LT1946
1
1946fb
V
IN
V
IN
3.3V
SW
FB
LT1946
4.7µHD1
100nF
470pF
49.9k
V
OUT
8V
430mA
1946 F01
20µF
2.2µF
V
C
GNDCOMPSS
SHDNOFF ON
C1: 2.2µF, X5R OR X7R, 6.3V
C2: 2 × 10µF, X5R OR X7R, 10V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
28.7k
5.23k
■
TFT-LCD Bias Supplies
■
GPS Receivers
■
DSL Modems
■
Local Power Supplies
■
1.5A, 36V Internal Switch
■
1.2MHz Switching Frequency
■
Integrated Soft-Start Function
■
Output Voltage Up to 34V
■
Low V
CESAT
Switch: 300mV at 1.5A (Typ)
■
8V at 430mA from a 3.3V Input
■
Small 8-Lead MSOP Package
1.2MHz Boost
DC/DC Converter with
1.5A Switch and Soft-Start
Figure 1. 3.3V to 8V, 430mA Step-Up DC/DC Converter
The LT
®
1946 is a fixed frequency step-up DC/DC converter
containing an internal 1.5A, 36V switch. Capable of gener-
ating 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 com-
pensation can be either internal or external, giving the user
flexibility in setting loop compensation and allowing opti-
mized transient response with low ESR ceramic output
capacitors. Soft-start is controlled with an external capaci-
tor, 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 1.2mm high.
LOAD CURRENT (mA)
0
EFFICIENCY (%)
65
70
75
300 500
1946 F01b
60
55
50 100 200 400
80
85
90
Efficiency
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
LT1946
2
1946fb
PACKAGE/ORDER I FOR ATIO
UUW
T
JMAX
= 125°C, θ
JA
= 40°C/W,
θ
JC
= 10°C/W
ORDER PART
NUMBER
MS8 PART MARKING
T
JMAX
= 125°C, θ
JA
= 125°C/W
(4-LAYER BOARD) LTUG
LT1946EMS8
1
2
3
4
V
C
FB
SHDN
GND
8
7
6
5
SS
COMP
V
IN
SW
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
ORDER PART
NUMBER
MS8 PART MARKING
LTBNW
LT1946EMS8E
1
2
3
4
8
7
6
5
TOP VIEW
MS8E PACKAGE
8-LEAD PLASTIC MSOP
EXPOSED PAD (PIN 9) IS GROUND
(MUST BE SOLDERED TO PCB)
V
C
FB
SHDN
GND
SS
COMP
V
IN
SW
9
V
IN
Voltage ............................................................. 16V
SW Voltage ............................................... –0.4V to 36V
FB Voltage ............................................................. 2.5V
SHDN Voltage ......................................................... 16V
Current Into FB Pin .............................................. ±1mA
(Note 1)
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 TYP MAX UNITS
Minimum Operating Voltage 2.45 2.6 V
Maximum Operating Voltage 16 V
Feedback Voltage 1.230 1.250 1.270 V
●1.220 1.270 V
FB Pin Bias Current V
FB
= 1.250V (Note 3) ●20 120 nA
Error Amp Transconductance ∆I = 2µA40µmhos
Error Amp Voltage Gain 300 V/V
Quiescent Current V
SHDN
= 2.5V, Not Switching 3.2 5 mA
Quiescent Current in Shutdown V
SHDN
= 0V, V
IN
= 3V 0 1 µA
Reference Line Regulation 2.6V ≤ V
IN
≤ 16V 0.01 0.05 %/V
Switching Frequency 0.9 1.2 1.4 MHz
●0.8 1.5 MHz
Switching Frequency in Foldback V
FB
= 0V 0.4 MHz
Maximum Duty Cycle ●86 90 %
Switch Current Limit (Note 4) ●1.5 2.1 3.1 A
Switch V
CESAT
I
SW
= 1A 240 340 mV
Switch Leakage Current V
SW
= 5V 0.01 1 µA
Soft-Start Charging Current V
SS
= 0.5V 2.5 4 6 µA
ABSOLUTE AXI U RATI GS
WWWU
ELECTRICAL CHARACTERISTICS
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
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
LT1946
3
1946fb
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Feedback Pin Voltage
