LINER LT1946A 2.7mhz boost dc/dc converter with 1.5a switch and soft-start Datasheet

LT1946A
2.7MHz Boost DC/DC
Converter with 1.5A Switch
and Soft-Start
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FEATURES
■
■
■
■
■
■
■
DESCRIPTIO
1.5A, 36V Internal Switch
2.7MHz Switching Frequency
Integrated Soft-Start Function
Adjustable Output from VIN to 35V
Low VCESAT Switch: 300mV at 1.5A (Typical)
12V at 430mA from a 5V Input
Small Thermally Enhanced 8-Lead MSOP Package
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APPLICATIO S
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TFT-LCD Bias Supplies
GPS Receivers
DSL Modems
Local Power Supply
The LT®1946A is a fixed frequency step-up DC/DC converter containing an internal 1.5A, 36V switch. Capable of
generating 12V at 430mA from a 5V input, the LT1946A is
ideal for powering large TFT-LCD panels. The LT1946A
switches at 2.7MHz, 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. The 8-lead MSOP package and high switching
frequency ensure a low profile overall solution less than
1.1mm high.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
L1
2.2µH
VIN
5V
6
C1
2.2µF
3
1
RC
27.4k
CC
270pF
VIN
90
R1
182k
85
SHDN
80
2
LT1946A FB
7
COMP
VC
SS
CSS
100nF
5
SW
Efficiency
VOUT
12V
430mA
8
GND*
4
C2
2.2µF
R2
21k
EFFICIENCY (%)
OFF ON
D1
75
70
65
60
C1: 2.2µF, X5R or X7R, 6.3V
C2: 2.2µF, X5R or X7R, 16V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: SUMIDA CR43-2R2
* EXPOSED PAD MUST ALSO BE GROUNDED
1946A TA01
Figure 1. 5V to 12V, 430mA Step-Up DC/DC Converter
55
50
0
100
200
300
400
LOAD CURRENT (mA)
500
1946A TA01
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LT1946A
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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
Current into FB Pin ............................................... ±1mA
SHDN Voltage .......................................................... 16V
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
LT1946AEMS8E
MS8E PART
MARKING
MS8E PACKAGE
8-LEAD PLASTIC MSOP
EXPOSED PAD IS GROUND
(MUST BE SOLDERED TO PCB)
LTYZ
TJMAX = 125°C, θJA = 40°C/W,
θJC = 10°C/W
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 noted. (Note 2)
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
2.45
2.6
V
16
V
1.25
1.27
1.27
V
V
20
120
Maximum Operating Voltage
Feedback Voltage
●
FB Pin Bias Current
VFB = 1.25V (Note 3)
Error Amp Transconductance
∆I = 2µA
1.23
1.22
●
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
2.4
2.3
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
3.6
5
mA
0
1
µA
0.01
0.05
%/V
2.7
3
3.1
MHz
MHz
0.85
MHz
●
73
80
●
1.5
2.1
3.1
A
240
340
mV
0.01
1
µA
4
6
µA
2.5
%
2.4
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 LT1946AE is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
nA
40
V
SHDN Input Voltage Low
SHDN Pin Bias Current
UNITS
16
0
0.5
V
32
0.1
µA
µA
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Current flows out of the 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.
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LT1946A
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TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
3000
1.27
2700
1.26
1.25
1.24
1.23
1.22
1.21
2400
TA = –30°C
2100
TA = 100°C
1800
1500
TA = 25°C
1200
900
600
300
1.20
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
0
125
0
0.2
0.4
0.6
0.8
FEEDBACK VOLTAGE (V)
1946A G01
1.2
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1946A G03
Switching Waveforms for
Figure 1 Circuit
Quiescent Current
0.35
4.0
VOUT
100mV/DIV
AC COUPLED
3.8
QUIESCENT CURRENT (mA)
0.30
0.25
VCESAT (V)
1
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
1946A G02
Switch Saturation Voltage
0.20
0.15
0.10
0.05
0
Current Limit
CURRENT LIMIT (A)
1.28
OSCILLATOR FREQUENCY (kHz)
FEEDBACK VOLTAGE (V)
Feedback Pin Voltage
3.6
VSW
10V/DIV
0V
3.4
3.2
3.0
ILI
0.5A/DIV
2.8
2.6
100ns/DIV
2.4
0
0.2
0.4 0.6 0.8 1 1.2
SWITCH CURRENT (A)
1.4
1.6
2.2
–50
1946A G04
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1946A G05
Transient Response for
Figure 1 Circuit
Start-Up Waveforms for
Figure 1 Circuit
VOUT
100mV/DIV
AC COUPLED
VOUT
2V/DIV
ILI
0.5A/DIV
IIN
200mA/DIV
0A
ILOAD 250mA
150mA
VSHDN 5V
0V
50µs/DIV
1946A G06
1946A G07
RLOAD = 250Ω
1ms/DIV
1946A G08
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LT1946A
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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.
