Datasheet

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LT3580

3580fg

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Boost/Inverting DC/DC

Converter with 2A Switch,

Soft-Start, and Synchronization

The LT

3580 is a PWM DC/DC converter containing an

internal 2A, 42V switch. The LT3580 can be configured

as either a boost, SEPIC or inverting converter. Capable

of generating 12V at 550mA or –12V at 350mA from a

5V input, the LT3580 is ideal for many local power supply

designs.

The LT3580 has an adjustable oscillator, set by a resistor

from the RT pin to ground. Additionally, the LT3580 can

be synchronized to an external clock. The free running or

synchronized switching frequency range of the part can

be set between 200kHz and 2.5MHz.

The LT3580 also features innovative SHDN pin circuitry

that allows for slowly varying input signals and an adjust-

able undervoltage lockout function.

Additional features such as frequency foldback and

soft-start are integrated. The LT3580 is available in tiny

3mm × 3mm 8-lead DFN and 8-lead MSOP packages.

1.2MHz, 5V to 12V Boost Converter Achieves Over 88% Efficiency

2A Internal Power Switch

Adjustable Switching Frequency

Single Feedback Resistor Sets V

OUT

Synchronizable to External Clock

High Gain SHDN Pin Accepts Slowly Varying

Input Signals

Wide Input Voltage Range: 2.5V to 32V

Low V

CESAT

Switch: 300mV at 1.5A (Typical)

Integrated Soft-Start Function

Easily Configurable as a Boost or Inverting Converter

User Configurable Undervoltage Lockout (UVLO)

Tiny 8-Lead 3mm × 3mm DFN and 8-Lead MSOP

Packages

VFD Bias Supplies

TFT-LCD Bias Supplies

GPS Receivers

DSL Modems

Local Power Supply

Efficiency and Power Loss

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

10μF

OUT

12V

550mA

4.2μH

130k

3580 TA01

LT3580

75k

10k

SHDN

GND

SYNC SS

1nF

0.1μF

2.2μF

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

400

3580 TA01b

200

100

500

300 600

200

600

1200

400

800

1000

Downloaded from Arrow.com.

Summary of content (28 pages)

