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Analog Devices Inc. LTC3408EDD#TRPBF
- Part No.:
- LTC3408EDD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Special Purpose Regulators
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LTC3408EDD#TRPBF.pdf
- Description:
- IC REG CONV WCDMA 1OUT 8DFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,141
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Product details
Overview
LTC3408EDD#TRPBF from Analog Devices (formerly Linear Technology) is a high-efficiency monolithic synchronous step-down regulator optimized for WCDMA power amplifier supply, featuring dynamically adjustable output (0.3V–3.5V), 600mA output current, 1.5MHz fixed switching frequency, and integrated 0.08Ω bypass P-channel MOSFET for low-dropout operation in battery-powered RF transmitters.
For engineers reviewing the LTC3408EDD#TRPBF datasheet, LTC3408EDD#TRPBF pinout, LTC3408EDD#TRPBF application, or LTC3408EDD#TRPBF equivalent, this page delivers verified technical context, validated package mapping, confirmed pin functions, real-world application constraints, and two rigorously cross-checked alternative parts for WCDMA PA power management design.
Technical Context
The LTC3408EDD#TRPBF employs a constant-frequency current-mode control architecture with internal P-channel main switch, N-channel synchronous rectifier, and dedicated bypass P-channel FET - enabling seamless transition between buck regulation and direct VIN-to-VOUT conduction when VREF > 1.2V. Its forced continuous conduction mode ensures rapid output voltage slewing required for dynamic PA bias control.
Output voltage is set to 3× the external REF voltage, with bypass FET activation threshold precisely defined at 1.20V–1.26V (turn-on) and 1.167V–1.20V (turn-off). The device supports 100% duty cycle dropout operation and integrates overtemperature protection with thermal shutdown at ~150°C junction temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 5V - compatible with single-cell Li-ion battery systems (2.7V–4.2V typical operating range) |
| Output Voltage Range | 0.3V to 3.5V - programmable via external REF voltage (0.1V–1.167V), enabling dynamic PA bias tuning |
| Max Output Current | 600mA - sustained DC load capability with internal switches rated for 800mA peak sink/source |
| Switching Frequency | 1.5MHz (typ.) - enables use of compact 4.7µH inductors and ceramic capacitors without external compensation |
| Bypass FET RDS(ON) | 0.08Ω (DD package) - reduces conduction loss during high-VOUT/low-VIN conditions (e.g., VOUT > 3.6V) |
| Efficiency | Up to 96% - achieved by synchronous rectification and elimination of external Schottky diode |
| Shutdown Current | <1µA - preserves battery life in standby modes of cellular handsets and modems |
Pinout & Package
Package: 8-lead 3mm × 3mm DFN (DD), 0.75mm height, exposed pad (Pin 9) soldered to PCB ground plane for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT (Pins 1, 8) | Output feedback node / bypass FET drain | Internally divided by 3 for error amplifier comparison; connects directly to bypass FET drain - critical for accurate output sensing and bypass activation |
| VIN (Pins 2, 7) | Main power input | Dual-pin configuration minimizes high-frequency AC path impedance; requires ≥10µF ceramic decoupling close to pins |
| GND (Pin 3) | Analog/digital ground reference | Common return for internal circuitry, SW node, and exposed pad - must be low-inductance connection to system ground plane |
| SW (Pin 4) | Switch node | Connects to drains of main P-FET and synchronous N-FET; carries high di/dt square-wave current - layout demands shortest possible trace to inductor |
| RUN (Pin 5) | Enable/disable control | Logic-level input: >1.5V enables regulation; <0.3V forces shutdown (<1µA IQ); floating state prohibited |
| REF (Pin 6) | External reference input | Sets VOUT = 3 × VREF; also controls bypass FET activation (VREF > 1.2V turns on bypass path) |
Key Features
| Feature | Design Value |
|---|---|
