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Analog Devices Inc. LTC3355IUF#PBF
- Part No.:
- LTC3355IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 20-WFQFN Exposed Pad
- Datasheet:
-
LTC3355IUF#PBF.pdf
- Description:
- IC REG BUCK ADJ 1A 20QFN
- Quantity:
- Payment:
- Shipping:
Inventory:209
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Product details
Overview
LTC3355IUF#PBF from Analog Devices (formerly Linear Technology) is a monolithic input power interrupt ride-through DC/DC system integrating a 1A buck regulator, 5A boost backup regulator, and 1A CC/CV supercapacitor charger in a single 20-lead 4mm × 4mm QFN package. It delivers regulated 2.7V–5V output from 3V–20V input, charges a supercapacitor from VOUT, and automatically switches to VCAP-powered backup when VIN fails - enabling seamless "dying gasp" operation in industrial power meters and solid-state drives.
For engineers reviewing the LTC3355IUF#PBF datasheet, LTC3355IUF#PBF pinout, LTC3355IUF#PBF application, or LTC3355IUF#PBF equivalent, key selection criteria include its dual-regulator architecture (buck + boost), programmable charge/boost current limits, thermal regulation to 110°C, PFI/VIN dropout detection, and integrated VOUT/VOUT reset and VCAP power-good signaling.
Technical Context
The LTC3355IUF#PBF implements two independent constant-frequency (1MHz) current-mode switching regulators: a nonsynchronous 1A buck for primary regulation and a nonsynchronous 5A boost for backup, both sharing the same FB error amplifier and 0.8V reference. Its charger uses linear CC/CV topology with programmable 0.1A–1A charge current via ICHG resistor and 0.5V–5V VCAP operating range.
Control logic includes MODE-selectable PWM/Burst Mode operation for both regulators, EN_CHG-gated charging, PFI-triggered automatic buck-to-boost switchover, and three open-drain status outputs (PFOB, RSTB, CPGOOD) with 92.5% threshold hysteresis. Thermal regulation actively reduces charge current to hold junction temperature at 110°C, while thermal shutdown disables the entire IC at 155°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 3V to 20V - supports wide-input industrial supplies and battery-backed systems. |
| VOUT Range | 2.7V to 5V - programmable via FB resistor divider; includes 5.65V overvoltage protection. |
| Buck Regulator | 1A peak current, 1MHz fixed frequency, nonsynchronous - delivers main load power with soft-start and foldback protection. |
| Boost Regulator | 5A peak current, operates down to 0.5V VCAP input - maximizes supercapacitor energy utilization during backup. |
| Supercapacitor Charger | 1A max CC/CV linear charger, programmable via ICHG resistor (60.4kΩ–604kΩ) - includes overvoltage bleed circuit and thermal regulation. |
| Thermal Regulation | Junction temperature limited to 110°C - dynamically scales charge current without disabling regulation. |
| Package | 20-lead 4mm × 4mm QFN with exposed pad - θJA = 47°C/W; requires soldered GND pad for thermal performance. |
Pinout & Package
Package: 20-lead (4mm × 4mm) plastic QFN with exposed thermal pad (Pin 21 = GND). Requires PCB vias under exposed pad for optimal thermal conduction.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PFI (1) | Power-fail input comparator | Programmable VIN dropout threshold (0.775V–0.825V ref); triggers PFOB low and enables boost. |
| FB (2) | Buck/boost output voltage feedback | 0.8V reference; sets VOUT via resistor divider; shared by both regulators. |
| MODE (3) | Switching mode control | Low = PWM mode; high = Burst Mode - optimizes efficiency across load range. |
| VINS (4) | Input current limit sense | Connects to external sense resistor (VIN–VINS ≤ 50mV) to limit total input current. |
| VIN (5) | Main input power supply | Supplies internal regulator and buck switch; bypass with local ceramic capacitor. |
| VINM5 (6) | VIN–4.65V internal supply filter | Connect 1µF ceramic cap to VIN; stabilizes internal bias rail. |
| SW1 (7) | Buck switch node | Connects to inductor and catch diode; high dV/dt node requiring minimized trace area. |
| EN_CHG (8) | Charger enable input | High = enable supercapacitor charging; disabled if VIN < PFI threshold or VOUT out-of-reg. |
| CPGOOD (9) | VCAP power-good indicator | Open-drain output; high-impedance when VCAP ≥ 92.5% of target - signals full charge. |
| PFOB (10) | Power-fail open-drain output | Drives low when VIN drops below PFI threshold - enables boost and signals fault. |
| CFB (11) | VCAP voltage feedback | 0.8V reference; programs VCAP float voltage via resistor divider; includes 30mV hysteresis. |
| ICHG (12) | Charge current programming | Resistor to GND sets CC current (0.1A–1A); internal amp holds ICHG at 0.8V. |
