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Analog Devices Inc. LTC3521EFE#PBF
- Part No.:
- LTC3521EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LTC3521EFE#PBF.pdf
- Description:
- IC REG BUCK BST ADJ TRPL 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,627
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Product details
Overview
LTC3521EFE#PBF from Analog Devices (formerly Linear Technology) is a triple-output monolithic DC/DC converter integrating one 1A buck-boost and two 600mA synchronous buck regulators in a thermally enhanced 20-pin TSSOP package. It operates from 1.8V to 5.5V input, delivers regulated outputs at 1.8–5.25V (buck-boost) and 0.6–VIN (dual buck), and supports Burst Mode® operation with 30µA total quiescent current - ideal for battery-powered handheld medical instruments and GPS receivers.
For engineers reviewing the LTC3521EFE#PBF datasheet, LTC3521EFE#PBF pinout, LTC3521EFE#PBF application, or LTC3521EFE#PBF equivalent, key selection criteria include its 1.1MHz fixed-frequency PWM/Burst Mode dual-control logic, independent PGOOD indicators per output, integrated soft-start, and thermal/overcurrent protection across all three converters.
Technical Context
The LTC3521EFE#PBF implements a proprietary 4-switch buck-boost topology enabling seamless mode transitions (buck → buck-boost → boost) without inductor current discontinuity or loop instability. Its voltage-mode controlled buck-boost stage uses internal compensation and an average current limit (1.65–2.1A typ) plus reverse current limit (375mA) on switch D.
The dual buck converters employ current-mode control with internal synchronous rectification, 100% duty cycle capability, and slope-compensated peak-current limiting (750–1050mA typ). All three regulators share a single 1.1MHz oscillator and are synchronized internally.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 1.8V to 5.5V - supports single-cell Li-ion (2.4–4.2V) and multi-cell alkaline/NiMH inputs without external LDO pre-regulation. |
| Buck-Boost Output | 1.8V to 5.25V @ 1A - enables VOUT > VIN, VOUT < VIN, or VOUT ≈ VIN operation with continuous conduction mode for low noise. |
| Dual Buck Outputs | 0.6V to VIN @ 600mA each - supports core logic and I/O rails with 100% duty cycle for maximum battery runtime. |
| Switching Frequency | 0.85–1.35MHz (typ 1.1MHz) - allows compact 4.7µH inductors and minimizes EMI filtering requirements. |
| Quiescent Current | 30µA total in Burst Mode - extends battery life in standby; <2µA in shutdown via individual SHDN pins. |
| Feedback Reference | 0.585–0.612V (typ 0.6V) - enables precise output regulation with standard resistor dividers; low FB input current (1–50nA) minimizes divider error. |
| Package | 20-pin thermally enhanced TSSOP - exposes die pad for direct PCB ground connection; θJA = 40°C/W enables high-power density in space-constrained designs. |
Pinout & Package
Package: 20-Lead Plastic TSSOP (FE), –40°C to 125°C operating junction temperature range. Exposed pad (Pin 21) is PGND1A and must be soldered to PCB ground.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FB3 (Pin 1) | Buck 3 feedback input | Connects to resistor divider on VOUT3; sets output via VOUT = 0.6V × (1 + R2/R1); 1–50nA input bias enables high-impedance dividers. |
| SHDN2 (Pin 3) | Buck 2 enable control | Logic-high (>1.4V) enables SW2 output; logic-low (<0.4V) disables converter and forces PGOOD2 low; must not float. |
| PGOOD3 (Pin 4) | Buck 3 power-good flag | Open-drain output pulled low if VOUT3 deviates >9% below regulation, during overtemperature, UVLO, or SHDN3 assertion. |
| VIN (Pin 7) | Internal circuitry supply | Powers bias circuitry and logic; requires ≥4.7µF ceramic bypass close to pin; tied to PVIN1/PVIN2 in layout. |
| PWM (Pin 9) | Mode select input | Low = Burst Mode (30µA IQ, variable frequency); High = forced 1.1MHz PWM on all three converters. |
| PGND2 (Pin 18) | High-current ground for buck converters | Must connect via short, wide PCB trace to minimize noise coupling into sensitive analog circuits. |
| SW2 (Pin 19) | Buck 2 switch node | Connects to inductor side opposite VOUT2; carries high di/dt switching current; requires tight layout with low-inductance path to PGND2. |
