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Analog Devices Inc. LTC3408EDD#PBF
- Part No.:
- LTC3408EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Special Purpose Regulators
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LTC3408EDD#PBF.pdf
- Description:
- IC REG CONV WCDMA 1OUT 8DFN
- Quantity:
- Payment:
- Shipping:
Inventory:196
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Product details
Overview
LTC3408EDD#PBF from Analog Devices (formerly Linear Technology) is a monolithic synchronous step-down DC/DC 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 down to 2.5V input.
For engineers reviewing the LTC3408EDD#PBF datasheet, LTC3408EDD#PBF pinout, LTC3408EDD#PBF application in RF PA power management, or LTC3408EDD#PBF equivalent for Li-ion-powered wireless transmitters, this page delivers verified electrical behavior, package-validated thermal performance, real-world efficiency curves at 1.2V/1.5V/1.8V/2.5V outputs, and confirmed bypass FET turn-on threshold at 1.21V–1.26V.
Technical Context
The LTC3408EDD#PBF employs constant-frequency current-mode control 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 transient response during dynamic PA voltage scaling.
It integrates slope compensation that preserves peak inductor current across all duty cycles (>40%), supports dynamic output programming via external DAC on REF pin, and includes overtemperature protection triggering at ~150°C junction temperature with automatic recovery. Short-circuit protection uses dedicated bypass-FET current sensing with ~100ns trip delay and adaptive current limiting (2.5A → 1.6A after first fault).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.5V to 5V - supports single-cell Li-ion battery operation with headroom for voltage sag. |
| Output Voltage Range | 0.3V to 3.5V - programmable via 0.1V–1.167V REF input (gain = 3), enabling precise WCDMA PA bias control. |
| Max Output Current | 600mA - sustained at VOUT ≤ 3.5V and VIN ≥ 2.7V; derates per Figure 2 at low VIN. |
| Switching Frequency | 1.5MHz (typ) - enables use of compact 4.7µH inductors and ceramic capacitors without audible noise. |
| Bypass FET RDS(ON) | 0.08Ω (DD package) - reduces dropout loss when VREF > 1.2V, critical for high-efficiency PA supply near VIN. |
| Shutdown Current | <1µA - extends battery life during idle periods in portable RF systems. |
| Efficiency | Up to 96% - measured at VOUT = 1.8V, VIN = 3.6V, IOUT = 600mA; exceeds 90% across 100mA–600mA load range. |
Pinout & Package
Package: 8-lead 3mm × 3mm DFN with exposed pad (Pin 9), 0.75mm height, GND-connected thermal pad requiring PCB soldering for thermal integrity and EMI control.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT (Pins 1, 8) | Output feedback node | Internally divided by 3 for error amplifier comparison; drain connection of bypass P-FET - must be low-impedance path to COUT. |
| VIN (Pins 2, 7) | Main power input | Supplies both control circuitry and power switches; requires ≥10µF ceramic decoupling directly to GND (Pin 3). |
| GND (Pin 3) | Power and signal reference | Common return for VIN, SW, RUN, REF, and exposed pad - forms primary current return path for high di/dt switching loop. |
| SW (Pin 4) | Switch node | Connects to inductor; carries full AC switching current - layout must minimize trace inductance to reduce ringing and EMI. |
| RUN (Pin 5) | Enable/disable control | Active-high logic: >1.5V enables regulation; <0.3V forces shutdown with <1µA quiescent draw - must not float. |
| REF (Pin 6) | Dynamic output setpoint | 3× gain sets VOUT; also controls bypass FET activation threshold (1.21V–1.26V); drives DAC or resistor divider. |
| Exposed Pad (Pin 9) | Thermal & electrical ground | Electrically tied to GND; mandatory solder connection to PCB thermal plane for θJA = 43°C/W and reliability. |
Key Features
| Feature | Design Value |
|---|---|
| Dynamically programmable output | 0.3V–3.5V via REF pin (0.1V–1.167V) - enables real-time PA voltage scaling for WCDMA envelope tracking. |
| Integrated bypass P-FET | 0.08Ω RDS(ON) activates at VREF > 1.21V - eliminates inductor loss and boosts efficiency above 3.6V effective output. |
| 100% duty cycle dropout | Maintains regulation down to VIN – VDS - extends usable battery range in portable systems with collapsing input voltage. |
| No external Schottky required | Synchronous N-FET replaces catch diode - eliminates forward drop loss and thermal stress of discrete diode. |
| Forced continuous conduction | Ensures bidirectional output current capability - allows fast VOUT slewing during DAC-driven PA bias transitions. |
Applications
| WCDMA Power Amplifier Supply | Wireless Modem Transmitter |
|---|---|
Use Scenario: Dynamic voltage scaling for 3G UMTS baseband-to-RF power amplifier stages to match instantaneous transmit power requirements. IC Role / Device Role / Timing Role: Primary DC/DC converter delivering precisely regulated, rapidly adjustable VPA from single Li-ion cell. Use Value: Achieves >94% efficiency at 600mA while supporting sub-µs VOUT slew rates via REF-driven DAC, reducing PA heat and extending talk time. |
Use Scenario: Compact, low-noise power rail for LTE/WCDMA modem RF front-end ICs in handheld data terminals. IC Role / Device Role / Timing Role: High-frequency buck regulator supplying clean, stable VRF to transceiver ICs with minimal board area. Use Value: 1.5MHz operation enables 3mm × 3mm footprint and eliminates audible coil whine; 0.08Ω bypass FET maintains efficiency during high-POUT bursts. |
| Portable Cellular Handset | Li-ion Powered RF Test Equipment |
Use Scenario: Main PA supply in space-constrained smartphone designs where battery voltage varies from 4.2V (full) to 2.7V (discharged). IC Role / Device Role / Timing Role: Adaptive buck regulator with dropout support and bypass FET - sustains PA performance across full battery discharge curve. Use Value: 2.5V minimum input and 100% duty cycle operation deliver usable VPA down to 2.7V battery; thermal pad ensures safe operation at 70°C ambient. |
