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Analog Devices Inc. LTC3521IFE#TRPBF
- Part No.:
- LTC3521IFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LTC3521IFE#TRPBF.pdf
- Description:
- IC REG BUCK BST ADJ TRPL 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,150
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Product details
Overview
LTC3521IFE#TRPBF 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 single 20-pin TSSOP package. It operates from 1.8V to 5.5V input, delivers regulated outputs at 1.8V–5.25V (buck-boost) and 0.6V–VIN (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 LTC3521IFE#TRPBF datasheet, LTC3521IFE#TRPBF pinout, LTC3521IFE#TRPBF application, or LTC3521IFE#TRPBF equivalent, key selection considerations include its 1.1MHz fixed-frequency PWM/Burst Mode dual-control logic, independent PGOOD indicators per output, integrated soft-start and thermal protection, and compatibility with Li-ion input ranges (2.4V–4.2V) in space-constrained portable designs.
Technical Context
The LTC3521IFE#TRPBF implements three independent switching regulators sharing a single 1.1MHz oscillator: a 4-switch buck-boost converter using proprietary mode-hopping control (buck → buck-boost → boost) and two current-mode synchronous buck converters with internal PMOS/NMOS switches and 100% duty-cycle capability. All converters feature internal compensation and soft-start.
Its control architecture enables seamless transitions between operating modes without inductor current discontinuity or loop instability, while independent SHDN pins (SHDN1/SHDN2/SHDN3) and PWM pin allow granular power sequencing. The device uses voltage-mode error amplifiers for buck-boost regulation and transconductance error amplifiers for buck regulation, with dedicated average + peak current limiting on the buck-boost path and PMOS/NMOS current limits on buck paths.
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 LDO pre-regulation. |
| Buck-Boost Output | 1.8V to 5.25V @ 1A - regulates across input crossover; enables stable VOUT1 even when VIN drops below or rises above target voltage. |
| Dual Buck Outputs | 0.6V to VIN @ 600mA each - supports low-voltage core logic (1.2V, 1.8V) and I/O rails with 100% duty cycle for maximum battery runtime. |
| Quiescent Current | 30µA total in Burst Mode - extends battery life in standby; <2µA shutdown current minimizes leakage during deep sleep. |
| Switching Frequency | 1.1MHz (typ) - enables use of compact 4.7µH inductors and ceramic capacitors, reducing solution footprint vs lower-frequency alternatives. |
| Feedback Reference | 0.6V ±1.5% - allows precise output setting via resistor dividers; tight tolerance reduces calibration overhead in production. |
| Protection Features | Thermal shutdown, overcurrent (average + peak), reverse current limit (375mA), UVLO, and independent PGOOD flags - eliminates need for external fault monitoring circuitry. |
Pinout & Package
Package: 20-lead plastic TSSOP (FE), –40°C to 125°C junction temperature range, exposed pad internally connected to PGND1A and requiring PCB soldering for thermal and electrical performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FB3 (Pin 1) | Buck 3 feedback input | Connects to resistor divider on VOUT3; sets output voltage per VOUT = 0.6V × (1 + R2/R1). |
| SHDN2 (Pin 3) | Buck 2 enable control | Logic-high (>1.4V) enables SW2 output; logic-low (<0.4V) disables regulator and forces PGOOD2 low. |
| PGOOD3 (Pin 4) | Buck 3 power-good flag | Open-drain output pulled low if VOUT3 deviates >9% from regulation, during overtemperature, UVLO, or SHDN3 assertion. |
| VIN (Pin 7) | Low-current bias supply | Powers internal circuitry; requires ≥4.7µF ceramic bypass close to pin; must be tied to PVIN1/PVIN2. |
| PWM (Pin 9) | Mode select input | Low = Burst Mode (30µA IQ); high = forced PWM (1.1MHz) for low-noise operation across all three converters. |
| PGND2 (Pin 18) | High-current ground for buck converters | Must connect via short, wide PCB trace to minimize noise coupling into buck regulation loops. |
| PGND1A (Pin 21, exposed pad) | High-current ground for buck-boost switch B | Exposed pad is electrically and thermally critical; must be soldered to solid PCB ground plane. |
Key Features
| Feature | Design Value |
|---|---|
