LINER LT1946

LT1946
1.2MHz Boost
DC/DC Converter with
1.5A Switch and Soft-Start
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FEATURES
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■
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DESCRIPTIO
The LT®1946 is a fixed frequency step-up DC/DC converter
containing an internal 1.5A, 36V switch. Capable of generating 8V at 430mA from a 3.3V input, the LT1946 is ideal
for large TFT-LCD panel power supplies. The LT1946
switches at 1.2MHz, allowing the use of tiny, low profile
inductors and low value ceramic capacitors. Loop compensation can be either internal or external, giving the user
flexibility in setting loop compensation and allowing optimized transient response with low ESR ceramic output
capacitors. Soft-start is controlled with an external capacitor, which determines the input current ramp rate during
start-up.
1.5A, 36V Internal Switch
1.2MHz Switching Frequency
Integrated Soft-Start Function
Output Voltage Up to 34V
Low VCESAT Switch: 300mV at 1.5A (Typ)
8V at 430mA from a 3.3V Input
Small 8-Lead MSOP Package
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APPLICATIO S
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TFT-LCD Bias Supplies
GPS Receivers
DSL Modems
Local Power Supplies
The 8-lead MSOP package and high switching frequency
ensure a low profile overall solution less than 1.2mm high.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Efficiency
6
OFF ON
C1
2.2µF
3
1
RC
49.9k
CC
470pF
LT1946
FB
VC
8
COMP GND
7
4
VOUT
8V
430mA
2
85
80
R1
28.7k
SHDN
SS
CSS
100nF
5
SW
VIN
90
D1
C2
20µF
R2
5.23k
EFFICIENCY (%)
L1
4.7µH
VIN
3.3V
75
70
65
60
55
C1: 2.2µF, X5R OR X7R, 6.3V
C2: 2 × 10µF, X5R OR X7R, 10V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
1946 F01
50
0
100
200
400
300
LOAD CURRENT (mA)
500
1946 F01b
Figure 1. 3.3V to 8V, 430mA Step-Up DC/DC Converter
sn1946 1946fs
1
LT1946
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN Voltage ............................................................. 16V
SW Voltage ............................................... – 0.4V to 36V
FB Voltage ............................................................. 2.5V
SHDN Voltage ......................................................... 16V
Current Into FB Pin .............................................. ±1mA
Maximum Junction Temperature ......................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
TOP VIEW
VC
FB
SHDN
GND
1
2
3
4
8
7
6
5
SS
COMP
VIN
SW
LT1946EMS8
MS8 PACKAGE
8-LEAD PLASTIC MSOP
MS8 PART MARKING
TJMAX = 125°C, θJA = 125°C/W
(4-LAYER BOARD)
LTUG
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VSHDN = VIN unless otherwise specified. (Note 2)
SYMBOL
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
UNITS
2.45
2.6
V
16
V
1.250
1.270
1.270
V
V
20
120
Maximum Operating Voltage
Feedback Voltage
●
FB Pin Bias Current
VFB = 1.250V (Note 3)
Error Amp Transconductance
∆I = 2µA
1.230
1.220
●
Error Amp Voltage Gain
Quiescent Current
VSHDN = 2.5V, Not Switching
Quiescent Current in Shutdown
VSHDN = 0V, VIN = 3V
Reference Line Regulation
2.6V ≤ VIN ≤ 16V
Switching Frequency
●
Switching Frequency in Foldback
0.9
0.8
VFB = 0V
Maximum Duty Cycle
Switch Current Limit
(Note 4)
Switch VCESAT
ISW = 1A
Switch Leakage Current
VSW = 5V
Soft-Start Charging Current
VSS = 0.5V
SHDN Input Voltage High
µmhos
300
V/V
3.2
5
mA
0
1
µA
0.01
0.05
%/V
1.2
1.4
1.5
MHz
MHz
0.4
MHz
●
86
90
●
1.5
2.1
3.1
A
240
340
mV
0.01
1
µA
4
6
µA
2.5
%
2.4
V
SHDN Input Voltage Low
SHDN Pin Bias Current
VSHDN = 3V
VSHDN = 0V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1946E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
nA
40
16
0
0.5
V
32
0.1
µA
µA
Note 3: Current flows out of FB pin.
