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LT1946A 2.7MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start
FEATURES
s s s s s s s
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
APPLICATIO S
s s s s
TFT-LCD Bias Supplies GPS Receivers DSL Modems Local Power Supply
The LT(R)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.
TYPICAL APPLICATIO
VIN 5V 3 1 L1 2.2H 6 VIN SHDN VC SS CSS 100nF 8 OFF ON C1 2.2F RC 27.4k CC 270pF 5 SW
D1
VOUT 12V 430mA R1 182k EFFICIENCY (%)
90 85 80
2 LT1946A FB 7 COMP GND* 4 R2 21k
C2 2.2F
75 70 65 60
C1: 2.2F, X5R or X7R, 6.3V C2: 2.2F, X5R or X7R, 16V D1: MICROSEMI UPS120 OR EQUIVALENT L1: SUMIDA CR43-2R2 * EXPOSED PAD MUST ALSO BE GROUNDED
1946A TA01
55 50 0 100 200 300 400 LOAD CURRENT (mA) 500
1946A TA01
Figure 1. 5V to 12V, 430mA Step-Up DC/DC Converter
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Efficiency
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LT1946A
ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 SS COMP VIN SW
VIN Voltage .............................................................. 16V SW Voltage ................................................- 0.4V to 36V FB Voltage .............................................................. 2.5V Current into FB Pin ............................................... 1mA SHDN Voltage .......................................................... 16V Maximum Junction Temperature .......................... 125C Operating Temperature Range (Note 2) ....................................... - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1946AEMS8E MS8E PART MARKING LTYZ
MS8E PACKAGE 8-LEAD PLASTIC MSOP EXPOSED PAD IS GROUND (MUST BE SOLDERED TO PCB)
TJMAX = 125C, JA = 40C/W, JC = 10C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3V, VSHDN = VIN unless otherwise noted. (Note 2)
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP 2.45
MAX 2.6 16 1.27 1.27 120
UNITS V V V V nA mhos V/V
1.23 1.22
1.25 20 40 300 3.6 0 0.01
FB Pin Bias Current Error Amp Transconductance Error Amp Voltage Gain Quiescent Current Quiescent Current in Shutdown Reference Line Regulation Switching Frequency
VFB = 1.25V (Note 3) I = 2A VSHDN = 2.5V, Not Switching VSHDN = 0V, VIN = 3V 2.6V VIN 16V
q
5 1 0.05 3 3.1
q
2.4 2.3 73 1.5
2.7 0.85
Switching Frequency in Foldback Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current Soft-Start Charging Current SHDN Input Voltage High SHDN Input Voltage Low SHDN Pin Bias Current
VFB = 0V
q
80 2.1 240 0.01 2.8 340 1 6 0.5
(Note 4) ISW = 1A VSW = 5V VSS = 0.5V
q
2.5 2.4
4
VSHDN = 3V VSHDN = 0V
16 0
32 0.1
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 0C to 70C. Specifications over the -40C to 85C operating
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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mA A %/V MHz MHz MHz % A mV A A V V A A
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LT1946A TYPICAL PERFOR A CE CHARACTERISTICS
Feedback Pin Voltage
1.28 1.27 3000 2700
OSCILLATOR FREQUENCY (kHz)
FEEDBACK VOLTAGE (V)
1.26 1.25 1.24 1.23 1.22 1.21 1.20 -50
1800 1500 1200 900 600 300 TA = 25C
-25
0 25 50 75 TEMPERATURE (C)
100
125
0
0
0.2
0.4 0.6 0.8 FEEDBACK VOLTAGE (V)
1
1.2
1946A G02
CURRENT LIMIT (A)
Switch Saturation Voltage
0.35 0.30 QUIESCENT CURRENT (mA) 0.25 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 0 0.2 0.4 0.6 0.8 1 1.2 SWITCH CURRENT (A) 1.4 1.6
VCESAT (V)
0.20 0.15 0.10 0.05 0
Transient Response for Figure 1 Circuit
VOUT 100mV/DIV AC COUPLED VOUT 2V/DIV
ILI 0.5A/DIV ILOAD 250mA 150mA 50s/DIV
1946A G07
UW
Oscillator Frequency
Current Limit
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
2400 2100
TA = -30C
TA = 100C
-25
0 25 50 75 TEMPERATURE (C)
100
125
1946A G01
1946A G03
Quiescent Current
VOUT 100mV/DIV AC COUPLED VSW 10V/DIV 0V
Switching Waveforms for Figure 1 Circuit
ILI 0.5A/DIV 100ns/DIV
1946A G06
2.2 -50
-25
0 25 50 75 TEMPERATURE (C)
100
125
1946A G04
1946A G05
Start-Up Waveforms for Figure 1 Circuit
IIN 200mA/DIV 0A VSHDN 5V 0V RLOAD = 250 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. 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. 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, 4A of current charges the capacitor to 1.5V. Use a larger capacitor for slower start-up. Leave floating if not in use.
