ON CS51414GD8G 1.5 a, 260 khz and 520 khz, low voltage buck regulators with external bias or synchronization capability Datasheet

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 fixed−frequency operating at 260 kHz and 520 kHz. The regulators
use the V2™ control architecture to provide unmatched transient
response, the best overall regulation and the simplest loop
compensation for today’s high−speed 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 on−chip 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 on−chip power dissipation.
Protection circuitry includes thermal shutdown, cycle−by−cycle
current limiting and frequency foldback. The CS51411 and CS51413
are functionally pin−compatible with the LT1375. The CS51412 and
CS51414 are functionally pin−compatible 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 Lead Allows “Bootstrapped” Operation to Maximize
Efficiency
Sync Function for Parallel Supply Operation or Noise Minimization
Shutdown Lead Provides Power−Down Option
85 mA Quiescent Current During Power−Down
Thermal Shutdown
Soft−Start
Pin−Compatible with LT1375 and LT1376
Pb−Free Packages are Available
© Semiconductor Components Industries, LLC, 2007
February, 2007 − Rev. 17
1
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MARKING DIAGRAMS
8
8
5141x
ALYWy
G
1
SOIC−8
D SUFFIX
CASE 751
1
18
1
18−LEAD DFN
MN SUFFIX
CASE 505
1
18
CS5141xy
AWLYYWW G
G
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
= Pb−Free Package
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 18 of this data sheet.
Publication Order Number:
CS51411/D
CS51411, CS51412, CS51413, CS51414
PIN CONNECTIONS
CS51411/3
CS51411/3
VIN
VSW
VC
VFB
GND
SHDNB
SYNC
CS51412/4
BOOST
1
8
CS51412/4
VC
VIN
VSW
VFB
GND
BIAS
SHDNB
BOOST
VIN
VIN
VIN
Vsw
VSW
VSW
SHDNB
NC
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
NC
VC
VFB
NC
NC
GND
NC
NC
SYNC
BOOST
VIN
VIN
VIN
Vsw
VSW
VSW
BIAS
NC
1
2
3
4
5
6
7
8
9
18−Lead DFN
8
18−Lead DFN
BOOST
1
18
17
16
15
14
13
12
11
10
NC
VC
VFB
NC
NC
GND
NC
NC
SHDNB
PACKAGE PIN DESCRIPTION
SOIC−8
Package Pin #
DFN18
Package Pin #
Pin Symbol
1
1
BOOST
2
2, 3, 4
VIN
This pin is the main power input to the IC.
3
5, 6, 7
VSW
This is the connection to the emitter of the on−chip NPN power transistor
and serves as the switch output to the inductor. This pin may be
subjected to negative voltages during switch off−time. 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 on−chip 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
5
(CS51412/CS51414)
4
(CS51411/CS51413)
10
(CS51412/CS51414)
8
(CS51411/CS51413)
SHDNB
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
VC
The 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 on−chip test circuitry becomes active whenever
current exceeding 0.5 mA is forced into the IC.
−
9, 11, 12, 14, 15, 18
NC
No Connection
Function
The BOOST pin provides additional drive voltage to the on−chip NPN
power transistor. The resulting decrease in switch on voltage increases
efficiency.
This pin provides the synchronization input.
The shutdown pin is active low and TTL compatible. The IC goes into
sleep mode, drawing less than 85 mA when the pin voltage is pulled
below 1.0 V. This pin should be left floating in normal position.
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CS51411, CS51412, CS51413, CS51414
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
1N4148
D1
C1
0.1 mF
4.5 V − 16 V
C2
100 mF
Shutdown
1
U1 2
VIN
4
BOOST
SHDNB
5
SYNC
VSW
3
CS51411/3
SYNC
VC
8
GND
VFB
6
7
3.3 V
L1
15 mH
D3
1N5821
R1
205
C3
100 mF
R2
127
C4
0.1 mF
Figure 1. Application Diagram, 4.5 V − 16 V to 3.3 V @ 1.0 A Converter
MAXIMUM RATINGS
Rating
Operating Junction Temperature Range, TJ
Lead Temperature Soldering:
Reflow: (SMD styles only) (Note 1)
Storage Temperature Range, TS
ESD Damage Threshold (Human Body Model)
Value
Unit
−40 to 150
°C
230 peak
°C
−65 to +150
°C
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. 60 second maximum above 183°C.