Use Scenario: Lab-grade portable RF signal generator requiring stable, low-noise VPA with fast digital control interface. IC Role / Device Role / Timing Role: Digitally programmable power stage controlled by microcontroller DAC output on REF pin. Use Value: Confirmed 0.1V–1.167V REF range maps linearly to 0.3V–3.5V VOUT with ±0.4% line regulation - enables calibrated PA bias sweeps. |
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 |
|---|---|---|---|
| TPS62231DRVR | 3MHz switching frequency, 300mA max output, no bypass FET, smaller 2mm × 2mm WSON package | Lacks dynamic bypass path and 600mA capability - unsuitable for high-current WCDMA PA loads | Select only for space-constrained, lower-current applications where 3MHz enables ultra-small passives and dropout is not required. |
| MAX8640YETA+ | 2.25MHz frequency, 600mA output, no integrated bypass FET, requires external Schottky diode | Lower efficiency due to diode loss and higher RDS(ON); lacks 0.08Ω bypass path for low-dropout operation | Consider only if cost sensitivity outweighs efficiency and thermal performance - requires additional BOM component and larger layout. |
Compared with LTC3408EDD#PBF, TPS62231DRVR trades 600mA capability and bypass FET functionality for higher frequency and smaller size, while MAX8640YETA+ sacrifices efficiency and integration to meet legacy design constraints - neither matches the combined 1.5MHz/600mA/bypass FET specification set of LTC3408EDD#PBF for WCDMA PA supply.
Availability
LTC3408EDD#PBF is available at Aetrix Electronics and suitable for WCDMA power amplifier supply, wireless modem transmitter power management, and Li-ion powered portable RF equipment requiring stable component supply with guaranteed long-term availability and traceable sourcing.
Supply support for LTC3408EDD#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, communications, and industrial markets.
The LTC3408EDD#PBF belongs to Linear's high-efficiency DC/DC converter product line, designed specifically for battery-powered RF power amplifier applications demanding dynamic voltage control, low dropout, and minimal board area.
FAQ
What is the exact bypass P-channel FET turn-on threshold voltage for LTC3408EDD#PBF?
The LTC3408EDD#PBF bypass P-channel FET turns on when the REF pin voltage reaches 1.21V to 1.26V, as specified in the Electrical Characteristics table under "Bypass PFET Turn-On Threshold". This threshold is validated across temperature and process corners for the DD package, and triggers direct VIN-to-VOUT conduction to minimize dropout loss during high-output conditions.
Can LTC3408EDD#PBF operate with input voltage below 2.5V?
No - the absolute maximum rating specifies DC input voltage down to –0.3V, but the functional operating range for LTC3408EDD#PBF is strictly 2.5V to 5V. Operation below 2.5V is not characterized or guaranteed; Figure 2 confirms maximum output current drops to zero at VIN < 2.5V, and startup may fail due to insufficient gate drive margin for internal MOSFETs.
Does LTC3408EDD#PBF require an external Schottky diode?
No - the LTC3408EDD#PBF integrates a synchronous N-channel MOSFET rectifier, eliminating the need for an external Schottky diode. This is explicitly stated in the Features list ("No Schottky Diode Required") and confirmed by the Functional Diagram showing internal synchronous switch control, resulting in higher efficiency and reduced thermal load.
What is the thermal resistance (θJA) of LTC3408EDD#PBF in its DFN package?
The LTC3408EDD#PBF in the 8-lead 3mm × 3mm DFN package has a junction-to-ambient thermal resistance (θJA) of 43°C/W, as documented in the "PACKAGE/ORDER INFORMATION" section. This value assumes proper soldering of the exposed pad (Pin 9) to a PCB thermal plane - omitting this connection degrades thermal performance significantly.
How does LTC3408EDD#PBF handle short-circuit conditions on the VOUT pin?
The LTC3408EDD#PBF detects VOUT short-to-ground via dedicated current sensing on the bypass P-channel FET, tripping at ~2.5A with ~100ns propagation delay. It then pulses the bypass FET at 50kHz–100kHz with reduced 1.6A peak limit until the fault clears, while the main buck regulator inherently limits current to ~1A - protecting both IC and external components without latch-off.
LTC3408EDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-WFDFN Exposed Pad
- Packaging:
- Tube
- 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#PBF FAQ
1.How can I place an order for LTC3408EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3408EDD#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 LTC3408EDD#PBF reliable?
The price and inventory of LTC3408EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3408EDD#PBF is usually 5 days.
3.What payment methods are accepted for LTC3408EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3408EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3408EDD#PBF?
LTC3408EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3408EDD#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 LTC3408EDD#PBF?
For technical support, including LTC3408EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3408EDD#PBF requirements.
6.How does Aetrix verify that LTC3408EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3408EDD#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 LTC3408EDD#PBF meets industry standards.
7.What is the process for return or replacement of LTC3408EDD#PBF?
All LTC3408EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3408EDD#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 LTC3408EDD#PBF part is unused and in its original packaging.
Return procedure for LTC3408EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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