| PVIN2 (Pin 20) | High-current input for buck switches | Supplies buck converter power FETs; requires ≥10µF ceramic bypass; tied to VIN/PVIN1 in application circuit. |
Key Features
| Feature | Design Value |
|---|---|
| Triple integrated DC/DC conversion | Eliminates need for three discrete regulators - reduces BOM count, PCB area, and design complexity in multi-rail portable systems. |
| Independent PGOOD outputs | Enables system-level power sequencing and fault isolation without external monitoring ICs or GPIO overhead. |
| Internal soft-start (800µs) | Prevents inrush current and output overshoot during startup; maintains regulation throughout ramp, supporting dynamic load transients. |
| Thermal and overcurrent protection | Automatic shutdown at TJ > 125°C and current limit on all converters ensures robustness under overload or short-circuit conditions. |
| Pin-selectable Burst Mode® | Single PWM pin controls low-noise PWM or ultra-low-IQ Burst Mode across all three regulators - simplifies firmware control and power-state management. |
Applications
| Bar Code Readers | Medical Instruments |
|---|---|
Use Scenario: Portable handheld scanners requiring simultaneous 3.3V logic rail, 1.8V sensor interface, and 5V laser driver from a single Li-ion cell. IC Role / Device Role / Timing Role: LTC3521EFE#PBF provides three tightly regulated, independently enabled outputs with fast transient response and low noise in Burst Mode during idle scanning. Use Value: Enables >10-hour battery life with full functionality; eliminates discrete DC/DCs and associated layout complexity. | Use Scenario: Battery-powered patient monitors needing isolated 1.2V ADC reference, 3.3V microcontroller core, and 5V display backlight from 2.4–4.2V input. IC Role / Device Role / Timing Role: LTC3521EFE#PBF delivers stable, low-ripple outputs with independent shutdown and PGOOD monitoring per rail for safety-critical power sequencing. Use Value: Meets IEC 60601-1 leakage and reliability requirements while reducing bill-of-materials by 60% vs. discrete solution. |
| Handy Terminals | GPS Receivers |
Use Scenario: Rugged field terminals operating in extreme temperatures (-40°C to 85°C ambient) with 1.8V RF front-end, 3.3V baseband processor, and 5V SIM card interface. IC Role / Device Role / Timing Role: LTC3521EFE#PBF sustains regulation across full industrial temperature range with thermal shutdown and robust current limiting on all outputs. Use Value: Guarantees uninterrupted operation in cold storage or desert environments without derating or external thermal management. | Use Scenario: Ultra-low-power GPS modules requiring 1.2V GNSS SoC core, 1.8V RF LNA, and 3.3V serial interface from coin-cell or energy-harvested source. IC Role / Device Role / Timing Role: LTC3521EFE#PBF operates in Burst Mode at 30µA total IQ, enabling weeks of standby time while maintaining fast wake-up response via PGOOD-driven interrupt. Use Value: Extends location-tracking interval by 3× versus conventional PMICs; supports cold-start acquisition within 1.5 seconds. |
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 |
|---|---|---|---|
| LT8640S-1 | Single-channel 6A synchronous buck with integrated MOSFETs; no buck-boost or dual-buck capability; higher IQ (2.5µA) but no Burst Mode. | Requires two additional regulators to match LTC3521EFE#PBF's triple-output architecture; better suited for high-current single-rail systems. | Select only when primary need is high-efficiency 12V→3.3V conversion with minimal external components - not a functional replacement. |
| TPS65218D0 | Power management IC with quad buck, LDOs, and battery charger; wider input (2.7–5.5V); higher integration but no buck-boost topology. | Targets AM335x/AM437x processors; includes PMIC-specific features (RTC, reset logic) absent in LTC3521EFE#PBF. | Choose for TI Sitara-based designs where system-level integration outweighs need for buck-boost flexibility. |
Compared with LT8640S-1 and TPS65218D0, the LTC3521EFE#PBF uniquely combines buck-boost and dual-buck topologies in one package, enabling single-input multi-rail solutions where input voltage may fall below or exceed required outputs - critical for Li-ion-powered portable instrumentation.