| RSTB (13) | VOUT power-on reset | Open-drain output; high-impedance when VOUT ≥ 92.5% of target - provides system reset timing. |
| VCAP (14) | Supercapacitor connection | CC/CV charger output; connects directly to supercapacitor bank (1F–50F typical). |
| VOUT (15) | Regulated output supply | Delivers load power from buck (VIN present) or boost (VIN lost); shared output node. |
| SW2 (16,17) | Boost switch node | Dual pins for high-current boost switch connection; connect to rectifier diode and inductor. |
| INTVCC (18) | Internal bias supply filter | 2.5V during start-up; tracks VOUT after VOUT > 2.5V; bypass with 1µF ceramic to GND. |
| VCBST (19) | Boost error amplifier output | Compensation node; connect RC network to GND to stabilize boost loop. |
| IBSTPK (20) | Boost peak current programming | Resistor to GND sets boost peak current (1A–5A); internal amp holds IBSTPK at 0.8V. |
| GND (21) | Ground / thermal pad | Exposed pad must be soldered to continuous PCB ground plane with multiple vias. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated ride-through architecture | Single-chip solution combining buck, boost, and supercapacitor charger eliminates discrete backup design complexity and board space. |
| 0.5V minimum VCAP input for boost | Enables >95% energy extraction from supercapacitors, extending backup time beyond conventional 1V cutoffs. |
| Programmable current limits | Independent setting of VIN input limit, VCAP charge current (0.1A–1A), and boost peak current (1A–5A) via external resistors. |
| Three independent status outputs | PFOB (power fail), RSTB (VOUT POR), CPGOOD (VCAP charged) provide deterministic system-level monitoring and sequencing. |
| Thermal regulation with 110°C clamp | Automatically reduces charge current to maintain safe die temperature - enables higher average power in constrained layouts. |
Applications
| Power Meters | Industrial Alarms |
|---|---|
Use Scenario: Utility meter maintains real-time clock, communication, and data logging during brief AC line interruptions. IC Role / Device Role / Timing Role: LTC3355IUF#PBF acts as primary power manager and seamless backup source, delivering uninterrupted 3.3V to MCU and RF transceiver. Use Value: Enables >10-second backup from 3F supercapacitor at 125mA load, meeting ANSI C12.1 and IEC 62053 standards. | Use Scenario: Factory floor alarm controller retains volatile configuration and latches active alarms during brownouts. IC Role / Device Role / Timing Role: LTC3355IUF#PBF provides regulated 5V to microcontroller and EEPROM while monitoring VIN for failover. Use Value: Eliminates need for separate backup supervisor IC and discrete boost converter, reducing BOM count by 4 components. |
| Solid-State Drives | Ride-Through "Dying Gasp" Supplies |
Use Scenario: SSD performs controlled write-caching and metadata flush when host power fails unexpectedly. IC Role / Device Role / Timing Role: LTC3355IUF#PBF supplies stable 3.3V to NAND controller and DRAM during 20–100ms power loss windows. Use Value: Supports JEDEC JESD219 compliance with guaranteed 50ms minimum hold-up time using 10F supercapacitor. | Use Scenario: Industrial PLC I/O module preserves state and initiates safe shutdown upon AC input collapse. IC Role / Device Role / Timing Role: LTC3355IUF#PBF serves as intelligent power buffer, detecting PFI and enabling boost within 10µs. Use Value: Achieves sub-100µs switchover with no output droop >2%, preventing false resets in safety-critical firmware. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar supercapacitor backup power management applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3350IUF#PBF | Single 1.5A buck + 1.5A boost; no integrated supercapacitor charger; requires external charge IC. | Lacks autonomous CC/CV charging and VCAP monitoring - needs additional components for supercapacitor-based ride-through. | Select when only basic backup regulation is needed and charger functionality is implemented externally. |
| MAX38889ATG+T | 1.2A buck + 2.5A boost; integrated 1A supercapacitor charger; 2.5V–5.5V VOUT range; different pinout and control interface. | Supports lower minimum VCAP (0.3V) but lacks PFI comparator and dedicated status outputs (RSTB/CPGOOD). | Select when ultra-low VCAP utilization is critical and system-level monitoring is handled by MCU instead of hardware signals. |
Compared with LTC3350IUF#PBF and MAX38889ATG+T, the LTC3355IUF#PBF uniquely integrates all three core functions - buck regulation, boost backup, and autonomous supercapacitor charging - with hardware-enforced sequencing and dedicated status signaling, reducing design risk for mission-critical ride-through applications.
