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Analog Devices Inc. LTC3521EUF#PBF
- Part No.:
- LTC3521EUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LTC3521EUF#PBF.pdf
- Description:
- IC REG BUCK BOOST ADJ TRPL 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:674
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Product details
Overview
LTC3521EUF#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. It is designed for space-constrained portable electronics requiring multiple rail generation from a single-cell Li-ion source.
For engineers reviewing the LTC3521EUF#PBF datasheet, LTC3521EUF#PBF pinout, LTC3521EUF#PBF application, or LTC3521EUF#PBF equivalent, key selection considerations include its integrated 4-switch buck-boost topology with seamless mode transition, independent shutdown control per converter, 30µA total quiescent current in Burst Mode, and thermal protection in a thermally enhanced QFN package.
Technical Context
The LTC3521EUF#PBF implements a proprietary 4-switch buck-boost architecture enabling continuous conduction across input-to-output voltage ratios - operating as buck when VIN > VOUT1, boost when VIN < VOUT1, and buck-boost at crossover - with no discontinuity in inductor current or loop dynamics. Its dual buck converters use current-mode control with internal synchronous rectifiers, 100% duty cycle capability, and slope compensation to prevent subharmonic oscillation.
All three converters share a 1.1MHz internal oscillator, feature integrated soft-start (800µs nominal), internal compensation, and independent open-drain PGOOD indicators with 9% regulation threshold and 2% hysteresis. Shutdown current is <2µA, and Burst Mode entry is controlled globally via the PWM pin, enabling automatic light-load efficiency optimization without external circuitry.
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 regulated 3.3V/5V rails without external pre-regulation. |
| Buck-Boost Output | 1.8V to 5.25V @ 1A - programmable via FB1 resistor divider; enables output above, below, or equal to input. |
| Dual Buck Outputs | 0.6V to VIN @ 600mA each - supports core logic, memory, and I/O rails with 100% duty cycle for maximum battery runtime. |
| Quiescent Current (Burst) | 30µA total - minimizes battery drain in standby, enabling multi-week shelf life in handheld medical instruments. |
| Switching Frequency | 1.1MHz (typ) - allows compact 4.7µH inductors and ceramic output capacitors, reducing solution footprint. |
| Protection Features | Thermal shutdown, overcurrent limit (1.65A avg / 2.1A peak for buck-boost; 750mA–1050mA for bucks), and <2µA shutdown mode - ensures robust operation under fault conditions. |
| Package | 24-pin 4mm × 4mm QFN with exposed PGND1A pad - provides low θJA = 37°C/W for high-power density thermal management. |
Pinout & Package
Package: 24-lead (4mm × 4mm) plastic QFN with exposed thermal pad (Pin 25 = PGND1A). Must be soldered to PCB ground for thermal and electrical performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FB1 (Pin 8) | Buck-boost feedback input | Connects to resistor divider on VOUT1; sets output voltage 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 tight coupling to minimize EMI and switching losses. |
| VOUT1 (Pin 16) | Buck-boost output node | High-current output requiring low-ESR ceramic capacitor (≥22µF) placed adjacent to IC with short ground return. |
| SHDN1 (Pin 10) | Buck-boost enable control | Logic-high (>1.4V) enables buck-boost; logic-low (<0.4V) disables it independently of other converters. |
| PWM (Pin 7) | Global mode select | Low = Burst Mode (30µA IQ); High = forced 1.1MHz PWM - determines noise-efficiency trade-off for all three converters. |
| PGOOD1 (Pin 4) | Buck-boost power-good flag | Open-drain output pulls low if VOUT1 deviates >9% from target, during overtemperature, UVLO, or SHDN1 assertion. |
| PGND1A (Pin 25, Exposed Pad) | Buck-boost switch B ground | Primary high-current return path for buck-boost; must be solidly connected to PCB ground plane for thermal and EMI control. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 4-switch buck-boost topology | Enables seamless VIN-to-VOUT conversion across buck/boost/buck-boost modes without output glitch or loop instability. |
| Independent shutdown per converter | Allows dynamic rail sequencing and power gating - e.g., disable buck-boost while keeping dual bucks active for system sleep states. |
| Internal slope-compensated current-mode control | Eliminates need for external compensation components and ensures stable operation up to 94% duty cycle in buck-boost mode. |
| Programmable PGOOD thresholds | 9% undervoltage detection with 2% hysteresis and 60µs deglitching - prevents false trips during load transients in battery-powered systems. |
| Reverse current limiting (375mA) | Prevents backfeed from VOUT1 into PVIN during input dropout or hot-swap events, protecting upstream power sources. |
Applications
| Bar Code Readers | Medical Instruments |
|---|---|
|
Use Scenario: Portable handheld scanner powered by single Li-ion cell with rapidly varying load (laser diode, imager, Bluetooth radio). IC Role / Device Role / Timing Role: Primary power manager generating 3.3V for MCU/radio, 1.8V for imager, and 5.0V for laser driver - all from 2.4V–4.2V input. Use Value: Seamless buck-boost operation maintains stable 5.0V output even as battery discharges below 3.0V, eliminating brownouts during scan bursts. |
Use Scenario: Battery-operated glucose meter or pulse oximeter requiring long shelf life and reliable multi-rail startup. IC Role / Device Role / Timing Role: Single-chip solution delivering 1.2V for sensor ADC, 1.8V for microcontroller core, and 3.3V for display interface - with <2µA shutdown current. Use Value: 30µA Burst Mode quiescent current extends battery life to >2 years in standby, meeting ISO 13485 device longevity requirements. |
| Handy Terminals | GPS Receivers |
|
Use Scenario: Ruggedized field terminal with RF modem, touchscreen, and flash memory - subject to wide temperature (-20°C to 70°C) and input ripple. IC Role / Device Role / Timing Role: Triple-output regulator providing 1.2V (core), 1.8V (I/O), and 3.3V (RF) with independent PGOOD monitoring for system-level fault reporting. Use Value: Thermal shutdown and overcurrent protection ensure safe operation during extended outdoor use; QFN package withstands mechanical shock and vibration. |