External compensation consists of placing a resistor and
capacitor in series from VC to GND. Typical capacitor
range is from 90pF to 270pF. Typical resistor range is from
25k to 120k.
FB (Pin 2): Feedback Pin. Reference voltage is 1.25V.
Connect resistive divider tap here. Minimize trace area at
FB. Set VOUT according to VOUT = 1.25 • (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.
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.
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, Exposed Pad): Ground. Tie both Pin 4 and
the exposed pad directly to local ground plane. The
ground metal to the exposed pad should be wide for better
heat dissipation. Multiple vias (local ground plane ↔
ground backplane) placed close to the exposed pad can
further aid in reducing thermal resistance.
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LT1946A
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BLOCK DIAGRA
SS
VC
COMP
8
1
7
4µA
120k
90pF
–
DRIVER
A2
VIN 6
1.25V
REFERENCE
+
+
A1
FB
0.5V
Q1
+
0.01Ω
–
+
R2 (EXTERNAL)
4 GND
A3
÷3
2.7MHz
OSCILLATOR
–
SHDN
S
Q
RAMP
GENERATOR
R1 (EXTERNAL)
SHUTDOWN
R
Σ
–
VOUT
5 SW
COMPARATOR
3
2
EXPOSED
PAD
1946A F02
FB
Figure 2. Block Diagram
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LT1946A
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OPERATIO
The LT1946A 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 LT1946A. Frequency foldback is used to reduce the
oscillator frequency by one-third 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
goes above 0.5V, the oscillator returns to the normal
frequency of 2.7MHz. A soft-start function is also provided
by the LT1946A. 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
protects the power switch as well as various external
components connected to the LT1946A.
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APPLICATIO S I FOR ATIO
Inductor Selection
Several inductors that work well with the LT1946A are
listed in Table 1. This table is not complete, and there are
many other manufacturers and devices 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 2.7MHz 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 1.5µH to 4.7µH inductor
will be the best choice for most LT1946A 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 - LT1946A
PART
L
(µH)
MAX
DCR
(mΩ)
Size
LxWxH
(mm)
RLF5018-1R5M2R1
RLF5018-2R7M1R8
RLF5018-4R7M1R4
RLF5018-100MR94
1.5
2.7
4.7
10.0
25
33
45
67
5.2x5.6x1.8
TDK
(847) 803-6100
www.tdk.com
LPO1704-122MC
LPO1704-222MC
1.2
2.2
80
120
5.5x6.6x1.0
Coilcraft
(800) 322-2645
www.coilcraft.com
CR43-2R2
CR43-3R3
2.2
3.3
71
86
4.5x4.0x3.2
Sumida
(847) 956-0666
www.sumida.com
VENDOR
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 2.2µF to 20µF output
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LT1946A
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APPLICATIO S I FOR ATIO
capacitor is sufficient for most applications, but systems
with very low output currents may need only a 1µF or
smaller output capacitor. Solid tantalum or OSCON 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 LT1946A. 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.
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
Compensation
To compensate the feedback loop of the LT1946A, a series
resistor-capacitor network should be connected from the
COMP pin to GND. For most applications, a capacitor in the
range of 90pF to 470pF will suffice. A good starting value
for the compensation capacitor, CC, is 270pF. 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 100k potentiometer in place of RC, and use a
270pF capacitor for CC. By adjusting the potentiometer
while observing the transient response, the optimum
value for RC can be found. Figures 3a-3c illustrate this
process for the circuit of Figure 1. Figure 3a shows the
transient response with RC equal to 2.5k. The phase
margin is poor as evidenced by the excessive ringing in the
output voltage and inductor current. In Figure 3b the value
of RC is increased to 6.5k, which results in a more damped
response. Figure 3c shows the results when RC is increased further to 27.4k. 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.
VOUT
200mV/DIV
AC COUPLED
IL1
0.5A/DIV
RC = 2.5k
50µs/DIV
1946A F03a
Figure 3a. Transient Response Shows Excessive Ringing
VOUT
200mV/DIV
AC COUPLED
IL1
0.5A/DIV
RC = 6.5k
50µs/DIV
1946A F03b
Figure 3b. Transient Response is Better
VOUT
200mV/DIV
AC COUPLED
IL1
0.5A/DIV
RC = 27.4k
50µs/DIV
1946A F03c
Figure 3c. Transient Response is Well Damped
Compensation-Theory
Like all other current mode switching regulators, the
LT1946A needs to be compensated for stable and efficient
operation. Two feedback loops are used in the LT1946A:
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.
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LT1946A
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APPLICATIO S I FOR ATIO
1
2 • π • ESR • C OUT
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.
