---
type: Analog Component
title: "LT3471 — Dual 1.3A, 1.2MHz Boost/Inverter in 3mm × 3mm DFN"
description: "Dual 1.3A, 1.2MHz Boost/Inverter in 3mm × 3mm DFN"
resource: "https://www.analog.com/en/products/lt3471.html"
tags: ["datasheet", "okf-r12-batch1", "linear"]
generated: { by: "agentforge/aa0b0641", at: "2026-09-29T20:23:52Z" }
status: draft
sources:
- id: "datasheet"
resource: "https://www.analog.com/media/en/technical-documentation/data-sheets/lt3471.pdf"
title: "LT3471 data sheet"
author: "team:analog-devices"
tables:
- file: "lt3471/tables/table-00-p2-abs_max.csv"
title: "Absolute Maximum Ratings"
page: 2
- file: "lt3471/tables/table-01-p2-data.csv"
title: "Order Information"
page: 2
- file: "lt3471/tables/table-02-p2-spec.csv"
title: "Electrical Characteristics"
page: 2
- file: "lt3471/tables/table-03-p6-data.csv"
title: "Table 1. Inductor Manufacturers"
page: 6
- file: "lt3471/tables/table-04-p7-data.csv"
title: "Table 2. Ceramic Capacitor Manufacturers"
page: 7
- file: "lt3471/tables/table-05-p11-data.csv"
title: "Table 3. Bode Plot Parameters"
page: 11
- file: "lt3471/tables/table-06-p16-data.csv"
title: "Revision History"
page: 16
- file: "lt3471/tables/table-07-p17-data.csv"
title: "Related Parts"
page: 17
figures:
- file: "lt3471/figures/lt3471-f000.png"
caption: ""
type: "application_circuit"
page: 1
- file: "lt3471/figures/lt3471-f001.png"
caption: "OLED Driver Efficiency"
type: "characteristic_curve"
page: 1
- file: "lt3471/figures/lt3471-f005.png"
caption: ""
type: "pinout"
page: 2
- file: "lt3471/figures/lt3471-f006.png"
caption: "Quiescent Current vs Temperature"
type: "characteristic_curve"
page: 3
- file: "lt3471/figures/lt3471-f009.png"
caption: "Figure 1. Block Diagram"
type: "block_diagram"
page: 5
- file: "lt3471/figures/lt3471-f011.png"
caption: ""
type: "scope_capture"
page: 8
- file: "lt3471/figures/lt3471-f012.png"
caption: "Figure 2. Li-Ion OLED Driver"
type: "application_circuit"
page: 8
- file: "lt3471/figures/lt3471-f013.png"
caption: ""
type: "scope_capture"
page: 8
- file: "lt3471/figures/lt3471-f014.png"
caption: "Figure 3. Transient Response of Figure 2's Step-Up Converter without Phase Lead Capacitor"
type: "scope_capture"
page: 9
- file: "lt3471/figures/lt3471-f015.png"
caption: "Figure 4. Transient Response of Figure 2's Step-Up Converter with 33pF Phase Lead Capacitor"
type: "scope_capture"
page: 9
- file: "lt3471/figures/lt3471-f017.png"
caption: "Figure 5. Suggested Layout Showing a Boost on SW1 and an Inverter on SW2. Note the Separate Ground Returns for All High Current Paths (Using a Multilayer Board)"
type: "layout_drawing"
page: 10
- file: "lt3471/figures/lt3471-f019.png"
caption: "Figure 6. Boost Converter Equivalent Model"
type: "block_diagram"
page: 10
- file: "lt3471/figures/lt3471-f020.png"
caption: "Figure 7. Bode Plot of 3.3V to 7V Application"
type: "characteristic_curve"
page: 11
- file: "lt3471/figures/lt3471-f021.png"
caption: ""
type: "application_circuit"
page: 12
- file: "lt3471/figures/lt3471-f022.png"
caption: "Li-Ion OLED Driver Efficiency"
type: "characteristic_curve"
page: 12
- file: "lt3471/figures/lt3471-f023.png"
caption: ""
type: "application_circuit"
page: 13
- file: "lt3471/figures/lt3471-f024.png"
caption: ""
type: "application_circuit"
page: 14
- file: "lt3471/figures/lt3471-f025.png"
caption: ""
type: "other"
page: 15
- file: "lt3471/figures/lt3471-f026.png"
caption: "3mm) (Reference LTC DWG # 05-08-1699)"
type: "other"
page: 15
- file: "lt3471/figures/lt3471-f027.png"
caption: ""
type: "application_circuit"
page: 17
- file: "lt3471/figures/lt3471-f029.png"
