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Analog Devices Inc. LTC3520IUF#PBF
- Part No.:
- LTC3520IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LTC3520IUF#PBF.pdf
- Description:
- IC REG BUCK BOOST ADJ DL 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:104
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Product details
Overview
LTC3520IUF#PBF from Analog Devices (formerly Linear Technology) is a dual-output synchronous DC/DC converter integrating a 1A buck-boost and a 600mA buck regulator in a single 24-lead 4mm × 4mm QFN package. It supports 2.2V–5.5V input, delivers 3.3V@500mA (buck-boost) and 1.8V@600mA (buck), and features pin-selectable Burst Mode® operation for ultra-low quiescent current in portable power management applications.
For engineers reviewing the LTC3520IUF#PBF datasheet, LTC3520IUF#PBF pinout, LTC3520IUF#PBF application, or LTC3520IUF#PBF equivalent, key selection criteria include dual-converter integration, programmable 100kHz–2MHz switching frequency, <1μA shutdown current, thermal/overcurrent protection, and uncommitted gain block configurability for LDO control or battery-good indication.
Technical Context
The LTC3520IUF#PBF implements two independent, internally synchronized converters: a four-switch buck-boost using voltage-mode control with seamless mode transitions (buck → buck-boost → boost), and a current-mode synchronous buck with internal PMOS/NMOS switches. Both share a programmable oscillator and soft-start circuitry.
Its uncommitted gain block operates as a transconductance amplifier (80dB open-loop gain, 45μA quiescent) with configurable AIN/AOUT pins for battery-comparator or external-PNP LDO functions. The device enforces thermal shutdown at 125°C junction temperature and provides separate active-low shutdown pins (SD1, SD2, SD3) with defined logic thresholds (1.4V high, 0.4V low).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.2V to 5.5V - supports single-cell Li-ion, NiMH, or regulated 3.3V/5V rails without external pre-regulation. |
| Buck-Boost Output | 2.2V to 5.25V, 1A max @ VOUT=3.3V & VIN≥3V - enables output regulation above, below, or equal to input voltage. |
| Buck Output | 0.8V to VIN, 600mA max - includes 100% duty-cycle dropout operation for extended battery runtime. |
| Switching Frequency | Programmable 100kHz–2MHz via RT pin resistor - allows trade-off between efficiency, size, and EMI performance. |
| Quiescent Current | 55μA typical in Burst Mode for both converters - enables >100-hour standby in low-power IoT sensors. |
| Shutdown Current | <1μA - ensures minimal battery drain during system sleep or storage. |
| Package | 24-lead 4mm × 4mm QFN, 0.75mm profile - supports high-density PCB layouts with exposed pad for thermal dissipation. |
Pinout & Package
Package: 24-lead plastic QFN (4mm × 4mm, 0.75mm height) with exposed thermal pad (Pin 25, GND). Requires soldering of exposed pad to PCB ground plane for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SVIN (1) | Small-signal power supply | Powers internal analog circuitry; must be tied to PVIN1/PVIN2/PVIN3 and bypassed with ≥0.1μF ceramic capacitor. |
| AOUT (2) | Uncommitted amplifier output | Drives external PNP base for LDO or acts as comparator output for battery-good indication (17mA sink capability). |
| AIN (3) | Non-inverting amplifier input | Sets LDO feedback threshold or battery-comparator reference (0.770–0.802V typical). |
| RT (4) | Oscillator frequency programming | Resistor-to-ground sets switching frequency (e.g., 54.9kΩ → 1MHz); enables footprint-optimized design. |
| PWM1 (5) | Buck-boost mode control | High = fixed-frequency PWM; Low = variable-frequency Burst Mode (reduced light-load noise/efficiency trade-off). |
| SD1 (6) | Buck-boost shutdown | Active-low enable; <0.4V disables buck-boost converter, reducing system-level standby power. |
| SD2 (7) | Buck shutdown | Independent active-low enable for buck converter; supports dynamic rail gating in multi-rail systems. |
| SD3 (8) | Gain block shutdown | Disables uncommitted amplifier independently-preserves buck/buck-boost operation while disabling LDO/comparator. |
| PVIN2 (9) | Buck high-current input | Power path for buck PMOS switch; requires ≥22μF local ceramic bypass for transient current handling. |
| SW2 (10) | Buck switch node | Connects to buck inductor; carries high di/dt; requires short, low-inductance PCB routing. |
| PGND2 (11) | Buck power ground | Return path for buck NMOS switch; must be wide, low-impedance trace connected to exposed pad. |
| PWM2 (12) | Buck mode control | Configures buck operation: High = forced PWM; resistor-to-ground = adjustable Burst Mode entry point; Low = forced Burst Mode. |
| SS2 (13) | Buck soft-start | External capacitor sets soft-start duration (tSS ≈ 0.15·CSS in ms); prevents inrush current during power-up. |
| FB2 (14) | Buck feedback | 0.771–0.809V reference; resistor divider sets output voltage (e.g., 1.8V = R1/R2 = 1.28). |
| VC1 (15) | Buck-boost error amp output | Compensation node; external RC network between FB1 and VC1 stabilizes loop across all operating modes. |