Note 4: Current limit guaranteed by design and/or correlation to static test.
Current limit is independent of duty cycle and is guaranteed by design.
sn1946 1946fs
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LT1946
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TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
1400
1.27
1200
1.26
1.25
1.24
1.23
1.22
1.21
1.20
– 50 – 25
1000
TA = –30°C
TA = 100°C
800
TA = 25°C
600
400
200
0
75
50
25
TEMPERATURE (°C)
0
100
125
0
0.2
0.8
0.6
1.0
0.4
FEEDBACK VOLTAGE (V)
1946 G01
1.2
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50
–25
75
0
50
25
TEMPERATURE (°C)
100
125
1946 G03
1946 G02
Switch Saturation Voltage
Switching Waveforms
for Figure 1 Circuit
Quiescent Current
3.8
0.35
VOUT
20mV/DIV
AC COUPLED
3.6
QUIESCENT CURRENT (mA)
0.30
0.25
VCESAT (V)
Current Limit
CURRENT LIMIT (A)
OSCILLATOR FREQUENCY (kHz)
FEEDBACK VOLTAGE (V)
Feedback Pin Voltage
1.28
0.20
0.15
0.10
0.05
3.4
3.2
3.0
VSW
5V/DIV
2.8
0V
2.6
ILI
0.5A/DIV
AC COUPLED
2.4
0.5µs/DIV
2.2
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
SWITCH CURRENT (A)
1946 G04
2.0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
1946 G06
125
1946 G05
sn1946 1946fs
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LT1946
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PI FU CTIO S
VC (Pin 1): Error Amplifier Output Pin. Tie external compensation network to this pin, or use the internal compensation network by shorting the VC pin to the COMP pin.
FB (Pin 2): Feedback Pin. Reference voltage is 1.250V.
Connect resistive divider tap here. Minimize trace area at
FB. Set VOUT according to VOUT = 1.250(1 + R1/R2).
SHDN (Pin 3): Shutdown Pin. Tie to 2.4V or more to enable
device. Ground to shut down. Do not float this pin.
VIN (Pin 6): Input Supply Pin. Must be locally bypassed.
COMP (Pin 7): Internal Compensation Pin. Provides an
internal compensation network. Tie directly to the VC pin
for internal compensation. Tie to GND if not used.
SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor
here. Upon start-up, 4µA of current charges the capacitor
to 1.5V. Use a larger capacitor for slower start-up. Leave
floating if not in use.
GND (Pin 4): Ground. Tie directly to local ground plane.
SW (Pin 5): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI.
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BLOCK DIAGRA
SS
VC
COMP
8
1
7
120k
90pF
4µA
SW
5
–
COMPARATOR
DRIVER
+
A2
R
Q
Q1
S
VIN
6
1.250V
REFERENCE
+
+
Σ
A1
–
VOUT
0.01Ω
–
RAMP
GENERATOR
R1 (EXTERNAL)
4
FB
0.5V
R2 (EXTERNAL)
+
A3
÷3
GND
1.2MHz
OSCILLATOR
1946 BD
–
SHUTDOWN
3
2
SHDN
FB
Figure 2. Block Diagram
sn1946 1946fs
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LT1946
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OPERATIO
The LT1946 uses a constant frequency, current mode
control scheme to provide excellent line and load regulation. Please refer to Figure 2 for the following description
of the part’s operation. At the start of the oscillator cycle,
the SR latch is set, turning on the power switch Q1. The
switch current flows through the internal current sense
resistor generating a voltage. This voltage is added to a
stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the SR
latch is reset, turning off the power switch. The level at the
negative input of A2 (VC pin) is set by the error amplifier
(A1) and is simply an amplified version of the difference
between the feedback voltage and the reference voltage of
1.250V. In this manner, the error amplifier sets the correct
peak current level to keep the output in regulation.
