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Analog Devices Inc. LTC3521IUF#PBF
- Part No.:
- LTC3521IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LTC3521IUF#PBF.pdf
- Description:
- IC REG BUCK BOOST ADJ TRPL 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,091
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Product details
Overview
LTC3521IUF#PBF from Analog Devices (formerly Linear Technology) is a triple-output monolithic power management IC integrating one 1A buck-boost DC/DC converter and two independent 600mA synchronous buck DC/DC converters in a single 24-pin 4mm × 4mm QFN package. It operates from 1.8V to 5.5V input, delivers regulated outputs of 1.8V–5.25V (buck-boost) and 0.6V–VIN (dual buck), and supports pin-selectable Burst Mode® operation for ultra-low quiescent current - enabling use in battery-powered medical instruments and handheld terminals.
For engineers reviewing the LTC3521IUF#PBF datasheet, LTC3521IUF#PBF pinout, LTC3521IUF#PBF application, or LTC3521IUF#PBF equivalent, key selection considerations include its 1.1MHz fixed-frequency PWM/Burst Mode dual-control logic, integrated soft-start and compensation, thermal/overcurrent protection, and three independent power-good indicators for system-level rail sequencing and fault monitoring.
Technical Context
The LTC3521IUF#PBF implements a proprietary 4-switch buck-boost topology with seamless mode transition (buck → buck-boost → boost) and voltage-mode control, eliminating inductor current discontinuity across input/output voltage ratios. Its dual buck converters use current-mode control with internal synchronous rectifiers, slope compensation, and 100% duty-cycle dropout capability.
All three regulators share a single 1.1MHz oscillator, support independent enable/shutdown via SHDN1–SHDN3, and feature open-drain PGOOD outputs with –9% regulation threshold and 2% hysteresis. The device integrates reverse current limiting (375mA) on the buck-boost path and average current limiting (2.1A typ.) with fast peak-current override (≈165% of average limit).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 1.8V to 5.5V - supports single-cell Li-ion (2.4V–4.2V) and wide-input portable systems without external LDO pre-regulation. |
| Buck-Boost Output | 1.8V to 5.25V at up to 1A - regulates output above, below, or equal to input; enables single-rail power for mixed-voltage SoCs. |
| Dual Buck Output | 0.6V to VIN at up to 600mA each - supports core/logic rails with 100% duty cycle for maximum battery runtime in dropout. |
| Quiescent Current | 30µA total in Burst Mode - extends shelf life and standby time in always-on handheld devices like GPS receivers. |
| Shutdown Current | <2µA - ensures negligible battery drain during deep sleep or transport mode. |
| Switching Frequency | 1.1MHz (typ.) - enables compact 4.7µH inductors and low-profile ceramic capacitors, minimizing PCB area. |
| Feedback Reference | 0.60V ±1.2% - allows precise output setting with standard resistor dividers; supports tight tolerance rails for DSP/FPGA cores. |
Pinout & Package
Package: 24-lead (4mm × 4mm) plastic QFN with exposed thermal pad (PGND1A, Pin 25). RoHS-compliant, lead-free finish. Operating temperature range: –40°C to 125°C.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FB1 (Pin 8) | Buck-boost feedback input | Connects to resistor divider on VOUT1; sets output via 0.6V reference; determines regulation accuracy and loop stability. |
| SW1A/SW1B (Pins 15/14) | Buck-boost switch nodes | Drive external inductor; require low-inductance layout and Kelvin connection to minimize switching loss and EMI. |
| VOUT1 (Pin 16) | Buck-boost output | High-current output node; must connect directly to low-ESR ceramic capacitor (≥22µF) with short ground return. |
| SHDN1 (Pin 10) | Buck-boost enable control | Logic-high (>1.4V) enables converter; logic-low (<0.4V) forces shutdown with <2µA draw; not floating-tolerant. |
| PGOOD1 (Pin 4) | Buck-boost power-good flag | Open-drain output pulls low if VOUT1 deviates >9%, during overtemperature, UVLO, or SHDN1 assertion. |
| PVIN1/PVIN2 (Pins 11/22) | High-current power inputs | Separate high-side paths for buck-boost and dual-buck switches; require local 4.7µF/10µF ceramic bypassing. |