caption: "VREF Voltage vs VREF Current"
type: "scope_capture"
page: 3
- file: "lt3471/figures/lt3471-f030.png"
caption: "VREF Voltage vs Temperature"
type: "characteristic_curve"
page: 3
- file: "lt3471/figures/lt3471-f031.png"
caption: "Switch Saturation Voltage vs Switch Current"
type: "characteristic_curve"
page: 3
- file: "lt3471/figures/lt3471-f032.png"
caption: "SHDN/SS Current vs SHDN/SS Voltage"
type: "scope_capture"
page: 3
- file: "lt3471/figures/lt3471-f033.png"
caption: "Current Limit vs Duty Cycle"
type: "characteristic_curve"
page: 3
- file: "lt3471/figures/lt3471-f034.png"
caption: "Oscillator Frequency vs Temperature"
type: "characteristic_curve"
page: 4
- file: "lt3471/figures/lt3471-f035.png"
caption: "Peak Switch Current vs SHDN/SS Voltage"
type: "characteristic_curve"
page: 4
- file: "lt3471/figures/lt3471-f036.png"
caption: "Start-Up Waveform (Figure 2 Circuit)"
type: "scope_capture"
page: 4
- file: "lt3471/figures/lt3471-eq01.png"
caption: "Equation as printed (p. 6)"
type: equation
page: 6
- file: "lt3471/figures/lt3471-eq02.png"
caption: "Equation as printed (p. 6)"
type: equation
page: 6
- file: "lt3471/figures/lt3471-eq03.png"
caption: "Equation as printed (p. 6)"
type: equation
page: 6
- file: "lt3471/figures/lt3471-eq04.png"
caption: "Equation as printed (p. 6)"
type: equation
page: 6
- file: "lt3471/figures/lt3471-eq05.png"
caption: "Equation as printed (p. 6)"
type: equation
page: 6
- file: "lt3471/figures/lt3471-eq06.png"
caption: "Equation as printed (p. 7)"
type: equation
page: 7
- file: "lt3471/figures/lt3471-eq07.png"
caption: "Equation as printed (p. 9)"
type: equation
page: 9
agentforge:
part_number: "LT3471"
collection: "okf-r12-batch1"
---
# LT3471 — Dual 1.3A, 1.2MHz Boost/Inverter in 3mm × 3mm DFN
*Datasheet: [LT3471 data sheet (PDF)](https://www.analog.com/media/en/technical-documentation/data-sheets/lt3471.pdf)*
### FEATURES
- 1.2MHz Switching Frequency
- Low V CESAT Switches: 330mV at 1.3A
- High Output Voltage: Up to 40V
- Wide Input Range: 2.4V to 16V
- Inverting Capability
- 5V at 630mA from 3.3V Input
- 12V at 320mA from 5V Input
- -12V at 200mA from 5V Input
- Uses Tiny Surface Mount Components
- Low Shutdown Current: <1µA
- Low Profile (0.75mm) 10-Lead 3mm × 3mm DFN Package
### APPLICATIONS
- Organic LED Power Supply
- Digital Cameras
- White LED Power Supply
- Cellular Phones
- Medical Diagnostic Equipment
- Local ±5V or ±12V Supply
- TFT-LCD Bias Supply
- xDSL Power Supply
All registered trademarks and trademarks are the property of their respective owners.
### DESCRIPTION
The LT ® 3471 dual switching regulator combines two 42V, 1.3A switches with error amplifiers that can sense to ground providing boost and inverting capability. The low VCESAT bipolar switches enable the device to deliver high current outputs in a small footprint. The LT3471 switches at 1.2MHz, allowing the use of tiny, low cost and low profile inductors and capacitors. High inrush current at start-up is eliminated using the programmable soft-start function, where an external RC sets the current ramp rate. A constant frequency current mode PWM architecture results in low, predictable output noise that is easy to filter.
The LT3471 switches are rated at 42V, making the device ideal for boost converters up to ±40V as well as SEPIC and flyback designs. Each channel can generate 5V at up to 630mA from a 3.3V supply, or 5V at 510mA from four alkaline cells in a SEPIC design. The device can be configured as two boosts, a boost and inverter or two inverters.
The LT3471 is available in a low profile (0.75mm) 10-lead 3mm × 3mm DFN package.