Two functions are provided to enable a very clean start-up
for the LT1946. Frequency foldback is used to reduce the
oscillator frequency by a factor of 3 when the FB pin is
below a nominal value of 0.5V. This is accomplished via
comparator A3. This feature reduces the minimum duty
cycle that the part can achieve thus allowing better control
of the switch current during start-up. When the FB pin
voltage exceeds 0.5V, the oscillator returns to the normal
frequency of 1.2MHz. A soft-start function is also provided
by the LT1946. When the part is brought out of shutdown,
4µA of current is sourced out of the SS pin. By connecting
an external capacitor to the SS pin, the rate of voltage rise
on the pin can be set. Typical values for the soft-start
capacitor range from 10nF to 200nF. The SS pin directly
limits the rate of rise on the VC pin, which in turn limits the
peak switch current. Current limit is not shown in Figure 2.
The switch current is constantly monitored and not allowed to exceed the nominal value of 2.1A. If the switch
current reaches 2.1A, the SR latch is reset regardless of
the output of comparator A2. This current limit helps
protect the power switch as well as the external components connected to the LT1946.
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APPLICATIO S I FOR ATIO
Inductor Selection
Several inductors that work well with the LT1946 are listed
in Table 1. This table is not exclusive; there are many other
manufacturers and inductors that can be used. Consult
each manufacturer for more detailed information and for
their entire selection of related parts, as many different
sizes and shapes are available. Ferrite core inductors
should be used to obtain the best efficiency, as core losses
at 1.2MHz are much lower for ferrite cores than for the
cheaper powdered-iron ones. Choose an inductor that can
handle at least 1.5A without saturating, and ensure that the
inductor has a low DCR (copper wire resistance) to minimize I2R power losses. A 4.7µH to 10µH inductor will be
the best choice for most LT1946 designs. Note that in
some applications, the current handling requirements of
the inductor can be lower, such as in the SEPIC topology
where each inductor only carries one-half of the total
switch current.
The inductors shown in Table 1 were chosen for small size.
For better efficiency, use similar valued inductors with a
larger volume.
Table 1. Recommended Inductors
PART
L
(µH)
MAX
DCR
(mΩ)
SIZE
L×W×H
(mm)
CDRH5D18-4R1
CDRH5D18-5R4
CDRH5D28-5R3
CDRH5D28-6R2
CDRH5D28-8R2
4.1
5.4
5.3
6.2
8.2
57
76
38
45
53
5.7 × 5.7 × 2
ELL6SH-4R7M
ELL6SH-5R6M
ELL6SH-6R8M
4.7
5.6
6.8
50
59
62
6.4 × 6 × 3
RLF5018T4R7M1R4
4.7
45
5.6 × 5.2 × 1.8
5.7 × 5.7 × 3
VENDOR
Sumida
(847) 956-0666
www.sumida.com
Panasonic
(408) 945-5660
www.panasonic.com
TDK
(847) 803-6100
www.tdk.com
sn1946 1946fs
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LT1946
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APPLICATIO S I FOR ATIO
Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multilayer ceramic capacitors are an excellent choice, as
they have an extremely low ESR and are available in very
small packages. X5R dielectrics are preferred, followed by
X7R, as these materials retain the capacitance over wide
voltage and temperature ranges. A 4.7µF to 20µF output
capacitor is sufficient for most applications, but systems
with very low output currents may need only a 1µF or 2.2µF
output capacitor. Solid tantalum or OS-CON capacitors
can be used, but they will occupy more board area than a
ceramic and will have a higher ESR. Always use a capacitor
with a sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1946. A 2.2µF to 4.7µF input capacitor is
sufficient for most applications. Table 2 shows a list of
several ceramic capacitor manufacturers. Consult the
manufacturers for detailed information on their entire
selection of ceramic parts.