PAGE 1
LT3580 Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization FEATURES DESCRIPTION n The LT®3580 is a PWM DC/DC converter containing an internal 2A, 42V switch. The LT3580 can be configured as either a boost, SEPIC or inverting converter. Capable of generating 12V at 550mA or –12V at 350mA from a 5V input, the LT3580 is ideal for many local power supply designs.
PAGE 2
LT3580 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN Voltage ................................................. –0.3V to 32V SW Voltage ................................................ –0.4V to 42V RT Voltage ................................................... –0.3V to 5V SS and FB Voltage .................................... –0.3V to 2.5V VC Voltage ................................................... –0.3V to 2V SHDN Voltage ............................................ –0.3V to 32V SYNC Voltage....................
PAGE 3
LT3580 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = VIN unless otherwise noted. (Note 2) PARAMETER Operating Voltage Range Positive Feedback Voltage Negative Feedback Voltage Positive FB Pin Bias Current Negative FB Pin Bias Current CONDITIONS MIN TYP MAX UNITS l 2.5 1.195 0 81 1.215 5 83.3 32 1.230 12 85 V V mV μA l l 81 81 85.
PAGE 4
LT3580 TYPICAL PERFORMANCE CHARACTERISTICS Switch Current Limit at 1MHz TA = 25°C unless otherwise specified Switch Current Limit at Minimum Duty Cycle Switch Saturation Voltage 400 2.5 350 SATURATION VOLTAGE (mV) 2.0 1.5 1.0 300 SWITCH CURRENT (A) SWITCH CURRENT LIMIT (A) 2.5 250 200 150 2.0 1.5 1.0 100 0.5 0.5 50 0 10 20 30 40 50 60 70 DUTY CYCLE (%) 80 0 90 0 1 0.5 1.
PAGE 5
LT3580 TYPICAL PERFORMANCE CHARACTERISTICS SHDN Pin Current TA = 25°C unless otherwise specified SHDN Pin Current 30 300 25 250 Active/Lockout Threshold 1.40 20 15 10 –50°C 5 100°C 0.5 1.36 20°C 200 100°C 150 100 1.34 1.32 SHDN RISING 1.30 1.28 1.26 SHDN FALLING 1.24 50 1.22 20°C 0 0 1.38 SHDN VOLTAGE (V) SHDN PIN CURRENT (μA) SHDN PIN CURRENT (μA) –50°C 1 1.5 SHDN VOLTAGE (V) 2 0 0 5 20 15 25 10 SHDN VOLTAGE (V) 3580 G10 30 3580 G11 1.
PAGE 6
LT3580 BLOCK DIAGRAM RC VIN CSS 7 SHDN 5 1.3V – + CC 2 SS CIN VC DISCHARGE DETECT L1 275k UVLO SR2 SOFTSTART R Q VIN 3 4 ILIMIT COMPARATOR – Q2 A3 1.215V REFERENCE + R S + ∑ A1 – A4 + A2 FREQUENCY FOLDBACK RFB 0.01Ω – RAMP GENERATOR GND FB 14.6k C1 Q1 Q + 1 VOUT SR1 DRIVER S 14.
PAGE 7
LT3580 OPERATION SEPIC Topology The LT3580 can be configured as a SEPIC (single-ended primary inductance converter). This topology allows for the input to be higher, equal, or lower then the desired output voltage. Output disconnect is inherently built into the SEPIC topology, meaning no DC path exists between the input and output. This is useful for applications requiring the output to be disconnected from the input source when the circuit is in shutdown.
PAGE 8
LT3580 APPLICATIONS INFORMATION Setting Output Voltage Inductor Selection The output voltage is set by connecting a resistor (RFB) from VOUT to the FB pin. RFB is determined from the following equation: |V − V | RFB = OUT FB 83.3µA General Guidelines: The high frequency operation of the LT3580 allows for the use of small surface mount inductors. For high efficiency, choose inductors with high frequency core material, such as ferrite, to reduce core losses.
PAGE 9
LT3580 APPLICATIONS INFORMATION provided to a load (IOUT). In order to provide adequate load current, L should be at least: L> DC • VIN ⎛ |V |• I ⎞ 2(f) ⎜ ILIM − OUT OUT ⎟ VIN • η ⎠ ⎝ for boost, topologies, or: L> ⎛ 2(f) ⎜⎜ILIM − ⎝ DC • VIN VOUT • IOUT VIN • η ⎞ − IOUT ⎟⎟ ⎠ for the SEPIC and inverting topologies. where: L = L1||L2 for uncoupled dual inductor topologies DC = switch duty cycle (see previous section) ILIM = switch current limit, typically about 2.
PAGE 10