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CS51411, CS51412, CS51413, CS51414
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
VC
7.0 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
−
0.05
0.15
%/V
Frequency Line Regulation
−
Maximum Duty Cycle
−
85
90
95
%
VFB Frequency Foldback Threshold
−
0.29
0.32
0.36
V
8.0
25
17
50
26
75
mV/ms
mV/ms
−
−
150
−
300
230
ns
ns
PWM Comparator
Slope Compensation Voltage
CS51411/CS51412, Fix VFB, DVC/DTON
CS51413/CS51414
Minimum Output Pulse Width
CS51411/CS51412, VFB to VSW
CS51413/CS51414, VFB to VSW
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 2)
−
120
160
ns
1.244
1.270
1.296
V
−
40
−
dB
Error Amplifier
Internal Reference Voltage
Reference PSRR
−
(Note 2)
−
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 2)
−
500
−
kHz
Open Loop Amplifier Gain
(Note 2)
−
70
−
dB
Amplifier Transconductance
(Note 2)
−
6.4
−
mA/V
FB Input Bias Current
−
2. Guaranteed by design, not 100% tested in production.
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CS51411, CS51412, CS51413, CS51414
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
−
470
kHz
Sync
Sync Frequency Range
CS51411/CS51412
305
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
1.0
1.5
1.9
V
Sync Threshold Voltage
−
Shutdown
Shutdown Threshold Voltage
1.0
1.3
1.6
V
VSHDNB = 0 V
0.14
5.00
35
mA
Overtemperature Trip Point
(Note 3)
175
185
195
°C
Thermal Shutdown Hysteresis
(Note 3)
−
42
−
°C
Shutdown Pin Bias Current
−
Thermal Shutdown
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 3)
−
−
2.5
V
Startup Voltage
−
2.2
3.3
4.4
V
Minimum Output Current
−
−
7.0
12
mA
3. Guaranteed by design, not 100% tested in production.
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CS51411, CS51412, CS51413, CS51414
SHDNB
SYNC
VIN
5.0 mA
BIAS
2.9 V LDO
Voltage
Regulator
Shutdown
Comparator
+
Artificial
Ramp
−
Thermal
Shutdown
Oscillator
BOOST
+
1.3 V −
S
Q
Output
Driver
R
VSW
∑
+
Current
Limit
Comparator
−
PWM
Comparator
+
1.46 V
IREF
−
−
VFB
−
+
+
0.32 V −
+
1.270 V
+
−
Frequency
and Current
Limit Foldback
Error
Amplifier
VC
Figure 2. Block Diagram
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IFOLDBACK
GND
CS51411, CS51412, CS51413, CS51414
APPLICATIONS INFORMATION
THEORY OF OPERATION
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.
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.
S1
VIN
L1
VO
R1
Duty Cycle
Buck
Controller
Slope
Comp
Oscillator
+
Error Amplifier
Latch/Drive
PWM
Z2
VREF
VFB
Clock
FFB
Latch S
R
−
+
−
+
Switch
C1
D1
Z1
VC
PWM
Comparator
VO
V2 Control Ramp
V2
R2
SFB
+
−
V2
Error
Amplifier
VREF
+
−
Control
Figure 3. V2 Control
Figure 4. Buck Converter with V2 Control
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 converter’s 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
VSWITCH
VC
VFB
Figure 5.
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 converter’s
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.
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CS51411, CS51412, CS51413, CS51414
Control Ramp Generation
VIN
In original V2 designs, the control ramp VCR was
generated from the converter’s 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.
VIN
VOUT
R
C
VFB
Figure 7. Control Ramp Generated from DCR
Inductor Sensing
VOUT
L
Cesr
C
VFB
Figure 6. Control Ramp Generated from Output
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 converter’s 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 8.
Ramp generation using a voltage feed forward technique
is illustrated in Figure 9.
