.3 V
D3
15 mH
VIN
100 mF
100 mF
0.1 mF
Figure 1. Application Diagram, 4.5 V 16 V to 3.3 V @ 1.0 A Converter
C1
C3
R1
R2
C4
0.1 mF
SYNC
Shutdown
L1
C2
4.5 V 16 V
D1
205
127
1
3
768
4
5
1N5821
BOOST
U1
VC
MAXIMUM RATINGS
Rating Value Unit
Operating Junction Temperature Range, TJ40 to 150 °C
Lead Temperature Soldering: Reflow for Leaded: (SMD styles only) (Note 1)
Reflow for PbFree: (SMD styles only) (Note 2)
230 peak
260 peak
(Note 3)
°C
Storage Temperature Range, TS65 to +150 °C
ESD Damage Threshold (Human Body Model) 2.0 kV
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
1. 60150 second above 183°C, 30 second maximum at peak.
2. 60150 second above 217°C, 40 second maximum at peak.
3. +5°C/0°C allowable conditions, applies to both Pb and PbFree Devices.
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MAXIMUM RATINGS
Pin Name VMax VMIN ISOURCE ISINK
VIN 40 V 0.3 V N/A 4.0 A
BOOST 40 V 0.3 V N/A 100 mA
VSW 40 V 0.6 V/1.0 V, t < 50 ns 4.0 A 10 mA
VC7.0 V 0.3 V 1.0 mA 1.0 mA
SHDNB 7.0 V 0.3 V 1.0 mA 1.0 mA
SYNC 7.0 V 0.3 V 1.0 mA 1.0 mA
BIAS 7.0 V 0.3 V 1.0 mA 50 mA
VFB 7.0 V 0.3 V 1.0 mA 1.0 mA
GND 7.0 V 0.3 V 50 mA 1.0 mA
ELECTRICAL CHARACTERISTICS (40°C < TJ < 125°C (CS51411E/2E/3E/4E); 40°C < TA < 85°C (CS51411E/2E/3E/4E);
0°C < TA < 70°C (CS51411G/2G/3G/4G), 4.5 V< VIN < 40 V; unless otherwise specified.)
Characteristic Test Conditions Min Typ Max Unit
Oscillator
Operating Frequency CS51411/CS51412 224 260 296 kHz
Operating Frequency CS51413/CS51414 446 520 594 kHz
Frequency Line Regulation 0.05 0.15 %/V
Maximum Duty Cycle 85 90 95 %
VFB Frequency Foldback Threshold 0.29 0.32 0.36 V
PWM Comparator
Slope Compensation Voltage CS51411/CS51412, Fix VFB, DVC/DTON
CS51413/CS51414
8.0
25
17
50
26
75
mV/ms
mV/ms
Minimum Output Pulse Width CS51411/CS51412, VFB to VSW
CS51413/CS51414, VFB to VSW
150
300
230
ns
ns
Power Switch
Current Limit VFB > 0.36 V 1.6 2.3 3.0 A
Foldback Current VFB < 0.29 V 0.9 1.5 2.1 A
Saturation Voltage IOUT = 1.5 A, VBOOST = VIN + 2.5 V 0.4 0.7 1.0 V
Current Limit Delay (Note 4) 120 160 ns
Error Amplifier
Internal Reference Voltage 1.244 1.270 1.296 V
Reference PSRR (Note 4) 40 dB
FB Input Bias Current 0.02 0.1 mA
Output Source Current VC = 1.270 V, VFB = 1.0 V 15 25 35 mA
Output Sink Current VC = 1.270 V, VFB = 2.0 V 15 25 35 mA
Output High Voltage VFB = 1.0 V 1.39 1.46 1.53 V
Output Low Voltage VFB = 2.0 V 5.0 20 60 mV
Unity Gain Bandwidth (Note 4) 500 kHz
Open Loop Amplifier Gain (Note 4) 70 dB
Amplifier Transconductance (Note 4) 6.4 mA/V
4. Guaranteed by design, not 100% tested in production.
CS51411, CS51412, CS51413, CS51414
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ELECTRICAL CHARACTERISTICS (40°C < TJ < 125°C (CS51411E/2E/3E/4E); 40°C < TA < 85°C (CS51411E/2E/3E/4E);
0°C < TA < 70°C (CS51411G/2G/3G/4G), 4.5 V< VIN < 40 V; unless otherwise specified.)