### TYPICAL APPLICATION
### ABSOLUTE MAXIMUM RATINGS
(Note 1)
**Absolute Maximum Ratings** ([table-00-p2-abs_max.csv](lt3471/tables/table-00-p2-abs_max.csv), p. 2)
| PARAMETER | RATING |
|---|---|
| V_IN Voltage | 16V |
| SW1, SW2 Voltage | −0.4V to 42V |
| FB1N, FB1P, FB2N, FB2P Voltage | 12V or V_IN − 1.5V |
| S̅H̅D̅N̅/SS1, S̅H̅D̅N̅/SS2 Voltage | 16V |
| V_REF Voltage | 1.5V |
| Maximum Junction Temperature | 125°C |
| Operating Temperature Range (Note 2) | −40°C to 85°C |
| Storage Temperature Range | −65°C to 125°C |
### ORDER INFORMATION
**Order Information** ([table-01-p2-data.csv](lt3471/tables/table-01-p2-data.csv), p. 2)
| LEAD FREE FINISH | TAPE AND REEL | PART MARKING | PACKAGE DESCRIPTION | TEMPERATURE RANGE |
|---|---|---|---|---|
| LT3471EDD#PBF | LT3471EDD#TRPBF | LBHM | 10-Lead (3mm × 3mm) Plastic DFN | −40°C to 85°C |
| LEAD BASED FINISH | TAPE AND REEL | PART MARKING | PACKAGE DESCRIPTION | TEMPERATURE RANGE |
| LT3471EDD | LT3471EDD#TR | LBHM | 10-Lead (3mm × 3mm) Plastic DFN | −40°C to 85°C |
For more information on lead free part marking, go to: www.adi.com/leadfree/
This product is only offered in trays. For more information go to: www.adi.com/tapeandreel/
### ELECTRICAL CHARACTERISTICS
The
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T A = 25°C. V IN = V SHDN = 3V unless otherwise noted.
**Electrical Characteristics** ([table-02-p2-spec.csv](lt3471/tables/table-02-p2-spec.csv), p. 2)
| PARAMETER | CONDITIONS | MIN | TYP | MAX | UNITS | OVERTEMP |
|---|---|---|---|---|---|---|
| Minimum Operating Voltage | | | 2.1 | 2.4 | V | |
| Reference Voltage | | 0.991 | 1.000 | 1.009 | V | |
| Reference Voltage | | 0.987 | | 1.013 | V | ● |
| Reference Voltage Current Limit | (Note 3) | 1 | 1.4 | | mA | |
| Reference Voltage Load Regulation | 0mA ≤ I_REF ≤ 100µA (Note 3) | | 0.1 | 0.2 | %/100µA | |
| Reference Voltage Line Regulation | 2.6V ≤ V_IN ≤ 16V | | 0.03 | 0.08 | %/V | |
| Error Amplifier Offset | Transition from Not Switching to Switching, V_FBP = V_FBN = 1V | | ±2 | ±3 | mV | |
| FB Pin Bias Current | V_FB = 1V (Note 3) | | 60 | 100 | nA | ● |
| Quiescent Current | V_S̅H̅D̅N̅ = 1.8V, Not Switching | | 2.5 | 4 | mA | |
| Quiescent Current in Shutdown | V_S̅H̅D̅N̅ = 0.3V, V_IN = 3V | | 0.01 | 1 | µA | |
| Switching Frequency | | 1 | 1.2 | 1.4 | MHz | |
| Maximum Duty Cycle | | 90 | 94 | | % | |
| Maximum Duty Cycle | | 86 | | | % | ● |
| Minimum Duty Cycle | | | 15 | | % | |
| Switch Current Limit | At Minimum Duty Cycle | 1.5 | 2.05 | 2.6 | A | |
| Switch Current Limit | At Maximum Duty Cycle (Note 4) | 0.9 | 1.45 | 2.0 | A | |
| Switch V_CESAT | I_SW = 0.5A (Note 5) | | 150 | 250 | mV | |
| Switch Leakage Current | V_SW = 5V | | 0.01 | 1 | µA | |
| S̅H̅D̅N̅/SS Input Voltage High | | 1.8 | | | V | |
| S̅H̅D̅N̅ Input Voltage Low | Quiescent Current ≤ 1µA | | | 0.3 | V | |
| S̅H̅D̅N̅ Pin Bias Current | V_S̅H̅D̅N̅ = 3V, V_IN = 4V | | 22 | 36 | µA | |
| S̅H̅D̅N̅ Pin Bias Current | V_S̅H̅D̅N̅ = 0V | | 0 | 0.1 | µA | |
*OVERTEMP: ● marks a limit specified over the full operating temperature range; a blank cell means the limit is specified at TA = 25°C only.*
- **Note 4:** See Typical Performance Characteristics for guaranteed current limit vs duty cycle.
temperature range, otherwise specifications are T A = 25°C. V IN = V
● denotes specifications which apply over the full operating SHDN = 3V unless otherwise noted.
*Continuation of **Electrical Characteristics** — rows included in the table above.*
- **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.
temperature range are assured by design, characterization and correlation with statistical process controls.