VIN
VOUT
Rf
CZ
Cf
VFB
Figure 9. Control Ramp from Voltage Feed Forward
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CS51411, CS51412, CS51413, CS51414
Some representative efficiency data is shown in Figure 10.
100
EFFICIENCY (%)
80
60
40
Vin = 5.5 V, Vout= 3.3 V
20
Vin = 7.5 V, Vout = 5.0 V
Vin = 15V, Vout = 12 V
0
0
500
1000
IOUT, OUTPUT CURRENT (mA)
Figure 11. A CS51411 Buck Regulator is Synced by an
External 350 kHz Pulse Signal
1500
Figure 10. Efficiency versus Output Current
Power Switch and Current Limit
The collector of the built−in 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.
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 on−chip 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 amplifier’s 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.
0.7
0.6
VIN − VSW (V)
0.5
Oscillator and Sync Feature (CS51411 and CS51413 only)
The on−chip 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.
0.4
0.3
0.2
0.1
0
0
0.5
1.0
SWITCHING CURRENT (A)
1.5
Figure 12. The Saturation Voltage of the Power Switch
Increases with the Conducting Current
Members of the CS5141X family contain pulse−by−pulse
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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CS51411, CS51412, CS51413, CS51414
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.
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.
V (V * VO)
IO(MAX) + ILIM * O IN
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.
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
regulator’s input voltage reduces the IC power dissipation
and improves energy transfer efficiency.
BOOST PIN CURRENT (mA)
30
25
20
15
10
5
0
0
0.5
1.0
SWITCHING CURRENT (A)
1.5
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
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 enters a sleep mode when the SHDNB pin is pulled
below Shutdown Threshold Voltage. In the sleep mode, the
power switch keeps open and the supply current reduces to
Shutdown Quiescent Current. This pin has internal pull−up
current. So when this pin is not used, leave the SHDNB pin
open.
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
boost−strapping 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
Startup
During power up, the regulator tends to quickly charge up
the output capacitors to reach voltage regulation. This gives
rise to an excessive in−rush current which can be detrimental
to the inductor, IC and catch diode. In V2 control, the
compensation capacitor provides Soft−Start 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.
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.
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CS51411, CS51412, CS51413, CS51414
diode current. The short circuit waveforms are captured in
Figure 16, and the benefit of the foldback frequency and
current limit is self−evident.
The Soft−Start duration can be calculated by
V
CCOMP
TSS + C
ISOURCE
where:
VC = VC pin steady−state voltage, which is approximately
equal to error amplifier’s 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 15 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. 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
Figure 15. The Power Up Transition of CS5141X
Regulator
WQ + VIN
IQ
where:
IQ = quiescent current.
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
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 regulator’s 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
V 2
(VIN * VO ) O )
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.
http://onsemi.com
11
CS51411, CS51412, CS51413, CS51414
The power dissipated by the IC due to this current is
V 2
WBASE + O
VIN
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
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:
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
non−ideal 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.
P+V
VIN
2
30 ns
fS
P+V
The turn−on time is much shorter and thus turn−on loss is
not considered here.
The total power dissipated by the IC is sum of all the above
I+5
4e−3 + 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:
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
4e−3 + 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:
The switching loss occurs when the switch experiences
both high current and voltage during each switch transition.
This regulator has a 30 ns turn−off time and associated
power loss is equal to
I
WS + S
I + 14
P + 40
RqJA ) TA
6.25e−3 + 250 mW
Powered from the BIAS pin:
The maximum IC junction temperature shall not exceed
125°C to guarantee proper operation and avoid any damages
to the IC.
P + 3.3
6.25e−3 + 21 mW
The power savings is 229 mW.
Minimum Load Requirement
Using the BIAS Pin
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.
The efficiency savings in using the BIAS pin is most
notable at low load and high input voltage as will be
explained below.
Figure 17 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.
COMPONENT SELECTION
P1
BIAS
Internal
BIAS
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 18. 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.
P2
Vin
Figure 17.
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12
CS51411, CS51412, CS51413, CS51414
The RMS current of the input capacitor can be calculated
using:
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 OS−CON are solid
aluminum electrolytic capacitors, and therefore has a much
lower ESR. Recently, the price of the OS−CON capacitors
has dropped significantly so that it is now feasible to use
them for some low cost designs. Electrolytic capacitors are
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.