Availability
LTC3521EFE#PBF is available at Aetrix Electronics and suitable for bar code readers, medical instruments, and GPS receivers requiring stable component supply with guaranteed long-term availability and consistent parametric performance.
Supply support for LTC3521EFE#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 continues to develop high-performance power management ICs with emphasis on efficiency, integration, and reliability for demanding applications.
The LTC3521 product line was designed to address multi-rail power needs in space-constrained, battery-operated portable electronics - delivering high efficiency across wide input/output voltage ranges with minimal external components.
FAQ
What is the maximum output current capability of the buck-boost converter in the LTC3521EFE#PBF?
The LTC3521EFE#PBF buck-boost converter delivers up to 1A continuous output current. Its average current limit is specified at 1.65–2.1A (typ), with reverse current limiting at 375mA on switch D. Performance depends on input voltage, output voltage, inductor value, and thermal conditions - maximum load drops in Burst Mode (typically ~50mA) but reaches full 1A in PWM mode with adequate heatsinking.
Does the LTC3521EFE#PBF support 100% duty cycle operation on all outputs?
Only the dual buck converters (VOUT2 and VOUT3) support true 100% duty cycle operation to extend battery life during dropout conditions. The buck-boost converter does not operate in 100% duty cycle mode; its maximum duty cycle is 85–94% depending on input/output conditions, as defined by its 4-switch topology and mode-transition algorithm.
How does the PWM pin control operating mode across all three converters in the LTC3521EFE#PBF?
The PWM pin on the LTC3521EFE#PBF globally selects between two modes: logic-low (<0.4V) enables Burst Mode® on all three converters (30µA total IQ, variable frequency), while logic-high (>1.4V) forces constant 1.1MHz PWM operation on all three. This single-pin control simplifies firmware power-state management without requiring individual mode configuration per regulator.
What thermal protection mechanisms are implemented in the LTC3521EFE#PBF?
The LTC3521EFE#PBF includes overtemperature shutdown that activates when junction temperature exceeds 125°C. Once triggered, the device halts switching on all three converters until temperature falls below the hysteresis threshold. This protection is independent of input voltage or load condition and is designed to prevent permanent damage during sustained overload or poor PCB thermal design.
Can the LTC3521EFE#PBF be used with ceramic output capacitors only, or are electrolytic types required?
The LTC3521EFE#PBF is fully compatible with ceramic output capacitors only - no electrolytics required. Its internal compensation network is optimized for low-ESR ceramics (e.g., 10µF X5R/X7R), and typical application circuits use 10–22µF ceramic caps on VOUT1/VOUT2/VOUT3. Ceramic-only designs reduce size, improve reliability, and eliminate aging-related capacitance drift.
LTC3521EFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width) 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:
- 20-TSSOP-EP
LTC3521EFE#PBF FAQ
1.How can I place an order for LTC3521EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3521EFE#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 LTC3521EFE#PBF reliable?
The price and inventory of LTC3521EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3521EFE#PBF is usually 5 days.
3.What payment methods are accepted for LTC3521EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3521EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3521EFE#PBF?
LTC3521EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3521EFE#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 LTC3521EFE#PBF?
For technical support, including LTC3521EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3521EFE#PBF requirements.
6.How does Aetrix verify that LTC3521EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3521EFE#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 LTC3521EFE#PBF meets industry standards.
7.What is the process for return or replacement of LTC3521EFE#PBF?
All LTC3521EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3521EFE#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 LTC3521EFE#PBF part is unused and in its original packaging.
Return procedure for LTC3521EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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