- **Note 3:** Current flows out of the pin.
- **Note 2:** The LT3471E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the -40°C to 85°C operating Note 4: See Typical Performance Characteristics for guaranteed current limit vs duty cycle.
- **Note 5:** VCESAT is 100% tested at wafer level only.
### PIN CONFIGURATION
### TYPICAL PERFORMANCE CHARACTERISTICS
V IN = 3.3V
V IN > V
SHDN
/SS VOLTAGE 1V/DIV
/SS
SHDN
/SS
CURRENT
20µV/DIV
SHDN
V REF (V)
1.010
1.005
1.000
0.995
0.990
-50
-25
TEMPERATURE (°C)
CURRENT LIMIT (A)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
T A = 25°C
TYPICAL
GUARANTEED
DUTY CYCLE (%)
V CESAT (mV)
V REF
VOLTAGE
100mV/DIV
V REF CURRENT 200µA/DIV
0.2
0.4
0.8
1.2
1.4
0.6
1.0
SW CURRENT (A)
90°C
1.6
25°C
1.8
2.0
### PIN FUNCTIONS
FB1N (Pin 1): Negative Feedback Pin for Switcher 1. Connect resistive divider tap here. Minimize trace area at FB1N. Set V OUT = V FB1P (1 + R1/R2), or connect to ground for inverting topologies.
FB1P (Pin 2): Positive Feedback Pin for Switcher 1. Connect either to V REF or a divided down version of V REF , or connect to a resistive divider tap for inverting topologies.
VREF (Pin 3): 1.00V Reference Pin. Can supply up to 1mA of current. Do not pull this pin high. Must be locally bypassed with no less than 0.01µF and no more than 1µF. A 0.1µF ceramic capacitor is recommended. Use this pin as the positive feedback reference or connect a resistor divider here for a smaller reference voltage.
FB2P (Pin 4): Same as FB1P but for Switcher 2.
FB2N (Pin 5): Same as FB1N but for Switcher 2.
SW2 (Pin 6): Switch Pin for Switcher 2 (Collector of internal NPN power switch). Connect inductor/diode here and minimize the metal trace area connected to this pin to minimize EMI.
SHDN /SS2 (Pin 7): Shutdown and Soft-Start Pin. Tie to 1.8V or more to enable device. Ground to shut down. Softstart function is provided when the voltage at this pin is ramped slowly to 1.8V with an external RC circuit.
VIN (Pin 8): Input Supply. Must be locally bypassed.
SHDN /SS1 (Pin 9): Same as SHDN /SS2 but for Switcher 1. Note: taking either SHDN /SS pin high will enable the part. Each switcher is individually enabled with its respective SHDN /SS pin.
SW1 (Pin 10): Same as SW2 but for Switcher 1.
Exposed Pad (Pin 11): Ground. Connect directly to local ground plane. This ground plane also serves as a heat sink for optimal thermal performance.
### BLOCK DIAGRAM
the output. Similarly, if the error decreases, less current is delivered. Each switcher functions independently but they share the same oscillator and thus the switchers are always in phase. Enabling the part is done by taking either SHDN /SS pin above 1.8V. Disabling the part is done by grounding both SHDN /SS pins. The soft-start feature of the LT3471 allows for clean start-up conditions by limiting the amount of voltage rise at the output of comparator A1 and A2, which in turn limits the peak switching current. The soft-start feature for each switcher is enabled by slowly ramping that switcher's SHDN /SS pin, using an RC network, for example. Typical resistor and capacitor values are 0.33µF and 4.7k, allowing for a start-up time on the order of milliseconds. The LT3471 has a current limit circuit not shown in the Block Diagram. The switch current is constantly monitored and not allowed to exceed the maximum switch current (typically 1.6A). If the switch
### OPERATION
The LT3471 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Refer to the Block Diagram. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch, Q1 (Q2). A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2 (A4). When this voltage exceeds the level at the negative input of A2 (A4), the SR latch is reset, turning off the power switch Q1 (Q2). The level at the negative input of A2 (A4) is set by the error amplifier A1 (A3) and is simply an amplified version of the difference between the negative feedback voltage and the positive feedback voltage, usually tied to the reference voltage V REG . In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to
current reaches this value, the SR latch is reset regardless of the state of the comparator A2 (A4). Also not shown in the Block Diagram is the thermal shutdown circuit. If the temperature of the part exceeds approximately 160°C,
### APPLICATIONS INFORMATION
### Duty Cycle
The typical maximum duty cycle of the LT3471 is 94%. The duty cycle for a given application is given by:
$$\ DC = \frac{| V_{OUT} | + | V_{D} | - | V_{IN} |}{| V_{OUT} | + | V_{D} | - | V_{CESAT} |}$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
Where V D is the diode forward voltage drop and V CESAT is in the worst case 330mV (at 1.3A)
The LT3471 can be used at higher duty cycles, but it must be operated in the discontinuous conduction mode so that the actual duty cycle is reduced.