VOUT
20mV/DIV
AC COUPLED
ILI
0.5A/DIV
AC COUPLED
RC = 7.5k
AVX
Murata
(408) 573-4150
www.t-yuden.com
(803) 448-9411
www.avxcorp.com
(714) 852-2001
www.murata.com
1946 F03a
Figure 3a. Transient Response Shows Excessive Ringing
VOUT
20mV/DIV
AC COUPLED
ILI
0.5A/DIV
AC COUPLED
RC = 18k
200µs/DIV
1946 F03b
Figure 3b. Transient Response is Better
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
200µs/DIV
VOUT
20mV/DIV
AC COUPLED
Compensation—Adjustment
To compensate the feedback loop of the LT1946, a series
resistor-capacitor network should be connected from the
COMP pin to GND. For most applications, a capacitor in
the range of 220pF to 680pF will suffice. A good starting
value for the compensation capacitor, CC, is 470pF. The
compensation resistor, RC, is usually in the range of 20k
to 100k. A good technique to compensate a new application is to use a 100kΩ potentiometer in place of RC, and
use a 470pF capacitor for CC. By adjusting the potentiometer while observing the transient response, the optimum
value for RC can be found. Figures 3a to 3c illustrate this
process for the circuit of Figure 1 with a load current
stepped from 250mA to 300mA. Figure 3a shows the transient response with RC equal to 7.5k. The phase margin is
ILI
0.5A/DIV
AC COUPLED
RC = 49.9k
200µs/DIV
1946 F03b
Figure 3c. Transient Response is Well Damped
poor as evidenced by the excessive ringing in the output
voltage and inductor current. In Figure 3b, the value of R C
is increased to 18k, which results in a more damped response. Figure 3c shows the results when RC is increased
further to 49.9k. The transient response is nicely damped
and the compensation procedure is complete. The COMP
pin provides access to an internal resistor (120k) and
capacitor (90pF). For some applications, these values will
suffice and no external RC and CC will be needed.
sn1946 1946fs
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LT1946
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APPLICATIO S I FOR ATIO
Compensation—Theory
–
Like all other current mode switching regulators, the
LT1946 needs to be compensated for stable and efficient
operation. Two feedback loops are used in the LT1946: a
fast current loop which does not require compensation,
and a slower voltage loop which does. Standard Bode plot
analysis can be used to understand and adjust the voltage
feedback loop.
gmp
VOUT
+
+
VC
1.250V
REFERENCE
gma
RC
RL
COUT
RO
R1
–
R2
CC
1946 F04
As with any feedback loop, identifying the gain and phase
contribution of the various elements in the loop is critical.
Figure 4 shows the key equivalent elements of a boost
converter. Because of the fast current control loop, the
power stage of the IC, inductor and diode have been
replaced by the equivalent transconductance amplifier
gmp. gmp acts as a current source where the output current
is proportional to the VC voltage. Note that the maximum
output current of gmp is finite due to the current limit in the
IC.
From Figure 4, the DC gain, poles and zeroes can be
calculated as follows:
2
2 • π •RL • C OUT
1
Error Amp Pole: P2 =
2 • π •RO • C C
1
Error Amp Zero: Z1=
2 • π •RC • C C
1.25
DC GAIN: A =
• gma • RO • gmp • RL
VOUT
1
ESR Zero: Z2 =
2 • π • ESR • C OUT
Output Pole: P1=
RHP Zero: Z3 =
VIN2 • RL
CC: COMPENSATION CAPACITOR
COUT: OUTPUT CAPACITOR
gma: TRANSCONDUCTANCE AMPLIFIER INSIDE IC
gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER
RC: COMPENSATION RESISTOR
RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD(MAX)
RO: OUTPUT RESISTANCE OF gma
R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK
Figure 4. Boost Converter Equivalent Model
The Current Mode zero is a right half plane zero which can
be an issue in feedback control design, but is manageable
with proper external component selection.
Using the circuit of Figure 1 as an example, the following
table shows the parameters used to generate the Bode plot
shown in Figure 5.