Characteristic Test Conditions Min Typ Max Unit
Sync
Sync Frequency Range CS51411/CS51412 305 470 kHz
Sync Frequency Range CS51413/CS51414 575 880 kHz
Sync Pin Bias Current VSYNC = 0 V
VSYNC = 5.0 V
250
0.1
360
0.2
460
mA
mA
Sync Threshold Voltage 1.0 1.5 1.9 V
Shutdown
Shutdown Threshold Voltage ICC = 2 mA 1.0 1.3 1.6 V
Shutdown Pin Bias Current VSHDNB = 0 V 0.14 5.00 35 mA
Thermal Shutdown
Overtemperature Trip Point (Note 5) 175 185 195 °C
Thermal Shutdown Hysteresis (Note 5) 42 °C
General
Quiescent Current ISW = 0 A 3.0 4.0 6.25 mA
Shutdown Quiescent Current VSHDNB = 0 V 8.0 20 85 mA
Boost Operating Current VBOOST VSW = 2.5 V 6.0 15 40 mA/A
Minimum Boost Voltage (Note 5) −−2.5 V
Startup Voltage 2.2 3.3 4.4 V
Minimum Output Current 7.0 12 mA
5. Guaranteed by design, not 100% tested in production.
CS51411, CS51412, CS51413, CS51414
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VIN
BIAS
GND
VSW
BOOST
R
SQ
1.270 V
VFB
+
+
+
+
+
+
+
+
Thermal
Shutdown
Oscillator
1.46 V
1.3 V
5.0 mA
Artificial
Ramp
Output
Driver
Current
Limit Com-
parator
Frequency
and Current
Limit Foldback
0.32 V
PWM Com-
parator
IFOLDBACK
IREF
Shutdown
Comparator
2.9 V LDO
Voltage
Regulator
SHDNB SYNC
VC
Error
Amplifier
Figure 2. Block Diagram
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APPLICATIONS INFORMATION
THEORY OF OPERATION
V2 Control
The CS5141X family of buck regulators utilizes a V2
control technique and provides a high level of integration to
enable high power density design optimization.
Every pulse width modulated controller configures basic
control elements such that when connected to the feedback
signal of a power converter, sufficient loop gain and
bandwidth is available to regulate the voltage set point
against line and load variations. The arrangement of these
elements differentiates a voltage mode, or a current mode
controller from a V2 device.
Figure 3 illustrates the basic architecture of a V2
controller.
Figure 3. V2 Control
Latch/Drive
Switch
Clock
PWM
V2 Control Ramp
Error Amplifier
VREF
VO
Z2
+
Z1
VFB
In common with V mode or I mode, the feedback signal
is compared with a reference voltage to develop an error
signal which is fed to one input of the PWM. The second
input to the PWM, however, is neither a fixed voltage ramp
nor the switch current, but rather the feedback signal from
the output of the converter. This feedback signal provides
both DC information as well as AC information (the control
ramp) for the converter to regulate its set point. The control
architecture is known as V2 since both PWM inputs are
derived from the converters output voltage. This is a little
misleading because the control ramp is typically generated
from current information present in the converter.
The feedback signal from the buck converter shown in
Figure 4 is processed in one of two ways before being routed
to the inputs of the PWM comparator. The Fast Feedback
path (FFB) adds slope compensation to the feedback signal
before passing it to one input of the PWM. The Slow
Feedback path (SFB) compares the original feedback signal
against a DC reference. The error signal generated at the
output of the error amplifier VC is filtered by a low
frequency pole before being routed to the second input of the
PWM. Each switch cycle is initiated (S1 on), when the
output latch is set by the oscillator. Each switch cycle
terminates (S1 off), when the FFB signal (AC plus output
DC) exceeds SFB (error DC), and the output latch is reset.
In the event of a load transient, the FFB signal changes
faster, in relation to the filtered SFB signal, causing duty
cycle modulation to occur. Actual oscilloscope waveforms
taken from the converter show the switch node VSWITCH,
the error signal VC and the feedback signal VFB (AC
component only) are shown in Figure 5.
Figure 4. Buck Converter with V2 Control
Buck
Controller
FFB
VREF
+
Duty Cycle
V2 Control
Error
Amplifier
PWM Com-
parator
R1
Oscillator
+
+
+
VO
SFB
VIN
Latch
Slope
Comp
L1
C1
D1
R2
S
R
VC
S1
Figure 5.
VSWITCH
VSWITCH
VC
VFB
In the event of a load transient, the FFB signal changes
faster, in relation to the filtered SFB signal, causing duty
cycle modulation to occur. By this means the converters
transient response time is independent of the error amplifier
bandwidth. The error amplifier is used here to ensure
excellent DC accuracy.
In order for the controller to operate optimally, a stable
ramp is required at the feedback pin.
CS51411, CS51412, CS51413, CS51414
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Control Ramp Generation
In original V2 designs, the control ramp VCR was
generated from the converters output ripple. Using a current
derived ramp provides the same benefits as current mode,
namely input feed forward, single pole output filter
compensation and fast feedback following output load
transients. Typically a tantalum or organic polymer
capacitor is selected having a sufficiently large ESR
component, relative to its capacitive and ESL ripple
contributions, to ensure the control ramp was sensing
inductor current and its amplitude was sufficient to maintain
loop stability. This technique is illustrated in Figure 6.