### Setting Output Voltage
Setting the output voltage depends on the topology used. For normal noninverting boost regulator topologies:
$$V_{OUT} = V_{FBP}\left(1 + \frac{R1}{R2}\right)$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
where V FBN is connected between R1 and R2 (see the Typical Applications section for examples).
Select values of R1 and R2 according to the following equation:
$$R1 = R2\left[\left(\frac{V_{OUT}}{V_{REF}}\right) - 1\right]$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
A good value for R2 is 15k which sets the current in the resistor divider chain to 1.00V/15k = 67µA.
VFBP is usually just tied to V REF = 1.00V, but V FBP can also be tied to a divided down version of V REF or some other voltage as long as the absolute maximum ratings for the feedback pins are not exceeded (see Absolute Maximum Ratings).
both latches are reset regardless of the state of comparators A2 and A4. The current limit and thermal shutdown circuits protect the power switch as well as the external components connected to the LT3471.
For inverting topologies, V FBN is tied to ground and V FBP is connected between R1 and R2. R2 is between V FBP and V REF and R1 is between V FBP and V OUT (see the Applications section for examples). In this case:
$$V_{OUT} = V_{REF} \left( \frac{R 1}{R 2} \right)$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
Select values of R1 and R2 according to the following equation:
$$R1 = R2 \left( \frac{V_{OUT}}{V_{REF}} \right)$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
A good value for R2 is 15k, which sets the current in the resistor divider chain to 1.00V/15k = 67µA.
### Switching Frequency and Inductor Selection
The LT3471 switches at 1.2 MHz, allowing for small valued inductors to be used. 4.7µH or 10µH will usually suffice. Choose an inductor that can handle at least 1.4A without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I 2 R power losses. 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. For better efficiency, use similar valued inductors with a larger volume. Many different sizes and shapes are available from various manufacturers. Choose a core material that has low losses at 1.2 MHz, such as ferrite core.
**Table 1. Inductor Manufacturers** ([table-03-p6-data.csv](lt3471/tables/table-03-p6-data.csv), p. 6)
| Sumida | (847) 956-0666 | www.sumida.com |
|---|---|---|
| TDK | (847) 803-6100 | www.tdk.com |
| Murata | (714) 852-2001 | www.murata.com |
### Soft-Start and Shutdown Features
To shut down the part, ground both SHDN /SS pins. To shut down one switcher but not the other one, ground that switcher's SHDN /SS pin. The soft-start feature provides a way to limit the inrush current drawn from the supply upon start-up. To use the soft-start feature for either switcher, slowly ramp up that switcher's SHDN /SS pin. The rate of voltage rise at the output of the switcher's comparator (A1 or A3 for switcher 1 or switcher 2 respectively) tracks the rate of voltage rise at the SHDN /SS pin once the SHDN /SS pin has reached about 1.1V. The soft-start function will go away once the voltage at the SHDN /SS pin exceeds 1.8V. See the Peak Switch Current vs SHDN /SS Voltage graph in the Typical Performance Characteristics section. The rate of voltage rise at the SHDN /SS pin can easily be controlled with a simple RC network connected between the control signal and the SHDN /SS pin. Typical values for the RC network are 4.7kΩ and 0.33µF, giving start-up times on the order of milliseconds. This RC time constant can be adjusted to give different start-up times. If different values of resistance are to be used, keep in mind the SHDN /SS Current vs SHDN /SS voltage graph along with the Peak Switch Current vs SHDN /SS Voltage graph, both found in the Typical Performance Characteristics section. The impedance looking into the SHDN /SS pin depends on whether the SHDN /SS is above or below V IN . Normally SHDN /SS will not be driven above V IN , and thus the impedance looks like 100kΩ in series with a diode. If the voltage of the SHDN /SS pin is above V IN , the impedance looks more like 50kΩ in series with a diode. This 100kΩ or 50kΩ impedance can have a slight effect on the start-up time if you choose the R in the RC soft-start network too large. Another consideration is selecting the soft-start time so that the soft-start feature is dominated by the RC network and not the capacitor on V REF . (See V REF voltage reference section of the Applications Information for details.)
The soft-start feature is of particular importance in applications where the switch will see voltage levels of 30V or higher. In these applications, the simultaneous presence of high current and voltage during startup may cause an overstress condition to the switch. Therefore, depending on input and output voltage conditions, higher RC time constant values may be necessary to improve the ruggedness of the design.