| Dynamically programmable output | VOUT adjusts from 0.3V to 3.5V in real time via DAC-driven REF pin - essential for envelope tracking in WCDMA PA stages |
| Integrated bypass P-FET | 0.08Ω RDS(ON) eliminates inductor and switch losses when VOUT approaches VIN - extends battery runtime in high-efficiency linear-like mode |
| No external Schottky diode required | Synchronous N-channel rectifier replaces lossy diode - improves efficiency by 5–10% vs. asynchronous designs at medium-to-high loads |
| 100% duty cycle dropout operation | Maintains regulation down to VIN − VOUT ≈ 0V - critical for sustaining PA bias as battery discharges below 3.0V |
| Low-noise forced continuous mode | Eliminates mode-hopping artifacts; enables clean, predictable transient response for RF-sensitive PA supply rails |
Applications
| WCDMA Power Amplifier Supply | Wireless Modem Transmitter |
|---|---|
Use Scenario: Dynamic bias control of WCDMA PA during varying RF output power levels (e.g., 0–30dBm). IC Role / Device Role / Timing Role: Primary voltage regulator delivering rapidly slewed VCC_PA synchronized to baseband envelope signal. Use Value: Enables >90% PA efficiency across full power range by matching supply voltage to instantaneous RF envelope - reducing average power dissipation by up to 40% vs. fixed supply. |
Use Scenario: Powering transmit chain in LTE/WCDMA data modems where PA efficiency and thermal management are critical. IC Role / Device Role / Timing Role: High-bandwidth, low-noise DC-DC converter supplying regulated VPA with sub-10µs response to digital envelope commands. Use Value: Supports burst-mode transmission with minimal voltage droop (<50mV) under 600mA load steps - preserving EVM and ACLR performance. |
| Single-Cell Li-Ion Portable Systems | RF Front-End Bias Management |
Use Scenario: Main PA supply in smartphones and tablets powered by 2.7V–4.2V Li-ion batteries. IC Role / Device Role / Timing Role: Buck regulator with integrated bypass FET ensuring stable VOUT across full battery discharge curve. Use Value: Delivers 3.3V output at >92% efficiency even at 2.8V input - extending usable battery capacity by ~12% compared to non-bypass solutions. |
Use Scenario: Precision bias rail for GaAs/GaN PA driver stages requiring low-noise, fast-settling voltage control. IC Role / Device Role / Timing Role: Low-ripple, digitally programmable supply with 10mV p-p output noise and <20µs settling time. Use Value: Reduces phase noise contribution from supply modulation - improving receiver sensitivity by up to 2dB in adjacent channel blocking tests. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS62260DRVR | Fixed 1.8V/2.5V/3.3V outputs (no dynamic REF programming); 2.25MHz switching; 300mA max output | Lacks VOUT slew capability and bypass FET - unsuitable for envelope-tracking PA bias | Select only for fixed-output, lower-current applications where dynamic control is unnecessary |
| MAX8640YETA+ | Programmable via I²C interface (not analog REF); 1.5MHz; 600mA; no integrated bypass FET | Requires microcontroller coordination; cannot achieve <100ns bypass activation latency needed for PA transient suppression | Prefer for digitally managed systems with firmware control, but avoid where analog envelope tracking is mandatory |
Compared with TPS62260DRVR and MAX8640YETA+, the LTC3408EDD#TRPBF uniquely combines analog REF-based dynamic output programming, sub-100ns bypass FET activation, and 600mA capability in a 3mm × 3mm DFN - making it the only qualified solution for WCDMA/LTE PA envelope tracking among these three.
Availability
LTC3408EDD#TRPBF is available at Aetrix Electronics and suitable for WCDMA cell phone power amplifiers, wireless modems, and RF transmitter power supply designs requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.
Supply support for LTC3408EDD#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) is a global leader in high-performance analog, mixed-signal, and power management ICs, serving precision instrumentation, communications, and industrial markets.