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1.27
25
1946 G01
1.24
1.22
–25 0 50
1.21
1.20
1.28
1.26
1.25
1.23
75 100 125
FEEDBACK VOLTAGE (V)
0
1400
1200
1000
800
600
400
200
00.6 1.0
1946 G02
0.2 0.4 0.8 1.2
OSCILLATOR FREQUENCY (kHz)
T
A
= –30°CT
A
= 100°C
T
A
= 25°C
TEMPERATURE (°C)
–50
0
CURRENT LIMIT (A)
0.6
0.4
0.2
0.8
1.0
1.4
1.2
2.6
2.4
2.2
2.0
–25 25 50 125
1946 G03
1.6
1.8
075 100
Oscillator Frequency Current Limit
Switch Saturation Voltage Quiescent Current
Switching Waveforms
for Figure 1 Circuit
SWITCH CURRENT (A)
0
V
CESAT
(V)
0.20
0.25
0.30
1.2
1946 G04
0.15
0.10
0.4 0.80.2 1.40.6 1.0 1.6
0.05
0
0.35
TEMPERATURE (°C)
–50
2.0
QUIESCENT CURRENT (mA)
2.2
2.6
2.8
3.0
75 100
3.8
1946 G05
2.4
–25 0 25 50 125
3.2
3.4
3.6
V
OUT
20mV/DIV
AC COUPLED
V
SW
5V/DIV
0V
I
LI
0.5A/DIV
AC COUPLED
0.5µs/DIV 1946 G06
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 TYP MAX UNITS
SHDN Input Voltage High 2.4 V
SHDN Input Voltage Low 0.5 V
SHDN Pin Bias Current V
SHDN
= 3V 16 32 µA
V
SHDN
= 0V 0 0.1 µA
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
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.
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.
LT1946
4
1946fb
Σ
–
+
–
+
A2
FBSHDN
SHUTDOWN
V
IN
0.5V
DRIVER
Q1
0.01Ω
120k
90pF SW
GND
COMPARATOR
5
V
C
4µA
1
SS
8
COMP
4
S
RQ
RAMP
GENERATOR
1.2MHz
OSCILLATOR
÷3
–
+
–
+
23
1.250V
REFERENCE
6
7
R1 (EXTERNAL)
FB
V
OUT
R2 (EXTERNAL)
A3
A1
GND
(MSE8 ONLY)
9
1946 BD
UU
U
PI FU CTIO S
V
C
(Pin 1): Error Amplifier Output Pin. Tie external com-
pensation network to this pin, or use the internal compen-
sation network by shorting the V
C
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 V
OUT
according to V
OUT
= 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.
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 con-
nected to this pin to minimize EMI.
V
IN
(Pin 6): Input Supply Pin. Must be locally bypassed.
COMP (Pin 7): Internal Compensation Pin. Provides an
internal compensation network. Tie directly to the V
C
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.
Exposed Pad (MS8E, Pin 9): Ground. Must be soldered to
PCB.
BLOCK DIAGRA
W
Figure 2. Block Diagram
LT1946
5
1946fb
OPERATIO
U
The LT1946 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. 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 (V
C
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 V
C
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 al-
lowed 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 compo-
nents connected to the LT1946.
APPLICATIO S I FOR ATIO
WUUU
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 mini-
mize I
2
R 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
MAX SIZE
L DCR L × W × H
PART (µH) (mΩ) (mm) VENDOR
CDRH5D18-4R1 4.1 57 5.7 × 5.7 × 2 Sumida
CDRH5D18-5R4 5.4 76 (847) 956-0666
CDRH5D28-5R3 5.3 38 5.7 × 5.7 × 3 www.sumida.com
CDRH5D28-6R2 6.2 45
CDRH5D28-8R2 8.2 53
ELL6SH-4R7M 4.7 50 6.4 × 6 × 3 Panasonic
ELL6SH-5R6M 5.6 59 (408) 945-5660
ELL6SH-6R8M 6.8 62 www.panasonic.com
RLF5018T- 4.7 45 5.6 × 5.2 × 1.8 TDK
4R7M1R4 (847) 803-6100
www.tdk.com
LT1946
6
1946fb
APPLICATIO S I FOR ATIO
WUUU
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 or X7R dielectrics are preferred, 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.