| PGND1A/PGND1B (Pins 25/12) | High-current ground returns | Exposed pad (Pin 25) and Pin 12 serve as dedicated low-impedance ground paths for buck-boost switches A/B/C/D. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated triple-converter architecture | Eliminates need for three discrete regulators and associated external components, reducing BOM count by ≥35% and layout area by >40%. |
| Proprietary 4-switch buck-boost algorithm | Enables continuous conduction and seamless mode transitions - avoids output glitches and loop instability when VIN crosses VOUT. |
| Independent PGOOD outputs (PGOOD1–PGOOD3) | Supports sequenced power-up/down and per-rail fault isolation in multi-domain systems (e.g., baseband + RF + sensor subsystems). |
| Internal compensation & soft-start | Removes requirement for external compensation networks and soft-start timing capacitors - simplifies design and improves repeatability. |
| Thermal and overcurrent protection | Includes junction temperature shutdown (TJMAX = 125°C), average + peak current limiting, and reverse current detection (375mA). |
Applications
| Bar Code Readers | Medical Instruments |
|---|---|
Use Scenario: Portable handheld scanner with laser diode, CMOS imager, and Bluetooth radio requiring multiple isolated rails from single Li-ion cell. IC Role / Device Role / Timing Role: LTC3521IUF#PBF provides 3.3V (VOUT1) for imager interface, 1.8V (VOUT2) for Bluetooth SoC I/O, and 1.2V (VOUT3) for processor core - all synchronized to 1.1MHz clock. Use Value: Burst Mode reduces no-load current to 30µA, extending battery life to >12 hours between charges while maintaining fast load transient response. |
Use Scenario: Battery-powered patient monitor with ECG front-end, display backlight, and wireless telemetry module. IC Role / Device Role / Timing Role: LTC3521IUF#PBF delivers clean, regulated 5.0V (VOUT1) for analog signal chain, 3.3V (VOUT2) for microcontroller, and 1.8V (VOUT3) for ADC/DAC - with independent PGOOD flags for safety-critical sequencing. Use Value: Integrated thermal protection prevents overheating during extended clinical use; <2µA shutdown current preserves battery during transport mode. |
| Handy Terminals | GPS Receivers |
Use Scenario: Ruggedized field terminal with cellular modem, touchscreen controller, and secure element operating from 3.7V Li-ion. IC Role / Device Role / Timing Role: LTC3521IUF#PBF generates 3.8V (VOUT1) for RF PA, 1.2V (VOUT2) for application processor, and 1.8V (VOUT3) for memory interface - using buck-boost to maintain regulation as battery discharges from 4.2V to 2.8V. Use Value: 100% duty cycle operation in buck mode extends usable battery voltage range by 0.5V, increasing operational time by ~18%. |
Use Scenario: Compact GNSS module requiring low-noise 3.3V for RF frontend, 1.8V for baseband processor, and 2.8V for active antenna supply. IC Role / Device Role / Timing Role: LTC3521IUF#PBF's 1.1MHz PWM mode minimizes conducted EMI near sensitive GPS bands; buck-boost VOUT1 supplies stable 2.8V regardless of battery sag. Use Value: Low 30µA Burst Mode quiescent current enables >10-day cold-start battery life; integrated soft-start prevents inrush-induced brownouts during satellite acquisition. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar triple-output DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS65217C | Single 1.2A buck-boost + dual 600mA bucks; integrated fuel gauge and PMIC sequencing logic; 2.7–5.5V input; no Burst Mode - 80µA IQ in LP mode. | Targeted at ARM-based tablets and embedded Linux platforms requiring battery telemetry and complex power sequencing. | Choose TPS65217C only if fuel gauging, I2C programmability, or advanced state-machine sequencing is required - not for cost- or size-sensitive portable instruments. |
| RT5782A | Triple buck-only (no buck-boost); 3×1.5A outputs; 2.5–5.5V input; 25µA IQ in PS mode; requires external buck-boost for VIN-crossing rails. | Suitable for systems where all outputs are ≤VIN (e.g., multi-core SoC with 1.1V/1.8V/3.3V rails powered from 3.8V battery). | Select RT5782A when output voltages never exceed input - avoids complexity of 4-switch topology but mandates separate buck-boost for higher rails. |
Compared with TPS65217C and RT5782A, the LTC3521IUF#PBF uniquely combines buck-boost flexibility with ultra-low quiescent current and minimal external component count - making it optimal for space-constrained, battery-limited applications where VIN may fall below or rise above critical output rails.
