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Analog Devices Inc. LT1940LEFE#TRPBF
- Part No.:
- LT1940LEFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT1940LEFE#TRPBF.pdf
- Description:
- IC REG BUCK ADJ 1.4A DL 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,150
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Product details
Overview
LT1940LEFE#TRPBF from Analog Devices (formerly Linear Technology) is a dual monolithic 1.4A, 1.1MHz step-down DC/DC switching regulator with internal bipolar NPN power switches, designed for regulated 5V input supplies (3.6V–7V input range). It integrates two independent current-mode PWM controllers, anti-phase switching to reduce input ripple, and dedicated RUN/SS and PG pins per channel for precise supply sequencing in DSP, DSL modem, and disk drive power systems.
For engineers reviewing the LT1940LEFE#TRPBF datasheet, LT1940LEFE#TRPBF pinout, LT1940LEFE#TRPBF application, or LT1940LEFE#TRPBF equivalent, key selection considerations include its 1.25V feedback reference, 1.1MHz fixed-frequency operation, thermal-enhanced 16-lead TSSOP package with exposed GND pad, and dual-channel independent soft-start and power-good signaling for reliable multi-rail power-up coordination.
Technical Context
The LT1940LEFE#TRPBF employs a current-mode PWM architecture with a master-slave oscillator configuration: one master 1.1MHz oscillator synchronizes both regulators while enforcing 180° anti-phase switching, minimizing input capacitor RMS current. Each channel features independent error amplifiers (VC pins), cycle-by-cycle current limiting, and frequency foldback under overload or short-circuit conditions.
Its bipolar NPN internal switches require external BOOST capacitors and Schottky diodes to generate gate-drive voltage above VIN; minimum BOOST-to-SW differential is 1.8V for full saturation. Power-good comparators monitor FB pins at 90% of regulation (±125mV offset), asserting open-collector PG outputs only when VIN > 2.4V and corresponding RUN/SS > 0.8V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 7V - Valid only for LT1940L variant; enables direct use with regulated 5V rails without pre-regulation. |
| Switching Frequency | 1.1MHz (TYP), ±15% over temp - Enables use of sub-5µH inductors and ceramic output caps for compact, low-ripple designs. |
| Output Current per Channel | 1.4A continuous - Guaranteed maximum load with proper inductor selection (e.g., 3.3µH for 3.3V out) and thermal layout. |
| Feedback Reference Voltage | 1.25V ±1.2% over –40°C to 85°C - Sets output via resistor divider; tolerance directly impacts output accuracy. |
| Power-Good Threshold | 90% of VOUT (±125mV offset) - Ensures robust sequencing margin before enabling downstream logic or processors. |
| Shutdown Current | 45µA max - Enables ultra-low quiescent power during system sleep modes without external enable circuitry. |
| Thermal Resistance | θJA = 45°C/W, θJC = 10°C/W - Requires soldered exposed pad (Pin 17) to PCB copper for safe 1.4A operation at 85°C ambient. |
Pinout & Package
LT1940LEFE#TRPBF is housed in a 16-lead thermally enhanced TSSOP package (FE) with an exposed GND pad (Pin 17) that must be soldered to PCB for electrical integrity and thermal performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOST1 / BOOST2 (1, 8) | Bootstrap drive voltage supply | Provides >VIN gate drive to internal NPN switches; requires external diode + 0.1µF capacitor tied to SW or VOUT. |
| SW1 / SW2 (2, 7) | Internal switch collector output | Connects to inductor and catch diode; voltage swings from GND to VIN during operation. |
| VIN (3–6) | Main power input | Four parallel pins share input current path; must be locally bypassed with ≥4.7µF ceramic cap. |
| FB1 / FB2 (9, 16) | Output voltage sense input | Regulated to 1.25V; sets VOUT via R1/R2 divider; bias current ≤1.2µA affects high-R divider accuracy. |
| VC1 / VC2 (10, 15) | Error amplifier output | Controls peak switch current; clamped at 0.75V (threshold) and 1.8V (max); used for loop compensation or override. |
| PG1 / PG2 (11, 14) | Open-collector power-good indicator | Active-high when FB within 10% of target; pulls low until regulation achieved; requires external pull-up. |
| RUN/SS1 / RUN/SS2 (12, 13) | Enable + soft-start control | Pulled high (>0.8V) to start; internal 2µA current source charges external cap for controlled ramp-up. |
| GND (17) | Power and signal ground | Exposed thermal pad - mandatory solder connection to PCB ground plane for thermal and EMI performance. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent regulators | Enables simultaneous 3.3V/5V or 1.8V/3.3V generation with separate sequencing, shutdown, and monitoring per rail. |