### CAPACITOR SELECTION
Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. Multi-layer ceramic capacitors are an excellent choice, as they have 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 15µF 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 LT3471. A 4.7µF to 10µF 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** ([table-04-p7-data.csv](lt3471/tables/table-04-p7-data.csv), p. 7)
| Taiyo Yuden | (408) 573-4150 | www.t-yuden.com |
|---|---|---|
| AVX | (803) 448-9411 | www.avxcorp.com |
| Murata | (714) 852-2001 | www.murata.com |
The decision to use either low ESR (ceramic) capacitors or the higher ESR (tantalum or OS-CON) capacitors can affect the stability of the overall system. The ESR of any capacitor, along with the capacitance itself, contributes a zero to the system. For the tantalum and OS-CON capacitors, this zero is located at a lower frequency due to the higher value of the ESR, while the zero of a ceramic capacitor is at a much higher frequency and can generally be ignored.
A phase lead zero can be intentionally introduced by placing a capacitor (C PL ) in parallel with the resistor (R3) between VOUT and V FB as shown in Figure 2. The frequency of the zero is determined by the following equation.
$$f_{Z} = \frac{1}{2 \pi \cdot R 3 \cdot C_{PL}}$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
C1, C2: X5R OR X7R 6.3V
C3, C4: X5R OR X7R 10V
C5: XR5 OR X7R 16V
C PL : OPTIONAL
D1, D2: ON SEMICONDUCTOR MBRM-120
L1: SUMIDA CR43-2R2
L2: SUMIDA CDRH4D18-100
L3: SUMIDA CDRH4D18-150
### Supply Current of Figure 2 During Start-Up with Soft-Start RC Network
### Supply Current of Figure 2 During Start-Up without Soft-Start RC Network
By choosing the appropriate values for the resistor and capacitor, the zero frequency can be designed to improve the phase margin of the overall converter. The typical target value for the zero frequency is between 35kHz to 55kHz. Figure 3 shows the transient response of the step-up converter from Figure 2 without the phase lead capacitor C PL . Although adequate for many applications, phase margin is not ideal as evidenced by 2-3 'bumps' in both the output voltage and inductor current. A 33pF capacitor for C PL results in ideal phase margin, which is revealed in Figure 4 as a more damped response and less overshoot.
### VREG VOLTAGE REFERENCE
Pin 3 of the LT3471 is a bandgap voltage reference that has been divided down to 1.00V and buffered for external use. This pin must be bypassed with at least 0.01µF and no more than 1µF. This will ensure stability as well as reduce the noise on this pin. The buffer has a built-in current limit of at least 1mA (typically 1.4mA). This not only means that you can use this pin as an external reference for supplemental circuitry, but it also means that it is possible to provide a soft-start feature if this pin is used as one of the feedback pins for the error amplifier. Normally the soft-start time will be dominated by the RC time constant discussed in the soft-start and shutdown section. However, because of the finite current limit of the buffer for the V REG pin, it will take some time to charge up the bypass capacitor. During this time, the voltage at the V REG pin will ramp up, and this action provides an alternate means for soft-starting the circuit. If the largest recommended bypass capacitor is used, 1µF, the worst-case (longest) soft-start function that would be provided from the V REF pin is:
$$\frac{1 \mu F \cdot 1.00 V}{1.0 mA} = 1.0 ms$$
*LaTeX transcription of the equation above, checked against the symbols printed on the page.*
Choose the RC network such that the soft-start time is longer than this time, or choose a smaller bypass capacitor for the V REF pin (but always larger than 0.01µF) so that the RC network dominates the soft-starting of the LT3471. The voltage at the V REF pin can also be divided down and used for one of the feedback pins for the error amplifier. This is especially useful in LED driver applications, where the current through the LEDs is set using the voltage reference across a sense resistor in the LED chain. Using a smaller or divided down reference leads to less wasted power in the sense resistor. See the Typical Applications section for an example of LED driving applications.
### DIODE SELECTION
A Schottky diode is recommended for use with the LT3471. For high efficiency, a diode with good thermal characteristics at high currents should be used such as the On Semiconductor MBRM120. This is a 20V diode. Where the switch voltage exceeds 20V, use the MBRM140, a 40V diode. These diodes are rated to handle an average forward current of 1.0A. In applications where the average forward current of the diode is less than 0.5A, use the Philips PMEG 2005, 3005, or 4005 (a 20V, 30V or 40V diode, respectively).
### LAYOUT HINTS
The high speed operation of the LT3471 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 5 shows the recommended component placement.