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LT1946A
BLOCK DIAGRA
VIN 6
VOUT R1 (EXTERNAL) FB R2 (EXTERNAL) 0.5V
SHUTDOWN
SHDN
3
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SS 8 VC 1 COMP 7 4A 120k 90pF
-
1.25V REFERENCE
COMPARATOR DRIVER A2 R S Q
5 SW
Q1
+
A1
+
+
0.01
-
-
RAMP GENERATOR
+
A3
4 GND /3 2.7MHz OSCILLATOR EXPOSED PAD
-
2 FB
1946A F02
Figure 2. Block Diagram
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LT1946A
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
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 1.5H to 4.7H 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.
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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, 4A 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.
Table 1. Recommended Inductors - LT1946A
L (H) 1.5 2.7 4.7 10.0 1.2 2.2 2.2 3.3 MAX DCR (m) 25 33 45 67 80 120 71 86 Size LxWxH (mm) 5.2x5.6x1.8 PART RLF5018-1R5M2R1 RLF5018-2R7M1R8 RLF5018-4R7M1R4 RLF5018-100MR94 LPO1704-122MC LPO1704-222MC CR43-2R2 CR43-3R3 VENDOR TDK (847) 803-6100 www.tdk.com Coilcraft (800) 322-2645 www.coilcraft.com Sumida (847) 956-0666 www.sumida.com 5.5x6.6x1.0 4.5x4.0x3.2
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 2.2F to 20F output
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LT1946A
APPLICATIO S I FOR ATIO
capacitor is sufficient for most applications, but systems with very low output currents may need only a 1F 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 2.2F to 4.7F 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 AVX Murata (408) 573-4150 (803) 448-9411 (714) 852-2001 www.t-yuden.com www.avxcorp.com 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.
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VOUT 200mV/DIV AC COUPLED IL1 0.5A/DIV RC = 2.5k 50s/DIV
1946A F03a
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Figure 3a. Transient Response Shows Excessive Ringing
VOUT 200mV/DIV AC COUPLED
IL1 0.5A/DIV
RC = 6.5k
50s/DIV
1946A F03b
Figure 3b. Transient Response is Better
VOUT 200mV/DIV AC COUPLED
IL1 0.5A/DIV
RC = 27.4k
50s/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. 1946af
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LT1946A
APPLICATIO S I FOR ATIO U
ESR Zero: Z2 =
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: Output Pole: P1 =
2 2 * * RL * C OUT 1 2 * * RO * C C
1 2 * * RC * C C
Error Amp Pole: P2 =
Error Amp Zero: Z1 =
DC Gain: A =
1.25 * G MA * RO * G MP * RL VOUT
-
GMP VOUT ESR 1.250V REFERENCE COUT R1 RL
+
VC GMA RC CC RO R2
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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1 2 * * ESR * C OUT
VIN * RL 2 * * VOUT * L
FS 3
2 2
RHP Zero: Z3 =
High Frequency Pole: P3 >
Using the circuit of Figure 1 as an example, Table 3 shows the parameters used to generate the bode plot shown in Figure 5.