ESR Zero: Z2 =
From Figure 4, the DC gain, poles and zeroes can be
calculated as follows:
Using the circuit of Figure 1 as an example, Table 3 shows
the parameters used to generate the bode plot shown in
Figure 5.
Output Pole: P1 =
2
2 • π • RL • C OUT
Error Amp Pole: P2 =
Error Amp Zero: Z1 =
DC Gain: A =
1
2 • π • RO • C C
1
2 • π • RC • C C
GMP
FS
3
Value
Units
RL
28
Ω
Application Specific
Comment
COUT
2.2
µF
Application Specific
RO
10
MΩ
Not Adjustable
CC
270
pF
Adjustable
RC
27.4
kΩ
Adjustable
VOUT
12
V
Application Specific
VIN
5
V
Application Specific
GMA
40
µmho
GMP
Not Adjustable
5
mho
L
2.2
µH
Not Adjustable
FS
2.7
MHz
Not Adjustable
ESR
10
mΩ
Not Adjustable
Application Specific
VOUT
+
ESR
+
GMA
1.250V
REFERENCE
COUT
R1
–
CC
2
2 • π • VOUT • L
High Frequency Pole: P3 >
Parameter
–
RC
RHP Zero: Z3 =
Table 3. Bode Plot Parameters
1.25
• G MA • RO • G MP • RL
VOUT
VC
2
VIN • RL
RO
R2
RL
From Figure 5, the phase when the gain reaches 0dB is
122° giving a phase margin of 58°. This is more than
adequate. The cross-over frequency is 90kHz, which is
about 30 times lower than the frequency of the right half
plane zero Z2. It is important that the cross-over frequency
be at least 3 times lower than the frequency of the RHP zero
to achieve adequate phase margin.
GMA: TRANSCONDUCTANCE AMPLIFIER INSIDE IC
GMP: POWER STAGE TRANSCONDUCTANCE AMPLIFIER
COUT: OUTPUT CAPACITOR
RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD (MAX)
R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK
RO: OUTPUT RESISTANCE OF GMA
RC: COMPENSATION RESISTOR
CC: COMPENSATION CAPACITOR
Figure 4. Boost Converter Equivalent Model
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LT1946A
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APPLICATIO S I FOR ATIO
Setting Output Voltage
100
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
GAIN (f)
50
V

R1 = R2  OUT – 1
 1.25V 
0
A good range for R2 is from 5k to 30k.
–50
100
1k
10k
100k
FREQUENCY (Hz)
1M
1946A FO5a
PHASE (f)
0
–100
Layout Hints
The high speed operation of the LT1946A demands careful
attention to board layout. You will not get advertised
performance with careless layouts. Figure 6 shows the
recommended component placement for a boost converter.
GROUND PLANE
CSS
C1
58°
CC
VIN
RC
–180
–200
100
+
1
1k
10k
100k
FREQUENCY (Hz)
1M
2
1946A FO5b
R2
SHUTDOWN
Figure 5. Gain and Phase Plots of Figure 1 Circuit
Diode Selection
A Schottky diode is recommended for use with the LT1946A.
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.
8
R1
LT1946A
7
3
6
4
5
L1
MULTIPLE
VIAs
GND
C2
VOUT
19949 F04
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.
Figure 6. Recommended Component
Placement for Boost Converter
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LT1946A
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TYPICAL APPLICATIO S
Low Profile (< 1.1mm Tall) Triple Output TFT Supply (10V, –10V, 20V)
D2
D3
VON
20V
5mA
C5
0.1µF
L1
1.5µH
VIN
5V
OFF ON
3
8
+
C1
4.7µF
7
CSS
100nF
D1
6
VIN
5
SW
R1
75k
SHDN
SS
LT1946A
COMP
VC
FB
AVDD
10V
475mA
2
C2
20µF
GND*
1
RC
59k
CC
150pF
4
C1–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–D5: ZETEX BAT54S OR EQUIVALENT
L1: COILCRAFT LP01704-152MC
* EXPOSED PAD MUST ALSO BE GROUNDED
C3
1µF
R2
10.5k
C6
0.1µF
D4
C4
2.2µF
D5
VOFF
–10V
10mA
1946A TA02
Transient Response
Efficiency
90
85
AVDD
50mV/DIV
AC COUPLED