### Compensation-Theory
Like all other current mode switching regulators, the LT3471 needs to be compensated for stable and efficient operation. Two feedback loops are used in the LT3471: 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 6 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 6, the DC gain, poles and zeroes can be calculated as follows:
$$\text{Output Pole: P1} = \frac{2}{2 \cdot \pi \cdot R_L \cdot C_{OUT}} \\
\text{Error Amp Pole: P2} = \frac{1}{2 \cdot \pi \cdot RO \cdot CC} \\
\text{Error Amp Zero: Z1} = \frac{1}{2 \cdot \pi \cdot RC \cdot CC} \\
\text{DC GAIN: A} = \frac{V_{REF}}{V_{OUT}} \cdot g_{ma} \cdot RO \cdot g_{mp} \cdot RL \cdot \frac{1}{2} \\
\text{ESR Zero: Z2} = \frac{1}{2 \cdot \pi \cdot R_{ESR} \cdot C_{OUT}} \\
\text{RHP Zero: Z3} = \frac{V_{IN}^2 \cdot RL}{2 \cdot \pi \cdot V_{OUT}^2 \cdot L} \\
\text{High Frequency Pole: P3} > \frac{fS}{3} \\
\text{Phase Lead Zero: Z4} = \frac{1}{2 \cdot \pi \cdot R1 \cdot C_{PL}} \\
\text{Phase Lead Pole: P4} = \frac{1}{2 \cdot \pi \cdot C_{PL} \cdot \frac{R1 \cdot R2}{R1 + R2}}$$
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 2 as an example, Table 3 shows the parameters used to generate the Bode plot shown in Figure 7.
**Table 3. Bode Plot Parameters** ([table-05-p11-data.csv](lt3471/tables/table-05-p11-data.csv), p. 11)
| Parameter | Value | Units | Comment |
|---|---|---|---|
| R_L | 20 | Ω | Application Specific |
| C_OUT | 4.7 | µF | Application Specific |
| R_ESR | 10 | mΩ | Application Specific |
| R_O | 0.9 | MΩ | Not Adjustable |
| C_C | 90 | pF | Not Adjustable |
| C_PL | 33 | pF | Adjustable |
| R_C | 55 | kΩ | Not Adjustable |
| R1 | 90.9 | kΩ | Adjustable |
| R2 | 15 | kΩ | Adjustable |
| V_OUT | 7 | V | Application Specific |
| V_IN | 3.3 | V | Application Specific |
| g_ma | 50 | µmho | Not Adjustable |
| g_mp | 9.3 | mho | Not Adjustable |
| L | 2.2 | µH | Application Specific |
| f_S | 1.2 | MHz | Not Adjustable |
From Figure 7, the phase is -115° when the gain reaches 0dB giving a phase margin of 65°. This is more than adequate. The crossover frequency is 50kHz.
### TYPICAL APPLICATIONS
### Li-Ion OLED Driver
C3, C4: X5R OR X7R 10V
C5: XR5 OR X7R 16V
L1: SUMIDA CR43-2R2
L2: SUMIDA CDRH4D18-100
C6: OPTIONAL
L3: SUMIDA CDRH4D18-150
### Li-Ion OLED Driver Efficiency
### Single Li-Ion Cell to 5V, 12V Boost Converter
C1-C3: X5R OR X7R 6.3V
C4: X5R OR X7R 16V
D1, D2: ON SEMICONDUCTOR MBRM-120
L1: SUMIDA CR43-3R3
L2: SUMIDA CR43-6R8
### Li-Ion 20 White LED Driver
### Li-Ion or 4-Cell Alkaline to 3.3V and 5V SEPIC
### PACKAGE DESCRIPTION
DD Package 10-Lead Plastic DFN (3mm ×
### RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
### REVISION HISTORY (Revision history begins at Rev C)
**Revision History** ([table-06-p16-data.csv](lt3471/tables/table-06-p16-data.csv), p. 16)
| REV | DATE | DESCRIPTION | PAGE NUMBER |
|---|---|---|---|
| C | 6/25 | Updated Reference Number in the Package Description. | 15 |
### 5V to ±12V Dual Supply Boost/Inverting Converter
### RELATED PARTS
**Related Parts** ([table-07-p17-data.csv](lt3471/tables/table-07-p17-data.csv), p. 17)
| PART NUMBER | DESCRIPTION | COMMENTS |
|---|---|---|
| LT1611 | 550mA (I_SW), 1.4MHz, High Efficiency Micropower Inverting DC/DC Converter | V_IN: 1.1V to 10V, V_OUT(MAX) = −34V, I_Q = 3mA, I_SD < 1µA, ThinSOT Package |