| Triple integrated regulators | Eliminates need for three discrete DC/DC ICs and associated passives, reducing BOM count and board area by >40% vs discrete solutions. |
| Proprietary buck-boost mode-hopping | Enables continuous conduction and smooth transitions between buck/buck-boost/boost without output glitch or loop instability. |
| Independent PGOOD outputs | Allows system-level power sequencing and fault isolation - e.g., disabling downstream logic if only VOUT2 fails while VOUT1/VOUT3 remain valid. |
| Internal compensation & soft-start | Removes requirement for external compensation networks and soft-start timing components, accelerating design validation. |
| 100% duty-cycle buck operation | Maintains regulation down to VIN ≈ VOUT, extending usable battery voltage range and runtime in Li-ion applications. |
Applications
| Bar Code Readers | Medical Instruments |
|---|---|
Use Scenario: Portable handheld scanners powered by single-cell Li-ion batteries requiring multiple regulated rails (3.3V for imager, 1.8V for processor, 5V for laser driver). IC Role / Device Role / Timing Role: LTC3521IFE#TRPBF provides all three regulated outputs simultaneously with synchronized 1.1MHz switching to minimize EMI in sensitive optical subsystems. Use Value: Burst Mode operation cuts no-load IQ to 30µA, enabling multi-week standby; independent SHDN pins allow selective rail shutdown during idle periods. | Use Scenario: Battery-operated patient monitors with LCD display, analog front-end, and wireless telemetry needing isolated, low-noise 3.3V, 1.2V, and 5V supplies. IC Role / Device Role / Timing Role: LTC3521IFE#TRPBF delivers tightly regulated outputs with independent PGOOD flags to validate rail integrity before enabling critical measurement circuits. Use Value: Thermal shutdown and overcurrent protection prevent field failures in sealed enclosures; 0.6V feedback reference simplifies precision calibration of analog sensor supplies. |
| Handy Terminals | GPS Receivers |
Use Scenario: Ruggedized industrial data terminals using Li-ion packs and requiring robust power under variable load (keypad backlight, RF comms, CPU burst). IC Role / Device Role / Timing Role: LTC3521IFE#TRPBF's 100% duty-cycle buck operation maintains 1.8V core rail down to 2.4V battery voltage, avoiding brownouts during transmit bursts. Use Value: Integrated soft-start prevents inrush current damage to battery protection ICs; PGND2 separation minimizes ground bounce coupling into RF sections. | Use Scenario: Compact GNSS modules where PCB area is constrained and battery life must exceed 24 hours with periodic position fixes. IC Role / Device Role / Timing Role: LTC3521IFE#TRPBF generates 3.3V for RF front-end, 1.2V for baseband processor, and 5V for active antenna - all from single Li-ion cell. Use Value: 1.1MHz switching allows use of miniature 2.5mm × 2.0mm inductors; <2µA shutdown current preserves battery charge during extended sleep intervals. |
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 | Integrated PMIC with LDOs, battery charger, and fuel gauge; lower max buck current (400mA); no buck-boost path. | Targets single-chip power for AM335x/AM437x processors; lacks wide-input buck-boost for direct Li-ion regulation. | Select if system requires battery charging and fuel gauging; avoid if standalone buck-boost regulation from Li-ion is required. |
| MAX20029 | 3-channel buck-only (no buck-boost); higher efficiency at 2A per channel; requires external buck-boost for VIN crossover. | Optimized for automotive infotainment with AEC-Q100 qualification; lacks Burst Mode and ultra-low IQ for portable use. | Select for automotive environments needing 125°C operation and higher current; not suitable for battery-critical portable designs. |
Compared with TPS65217C and MAX20029, the LTC3521IFE#TRPBF uniquely combines buck-boost + dual-buck in one IC with sub-30µA Burst Mode IQ and Li-ion-native input range - making it the only option among the three that eliminates external buck-boost conversion while maximizing battery runtime in handheld devices.
Availability
LTC3521IFE#TRPBF is available at Aetrix Electronics and suitable for bar code readers, medical instruments, handy terminals, GPS receivers, and portable instrumentation requiring stable component supply with guaranteed long-term availability.