IRMS + IO ǸD(1 * D)
where:
D = switching duty cycle which is equal to VO/VIN.
IO = load 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 peak−to−peak ripple
current of the inductor is:
Figure 18. Input Voltage Ripple in a Buck Converter
To calculate the RMS current, multiply the load current
with the constant given by Figure 19 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.
0.6
0.5
V (V * VO)
IP * P + O IN
(VIN)(L)(fS)
IRMS (XIO)
0.4
VRIPPLE(ESR), the output ripple due to the ESR, is equal
to the product of IP−P 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
0.3
0.2
0.1
0
0
0.2
0.6
0.4
DUTY CYCLE
0.8
1.0
V * VO
V
V
VRIPPLE(ESL) + ESL( IN) ) ESL( IN
) + ESL( IN)
L
L
L
Figure 19. Input Capacitor RMS Current can be
Calculated by Multiplying Y Value with Maximum Load
Current at any Duty Cycle
The total output ripple is the sum of the VRIPPLE(ESR) and
VRIPPLE(ESR).
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13
CS51411, CS51412, CS51413, CS51414
Figure 20. The Output Voltage Ripple Using Two 10 mF
Ceramic Capacitors in Parallel
Figure 22. The Output Voltage Ripple Using
One 100 mF OS−CON
Figure 21. The Output Voltage Ripple Using One 100 mF
POSCAP Capacitor
Figure 23. The Output Voltage Ripple Using
One 100 mF Tantalum Capacitor
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14
CS51411, CS51412, CS51413, CS51414
Figure 20 to Figure 23 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 20. 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 21. 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
through−hole OS−CON capacitor give rise to the inductive
impedance. It is evident from Figure 22 which shows the
step rise of the output ripple on the switch turn−on and large
spike on the switch turn−off. 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 23 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 low−cost 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.
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
V (V * VO)
IL(PK) + IO ) O IN
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 pot−core and
toroid, generate low electro−magnetic 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.
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:
I (V * VO)
ID(AVG) + O IN
VIN
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15
CS51411, CS51412, CS51413, CS51414
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
SOD−123
MBR0530
30
0.5
0.43
SOD−123
MBR0540
40
0.5
0.53
SOD−123
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
UNI−Pac1/2: SMT, barrel
THIN−PAC: SMT, toroid, low profile
CTX: Leaded, toroid
www.coiltronics.com
(516) 241−7876
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) 322−2645
Pulse
−
www.pulseeng.com
(619) 674−8100
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16
CS51411, CS51412, CS51413, CS51414
U1
5.0 V − 12 V input
2
C1
22 mF
4
5
7
VFB
VIN
C5
0.1 mF
BOOST 1
SHDNB CS51411/3
SYNC
VSW 3
15 mH L1
VC
GND
6
R2
373
D2
1N4148
D1
MBR0520
8
R3
127
C6
22 m
C2
0.1 mF
−5.0 V output
C3
C4
0.01 mF
R1 50 k
0.1 mF
Figure 24. Additional Application Diagram, 5.0 V − 12 V to −5.0 V/400 mA Inverting Converter
D2 1N4148
1N4148
D1
12 V
C1
100 mF
Shutdown
U1 2
VIN
5 SHDNB
VC
8
1
BOOST
4
BIAS
C1
0.1 mF
VSW
3
CS51412/4
GND
VFB
6
7
5.0 V
L1
15 mH
D3
1N5821
R1
373
C3
100 mF
R2
127
C4
0.1 mF
Figure 25. Additional Application Diagram, 12 V to 5.0 V/1.0 A Buck Converter using the BIAS Pin
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17
CS51411, CS51412, CS51413, CS51414
ORDERING INFORMATION
Device
Operating Temperature Range
CS51411ED8
Package
Shipping†
SOIC−8
98 Units/Rail
CS51411ED8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51411EDR8