| LT1613 | 550mA (I_SW), 1.4MHz, High Efficiency Step-Up DC/DC Converter | V_IN: 0.9V to 10V, V_OUT(MAX) = 34V, I_Q = 3mA, I_SD < 1µA, ThinSOT Package |
| LT1614 | 750mA (I_SW), 600kHz, High Efficiency Micropower Inverting DC/DC Converter | V_IN: 1V to 12V, V_OUT(MAX) = −24V, I_Q = 1mA, I_SD < 10µA, MS8, S8 Packages |
| LT1615/LT1615-1 | 300mA/80mA (I_SW), High Efficiency Step-Up DC/DC Converters | V_IN = 1V to 15V, V_OUT(MAX) = 34V, I_Q = 20µA, I_SD < 1µA, ThinSOT Package |
| LT1617/LT1617-1 | 350mA/100mA (I_SW), High Efficiency Micropower Inverting DC/DC Converters | V_IN = 1.2V to 15V, V_OUT(MAX) = −34V, I_Q = 20µA, I_SD < 1µA, ThinSOT Package |
| LT1930/LT1930A | 1A (I_SW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converters | V_IN: 2.6V to 16V, V_OUT(MAX) = 34V, I_Q = 4.2mA/5.5mA, I_SD < 1µA, ThinSOT Package |
| LT1931/LT1931A | 1A (I_SW), 1.2MHz/2.2MHz High Efficiency Micropower Inverting DC/DC Converters | V_IN = 2.6V to 16V, V_OUT(MAX) = −34V, I_Q = 5.8mA, I_SD < 1µA, ThinSOT Package |
| LT1943 (Quad) | Quad Boost, 2.6A Buck, 2.6A Boost, 0.3A Boost, 0.4A Inverter 1.2MHz TFT DC/DC Converter | V_IN = 4.5V to 22V, V_OUT(MAX) = 40V, I_Q = 10µA, I_SD < 35µA, TSSOP28E Package |
| LT1945 (Dual) | Dual Output, Boost/Inverter, 350mA (I_SW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter | V_IN = 1.2V to 15V, V_OUT(MAX) = ±34V, I_Q = 40µA, I_SD < 1µA, 10-Lead MS Package |
| LT1946/LT1946A | 1.5A (I_SW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converters | V_IN: 2.45V to 16V, V_OUT(MAX) = 34V, I_Q = 3.2mA, I_SD < 1µA, MS8 Package |
| LT3436 | 3A (I_SW), 1MHz, 34V Step-Up DC/DC Converter | V_IN: 3V to 25V, V_OUT(MAX) = 34V, I_Q = 0.9mA, I_SD < 6µA, TSSOP16E Package |
| LT3462/LT3462A | 300mA (I_SW), 1.2MHz/2.7MHz, High Efficiency Inverting DC/DC Converters with Integrated Schottkys | V_IN = 2.5V to 16V, V_OUT(MAX) = −38V, I_Q = 2.9mA, I_SD < 1µA, ThinSOT Package |
| LT3463/LT3463A | Dual Output, Boost/Inverter, 250mA (I_SW), Constant Off-Time, High Efficiency Step-Up DC/DC Converters with Integrated Schottkys | V_IN = 2.3V to 15V, V_OUT(MAX) = ±40V, I_Q = 40µA, I_SD < 1µA, DFN Package |
| LT3464 | 85mA (I_SW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect | V_IN = 2.3V to 10V, V_OUT(MAX) = 34V, I_Q = 25µA, I_SD < 1µA, ThinSOT Package |
D1, D2: ON SEMICONDUCTOR MBRM-120
## Additional Figures
*OLED Driver Efficiency*
*Quiescent Current vs Temperature*
*Figure 1. Block Diagram*
*Figure 2. Li-Ion OLED Driver*
*Figure 3. Transient Response of Figure 2's Step-Up Converter without Phase Lead Capacitor*
*Figure 4. Transient Response of Figure 2's Step-Up Converter with 33pF Phase Lead Capacitor*
*Figure 5. Suggested Layout Showing a Boost on SW1 and an Inverter on SW2. Note the Separate Ground Returns for All High Current Paths (Using a Multilayer Board)*
*Figure 6. Boost Converter Equivalent Model*
*Figure 7. Bode Plot of 3.3V to 7V Application*
*Li-Ion OLED Driver Efficiency*
*3mm) (Reference LTC DWG # 05-08-1699)*
*VREF Voltage vs VREF Current*
*VREF Voltage vs Temperature*
*Switch Saturation Voltage vs Switch Current*
*SHDN/SS Current vs SHDN/SS Voltage*
*Current Limit vs Duty Cycle*
*Oscillator Frequency vs Temperature*
*Peak Switch Current vs SHDN/SS Voltage*
*Start-Up Waveform (Figure 2 Circuit)*