LT3580 APPLICATIONS INFORMATION these materials retain their capacitance over wider 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. Always use a capacitor with a sufficient voltage rating. Many capacitors rated at 2.2μF to 20μF, particularly 0805 or 0603 case sizes, have greatly reduced capacitance at the desired output voltage.
PAGE 11
LT3580 APPLICATIONS INFORMATION Compensation—Theory Like all other current mode switching regulators, the LT3580 needs to be compensated for stable and efficient operation. Two feedback loops are used in the LT3580— 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.
PAGE 12
LT3580 APPLICATIONS INFORMATION Using the circuit in Figure 14 as an example, Table 3 shows the parameters used to generate the bode plot shown in Figure 5. Table 3. Bode Plot Parameters PARAMETER VALUE UNITS COMMENT 21.8 Ω Application Specific COUT 10 μF Application Specific RESR 10 mΩ Application Specific RO 305 kΩ Not Adjustable CC 1000 pF Adjustable CF 0 pF Optional/Adjustable CPL 0 pF Optional/Adjustable RC 10 kΩ Adjustable R1 130 kΩ Adjustable R2 14.
PAGE 13
LT3580 APPLICATIONS INFORMATION (2) The SYNC frequency can always be higher than the free-running oscillator frequency, fOSC , but should not be less than 25% below fOSC . Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter. The first is staying clear of sensitive frequency bands, which cannot tolerate any spectral noise.
PAGE 14
LT3580 APPLICATIONS INFORMATION VIN VIN 1.3V RUVLO1 SHDN – ACTIVE/ LOCKOUT + RUVLO1 = 11.6μA AT 1.3V RUVLO2 (OPTIONAL) GND 3580 F07 Figure 7. Configurable UVLO source voltage conditions. UVLO prevents the regulator from operating at source voltages where these problems might occur. The shutdown pin comparator has voltage hysteresis with typical thresholds of 1.32V (rising) and 1.29V (falling). Resistor RUVLO2 is optional.
PAGE 15
LT3580 APPLICATIONS INFORMATION so they should not be used for calculating efficiency in discontinuous mode or at light load currents. •I V Average Input Current: IIN = OUT OUT VIN • η Switch I2R Loss: PSW = (DC)(IIN )2 (RSW ) Base Drive Loss (AC): PBAC =13n(IIN )(VOUT )(f) Base Drive Loss (DC): PBDC = (VIN )(IIN )(DC) 50 Input Power Loss: PINP = 7mA(VIN ) where: RSW = switch resistance (typically 200mΩ at 1.
PAGE 16
LT3580 APPLICATIONS INFORMATION Board layout also has a significant effect on thermal resistance. The exposed package ground pad is the copper plate that runs under the LT3580 die. This is a good thermal path for heat out of the package. Soldering the pad onto the board reduces die temperature and increases the power capability of the LT3580. Provide as much copper area as possible around this pad. Adding multiple feedthroughs around the pad to the ground plane will also help.
PAGE 17
LT3580 APPLICATIONS INFORMATION GND GND 1 2 C1 VIN 6 4 L1 VIN 7 3 2 C1 SYNC 8 9 L1 SHDN 5 SYNC 8 1 9 7 3 6 4 5 SHDN SW SW C2 L2 D1 VIAS TO GROUND PLANE REQUIRED TO IMPROVE THERMAL PERFORMANCE C2 D1 VIAS TO GROUND PLANE REQUIRED TO IMPROVE THERMAL PERFORMANCE C3 3580 F09 VOUT 3580 F10 VOUT Figure 9. Suggested Component Placement for Boost Topology (Both DFN and MSOP Packages. Not to Scale).
PAGE 18
LT3580 APPLICATIONS INFORMATION –(VIN + ⏐VOUT⏐) VCESAT L1 SW C2 L2 SWX VIN –VOUT D1 Q1 + C1 C3 RLOAD + 3580 F12 Figure 12. Switch-On Phase of an Inverting Converter. L1 and L2 Have Positive dI/dt VIN + |VOUT|+ VD L1 SW VD C2 L2 SWX VIN –VOUT D1 Q1 + C1 C3 RLOAD + 3580 F13 Figure 13. Switch-Off Phase of an Inverting Converter. L1 and L2 Currents Have Negative dI/dt L1 4.2μH VIN 5V VIN C2 10μF SW SHDN RT D1 VOUT 12V 550mA GND 130k LT3580 FB VC SYNC C1 2.
PAGE 19