Figure 6. Control Ramp Generated from Output
VIN VOUT
L
Cesr
C
VFB
Advances in multilayer ceramic capacitor technology are
such that MLCC’s can provide a cost effective filter solution
for low voltage (< 12 V), high frequency converters
(>200 kHz). For example, a 10 mF MLCC 16 V in a
805 SMT package has an ESR of 2 mW and an ESL of
100 nH. Using several MLCC’s in parallel, connected to
power and ground planes on a PCB with multiple vias, can
provide a “near perfect” capacitor. Using this technique,
output switching ripple below 10 mV can be readily
obtained since parasitic ESR and ESL ripple contributions
are nil. In this case, the control ramp is generated elsewhere
in the circuit.
Ramp generation using dcr inductor current sensing,
where the L/DCR time constant of the output inductor is
matched with the CR time constant of the integrating
network, is shown in Figure 7. The converters transient
response following a 1 A step load is shown in Figure 8. This
transient response is indicative of a closed loop in excess of
10 kHz having good gain and phase margin in the frequency
domain. Also note the amplitude of output switching ripple
provided by just two 10 mF MLCC’s.
Figure 7. Control Ramp Generated from DCR
Inductor Sensing
VIN VOUT
C
R
VFB
Figure 8.
Ramp generation using a voltage feed forward technique
is illustrated in Figure 9.
Figure 9. Control Ramp from Voltage Feed Forward
VIN VOUT
Rf
Cf
CZ
VFB
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Some representative efficiency data is shown in Figure 10.
0
20
40
60
80
100
0 500 1000 150
0
Vin = 5.5 V, Vout= 3.3 V
Vin = 7.5 V, Vout = 5.0 V
Vin = 15V, Vout = 12 V
Figure 10. Efficiency versus Output Current
IOUT
, OUTPUT CURRENT (mA)
EFFICIENCY (%)
More detailed information is available in the ON
Semiconductor application note AND8276/D on V2 and the
CS5141x demonstration board number.
Error Amplifier
The CS5141X has a transconductance error amplifier,
whose noninverting input is connected to an Internal
Reference Voltage generated from the onchip regulator. The
inverting input connects to the VFB pin. The output of the
error amplifier is made available at the VC pin. A typical
frequency compensation requires only a 0.1 mF capacitor
connected between the VC pin and ground, as shown in
Figure 1. This capacitor and error amplifiers output
resistance (approximately 8.0 MW) create a low frequency
pole to limit the bandwidth. Since V2 control does not require
a high bandwidth error amplifier, the frequency
compensation is greatly simplified.
The VC pin is clamped below Output High Voltage. This
allows the regulator to recover quickly from overcurrent or
short circuit conditions.
Oscillator and Sync Feature (CS51411 and CS51413 only)
The onchip oscillator is trimmed at the factory and requires
no external components for frequency control. The high
switching frequency allows smaller external components to be
used, resulting in a board area and cost savings. The tight
frequency tolerance simplifies magnetic components election.
The switching frequency is reduced to 25% of the nominal
value when the VFB pin voltage is below Frequency Foldback
Threshold. In short circuit or overload conditions, this reduces
the power dissipation of the IC and external components.
An external clock signal can sync CS51411/CS51414 to a
higher frequency. The rising edge of the sync pulse turns on the
power switch to start a new switching cycle, as shown in
Figure 11. There is approximately 0.5 ms delay between the
rising edge of the sync pulse and rising edge of the VSW pin
voltage. The sync threshold is TTL logic compatible, and duty
cycle of the sync pulses can vary from 10% to 90%. The
frequency foldback feature is disabled during the sync mode.
Figure 11. A CS51411 Buck Regulator is Synced by an
External 350 kHz Pulse Signal
Power Switch and Current Limit
The collector of the builtin NPN power switch is
connected to the VIN pin, and the emitter to the VSW pin.
When the switch turns on, the VSW voltage is equal to the
VIN minus switch Saturation Voltage. In the buck regulator,
the VSW voltage swings to one diode drop below ground
when the power switch turns off, and the inductor current is
commutated to the catch diode. Due to the presence of high
pulsed current, the traces connecting the VSW pin, inductor
and diode should be kept as short as possible to minimize the
noise and radiation. For the same reason, the input capacitor
should be placed close to the VIN pin and the anode of the
diode.
The saturation voltage of the power switch is dependent
on the switching current, as shown in Figure 12.
Figure 12. The Saturation Voltage of the Power Switch
Increases with the Conducting Current
0 0.5 1.0 1.5
SWITCHING CURRENT (A)
VIN VSW (V)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Members of the CS5141X family contain pulsebypulse
current limiting to protect the power switch and external
components. When the peak of the switching current reaches
the Current Limit, the power switch turns off after the
Current Limit Delay. The switch will not turn on until the
next switching cycle. The current limit threshold is
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10
independent of switching duty cycle. The maximum load
current, given by the following formula under continuous
conduction mode, is less than the Current Limit due to the
ripple current.
IO(MAX) +ILIM *VO(VIN *VO)
2(L)(VIN)(fs)
where:
fS = switching frequency,
ILIM = current limit threshold,
VO = output voltage,
VIN = input voltage,
L = inductor value.