Table 3. Bode Plot Parameters
Parameter
Value
Units
Comment
RL
18.6
Ω
Application Specific
COUT
20
µF
Application Specific
RO
10
MΩ
Not Adjustable
CC
470
pF
Adjustable
Adjustable
RC
49.9
kΩ
VOUT
8
V
Application Specific
VIN
3.3
V
Application Specific
gma
40
µmho
Not Adjustable
gmp
5
mho
Not Adjustable
L
5.4
µH
fS
1.2
MHz
Application Specific
Not Adjustable
2
2 • π • VOUT • L
f
High Frequency Pole: P3 > S
3
From Figure 5, the phase is 120° when the gain reaches
0dB giving a phase margin of 60°. This is more than
adequate. The crossover frequency is 25kHz, which is
about three times lower than the frequency of the right half
plane zero Z2. It is important that the crossover frequency
be at least three times lower than the frequency of the RHP
zero to achieve adequate phase margin.
sn1946 1946fs
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LT1946
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APPLICATIO S I FOR ATIO
Diode Selection
100
A Schottky diode is recommended for use with the LT1946.
The Microsemi UPS120 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
UPS140 (a 40V diode). These diodes are rated to handle an
average forward current of 1A. For applications where the
average forward current of the diode is less than 0.5A, an
ON Semiconductor MBR0520 diode can be used
GAIN (dB)
50
0
–50
100
1k
10k 25k 100k
FREQUENCY (Hz)
Setting Output Voltage
1M
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
1946 F05a
0
PHASE (DEG)
V

R1 = R2 OUT – 1
 1.25V 
A good range for R2 is from 5k to 30k.
–100
Layout Hints
60°
The high speed operation of the LT1946 demands careful
attention to board layout. You will not get advertised
performance with careless layout. Figure 6 shows the
recommended component placement for a boost
converter.
–180
–200
100
1k
10k 25k 100k
FREQUENCY (Hz)
1M
1946 F05b
Figure 5. Bode Plot of Figure 1’s Circuit
GROUND PLANE
CSS
C1
CC
+
VIN
RC
1
8
R1
2
R2
SHUTDOWN
LT1946
7
3
6
4
5
L1
MULTIPLE
VIAs
GND
C2
VOUT
1946 F06
Figure 6. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize
Trace Area at Pin 1 (VC) and Pin 2 (FB). Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use Vias at One Location Only to Avoid
Introducing Switching Currents Into the Ground Plane
sn1946 1946fs
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LT1946
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TYPICAL APPLICATIO S
Low Profile, Triple Output TFT Supply (10V, –10V, 20V)
D2
D3
VON
20V
5mA
C5
0.1µF
L1
5.4µH
VIN
3.3V TO 5V
3
OFF ON
8
+
7
C1
4.7µF
6
VIN
5
SW
R1
75k
SHDN
SS
LT1946
COMP
VC
1
RC
33.3k
CC
470pF
CSS
100nF
AVDD
10V
450mA, VIN = 5V
275mA, VIN = 3.3V
D1
FB
2
C2
20µF
GND
4
C1 TO C6: X5R OR X7R
C1: 4.7µF, 6.3V
C2: 2 × 10µF, 10V
C3: 1µF, 25V
C4: 2.2µF, 10V
C5, C6: 0.1µF, 10V
D1: MICROSEMI UPS120 OR EQUIVALENT
D2 TO D5: ZETEX BAT54S OR EQUIVALENT
L1: SUMIDA CDRH5D18-5R4
C3
1µF
R2
10.5k
C6
0.1µF
D4
C4
2.2µF
D5
1946 TA01
Efficiency
VOFF
–10V
10mA
Transient Response
90
85
80
EFFICIENCY (%)
AVDD
50mV/DIV
AC COUPLED
VIN = 5V
VIN = 3.3V
75
ILI
0.5A/DIV
70
65
60
55
50
AVDD 150mA
LOAD 100mA
VON LOAD = 5mA
VOFF LOAD = 10mA
0
100
200
400