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—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 applica-
tion is to use a 100kΩ potentiometer in place of RC, and
use a 470pF capacitor for CC. By adjusting the potentiom-
eter 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 tran-
sient response with RC equal to 7.5k. The phase margin is
V
OUT
20mV/DIV
AC COUPLED
I
LI
0.5A/DIV
AC COUPLED
R
C
= 7.5k 200µs/DIV 1946 F03a
Figure 3a. Transient Response Shows Excessive Ringing
V
OUT
20mV/DIV
AC COUPLED
I
LI
0.5A/DIV
AC COUPLED
R
C
= 18k 200µs/DIV 1946 F03b
Figure 3b. Transient Response is Better
V
OUT
20mV/DIV
AC COUPLED
I
LI
0.5A/DIV
AC COUPLED
R
C
= 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 RC
is increased to 18k, which results in a more damped re-
sponse. 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.
LT1946
7
1946fb
APPLICATIO S I FOR ATIO
WUUU
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.
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
g
mp
. g
mp
acts as a current source where the output current
is proportional to the V
C
voltage. Note that the maximum
output current of g
mp
is finite due to the current limit in the
IC.
From Figure 4, the DC gain, poles and zeroes can be
calculated as follows:
Output Pole: P1= 2
2• •R
Error Amp Pole: P2 = 1
2• •R
Error Amp Zero: Z1= 1
2• •R
DC GAIN: A = 1.25
V
ESR Zero:
RHP Zero: Z3 =
High Frequency Pole: P3 >
L
O
C
OUT
π
π
π
=π
π
•
•
•
••••
•• •
•
•• •
C
C
C
VgRgR
ZESR C
VR
VL
f
OUT
C
C
IN ma O mp L
OUT
IN L
OUT
S
2
2
2
2
21
2
2
3
–
+
–
+
gma
RCRO
R2
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
1946 F04
R1
COUT RL
VOUT
VC
CC
gmp
1.250V
REFERENCE
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
R
L
18.6 ΩApplication Specific
C
OUT
20 µF Application Specific
R
O
10 MΩNot Adjustable
C
C
470 pF Adjustable
R
C
49.9 kΩAdjustable
V
OUT
8 V Application Specific
V
IN
3.3 V Application Specific
g
ma
40 µmho Not Adjustable
g
mp
5 mho Not Adjustable
L 5.4 µH Application Specific
f
S
1.2 MHz Not Adjustable
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.
LT1946
8
1946fb
APPLICATIO S I FOR ATIO
WUUU
Diode Selection
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
Setting Output Voltage
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
RR
V
V
OUT
12
125 1=⎛
⎝
⎜⎞
⎠
⎟
.–
A good range for R2 is from 5k to 30k.
Layout Hints
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.
FREQUENCY (Hz)
0
GAIN (dB)
50
100
100 10k 25k 100k 1M
1946 F05a
–50
1k
FREQUENCY (Hz)
PHASE (DEG)
–100
0
100 10k 25k 100k 1M
1946 F05b
–200
–180
1k
60°
Figure 5. Bode Plot of Figure 1’s Circuit
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
1
2
8
7
3
4
6
5
L1
C2
LT1946
V
OUT
V
IN
GND
SHUTDOWN
R1
R2
MULTIPLE
VIAs
GROUND PLANE
1946 F06
C1
C
SS
C
C
R
C
+
LT1946
9
1946fb
TYPICAL APPLICATIO S
U
Low Profile, Triple Output TFT Supply (10V, –10V, 20V)
VIN
VIN
3.3V TO 5V
SW
FB
3
8
7
14
2
65
LT1946
L1
5.4µHD1
R2
10.5k
R1
75k
RC
33.3k
1946 TA01
C2
20µF
C5
0.1µF
C3
1µF
C4
2.2µF
C1
4.7µF
CC
470pF
CSS
100nF
D4
VOFF
–10V
10mA
AVDD
10V
450mA, VIN = 5V
275mA, VIN = 3.3V
VON
20V
5mA
D5
C6
0.1µF
VCGND
SHDN
SS
COMP
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
+
D2 D3
OFF ON
AV
DD
LOAD CURRENT (mA)
0
EFFICIENCY (%)
65
70
75
300 500
1946 TA01a
60
55
50 100 200 400
80
85
90
V
IN
= 5V
V
IN
= 3.3V
V
ON
LOAD = 5mA
V
OFF
LOAD = 10mA
Efficiency
AV
DD
50mV/DIV
AC COUPLED
I
LI
0.5A/DIV
V
IN
= 5V 100µs/DIV 1946 TA01b
Transient Response
150mA
100mA
AV
DD
LOAD
LT1946