When the regulator runs undercurrent limit, the
subharmonic oscillation may cause low frequency
oscillation, as shown in Figure 13. Similar to current mode
control, this oscillation occurs at the duty cycle greater than
50% and can be alleviated by using a larger inductor value.
The current limit threshold is reduced to Foldback Current
when the FB pin falls below Foldback Threshold. This
feature protects the IC and external components under the
power up or overload conditions.
Figure 13. The Regulator in Current Limit
BOOST Pin
The BOOST pin provides base driving current for the
power switch. A voltage higher than VIN provides required
headroom to turn on the power switch. This in turn reduces
IC power dissipation and improves overall system
efficiency. The BOOST pin can be connected to an external
booststrapping circuit which typically uses a 0.1 mF capacitor
and a 1N914 or 1N4148 diode, as shown in Figure 1. When the
power switch is turned on, the voltage on the BOOST pin is
equal to
VBOOST +VIN )VO*VF
where:
VF = diode forward voltage.
The anode of the diode can be connected to any DC voltage
other than the regulated output voltage. However, the
maximum voltage on the BOOST pin shall not exceed 40 V.
As shown in Figure 14, the BOOST pin current includes a
constant 7.0 mA predriver current and base current
proportional to switch conducting current. A detailed
discussion of this current is conducted in Thermal
Consideration section. A 0.1 mF capacitor is usually adequate
for maintaining the Boost pin voltage during the on time.
BIAS Pin (CS51412 and CS51414 Only)
The BIAS pin allows a secondary power supply to bias the
control circuitry of the IC. The BIAS pin voltage should be
between 3.3 V and 6.0 V. If the BIAS pin voltage falls below
that range, use a diode to prevent current drain from the
BIAS pin. Powering the IC with a voltage lower than the
regulators input voltage reduces the IC power dissipation
and improves energy transfer efficiency.
Figure 14. The Boost Pin Current Includes 7.0 mA
Predriver Current and Base Current when the Switch
is Turned On. The Beta Decline of the Power Switch
Further Increases the Base Current at High
Switching Current
0 0.5 1.0 1.5
SWITCHING CURRENT (A)
BOOST PIN CURRENT (mA)
0
5
10
15
20
25
30
Shutdown
The internal power switch will not turn on until the VIN
pin rises above the Startup Voltage. This ensures no
switching until adequate supply voltage is provided to the
IC. The IC transitions to sleep mode when the SHDNB pin
is pulled low. In sleep mode, the internal power switch
transistor remains off and supply current is reduced to the
Shutdown Quiescent Current value (20 mA typical). This pin
has an internal pull-up current source, so defaults to high
(enabled) state when not connected.
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Figure 15. SHDNB pin equivalent internal circuit (a)
and practical interface examples (b), (c).
0.65V
20k
8V
SHDNB
To internal
bias rails
SHDNB
2V to 5V
SHDNB
(a)
(b) (c)
Z1
Q1
Q2
D1
VIN
80k
I1
5mA
Figure 15(a) depicts the SHDNB pin equivalent internal
circuit. If the pin is open, current source I1 flows into the
base of Q1, turning both Q1 and Q2 on. In turn, Q2 collector
current enables the various internal power rails. In
Figure 15(b), a standard logic gate is used to pull the pin low
by shunting I1 to ground, which places the IC in sleep
(shutdown) mode. Note that, when the gate output is logical
high, the voltage at the SHDNB pin will rise to the internal
clamp voltage of 8 V. This level exceeds the maximum
output rating for most common logic families. Protection
Zener diode Z1 permits the pin voltage to rise high enough
to enable the IC, but remain less than the gate output voltage
rating. In Figure 15(c), a single open-collector general-
purpose NPN transistor is used to pull the pin low. Since
transistors generally have a maximum collector voltage
rating in excess of 8 V, the protection Zener diode in
Figure 15(b) is not required.
Startup
During power up, the regulator tends to quickly charge up
the output capacitors to reach voltage regulation. This gives
rise to an excessive inrush current which can be detrimental
to the inductor, IC and catch diode. In V2 control, the
compensation capacitor provides SoftStart with no need
for extra pin or circuitry. During the power up, the Output
Source Current of the error amplifier charges the
compensation capacitor which forces VC pin and thus output
voltage ramp up gradually.
The SoftStart duration can be calculated by
TSS +VC CCOMP
ISOURCE
where:
VC = VC pin steadystate voltage, which is approximately
equal to error amplifiers reference voltage.
CCOMP = Compensation capacitor connected to the VC pin
ISOURCE = Output Source Current of the error amplifier.
Using a 0.1 mF CCOMP
, the calculation shows a TSS over
5.0 ms which is adequate to avoid any current stresses.
Figure 16 shows the gradual rise of the VC, VO and envelope
of the VSW during power up. There is no voltage overshoot
after the output voltage reaches the regulation. If the supply
voltage rises slower than the VC pin, output voltage may
overshoot.