300
AVDD LOAD CURRENT (mA)
500
VIN = 5V
100µs/DIV
1946 TA01b
1946 TA01a
sn1946 1946fs
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LT1946
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TYPICAL APPLICATIO S
12V Output Boost Converter
L1
4.7µH
VIN
3.3V TO 5V
OFF ON
C1
4.7µF
3
1
RC
33.3k
6
VIN
CSS
100nF
5
SW
LT1946
FB
VC
8
2
C2
4.7µF
COMP GND
7
VOUT
12V
410mA, VIN = 5V
275mA, VIN = 3.3V
R1
84.5k
SHDN
SS
CC
470pF
D1
R2
9.76k
4
C1: 4.7µF, X5R OR X7R, 6.3V
C2: 4.7µF, X5R OR X7R, 16V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
1946 TA02
Efficiency
Transient Response
90
VIN = 5V
VOUT
100mV/DIV
AC COUPLED
85
VIN = 3.3V
EFFICIENCY (%)
80
75
70
ILI
0.5A/DIV
65
60
ILOAD 175mA
100mA
55
50
0
100
200
400
300
LOAD CURRENT (mA)
500
VIN = 3.3V
100µs/DIV
1946 TA02b
1946 TA02a
sn1946 1946fs
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LT1946
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PACKAGE DESCRIPTIO
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.2 – 3.45
(.126 – .136)
0.42 ± 0.04
(.0165 ± .0015)
TYP
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.65
(.0256)
BSC
8
7 6 5
0.52
(.206)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
NOTE 4
4.88 ± 0.1
(.192 ± .004)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
0.53 ± 0.015
(.021 ± .006)
DETAIL “A”
1
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.077)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
0.65
(.0256)
BCS
0.13 ± 0.05
(.005 ± .002)
MSOP (MS8) 1001
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
sn1946 1946fs
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT1946
U
TYPICAL APPLICATIO
Low Profile, Triple Output TFT Supply (8V, – 8V, 23V)
D2
D3
D4
C5
0.1µF
L1
5.4µH
VIN
3.3V
OFF ON
3
8
+
7
C1
4.7µF
C6
0.1µF
6
5
SW
C7
0.1µF
AVDD
8V
375mA
R2
28.7k
SHDN
LT1946
FB
COMP
VC
2
C2
20µF
GND
1
RC
49.9k
CC
470pF
CSS
100nF
VON
23V
5mA
D1
VIN
SS
D5
4
C1 TO C8: X5R OR X7R
C1: 4.7µF, 6.3V
C2: 2 × 10µF, 10V
C3: 2.2µF, 10V
C4: 1µF, 25V
C5, C6, C8: 0.1µF, 10V
C7: 0.1µF, 16V
D1: MICROSEMI UPS120 OR EQUIVALENT
D2 TO D5: ZETEX BAT54S OR EQUIVALENT
L1: SUMIDA CDRH5D18-5R4
C4
1µF
R3
5.23k
C8
0.1µF
D7
C3
2.2µF
D6
1946 TA03
Efficiency
VOFF
–8V
10mA
Start-Up Waveforms
85
80
AVDD
2V/DIV
EFFICIENCY (%)
75
VON
10V/DIV
70
65
VOFF
5V/DIV
60
55
VON LOAD = 5mA
VOFF LOAD = 10mA
IIN
200mA/V
50
0
100
200
300
AVDD LOAD CURRENT (mA)
400
1ms/DIV
1946 TA04
1946 TA03a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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LT1944/LT1944-1
Dual 350mA Boost Converter
VIN = 1.2V to 15V, VOUT to 34V, MS10 Package
LT1945
Dual ±250mA Boost Converter
VIN = 1.2V to 15V, VOUT to ±34V, MS10 Package
LT1946A
12.7MHz, 1.5A Boost DC/DC Converter
VIN = 2.45V to 16V, VOUT to 34V, MS8E Package
LT1947
3MHz, Dual Switching Regulator
8V at 200mA from 3.3V Input, 10-Lead MSOP Package
Burst Mode and ThinSOT are trademarks of Linear Technology Corporation.
12
Linear Technology Corporation
sn1946 1946fs
LT/TP 1002 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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 LINEAR TECHNOLOGY CORPORATION 2001