10
1946fb
TYPICAL APPLICATIO S
U
12V Output Boost Converter
Efficiency
V
OUT
100mV/DIV
AC COUPLED
I
LI
0.5A/DIV
V
IN
= 3.3V 100µs/DIV 1946 TA02b
Transient Response
175mA
100mA
I
LOAD
V
IN
V
IN
3.3V TO 5V
SW
FB
LT1946
L1
4.7µHD1
C
SS
100nF
C
C
470pF
R
C
33.3k
V
OUT
12V
410mA, V
IN
= 5V
275mA, V
IN
= 3.3V
1946 TA02
C2
4.7µF
C1
4.7µFV
C
GNDCOMPSS
SHDN
3
65
478
21
C1: 4.7µF, X5R OR X7R, 6.3V
C2: 4.7µF, X5R OR X7R, 16V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
R1
84.5k
R2
9.76k
OFF ON
LOAD CURRENT (mA)
0
EFFICIENCY (%)
65
70
75
300 500
1946 TA02a
60
55
50 100 200 400
80
85
90
V
IN
= 5V
V
IN
= 3.3V
LT1946
11
1946fb
U
PACKAGE DESCRIPTIO
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
MSOP (MS8) 0204
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
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
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.127 ± 0.076
(.005 ± .003)
0.86
(.034)
REF
0.65
(.0256)
BSC
0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
12
34
4.90 ± 0.152
(.193 ± .006)
8765
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
0.52
(.0205)
REF
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
MSOP (MS8E) 0603
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
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
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.127 ± 0.076
(.005 ± .003)
0.86
(.034)
REF
0.65
(.0256)
BSC
0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
12
34
4.90 ± 0.152
(.193 ± .006)
8
8
1
BOTTOM VIEW OF
EXPOSED PAD OPTION
765
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
0.52
(.0205)
REF 1.83 ± 0.102
(.072 ± .004)
2.06 ± 0.102
(.081 ± .004)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
2.083 ± 0.102
(.082 ± .004)
2.794 ± 0.102
(.110 ± .004)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
MS8E Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1662)
LT1946
12
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© LINEAR TECHNOLOGY CORPORATION 2001
LT 0207 REV B • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
Low Profile, Triple Output TFT Supply (8V, –8V, 23V)
Efficiency
VIN
VIN
3.3V
SW
FB
LT1946
L1
5.4µHD1
R3
5.23k
R2
28.7k
RC
49.9k
1946 TA03
C2
20µF
C5
0.1µF
C6
0.1µF
C7
0.1µF
C4
1µF
C3
2.2µF
C1
4.7µF
CC
470pF
CSS
100nF
D7
D2 D3
VOFF
–8V
10mA
AVDD
8V
375mA
VON
23V
5mA
D6
C8
0.1µF
VCGND
SHDN
3
8
7
14
2
56
SS
COMP
+
D4 D5
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
OFF ON
AV
DD
LOAD CURRENT (mA)
0
70
75
85
300
1946 TA03a
65
60
100 200 400
55
50
80
EFFICIENCY (%)
V
ON
LOAD = 5mA
V
OFF
LOAD = 10mA
Start-Up Waveforms
AV
DD
2V/DIV
V
ON
10V/DIV
V
OFF
5V/DIV
I
IN
200mA/V
1ms/DIV
1946 TA04
TYPICAL APPLICATIO
U
PART NUMBER DESCRIPTION COMMENTS
LT1613 1.4MHz Switching Regulator in 5-Lead ThinSOTTM 5V at 200mA from 3.3V Input, ThinSOT Package
LT1615 Micropower Constant Off-Time DC/DC Converter in 5-Lead ThinSOT 20V at 12mA from 2.5V, ThinSOT Package
LT1930/LT1930A 1.2MHz/2.2MHz, 1A Switching Regulator in 5-Lead ThinSOT 12V at 300mA from 5V Input, ThinSOT Package
LT1944/LT1944-1 Dual 350mA Boost Converter V
IN
= 1.2V to 15V, V
OUT
to 34V, MS10 Package
LT1945 Dual ±250mA Boost Converter V
IN
= 1.2V to 15V, V
OUT
to ±34V, MS10 Package
LT1946A 2.7MHz, 1.5A Boost DC/DC Converter V
IN
= 2.45V to 16V, V
OUT
to 34V, MS8E Package
LT1947 3MHz, Dual Switching Regulator 8V at 200mA from 3.3V Input, 10-Lead MSOP Package
ThinSOT is a trademark of Linear Technology Corporation.
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