Figure 16. The Power Up Transition of CS5141X
Regulator
Short Circuit
When the VFB pin voltage drops below Foldback
Threshold, the regulator reduces the peak current limit by
40% and switching frequency to 1/4 of the nominal
frequency. These features are designed to protect the IC and
external components during overload or short circuit
conditions. In those conditions, peak switching current is
clamped to the current limit threshold. The reduced
switching frequency significantly increases the ripple
current, and thus lowers the DC current. The short circuit can
cause the minimum duty cycle to be limited by Minimum
Output Pulse Width. The foldback frequency reduces the
minimum duty cycle by extending the switching cycle. This
protects the IC from overheating, and also limits the power
that can be transferred to the output. The current limit
foldback effectively reduces the current stress on the
inductor and diode. When the output is shorted, the DC
current of the inductor and diode can approach the current
limit threshold. Therefore, reducing the current limit by 40%
can result in an equal percentage drop of the inductor and
diode current. The short circuit waveforms are captured in
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Figure 17, and the benefit of the foldback frequency and
current limit is selfevident.
Figure 17. In Short Circuit, the Foldback Current and
Foldback Frequency Limit the Switching Current to
Protect the IC, Inductor and Catch Diode
Thermal Considerations
A calculation of the power dissipation of the IC is always
necessary prior to the adoption of the regulator. The current
drawn by the IC includes quiescent current, predriver
current, and power switch base current. The quiescent
current drives the low power circuits in the IC, which
include comparators, error amplifier and other logic blocks.
Therefore, this current is independent of the switching
current and generates power equal to
WQ+VIN IQ
where:
IQ = quiescent current.
The predriver current is used to turn on/off the power
switch and is approximately equal to 12 mA in worst case.
During steady state operation, the IC draws this current from
the Boost pin when the power switch is on and then receives
it from the VIN pin when the switch is off. The predriver
current always returns to the VSW pin. Since the predriver
current goes out to the regulators output even when the
power switch is turned off, a minimum load is required to
prevent overvoltage in light load conditions. If the Boost pin
voltage is equal to VIN + VO when the switch is on, the power
dissipation due to predriver current can be calculated by
WDRV +12 mA (VIN *VO)VO2
VIN )
The base current of a bipolar transistor is equal to collector
current divided by beta of the device. Beta of 60 is used here
to estimate the base current. The Boost pin provides the base
current when the transistor needs to be on.
The power dissipated by the IC due to this current is
WBASE +VO2
VIN IS
60
where:
IS = DC switching current.
When the power switch turns on, the saturation voltage
and conduction current contribute to the power loss of a
nonideal switch. The power loss can be quantified as
WSAT +VO
VIN IS VSAT
where:
VSAT = saturation voltage of the power switch which is
shown in Figure 12.
The switching loss occurs when the switch experiences
both high current and voltage during each switch transition.
This regulator has a 30 ns turnoff time and associated
power loss is equal to
WS+IS VIN
2 30 ns fS
The turnon time is much shorter and thus turnon loss is
not considered here.
The total power dissipated by the IC is sum of all the above
WIC +WQ)WDRV )WBASE )WSAT )WS
The IC junction temperature can be calculated from the
ambient temperature, IC power dissipation and thermal
resistance of the package. The equation is shown as follows,
TJ+WIC RqJA )TA
The maximum IC junction temperature shall not exceed
125°C to guarantee proper operation and avoid any damages
to the IC.
Using the BIAS Pin
The efficiency savings in using the BIAS pin is most
notable at low load and high input voltage as will be
explained below.
Figure 18 will help to understand the increase in efficiency
when the BIAS pin is used. The circuitry shown is not the
actual implementation, but is useful in the explanation.
Figure 18.
Internal
BIAS
BIAS
Vin
P1
P2
Internal bias to the IC can be supplied via the Vin pin or the
BIAS pin. When the BIAS pin is low, the logic turns P2 on
and current is routed to the internal bias circuitry from the
Vin pin. Conversely, when the BIAS pin is high, the logic
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turns P1 on and current is routed to the internal bias circuitry
from the BIAS pin.
Here is an example of the power savings:
The input voltage range for Vin is 4.5 V to 40 V. The input
voltage range for BIAS is 3.3 V to 6 V. The quiescent current
specification is 3 mA (min), 4 mA (typ), and 6.25 mA (max).
Using a typical battery voltage of 14 V and the typical
quiescent current number of 4 mA, the power would be:
P+V I+14 4e3+56 mW
We’ll assume the BIAS pin is connected to an external
regulator at 5 V instead of the output voltage. The BIAS pin
would normally be connected to the output voltage, but
adding an added switching regulator efficiency number here
would cloud this example. Now the internal BIAS circuitry
is being powered via 5 V. The resulting on chip power being
dissipated is:
P+V I+5 4e3+21 mW
The power savings is 35 mW.
Now, to demonstrate more notable savings using the
maximum battery input voltage of 40 V, the maximum
quiescent current of 6.25 mA, and the lowest allowed BIAS
voltage for proper operation of 3.3 V;
Powered from Vin:
P+40 6.25e3+250 mW
Powered from the BIAS pin:
P+3.3 6.25e3+21 mW
The power savings is 229 mW.