LT3580 TYPICAL APPLICATIONS 750kHz, 5V to 40V, 150mA Boost Converter L1 47μH VIN 5V VIN C2 2.2μF SW SHDN RT D1 VOUT 40V 150mA GND 464k LT3580 FB VC SYNC C1 2.2μF SS 121k 10k 0.1μF 47pF 4.7nF 3580 TA02 C1: 2.2μF, 25V, X5R, 1206 C2: 2.2μF, 50V, X5R, 1206 D1: MICROSEMI UPS140 L1: SUMIDA CDRH105R-470 Wide Input Range SEPIC Converter with 5V Output Switches at 2.5MHz C3 1μF L1 4.7μH VIN 2.
PAGE 20
LT3580 TYPICAL APPLICATIONS VFD (Vacuum Flourescent Display) Power Supply Switches at 2MHz to Avoid AM Band Danger High Voltage! Operation by High Voltage Trained Personnel Only D1 R2 10Ω VIN 9V TO 16V C7 1μF L1 10μH D2 D3 R1 10Ω 3.3V C6 1μF SW VIN D4 C4 1μF VOUT1 64V 40mA D5 SHDN C3 1μF LT3580 C1 4.7μF C5 1μF VOUT2 95V 80mA GND RT 383k FB VC C2 4.7μF SYNC SS 45.3k 10k 0.1μF 47pF 2.2nF 3580 TA04 C1, C2: 4.
PAGE 21
LT3580 TYPICAL APPLICATIONS High Voltage Positive Power Supply Uses Tiny 5.8mm × 5.8mm × 3mm Transformer and Switches at 200kHz Danger High Voltage! Operation by High Voltage Trained Personnel Only VOUT 350V 4.5mA (VIN = 5V) 2.5mA (VIN = 3.3V) T1 1:10.4 VIN 3.3V TO 5V 7, 8 • 1 D1 4.7μH • 5, 6 4 C2 68nF D2 SW VIN SHDN RT FOR ANY VOUT BETWEEN 50V TO 350V, CHOOSE RFB ACCORDING TO GND RFB 4.22M* LT3580 V – 1.215 RFB = OUT 83.3μA FB VC SYNC C1 2.2μF 464k SS 10k 0.
PAGE 22
LT3580 TYPICAL APPLICATIONS High Voltage Negative Power Supply Uses Tiny 5.8mm × 5.8mm × 3mm Transformer and Switches at 200kHz Danger High Voltage! Operation by High Voltage Trained Personnel Only T1 1:10.4 VIN 3.3V TO 5V 7, 8 • D1 1 4.7μH • 5, 6 C2 68nF 4 FOR ANY VOUT BETWEEN –50V TO –350V, CHOOSE RFB ACCORDING TO D2 SHDN RT RFB = SW VIN GND RFB 4.22M* LT3580 VOUT –350V 4.5mA (VIN = 5V) 2.5mA (VIN = 3.3V) FB VC SYNC C1 2.2μF 464k SS 10k 0.47μF 100pF 10nF VOUT 83.
PAGE 23
LT3580 TYPICAL APPLICATIONS 5V to 12V Boost Converter Switches at 2.5MHz and Uses a Tiny 4mm × 4mm × 1.7mm Inductor L1 3.3μH VIN 5V D1 VIN SHDN GND 130k LT3580 RT C2 4.7μF SW VOUT 12V 500mA FB VC SYNC C1 4.7μF SS 35.7k 10k 0.1μF 47pF 2.2nF 3580 TA07a C1, C2: 4.
PAGE 24
LT3580 TYPICAL APPLICATIONS –5V Output Inverting Converter Switches at 2.5MHz and Accepts Inputs Between 3.3V to 12V C3 1μF L1 4.7μH VIN 3.3V TO 12V VIN SW SHDN VOUT –5V 800mA (VIN = 12V) C2 620mA (VIN = 5V) 10μF 450mA (VIN = 3.3V) D1 GND 60.4k LT3580 RT L2 4.7μH FB VC SYNC C1 2.2μF 35.7k SS 10k 100pF 0.1μF 2.2nF 3580 TA08a C1: 2.
PAGE 25
LT3580 PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698 Rev C) 0.70 p0.05 3.5 p0.05 1.65 p0.05 2.10 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 p0.10 (4 SIDES) R = 0.125 TYP 5 0.40 p 0.10 8 1.65 p 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD8) DFN 0509 REV C 0.200 REF 0.75 p0.05 4 0.25 p 0.05 1 0.50 BSC 2.38 p0.10 0.00 – 0.
PAGE 26
LT3580 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 0.889 p 0.127 (.035 p .005) 1.88 p 0.102 (.074 p .004) 0.29 REF 1.68 (.066) 0.05 REF 5.23 (.206) MIN DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 p 0.102 3.20 – 3.45 (.066 p .004) (.126 – .136) 8 0.42 p 0.038 (.0165 p .0015) TYP 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.
PAGE 27
LT3580 REVISION HISTORY (Revision history begins at Rev F) REV DATE DESCRIPTION PAGE NUMBER F 06/10 Added GND to the Pin Configuration section. 2 Revised Note 2 in the Electrical Characteristics section. 3 Revised Graph G08 in the Typical Performance Characteristics section. Revised the Applications Information section. G 09/10 4 10-11 Revised Table 3 in the Applications Information section. 12 Revised Figure 13 in the Applications Information section.
PAGE 28
LT3580 TYPICAL APPLICATION 2MHz Inverting Converter Generates –12V from a 5V to 12V Input VIN 5V TO 12V SHDN RT C2 10μF D1 SW VOUT –12V 500mA (VIN = 12V) 350mA (VIN = 5V) GND 147k LT3580 FB VC SYNC C1 2.2μF SS 45.3k 10k 0.1μF 47pF 1400 VIN = 5V 85 1200 80 1000 75 800 70 600 65 400 60 2.2nF POWER LOSS (mw) VIN 90 L2 22μH EFFICIENCY (%) C3 1μF L1 10μH Efficiency and Power Loss vs Load Current 200 55 3580 TA09a C1: 2.