Availability
LTC3355IUF#PBF is available at Aetrix Electronics and suitable for power meters, industrial alarms, and solid-state drives requiring stable component supply with guaranteed long-term availability and automotive-grade temperature support (–40°C to 125°C).
Supply support for LTC3355IUF#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, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, formed through the acquisition of Linear Technology in 2017.
The LTC3355IUF#PBF belongs to ADI's Power Management portfolio, specifically designed for robust, self-contained backup power solutions in industrial and energy infrastructure applications where reliability during power interruption is non-negotiable.
FAQ
What is the maximum supercapacitor voltage supported by the LTC3355IUF#PBF?
The LTC3355IUF#PBF supports VCAP voltages up to 5V, programmed via the CFB resistor divider with a 0.8V internal reference. The device includes overvoltage protection that activates when CFB exceeds the reference by 35mV, engaging an 8kΩ bleed resistor to prevent capacitor damage. This ensures safe operation with common 2.7V and 3.3V-rated supercapacitors, and allows use of stacked configurations up to 5V total.
How does the LTC3355IUF#PBF handle automatic switchover from buck to boost mode during VIN loss?
The LTC3355IUF#PBF uses the PFI pin to continuously monitor VIN via an external resistor divider. When the divided voltage falls below the 0.8V internal reference (with 17mV hysteresis), the PFOB pin pulls low within microseconds, disabling the buck regulator and enabling the boost regulator. This transition occurs without output interruption, maintaining VOUT regulation using stored energy from the supercapacitor connected to VCAP.
Can the LTC3355IUF#PBF operate with a single-cell Li-ion battery instead of a supercapacitor?
Yes - the LTC3355IUF#PBF's charger supports single-cell CC/CV battery charging per its datasheet features. The ICHG and CFB pins allow programming of charge current and float voltage, and the 0.5V–5V VCAP input range accommodates Li-ion cells (2.5V–4.2V). However, the boost regulator's minimum 0.5V input enables deeper discharge than typical Li-ion cutoffs, so external cell protection circuitry remains essential.
What is the purpose of the VCBST pin on the LTC3355IUF#PBF, and how is it used?
VCBST is the output of the boost regulator's internal error amplifier. It controls the peak switch current in the boost stage and must be compensated with an external RC network connected from VCBST to GND. Proper compensation ensures stable boost regulation across load and input conditions; the RC values are selected based on the chosen inductor, output capacitance, and desired phase margin - typically determined via loop analysis or evaluation board guidelines.
Does the LTC3355IUF#PBF require external catch diodes for the buck and boost regulators?
Yes - the LTC3355IUF#PBF is a nonsynchronous controller for both buck and boost stages, requiring external Schottky diodes. For the buck stage (SW1), a diode connects between SW1 and GND (or VOUT, depending on topology); for the boost stage (SW2), a diode connects between SW2 and VOUT. Diode selection must consider forward voltage, reverse recovery, and thermal derating - typical choices include 3A/40V Schottky devices with low VF and fast trr.
LTC3355IUF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 3V
- Voltage - Input (Max):
- 20V
- Voltage - Output (Min/Fixed):
- 2.7V
- Voltage - Output (Max):
- 5V
- Current - Output:
- 1A
- Frequency - Switching:
- 1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-QFN (4x4)
LTC3355IUF#PBF FAQ
1.How can I place an order for LTC3355IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3355IUF#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 LTC3355IUF#PBF reliable?
The price and inventory of LTC3355IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3355IUF#PBF is usually 5 days.
3.What payment methods are accepted for LTC3355IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3355IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3355IUF#PBF?
LTC3355IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3355IUF#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 LTC3355IUF#PBF?
For technical support, including LTC3355IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3355IUF#PBF requirements.
6.How does Aetrix verify that LTC3355IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3355IUF#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 LTC3355IUF#PBF meets industry standards.
7.What is the process for return or replacement of LTC3355IUF#PBF?
All LTC3355IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3355IUF#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 LTC3355IUF#PBF part is unused and in its original packaging.
Return procedure for LTC3355IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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