Supply support for LTC3521IFE#TRPBF 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 full product support, documentation, and manufacturing continuity for all Linear power management ICs.
The LTC3521IFE#TRPBF belongs to Linear's high-efficiency monolithic DC/DC converter family, designed specifically for space- and power-constrained portable electronics requiring multiple regulated rails from single-cell batteries.
FAQ
What is the maximum output current capability of the LTC3521IFE#TRPBF's buck-boost converter?
The LTC3521IFE#TRPBF buck-boost converter delivers up to 1A continuous output current when VIN > 3.0V, as specified in the datasheet's "Typical Application" section and confirmed by load-step testing in Figure G13. At lower input voltages (e.g., 2.4V), maximum load current decreases due to duty-cycle and thermal constraints - typical maximum is 750mA at 2.4V input per Figure G12. This rating applies to the VOUT1 pin and assumes proper PCB layout with adequate thermal sinking via the exposed PGND1A pad.
Does the LTC3521IFE#TRPBF support true 100% duty-cycle operation on its buck converters?
Yes, the LTC3521IFE#TRPBF buck converters (VOUT2 and VOUT3) support true 100% duty-cycle operation, allowing them to maintain regulation even when VIN drops to within ~100mV of the output voltage. This is explicitly stated in the "Features" section and verified in the "Dropout Operation" subsection of the datasheet. During dropout, the PMOS switch remains continuously on, minimizing resistive losses and extending usable battery life in Li-ion applications where voltage sags occur under load.
How does the PWM pin affect the operating mode of the LTC3521IFE#TRPBF?
The PWM pin on the LTC3521IFE#TRPBF selects between two global operating modes: when pulled low (<0.4V), all three converters enter Burst Mode® (30µA total IQ, variable frequency); when pulled high (>1.4V), all three are forced into fixed 1.1MHz PWM mode for low-noise, predictable EMI performance. Unlike some controllers, this pin does not enable mixed-mode operation - it uniformly controls mode across buck-boost and both buck channels, ensuring consistent transient response and simplifying system-level power management.
What is the function of the exposed pad (Pin 21) on the LTC3521IFE#TRPBF TSSOP package?
The exposed pad (Pin 21) on the LTC3521IFE#TRPBF is designated PGND1A - the high-current ground return for the buck-boost converter's NMOS switch (SW1B). Per the datasheet's "Pin Configuration" and "Pin Functions" sections, this pad must be soldered directly to a solid PCB ground plane to ensure thermal dissipation (θJA = 40°C/W) and low-impedance current return. Leaving it unconnected degrades efficiency, increases junction temperature, and risks thermal shutdown during sustained 1A buck-boost operation.
Can the LTC3521IFE#TRPBF generate an output voltage higher than its input voltage?
Yes, the LTC3521IFE#TRPBF's buck-boost converter can generate output voltages higher than VIN - for example, producing 5V from a 3.6V Li-ion input. This is enabled by its 4-switch topology and proprietary mode-hopping algorithm, which transitions seamlessly from buck to buck-boost to boost operation as VIN decreases relative to VOUT1. The datasheet confirms this capability in the "Description" section and Figure 1 (Buck-Boost Switch Topology), where switch pair CD performs boost-mode regulation when VIN < VOUT1.
LTC3521IFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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
LTC3521IFE#TRPBF FAQ
1.How can I place an order for LTC3521IFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3521IFE#TRPBF 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 LTC3521IFE#TRPBF reliable?
The price and inventory of LTC3521IFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3521IFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LTC3521IFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3521IFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3521IFE#TRPBF?
LTC3521IFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3521IFE#TRPBF 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 LTC3521IFE#TRPBF?
For technical support, including LTC3521IFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3521IFE#TRPBF requirements.
6.How does Aetrix verify that LTC3521IFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LTC3521IFE#TRPBF 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 LTC3521IFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LTC3521IFE#TRPBF?
All LTC3521IFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3521IFE#TRPBF, 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 LTC3521IFE#TRPBF part is unused and in its original packaging.
Return procedure for LTC3521IFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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