The LTC3408EDD#TRPBF belongs to Linear's high-frequency synchronous buck regulator product line, specifically engineered for dynamic RF power amplifier biasing in cellular infrastructure and handheld devices - emphasizing fast transient response, analog programmability, and ultra-low quiescent current.
FAQ
What is the maximum output voltage achievable with LTC3408EDD#TRPBF?
The LTC3408EDD#TRPBF supports a regulated output voltage range of 0.3V to 3.5V when operating in buck mode. When VREF exceeds 1.2V and 3×VREF > VIN, the internal bypass P-channel MOSFET activates, allowing VOUT to track VIN directly - enabling output voltages up to the input rail (e.g., 4.2V from a fully charged Li-ion battery). This bypass mode is explicitly documented in the datasheet's "Controlling the Output Voltage" section and confirmed in Figure 2 (Maximum Output Current vs Input Voltage).
Does LTC3408EDD#TRPBF require an external Schottky diode?
No, the LTC3408EDD#TRPBF does not require an external Schottky diode. It integrates a synchronous N-channel MOSFET rectifier that replaces the diode in conventional buck topologies. This is explicitly stated in the FEATURES list ("No Schottky Diode Required") and confirmed in the functional diagram and efficiency curves - where efficiency reaches 96% without any external diode component.
What is the purpose of the exposed pad (Pin 9) on LTC3408EDD#TRPBF?
The exposed pad (Pin 9) on the LTC3408EDD#TRPBF is electrically connected to GND and serves dual thermal and electrical functions. Per the PACKAGE/ORDER INFORMATION section, it "MUST BE SOLDERED TO PCB" to ensure proper heat dissipation (θJA = 43°C/W) and low-impedance ground return for high-frequency switching currents. Omitting solder connection risks thermal runaway and degraded transient response due to elevated junction temperature.
Can LTC3408EDD#TRPBF operate with input voltage below 2.5V?
No - the absolute maximum rating specifies "Input Supply Voltage (DC) … –0.3V to 5.5V", but the guaranteed operational range is strictly 2.5V to 5V, as confirmed in the ELECTRICAL CHARACTERISTICS table (VIN MIN = 2.5V) and APPLICATIONS INFORMATION ("The LTC3408 will operate with input supply voltages as low as 2.5V"). Operation below 2.5V is not characterized and may result in failure to regulate or activate overtemperature protection.
How does the RUN pin function on LTC3408EDD#TRPBF?
The RUN pin on LTC3408EDD#TRPBF is a logic-controlled enable input: applying >1.5V enables regulation, while <0.3V forces shutdown with <1µA supply current. The datasheet explicitly warns "Do not leave RUN floating" and specifies ±1µA input current (IRUN) across all states. This behavior is validated in the ABSOLUTE MAXIMUM RATINGS and ELECTRICAL CHARACTERISTICS tables, and is critical for implementing controlled power sequencing in portable systems.
LTC3408EDD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Applications:
- Converter, WCDMA Power Amplifier Applications
- Voltage - Input:
- 2.5V ~ 5V
- Number of Outputs:
- 1
- Voltage - Output:
- 0.3V ~ 3.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-DFN (3x3)
LTC3408EDD#TRPBF FAQ
1.How can I place an order for LTC3408EDD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3408EDD#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 LTC3408EDD#TRPBF reliable?
The price and inventory of LTC3408EDD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3408EDD#TRPBF is usually 5 days.
3.What payment methods are accepted for LTC3408EDD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3408EDD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3408EDD#TRPBF?
LTC3408EDD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3408EDD#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 LTC3408EDD#TRPBF?
For technical support, including LTC3408EDD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3408EDD#TRPBF requirements.
6.How does Aetrix verify that LTC3408EDD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LTC3408EDD#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 LTC3408EDD#TRPBF meets industry standards.
7.What is the process for return or replacement of LTC3408EDD#TRPBF?
All LTC3408EDD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3408EDD#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 LTC3408EDD#TRPBF part is unused and in its original packaging.
Return procedure for LTC3408EDD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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