SOIC−8
2500 Tape & Reel
CS51411EDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51411EMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
SOIC−8 (Pb−Free)
98 Units/Rail
CS51412ED8
CS51412ED8G
CS51412EDR8
SOIC−8
2500 Tape & Reel
SOIC−8 (Pb−Free)
2500 Tape & Reel
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
CS51413ED8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51413EDR8
SOIC−8
2500 Tape & Reel
CS51413EDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51413EMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
CS51414ED8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51414EDR8
SOIC−8
2500 Tape & Reel
CS51414EDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51414EMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
CS51412EDR8G
CS51412EMNR2G
CS51413ED8
−40°C < TA < 85°C
CS51414ED8
CS51411GD8
SOIC−8
98 Units/Rail
CS51411GD8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51411GDR8
SOIC−8
2500 Tape & Reel
CS51411GDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51411GMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
CS51412GD8
CS51412GD8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51412GDR8
SOIC−8
2500 Tape & Reel
SOIC−8 (Pb−Free)
2500 Tape & Reel
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
CS51413GD8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51413GDR8
SOIC−8
2500 Tape & Reel
CS51413GDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51413GMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
SOIC−8
98 Units/Rail
CS51414GD8G
SOIC−8 (Pb−Free)
98 Units/Rail
CS51414GDR8
SOIC−8
2500 Tape & Reel
CS51414GDR8G
SOIC−8 (Pb−Free)
2500 Tape & Reel
CS51414GMNR2G
DFN18 (Pb−Free)
2500 Tape & Reel
CS51412GDR8G
CS51412GMNR2G
CS51413GD8
0°C < TA < 70°C
CS51414GD8
†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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18
CS51411, CS51412, CS51413, CS51414
PACKAGE DIMENSIONS
SOIC−8 NB
CASE 751−07
ISSUE AH
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. 751−01 THRU 751−06 ARE OBSOLETE. NEW
STANDARD IS 751−07.
−X−
A
8
5
0.25 (0.010)
S
B
1
M
Y
M
4
K
−Y−
G
C
N
DIM
A
B
C
D
G
H
J
K
M
N
S
X 45 _
SEATING
PLANE
−Z−
0.10 (0.004)
H
D
0.25 (0.010)
M
Z Y
S
X
M
J
S
MILLIMETERS
MIN
MAX
4.80
5.00
3.80
4.00
1.35
1.75
0.33
0.51
1.27 BSC
0.10
0.25
0.19
0.25
0.40
1.27
0_
8_
0.25
0.50
5.80
6.20
SOLDERING FOOTPRINT*
1.52
0.060
7.0
0.275
4.0
0.155
0.6
0.024
1.270
0.050
mm Ǔ
ǒinches
SCALE 6:1
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
PACKAGE THERMAL DATA
SOIC−8
Unit
RqJC
Typical
45
°C/W
RqJA
Typical
165
°C/W
Parameter
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19
INCHES
MIN
MAX
0.189
0.197
0.150
0.157
0.053
0.069
0.013
0.020
0.050 BSC
0.004
0.010
0.007
0.010
0.016
0.050
0 _
8 _
0.010
0.020
0.228
0.244
CS51411, CS51412, CS51413, CS51414
PACKAGE DIMENSIONS
DFN18
CASE 505−01
ISSUE C
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.
A
D
B
PIN 1 LOCATION
E
2X
DIM
A
A1
A3
b
D
D2
E
E2
e
K
L
0.15 C
2X
0.15 C
TOP VIEW
(A3)
0.10 C
A
18X
0.08 C
A1
C
SIDE VIEW
SOLDERING FOOTPRINT*
SEATING
PLANE
D2
18X
18X
L
5.30
e
1
MILLIMETERS
MIN
MAX
0.80
1.00
0.00
0.05
0.20 REF
0.18
0.30
6.00 BSC
3.98
4.28
5.00 BSC
2.98
3.28
0.50 BSC
0.20
−−−
0.45
0.65
18X
0.75
1
9
0.30
PITCH
E2
K
4.19
18
10
18X
BOTTOM VIEW
b
0.10 C A B
0.05 C
18X
0.30
NOTE 3
3.24
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
PACKAGE THERMAL DATA
Parameter
RqJA
Typical
DFN18
Unit
35
°C/W
V2 is a trademark of Switch Power, Inc.
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
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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
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