Minimum Load Requirement
As pointed out in the previous section, a minimum load is
required for this regulator due to the predriver current
feeding the output. Placing a resistor equal to VO divided by
12 mA should prevent any voltage overshoot at light load
conditions. Alternatively, the feedback resistors can be
valued properly to consume 12 mA current.
COMPONENT SELECTION
Input Capacitor
In a buck converter, the input capacitor witnesses pulsed
current with an amplitude equal to the load current. This
pulsed current and the ESR of the input capacitors determine
the VIN ripple voltage, which is shown in Figure 19. For VIN
ripple, low ESR is a critical requirement for the input
capacitor selection. The pulsed input current possesses a
significant AC component, which is absorbed by the input
capacitors.
The RMS current of the input capacitor can be calculated
using:
IRMS +IOD(1 *D)
Ǹ
where:
D = switching duty cycle which is equal to VO/VIN.
IO = load current.
Figure 19. Input Voltage Ripple in a Buck Converter
To calculate the RMS current, multiply the load current
with the constant given by Figure 20 at each duty cycle. It is
a common practice to select the input capacitor with an RMS
current rating more than half the maximum load current. If
multiple capacitors are paralleled, the RMS current for each
capacitor should be the total current divided by the number
of capacitors.
Figure 20. Input Capacitor RMS Current can be
Calculated by Multiplying Y Value with Maximum Load
Current at any Duty Cycle
0 0.2 0.4 1.0
DUTY CYCLE
0
0.1
0.3
0.4
0.5
0.6
0.2
0.6 0.8
IRMS (XIO)
Selecting the capacitor type is determined by each
design’s constraint and emphasis. The aluminum
electrolytic capacitors are widely available at lowest cost.
Their ESR and Equivalent Series Inductor (ESL) are
relatively high. Multiple capacitors are usually paralleled to
achieve lower ESR. In addition, electrolytic capacitors
usually need to be paralleled with a ceramic capacitor for
filtering high frequency noises. The OSCON are solid
aluminum electrolytic capacitors, and therefore has a much
lower ESR. Recently, the price of the OSCON capacitors
has dropped significantly so that it is now feasible to use
them for some low cost designs. Electrolytic capacitors are
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physically large, and not used in applications where the size,
and especially height is the major concern.
Ceramic capacitors are now available in values over 10 mF.
Since the ceramic capacitor has low ESR and ESL, a single
ceramic capacitor can be adequate for both low frequency
and high frequency noises. The disadvantage of ceramic
capacitors are their high cost. Solid tantalum capacitors can
have low ESR and small size. However, the reliability of the
tantalum capacitor is always a concern in the application
where the capacitor may experience surge current.
Output Capacitor
In a buck converter, the requirements on the output
capacitor are not as critical as those on the input capacitor.
The current to the output capacitor comes from the inductor
and thus is triangular. In most applications, this makes the
RMS ripple current not an issue in selecting output
capacitors.
The output ripple voltage is the sum of a triangular wave
caused by ripple current flowing through ESR, and a square
wave due to ESL. Capacitive reactance is assumed to be
small compared to ESR and ESL. The peaktopeak ripple
current of the inductor is:
IP*P+VO(VIN *VO)
(VIN)(L)(fS)
VRIPPLE(ESR), the output ripple due to the ESR, is equal
to the product of IPP and ESR. The voltage developed
across the ESL is proportional to the di/dt of the output
capacitor. It is realized that the di/dt of the output capacitor
is the same as the di/dt of the inductor current. Therefore,
when the switch turns on, the di/dt is equal to (VIN VO)/L,
and it becomes VO/L when the switch turns off. The total
ripple voltage induced by ESL can then be derived from
VRIPPLE(ESL) +ESL(VIN
L))ESL(VIN *VO
L)+ESL(VIN
L)
The total output ripple is the sum of the VRIPPLE(ESR) and
VRIPPLE(ESR).
Figure 21. The Output Voltage Ripple Using Two 10 mF
Ceramic Capacitors in Parallel
Figure 22. The Output Voltage Ripple Using One 100 mF
POSCAP Capacitor
Figure 23. The Output Voltage Ripple Using
One 100 mF OSCON
Figure 24. The Output Voltage Ripple Using
One 100 mF Tantalum Capacitor
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Figure 21 to Figure 24 show the output ripple of a 5.0 V
to 3.3 V/500 mA regulator using 22 mH inductor and various
capacitor types. At the switching frequency, the low ESR
and ESL make the ceramic capacitors behave capacitively
as shown in Figure 21. Additional paralleled ceramic
capacitors will further reduce the ripple voltage, but
inevitably increase the cost. “POSCAP”, manufactured by
SANYO, is a solid electrolytic capacitor. The anode is
sintered tantalum and the cathode is a highly conductive
polymerized organic semiconductor. TPC series, featuring
low ESR and low profile, is used in the measurement of
Figure 22. It is shown that POSCAP presents a good balance
of capacitance and ESR, compared with a ceramic capacitor.