Availability
LTC3521IUF#PBF is available at Aetrix Electronics and suitable for bar code readers, medical instruments, handy terminals, GPS receivers, and PDAs requiring stable component supply across industrial temperature ranges and long production lifecycles.
Supply support for LTC3521IUF#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 precision instrumentation, industrial, automotive, and communications markets.
The LTC3521IUF#PBF belongs to Linear's PowerPath™ and µPower™ DC/DC converter product line, designed specifically for ultra-low-power, multi-rail portable electronics where battery efficiency, small solution size, and robust fault protection are critical.
FAQ
What is the operating temperature range for the LTC3521IUF#PBF?
The LTC3521IUF#PBF is rated for –40°C to 125°C junction temperature. Its "I" grade designation confirms full specification compliance across this extended industrial range, including guaranteed performance for feedback voltage (0.6V ±1.2%), current limits, and PGOOD thresholds - essential for medical and outdoor handheld deployments.
Does the LTC3521IUF#PBF support independent enable/disable of each converter?
Yes. The LTC3521IUF#PBF provides three dedicated enable pins: SHDN1 controls the buck-boost converter (Pin 10), SHDN2 enables the first buck converter (Pin 3), and SHDN3 enables the second buck converter (Pin 11). Each responds to logic-high (>1.4V) for enable and logic-low (<0.4V) for shutdown, allowing dynamic rail gating in multi-mode systems.
How does the LTC3521IUF#PBF handle input voltage crossing the output voltage threshold?
The LTC3521IUF#PBF uses a proprietary 4-switch buck-boost topology that automatically transitions between buck, buck-boost, and boost modes without output disturbance. As VIN drops below VOUT1, the control algorithm seamlessly shifts switching phases (e.g., BD → AC/BD → AC) to maintain continuous inductor current and stable regulation - verified in Figure 1 and Typical Performance G12/G13.
What protection features are built into the LTC3521IUF#PBF?
The LTC3521IUF#PBF integrates overtemperature shutdown (125°C trip), cycle-by-cycle current limiting on all three converters, reverse current limiting (375mA) on the buck-boost path, undervoltage lockout, and open-drain PGOOD flags that assert on regulation loss, thermal fault, or enable pin deactivation - providing comprehensive fault coverage without external circuitry.
Can the LTC3521IUF#PBF operate with only two of its three converters enabled?
Yes. The LTC3521IUF#PBF allows any combination of converters to be independently enabled or disabled via SHDN1–SHDN3. When unused converters are disabled, their associated quiescent current contribution is eliminated - e.g., disabling both buck converters reduces total IQ to just the buck-boost's 30µA Burst Mode current, optimizing for minimal standby draw.
LTC3521IUF#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:
- 3
- Voltage - Input (Min):
- 1.8V
- Voltage - Input (Max):
- 5.5V
- Voltage - Output (Min/Fixed):
- 0.6V
- Voltage - Output (Max):
- 5.5V
- Current - Output:
- 600mA, 1A
- Frequency - Switching:
- 1.1MHz
- Synchronous Rectifier:
- Yes
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-QFN (4x4)
LTC3521IUF#PBF FAQ
1.How can I place an order for LTC3521IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3521IUF#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 LTC3521IUF#PBF reliable?
The price and inventory of LTC3521IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3521IUF#PBF is usually 5 days.
3.What payment methods are accepted for LTC3521IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3521IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3521IUF#PBF?
LTC3521IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3521IUF#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 LTC3521IUF#PBF?
For technical support, including LTC3521IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3521IUF#PBF requirements.
6.How does Aetrix verify that LTC3521IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3521IUF#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 LTC3521IUF#PBF meets industry standards.
7.What is the process for return or replacement of LTC3521IUF#PBF?
All LTC3521IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3521IUF#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 LTC3521IUF#PBF part is unused and in its original packaging.
Return procedure for LTC3521IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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