Table 3. Bode Plot Parameters
Parameter RL COUT RO CC RC VOUT VIN GMA GMP L FS ESR Value 28 2.2 10 270 27.4 12 5 40 5 2.2 2.7 10 Units F M pF k V V mho mho H MHz m Comment Application Specific Application Specific Not Adjustable Adjustable Adjustable Application Specific Application Specific Not Adjustable Not Adjustable Application Specific Not Adjustable Not Adjustable
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.
LT1946A
APPLICATIO S I FOR ATIO
100
50
GAIN (f)
0
-50 100
1k
10k 100k FREQUENCY (Hz)
1M
1946A FO5a
0
PHASE (f)
-100
58 -180 -200 100 1k 10k 100k FREQUENCY (Hz) 1M
1946A FO5b
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.
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Setting Output Voltage To set the output voltage, select the values of R1 and R2 (see Figure 1) according to the following equation:
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V R1 = R2 OUT - 1 1.25V
A good range for R2 is from 5k to 30k. 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 CC RC 1 R1 2 R2 SHUTDOWN 3 4 MULTIPLE VIAs GND C2 VOUT LT1946A 7 6 5 L1 8
+
VIN
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
TYPICAL APPLICATIO S
Low Profile (< 1.1mm Tall) Triple Output TFT Supply (10V, -10V, 20V)
D2 D3 VON 20V 5mA
VIN 5V 3 8
+
C1 4.7F CSS 100nF
C1-C6: X5R or X7R C1: 4.7F, 6.3V C2: 2x 10F, 10V C3: 1F, 25V C4: 2.2F, 10V C5-C6: 0.1F, 10V D1: MICROSEMI UPS120 OR EQUIVALENT D2-D5: ZETEX BAT54S OR EQUIVALENT L1: COILCRAFT LP01704-152MC * EXPOSED PAD MUST ALSO BE GROUNDED
Transient Response
90 AVDD 50mV/DIV AC COUPLED EFFICIENCY (%) 85 80 75 70 65 60 55 AVDD LOAD 350mA 200mA 100s/DIV
1946A TA03
ILI 0.5A/DIV
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C5 0.1F L1 1.5H 6 VIN SHDN SS LT1946A FB GND* 4 R2 10.5k 2 C2 20F C3 1F 5 SW D1 AVDD 10V 475mA R1 75k
OFF ON
7
COMP VC 1 RC 59k CC 150pF
C6 0.1F
D4 C4 2.2F D5 VOFF -10V 10mA
1946A TA02
Efficiency
VON LOAD = 5mA VOFF LOAD = 10mA 0 100 200 300 400 AVDD LOAD CURRENT (mA) 500
1946A TA04
50
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LT1946A
TYPICAL APPLICATIO S
Triple Output TFT Supply Uses SEPIC Topology for Output Disconnect
D2 C4 0.22F D3 C5 0.22F VIN 12V 10% 3 8 L1 10H 6 VIN SHDN SS LT1946A FB GND* 4 R2 9.76k 2 C2 20F VC COMP 7 5 SW C3 1F D1 VON 23V 10mA VOFF -12V 10mA
+
C1-C5: X5R or X7R C1: 2.2F, 6.3V C2: 2x 10F, 16V C3: 1F, 25V C4: 0.22F, 25V C5: 0.22F, 16V
2.794 0.102 (.110 .004)
0.889 0.127 (.035 .005)
5.23 (.206) MIN
2.083 0.102 3.2 - 3.45 (.082 .004) (.126 - .136)
0.42 0.04 (.0165 .0015) TYP
0.65 (.0256) BSC
GAUGE PLANE 0.53 0.015 (.021 .006) DETAIL "A" 0.18 (.077) 1 1.10 (.043) MAX 23 4 0.86 (.34) REF 8
RECOMMENDED SOLDER PAD LAYOUT
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
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.