In this application, the low ESR generates less than 5.0 mV
of ripple and the ESL is almost unnoticeable. The ESL of the
throughhole OSCON capacitor give rise to the inductive
impedance. It is evident from Figure 23 which shows the
step rise of the output ripple on the switch turnon and large
spike on the switch turnoff. The ESL prevents the output
capacitor from quickly charging up the parasitic capacitor of
the inductor when the switch node is pulled below ground
through the catch diode conduction. This results in the spike
associated with the falling edge of the switch node. The D
package tantalum capacitor used in Figure 24 has the same
footprint as the POSCAP, but doubles the height. The ESR
of the tantalum capacitor is apparently higher than the
POSCAP. The electrolytic and tantalum capacitors provide
a lowcost solution with compromised performance. The
reliability of the tantalum capacitor is not a serious concern
for output filtering because the output capacitor is usually
free of surge current and voltage.
Diode Selection
The diode in the buck converter provides the inductor
current path when the power switch turns off. The peak
reverse voltage is equal to the maximum input voltage. The
peak conducting current is clamped by the current limit of
the IC. The average current can be calculated from:
ID(AVG) +IO(VIN *VO)
VIN
The worse case of the diode average current occurs during
maximum load current and maximum input voltage. For the
diode to survive the short circuit condition, the current rating
of the diode should be equal to the Foldback Current Limit.
See Table 1 for Schottky diodes from ON Semiconductor
which are suggested for CS5141X regulator.
Inductor Selection
When choosing inductors, one might have to consider
maximum load current, core and copper losses, component
height, output ripple, EMI, saturation and cost. Lower
inductor values are chosen to reduce the physical size of the
inductor. Higher value cuts down the ripple current, core
losses and allows more output current. For most
applications, the inductor value falls in the range between
2.2 mH and 22 mH. The saturation current ratings of the
inductor shall not exceed the IL(PK), calculated according to
IL(PK) +IO)VO(VIN *VO)
2(fS)(L)(VIN)
The DC current through the inductor is equal to the load
current. The worse case occurs during maximum load
current. Check the vendor’s spec to adjust the inductor value
undercurrent loading. Inductors can lose over 50% of
inductance when it nears saturation.
The core materials have a significant effect on inductor
performance. The ferrite core has benefits of small physical
size, and very low power dissipation. But be careful not to
operate these inductors too far beyond their maximum
ratings for peak current, as this will saturate the core.
Powered Iron cores are low cost and have a more gradual
saturation curve. The cores with an open magnetic path, such
as rod or barrel, tend to generate high magnetic field
radiation. However, they are usually cheap and small. The
cores providing a close magnetic loop, such as potcore and
toroid, generate low electromagnetic interference (EMI).
There are many magnetic component vendors providing
standard product lines suitable for CS5141X. Table 2 lists
three vendors, their products and contact information.
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16
Table 1.
Part Number VBREAKDOWN (V) IAVERAGE (A) V(F) (V) @ IAVERAGE Package
1N5817 20 1.0 0.45 Axial Lead
1N5818 30 1.0 0.55 Axial Lead
1N5819 40 1.0 0.6 Axial Lead
MBR0520 20 0.5 0.385 SOD123
MBR0530 30 0.5 0.43 SOD123
MBR0540 40 0.5 0.53 SOD123
MBRS120 20 1.0 0.55 SMB
MBRS130 30 1.0 0.395 SMB
MBRS140 40 1.0 0.6 SMB
Table 2.
Vendor Product Family Web Site Telephone
Coiltronics UNIPac1/2: SMT, barrel
THINPAC: SMT, toroid, low profile
CTX: Leaded, toroid
www.coiltronics.com (516) 2417876
Coilcraft DO1608: SMT, barrel
DS/DT 1608: SMT, barrel, magnetically shielded
DO3316: SMT, barrel
DS/DT 3316: SMT, barrel, magnetically shielded
DO3308: SMT, barrel, low profile
www.coilcraft.com (800) 3222645
Pulse www.pulseeng.com (619) 6748100
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17
Figure 25. Additional Application Diagram, 5.0 V 12 V to 5.0 V/400 mA Inverting Converter
VFB
VSW
2
GND
SHDNB CS51412/4
1N4148
5.0 V
D3
15 mH
VIN
100 mF
100 mF
0.1 mF
C1
C3
R1
R2
C4
0.1 mF
Shutdown
L1
C1
12 V
D1
373
127
13
768
4
5
1N5821
BOOST
U1
BIAS
VC