EFFICIENCY (%)
80
ILI
0.5A/DIV
75
70
65
60
VON LOAD = 5mA
VOFF LOAD = 10mA
55
AVDD LOAD 350mA
200mA
50
100µs/DIV
1946A TA03
0
100
200
300
400
AVDD LOAD CURRENT (mA)
500
1946A TA04
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LT1946A
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TYPICAL APPLICATIO S
Triple Output TFT Supply Uses SEPIC Topology for Output Disconnect
D2
VON
23V
10mA
C4
0.22µF
D3
VOFF
–12V
10mA
C5
0.22µF
L1
10µH
VIN
12V ± 10%
3
OFF ON
8
+
1
C1
2.2µF
D1
6
VIN
5
SW
C1–C5: X5R or X7R
C1: 2.2µF, 6.3V
C2: 2× 10µF, 16V
C3: 1µF, 25V
C4: 0.22µF, 25V
C5: 0.22µF, 16V
L2
10µH
SHDN
SS
LT1946A
FB
R1
84.5k
2
C2
20µF
VC
COMP
GND*
4
7
CSS
100nF
C3
1µF
AVDD
12V
250mA
R2
9.76k
D1: MICROSEMI UPS120 OR EQUIVALENT
D2–D3: CENTRAL SEMI CMDSH-3
L1–L2: TDK RLF5018-100MR94
* EXPOSED PAD MUST ALSO BE GROUNDED
1946A TA09
MS8E Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1662)
0.889 ± 0.127
(.035 ± .005)
2.794 ± 0.102
(.110 ± .004)
5.23
(.206)
MIN
0.42 ± 0.04
(.0165 ± .0015)
TYP
2.083 ± 0.102 3.2 – 3.45
(.082 ± .004) (.126 – .136)
0.65
(.0256)
BSC
BOTTOM VIEW OF
EXPOSED PAD OPTION
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.254
(.010)
8
1
2.06 ± 0.102
(.080 ± .004)
1.83 ± 0.102
(.072 ± .004)
3.00 ± 0.102
(.118 ± .004)
NOTE 4
4.88 ± 0.1
(.192 ± .004)
DETAIL “A”
0.52
(.206)
REF
7 6 5
0° – 6° TYP
GAUGE PLANE
0.53 ± 0.015
(.021 ± .006)
RECOMMENDED SOLDER PAD LAYOUT
DETAIL “A”
1
2 3
4
1.10
(.043)
MAX
8
0.86
(.34)
REF
0.18
(.077)
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
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
0.65
(.0256)
BCS
0.13 ± 0.05
(.005 ± .002)
MSOP (MS8E) 1001
sn1946a 1946afs
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
LT1946A
U
TYPICAL APPLICATIO S
Low Profile (< 1.1mm Tall) Triple Output TFT Supply (8V, – 8V, 24V)
D2
D4
D3
C6
0.1µF
C5
0.1µF
D5
VON
23V
5mA
C7
0.1µF
Efficiency
OFF ON
3
8
+
C1
4.7µF
7
6
5
VIN
SW
LT1946A
COMP
VC
1
FB
AVDD
8V
375mA
2
C2
20µF
GND*
4
C4
1µF
R3
5.23k
CSS
100nF
85
80
R2
28.7k
SHDN
SS
90
D1
EFFICIENCY (%)
L1
1.2µH
VIN
3.3V
75
70
65
60
VON LOAD = 5mA
VOFF LOAD = 10mA
55
C1–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–D7: ZETEX BAT54S OR EQUIVALENT
L1: COILCRAFT LP01704-122MC
* EXPOSED PAD MUST ALSO BE GROUNDED
C8
0.1µF
50
D7
C3
2.2µF
0
100
200
300
AVDD LOAD CURRENT (mA)
400
D6
1946A TA06
VOFF
–8V
10mA
1946A TA05
Start-Up Waveforms
Transient Response
AVDD
5V/DIV
AVDD
50mV/DIV
AC COUPLED
VON
10V/DIV
ILI
0.5A/DIV
VOFF
5V/DIV
ILOAD 350mA
200mA
IIN
0.5A/DIV
50µs/DIV
1946A TA07
1ms/DIV
1946A TA08
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1613
550mA (ISW), 1.4MHz, Step-Up DC/DC Converter
VIN = 0.9V to 10V, VOUT to 34V, IQ = 3mA, ISD < 1µA, ThinSOTTM
LT1615/LT1615-1
300mA/0.75mA (ISW), Constant Off-Time Step-Up
DC/DC Converter
VIN = 1V to 15V, VOUT to 34V, IQ = 20µA, ISD < 1µA, ThinSOT
LT1930/LT1930A
1A (ISW), 1.2MHz/2.2MHz, Step-Up DC/DC Converter
VIN = 2.6V to 16V, VOUT to 34V, IQ = 4.2mA/5.5mA, ISD < 1µA, ThinSOT
LT1946
1.5A (ISW), 1.2MHz, Step-Up DC/DC Converter
VIN = 2.45V to 16V, VOUT to 34V, IQ = 3.2mA, ISD < 1µA, MS8
LT1961
1.5A (ISW), 1.25MHz, Step-Up DC/DC Converter
VIN = 3V to 25V, VOUT to 35V, IQ = 0.9mA, ISD < 6µA, MS8E
ThinSOT is a trademark of Linear Technology Corporation.
sn1946a 1946afs
12
Linear Technology Corporation
LT/TP 1102 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2001