Use Scenario: Compact GPS module in asset tracker or wearable, where size, efficiency, and cold-start performance are critical. IC Role / Device Role / Timing Role: Generates 1.8V for GPS baseband processor and 3.3V for RF front-end from low-voltage Li-ion, supporting cold-start acquisition at ≤2.5V input. Use Value: 100% duty cycle support in buck converters enables full functionality down to 2.4V input, ensuring first-fix time remains <30s even with depleted battery. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar multi-rail DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS65217C | Single 1.8V/3.3V buck + LDOs; no buck-boost; lower max output current (1A buck only); integrated fuel gauge. | Targeted at TI-based AM335x/AM437x processors; lacks true buck-boost rail for variable input scenarios. | Select when system uses TI Sitara SoCs and requires battery telemetry - not for standalone buck-boost functionality. |
| MAX20029 | 3-channel buck only (no buck-boost); higher IQ (50µA); supports 3.5V–36V input; AEC-Q100 qualified. | Designed for automotive infotainment; wider input range but cannot regulate output above input voltage. | Choose for 12V automotive systems needing robustness; avoid when Li-ion input and VIN < VOUT requirement exist. |
Compared with TPS65217C and MAX20029, the LTC3521EUF#PBF uniquely combines buck-boost and dual buck in one chip with sub-30µA quiescent current, making it optimal for portable Li-ion devices requiring flexible rail generation without sacrificing efficiency or board area.
Availability
LTC3521EUF#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 (–40°C to 125°C).
Supply support for LTC3521EUF#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 and maintains its high-performance analog and power management portfolio. Linear pioneered precision DC/DC conversion with emphasis on efficiency, integration, and reliability.
The LTC3521EUF#PBF belongs to Linear's Power Management IC family, engineered specifically for portable, battery-powered systems demanding multiple regulated rails, ultra-low quiescent current, and seamless input-to-output voltage coverage.
FAQ
What is the maximum output current capability of the LTC3521EUF#PBF's buck-boost converter?
The LTC3521EUF#PBF buck-boost converter delivers up to 1A continuous output current under typical conditions (VIN ≥ 3.0V). Its average current limit is specified at 1.65A (typ) to 2.1A (max), with reverse current limiting at 375mA to prevent backfeed. Performance depends on input voltage, output voltage, PCB layout, and thermal management - full 1A is sustained at VOUT1 = 3.3V with VIN = 3.6V and proper heatsinking via the exposed PGND1A pad.
Does the LTC3521EUF#PBF support independent enable/disable of each converter?
Yes, the LTC3521EUF#PBF provides independent shutdown control: SHDN1 enables/disables the buck-boost converter, SHDN2 controls the first buck (SW2/VOUT2), and SHDN3 controls the second buck (SW3/VOUT3). Each requires a logic-high (>1.4V) to enable and logic-low (<0.4V) to disable - no floating pins allowed. This enables precise power sequencing and dynamic rail management in complex portable systems.
How does the PWM pin affect operation modes across all three converters in the LTC3521EUF#PBF?
The PWM pin globally selects between two operating modes for all three converters in the LTC3521EUF#PBF: when pulled low, all converters enter Burst Mode® (30µA total IQ), with bucks automatically transitioning to PWM at ~15mA load; when pulled high, all remain in fixed 1.1MHz PWM mode regardless of load. This pin does not allow mixed-mode operation - it is a system-level efficiency/noise trade-off control.
What is the function of the exposed thermal pad (Pin 25) on the LTC3521EUF#PBF QFN package?
The exposed pad (Pin 25) on the LTC3521EUF#PBF is designated PGND1A - the high-current ground return for the buck-boost converter's SW1B switch. It must be soldered to a dedicated PCB ground plane with multiple vias to ensure low thermal resistance (θJA = 37°C/W) and low-impedance current return. Failure to connect this pad compromises thermal performance, efficiency, and EMI behavior - it is not optional.
Can the LTC3521EUF#PBF generate an output voltage higher than its input voltage?
Yes, the LTC3521EUF#PBF's integrated 4-switch buck-boost converter can generate VOUT1 up to 5.25V from inputs as low as 1.8V - including cases where VIN < VOUT1. Its proprietary switching algorithm seamlessly transitions between buck, buck-boost, and boost modes without output disturbance, enabling stable 5.0V rail generation even as a single Li-ion cell discharges from 4.2V to 2.4V.
LTC3521EUF#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)
LTC3521EUF#PBF FAQ
1.How can I place an order for LTC3521EUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3521EUF#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 LTC3521EUF#PBF reliable?
The price and inventory of LTC3521EUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3521EUF#PBF is usually 5 days.
3.What payment methods are accepted for LTC3521EUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3521EUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3521EUF#PBF?
LTC3521EUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3521EUF#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 LTC3521EUF#PBF?
For technical support, including LTC3521EUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3521EUF#PBF requirements.
6.How does Aetrix verify that LTC3521EUF#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3521EUF#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 LTC3521EUF#PBF meets industry standards.
7.What is the process for return or replacement of LTC3521EUF#PBF?
All LTC3521EUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3521EUF#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 LTC3521EUF#PBF part is unused and in its original packaging.
Return procedure for LTC3521EUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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