D2 1N4148
Figure 26. Additional Application Diagram, 12 V to 5.0 V/1.0 A Buck Converter using the BIAS Pin
VFB
2
GND
SHDNB CS51411/3
5.0 V output
D1
R2
VIN
0.01 mF
0.1 mF
22 mF
C1
C3
R1
R3
C4
0.1 mF
VSW L1
C2
5.0 V 12 V input
50 k
127
1
3
7
68
4
5
1N4148
BOOST
U1
SYNC VC
C6
22 m
C5
0.1 mF
D2 373
15 mH
MBR0520
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ORDERING INFORMATION
Device Operating Temperature Range Package Shipping
CS51411ED8
40°C < TA < 85°C
SOIC898 Units/Rail
CS51411ED8G SOIC8 (PbFree) 98 Units/Rail
CS51411EDR8 SOIC82500 Tape & Reel
CS51411EDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51411EMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51412ED8 SOIC898 Units/Rail
CS51412ED8G SOIC8 (PbFree) 98 Units/Rail
CS51412EDR8 SOIC82500 Tape & Reel
CS51412EDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51412EMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51413ED8 SOIC898 Units/Rail
CS51413ED8G SOIC8 (PbFree) 98 Units/Rail
CS51413EDR8 SOIC82500 Tape & Reel
CS51413EDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51413EMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51414ED8 SOIC898 Units/Rail
CS51414ED8G SOIC8 (PbFree) 98 Units/Rail
CS51414EDR8 SOIC82500 Tape & Reel
CS51414EDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51414EMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51411GD8
0°C < TA < 70°C
SOIC898 Units/Rail
CS51411GD8G SOIC8 (PbFree) 98 Units/Rail
CS51411GDR8 SOIC82500 Tape & Reel
CS51411GDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51411GMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51412GD8 SOIC898 Units/Rail
CS51412GD8G SOIC8 (PbFree) 98 Units/Rail
CS51412GDR8 SOIC82500 Tape & Reel
CS51412GDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51412GMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51413GD8 SOIC898 Units/Rail
CS51413GD8G SOIC8 (PbFree) 98 Units/Rail
CS51413GDR8 SOIC82500 Tape & Reel
CS51413GDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51413GMNR2G DFN18 (PbFree) 2500 Tape & Reel
CS51414GD8 SOIC898 Units/Rail
CS51414GD8G SOIC8 (PbFree) 98 Units/Rail
CS51414GDR8 SOIC82500 Tape & Reel
CS51414GDR8G SOIC8 (PbFree) 2500 Tape & Reel
CS51414GMNR2G DFN18 (PbFree) 2500 Tape & Reel
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
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19
PACKAGE DIMENSIONS
SOIC8 NB
CASE 75107
ISSUE AH
SEATING
PLANE
1
4
58
N
J
X 45 _
K
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
6. 75101 THRU 75106 ARE OBSOLETE. NEW
STANDARD IS 75107.
A
BS
D
H
C
0.10 (0.004)
DIM
A
MIN MAX MIN MAX
INCHES
4.80 5.00 0.189 0.197
MILLIMETERS
B3.80 4.00 0.150 0.157
C1.35 1.75 0.053 0.069
D0.33 0.51 0.013 0.020
G1.27 BSC 0.050 BSC
H0.10 0.25 0.004 0.010
J0.19 0.25 0.007 0.010
K0.40 1.27 0.016 0.050
M0 8 0 8
N0.25 0.50 0.010 0.020
S5.80 6.20 0.228 0.244
X
Y
G
M
Y
M
0.25 (0.010)
Z
Y
M
0.25 (0.010) ZSXS
M
____
1.52
0.060
7.0
0.275
0.6
0.024
1.270
0.050
4.0
0.155
ǒmm
inchesǓ
SCALE 6:1
*For additional information on our PbFree strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
PACKAGE THERMAL DATA
Parameter SOIC8 Unit
RqJC Typical 45 °C/W
RqJA Typical 165 °C/W
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PACKAGE DIMENSIONS
DFN18 6x5, 0.5P
CASE 50501
ISSUE D
C0.15
E2
D2
L
b18X
A
D
NOTES:
1. DIMENSIONS AND TOLERANCING PER
ASME Y14.5M, 1994.
2. DIMENSIONS IN MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED
TERMINAL AND IS MEASURED BETWEEN
0.25 AND 0.30 MM FROM TERMINAL
4. COPLANARITY APPLIES TO THE EXPOSED
PAD AS WELL AS THE TERMINALS.
E
C
e
A
B
DIM MIN MAX
MILLIMETERS
A0.80 1.00
A1 0.00 0.05
A3 0.20 REF
b0.18 0.30
D6.00 BSC
D2 3.98 4.28
E5.00 BSC
E2 2.98 3.28
e0.50 BSC
K0.20 −−−
L0.45 0.65
C0.15
PIN 1 LOCATION
A1
(A3)
SEATING
PLANE
C0.08
C0.10
18X
K18X
A0.10 BC
0.05 CNOTE 3
19
1018
2X
2X
18X
SIDE VIEW
TOP VIEW
BOTTOM VIEW
5.30 18X
3.24
0.75
18X
0.30
4.19
PITCH
DIMENSIONS: MILLIMETERS
0.50
1
SOLDERING FOOTPRINT
*For additional information on our PbFree strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
PACKAGE THERMAL DATA
Parameter DFN18 Unit
RqJA Typical 35 °C/W
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
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USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81357733850
CS51411/D
V2 is a trademark of Switch Power, Inc.
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
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