| SGND (16) | Small-signal ground | Analog reference for internal circuitry; must be isolated from PGND1/PGND2 until joined at single-point ground. |
| SS1 (17) | Buck-boost soft-start | Same function as SS2 but for buck-boost converter; enables coordinated startup of dual outputs. |
| FB1 (18) | Buck-boost feedback | 0.766–0.798V reference; defines buck-boost output (e.g., 3.3V = R1/R2 = 3.21). |
| VOUT1 (19) | Buck-boost output | Main regulated output node; requires low-ESR ceramic capacitor (e.g., 47μF) placed adjacent to pin. |
| SW1B (20) | Buck-boost switch B | One terminal of buck-boost inductor; part of four-switch topology enabling seamless mode transitions. |
| PGND1 (21) | Buck-boost power ground | Return for buck-boost NMOS devices; shares exposed pad connection with PGND2 and SGND. |
| SW1A (22) | Buck-boost switch A | Second buck-boost switch node; works with SW1B, PVIN1, PVIN3 to implement four-switch architecture. |
| PVIN1 (23), PVIN3 (24) | Buck-boost high-current inputs | Parallel power paths for buck-boost PMOS switches; each requires ≥22μF local bypass capacitance. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated dual-converter architecture | Eliminates need for two discrete regulators-reduces BOM count, PCB area, and design validation effort in space-constrained portable systems. |
| Four-switch buck-boost topology | Enables continuous conduction mode across full VIN/VOUT range (step-down, buck-boost, step-up) without output discontinuity or loop instability. |
| Configurable uncommitted gain block | Provides flexible third-function capability: battery voltage monitoring (comparator), low-noise LDO control, or supply sequencing-no extra IC required. |
| Pin-selectable Burst Mode® | Reduces total quiescent current to 55μA while maintaining regulation-critical for battery-powered devices requiring multi-day standby. |
| Thermal and overcurrent protection | Automatic shutdown at 125°C junction temperature and cycle-by-cycle current limiting prevent damage during fault conditions or overload. |
| Programmable switching frequency | Adjusts from 100kHz to 2MHz to optimize efficiency vs. size vs. EMI-supports use of smaller inductors/capacitors without sacrificing performance. |
Applications
| Portable Media Players | Digital Cameras |
|---|---|
Use Scenario: Powering DSP, display backlight, and image sensor from single Li-ion cell with varying voltage (4.2V–2.8V). IC Role / Device Role / Timing Role: LTC3520IUF#PBF delivers stable 3.3V for logic and 1.8V for sensors while maintaining regulation as battery discharges. Use Value: Eliminates need for separate buck and boost converters-reducing solution size by 40% and component count by 7 parts versus discrete implementation. |
Use Scenario: Supplying CMOS image sensor (1.2V), processor core (1.8V), and I/O (3.3V) in compact camera module. IC Role / Device Role / Timing Role: LTC3520IUF#PBF generates three regulated rails with coordinated soft-start to prevent reset glitches during power-up. Use Value: Uncommitted gain block monitors battery voltage and asserts "battery good" signal to processor before enabling high-current imaging sequence. |
| Handheld PCs / PDAs | GPS Receivers |
Use Scenario: Supporting ARM application processor (1.2V), DDR memory (1.8V), and USB PHY (3.3V) from shared battery rail. IC Role / Device Role / Timing Role: LTC3520IUF#PBF uses independent SD1/SD2 pins to dynamically gate buck-boost (for RF) and buck (for core) based on operational mode. Use Value: Burst Mode operation extends standby time to >120 hours; 100% duty-cycle buck operation maintains core voltage down to 1.3V input. |
Use Scenario: Powering GPS baseband IC (1.8V), RF front-end (3.3V), and backup SRAM (3.0V) in automotive-grade navigation unit. IC Role / Device Role / Timing Role: LTC3520IUF#PBF's –40°C to 125°C industrial grade rating ensures reliable cold-cranking and under-hood operation. Use Value: Exposed-pad QFN package achieves θJA = 37°C/W-enabling full 1A buck-boost output without external heatsink in sealed enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-output DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS65217CIRSLR | Single-chip PMIC with 3 buck + 1 LDO + fuel gauge; no buck-boost; 2.7–5.5V input; 12-bit ADC included. | Targeted at TI AM335x/AM437x processors; integrates system power management beyond conversion. | Select when full PMIC functionality (fuel gauging, thermal monitoring) is needed and processor compatibility exists. |
| MAX20004AATP+T | Single 2.2V–5.5V buck-boost IC (2.5A); no integrated buck; includes spread-spectrum and ASIL-B compliance. | Designed for automotive infotainment; supports AEC-Q100 Grade 1 (–40°C to +125°C) with enhanced EMI robustness. | Select for automotive applications requiring functional safety certification and higher current capability without secondary buck rail. |
Compared with TPS65217CIRSLR and MAX20004AATP+T, the LTC3520IUF#PBF uniquely combines buck-boost and buck topologies with an uncommitted gain block in a compact QFN-making it optimal for portable industrial and consumer devices needing three regulated rails with minimal footprint and ultra-low quiescent current.