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AVDD 12V 250mA R1 84.5k
OFF ON C1 2.2F CSS 100nF
L2 10H
1
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)
3.00 0.102 (.118 .004) (NOTE 3) 0.52 (.206) REF BOTTOM VIEW OF EXPOSED PAD OPTION 8 7 65 1 2.06 0.102 (.080 .004) 1.83 0.102 (.072 .004)
0.254 (.010)
DETAIL "A" 0 - 6 TYP
4.88 0.1 (.192 .004)
3.00 0.102 (.118 .004) NOTE 4
SEATING PLANE
0.22 - 0.38 (.009 - .015)
0.65 (.0256) BCS
0.13 0.05 (.005 .002)
MSOP (MS8E) 1001
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LT1946A
TYPICAL APPLICATIO S
Low Profile (< 1.1mm Tall) Triple Output TFT Supply (8V, - 8V, 24V)
D2 D3 D4 D5 VON 23V 5mA
VIN 3.3V 3 8
L1 1.2H 6 VIN SHDN SS LT1946A FB GND* 4 2 OFF ON 5 SW
EFFICIENCY (%)
+
C1 4.7F CSS 100nF
7
COMP VC 1
C1-C8: X5R or X7R C1: 4.7F, 6.3V C2: 2x 10F, 10V C3: 2.2F, 10V C4: 1F, 25V C5, C6, C8: 0.1F, 10V C7: 0.1F, 16V D1: MICROSEMI UPS120 OR EQUIVALENT D2-D7: ZETEX BAT54S OR EQUIVALENT L1: COILCRAFT LP01704-122MC * EXPOSED PAD MUST ALSO BE GROUNDED
Transient Response
AVDD 50mV/DIV AC COUPLED AVDD 5V/DIV
ILI 0.5A/DIV VOFF 5V/DIV ILOAD 350mA 200mA 50s/DIV
1946A TA07
RELATED PARTS
PART NUMBER LT1613 LT1615/LT1615-1 LT1930/LT1930A LT1946 LT1961 DESCRIPTION 550mA (ISW), 1.4MHz, Step-Up DC/DC Converter 300mA/0.75mA (ISW), Constant Off-Time Step-Up DC/DC Converter 1A (ISW), 1.2MHz/2.2MHz, Step-Up DC/DC Converter 1.5A (ISW), 1.2MHz, Step-Up DC/DC Converter 1.5A (ISW), 1.25MHz, Step-Up DC/DC Converter COMMENTS VIN = 0.9V to 10V, VOUT to 34V, IQ = 3mA, ISD < 1A, ThinSOTTM VIN = 1V to 15V, VOUT to 34V, IQ = 20A, ISD < 1A, ThinSOT VIN = 2.6V to 16V, VOUT to 34V, IQ = 4.2mA/5.5mA, ISD < 1A, ThinSOT VIN = 2.45V to 16V, VOUT to 34V, IQ = 3.2mA, ISD < 1A, MS8 VIN = 3V to 25V, VOUT to 35V, IQ = 0.9mA, ISD < 6A, MS8E
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ThinSOT is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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FAX: (408) 434-0507 q www.linear.com
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C5 0.1F
C6 0.1F
C7 0.1F
Efficiency
D1
90
AVDD 8V 375mA R2 28.7k
85 80 75 70 65 60 55 VON LOAD = 5mA VOFF LOAD = 10mA 0 100 200 300 AVDD LOAD CURRENT (mA) 400
1946A TA06
C2 20F R3 5.23k C8 0.1F
C4 1F
D7 C3 2.2F D6 VOFF -8V 10mA
1946A TA05
50
Start-Up Waveforms
VON 10V/DIV
IIN 0.5A/DIV 1ms/DIV
1946A TA08
LT/TP 1102 2K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 2001

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