Availability
LTC3520IUF#PBF is available at Aetrix Electronics and suitable for portable media players, digital cameras, handheld PCs, and GPS receivers requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LTC3520IUF#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LTC3520IUF#PBF belongs to Linear's high-efficiency power conversion product line, designed specifically for space- and power-constrained portable electronics requiring dual regulated outputs with intelligent power management features.
FAQ
What is the maximum output current capability of the LTC3520IUF#PBF buck-boost converter?
The LTC3520IUF#PBF buck-boost converter delivers up to 1A continuous output current at 3.3V when input voltage is ≥3V. At lower input voltages (e.g., 2.5V), maximum output current decreases due to power limitations and thermal constraints. The device specifies forward current limit of 1.25A (typical) and reverse current limit of 560mA, with Burst Mode operation limiting peak current to 325mA to maintain regulation efficiency.
How does the uncommitted gain block in the LTC3520IUF#PBF function as a battery-good comparator?
The LTC3520IUF#PBF's uncommitted gain block uses AIN (Pin 3) as non-inverting input with a precise 0.786V typical threshold. When battery voltage drops below this level (e.g., via resistor divider), AOUT (Pin 2) transitions low, signaling "battery low" to system controller. AOUT can sink 17mA, enabling direct drive of logic inputs or LEDs without external components-verified in the Electrical Characteristics table under AOUT Sink Current.
Can the LTC3520IUF#PBF operate with input voltage below its buck output voltage?
Yes-the LTC3520IUF#PBF buck converter supports 100% duty-cycle operation, allowing it to maintain regulation even when input voltage falls below the programmed output (e.g., 1.8V buck output with 1.5V input). In this dropout condition, output voltage equals input minus resistive losses across the internal PMOS switch and inductor DCR, as confirmed in the "Low Dropout Operation" section of the datasheet.
What is the purpose of the separate PGND1 and PGND2 pins on the LTC3520IUF#PBF?
PGND1 (Pin 21) and PGND2 (Pin 11) provide dedicated high-current return paths for the buck-boost and buck power stages respectively. This separation minimizes ground bounce coupling between converters, improves EMI performance, and enables cleaner feedback reference for each regulator. Both must connect to the exposed pad and system ground at a single point to avoid ground loops-explicitly required in the Pin Functions section.
Does the LTC3520IUF#PBF support synchronization to an external clock?
No-the LTC3520IUF#PBF does not support external clock synchronization. Its switching frequency is set solely by the RT pin resistor (100kHz–2MHz range) and cannot be overridden or locked to an external clock source. This is confirmed by absence of SYNC or CLKIN pins in the pin configuration diagram and omission from all functional descriptions in the datasheet.
LTC3520IUF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 24-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down, Step-Up/Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck, Buck-Boost
- Output Type:
- Adjustable
- Number of Outputs:
- 2
- Voltage - Input (Min):
- 2.2V
- Voltage - Input (Max):
- 5.5V
- Voltage - Output (Min/Fixed):
- 0.8V
- Voltage - Output (Max):
- 5.5V
- Current - Output:
- 600mA, 1A
- Frequency - Switching:
- 100kHz ~ 2MHz
- Synchronous Rectifier:
- Yes
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-QFN (4x4)
LTC3520IUF#PBF FAQ
1.How can I place an order for LTC3520IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3520IUF#PBF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LTC3520IUF#PBF reliable?
The price and inventory of LTC3520IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3520IUF#PBF is usually 5 days.
3.What payment methods are accepted for LTC3520IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3520IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3520IUF#PBF?
LTC3520IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3520IUF#PBF order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LTC3520IUF#PBF?
For technical support, including LTC3520IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3520IUF#PBF requirements.
6.How does Aetrix verify that LTC3520IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3520IUF#PBF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LTC3520IUF#PBF meets industry standards.
7.What is the process for return or replacement of LTC3520IUF#PBF?
All LTC3520IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3520IUF#PBF, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LTC3520IUF#PBF part is unused and in its original packaging.
Return procedure for LTC3520IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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