| Anti-phase 1.1MHz switching | Reduces input ripple current by ~30% vs. in-phase operation, allowing smaller input capacitance and lower EMI. |
| Integrated bipolar NPN switches | Eliminates need for external MOSFETs or drivers; optimized for efficiency at 5V input with minimal external components. |
| Independent RUN/SS and PG pins | Supports flexible power-up order (e.g., core before I/O) and fault detection without external supervisors or timers. |
| Current-mode control with foldback | Provides inherent cycle-by-cycle current limit and automatic frequency reduction during overload, improving fault robustness. |
Applications
| Disk Drive Power Supply | DSP Core & I/O Rail Generation |
|---|---|
Use Scenario: Dual-rail power for 2.5V spindle motor driver and 1.2V DSP core in portable HDDs. IC Role / Device Role / Timing Role: Primary DC/DC converter delivering regulated 2.5V and 1.2V from 5V bus with tight sequencing. Use Value: Anti-phase operation minimizes input ripple on shared 5V supply; independent PG signals ensure motor enables only after core is stable. |
Use Scenario: Generating 1.8V core and 3.3V I/O supplies for TI C6000 DSP in telecom baseband cards. IC Role / Device Role / Timing Role: Dual synchronous buck regulator managing rail ordering and brown-out detection. Use Value: RUN/SS1 and RUN/SS2 allow staggered startup; PG1/PG2 interface directly with DSP's reset controller for deterministic boot. |
| DSL/Cable Modem Power | Wall Adapter-Fed Embedded System |
Use Scenario: Powering ADSL line driver (5V), PHY (3.3V), and microcontroller (1.8V) from 5V wall adapter. IC Role / Device Role / Timing Role: Central dual-output regulator with integrated sequencing and fault reporting. Use Value: 3.6V–7V input range matches regulated 5V adapter output; low shutdown current (<45µA) extends standby time. |
Use Scenario: Compact dual-rail solution for industrial IoT gateway using 5V USB-C or barrel jack input. IC Role / Device Role / Timing Role: Main power IC converting 5V to 3.3V system rail and 1.2V sensor interface rail. Use Value: 16-lead TSSOP with exposed pad fits dense layouts; ceramic-capable design eliminates electrolytic bulk caps. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-output buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS54290RGER | MOSFET-based, 2.95–18V input, 2×2.2A, 300kHz–2MHz adjustable freq, no BOOST pins required. | Requires external FETs but supports wider input; lacks anti-phase sync and integrated PG sequencing logic. | Preferred for higher input voltages (>7V) or where programmable frequency and lower IQ are critical. |
| MP2491DS-LF-Z | Monolithic dual 1.5A buck, 4.5–18V input, 500kHz fixed freq, no independent RUN/SS or PG per channel. | Single enable and single PGOOD output; simpler control but no per-rail sequencing capability. | Selected when cost and board space are prioritized over independent rail management. |
Compared with LT1940LEFE#TRPBF, TPS54290RGER offers broader input range and flexibility but adds external FET complexity and loses anti-phase ripple reduction, while MP2491DS-LF-Z reduces component count but sacrifices per-channel sequencing and monitoring essential for DSP or multi-core SoC power.
Availability
LT1940LEFE#TRPBF is available at Aetrix Electronics and suitable for disk drive power supplies, DSL modem designs, and wall transformer-fed embedded systems requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT1940LEFE#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 semiconductors, serving precision instrumentation, communications, and industrial markets.
The LT1940/LT1940L product line was developed specifically for compact, high-density dual-rail power conversion in bandwidth-constrained applications such as networking equipment and portable storage, emphasizing sequencing integrity and thermal efficiency in regulated-input environments.
FAQ
What is the absolute maximum input voltage rating for LT1940LEFE#TRPBF?
The LT1940LEFE#TRPBF has an absolute maximum VIN rating of 7V, strictly limited to the LT1940L variant. Exceeding this voltage risks permanent damage to internal circuitry and violates the device's qualified operating range. This differs from the standard LT1940 (25V max), confirming LT1940LEFE#TRPBF is intended exclusively for regulated 5V supply rails.
Does LT1940LEFE#TRPBF support independent power-good signaling for each output?
Yes, LT1940LEFE#TRPBF provides two dedicated open-collector PG pins (PG1 and PG2), each monitoring its respective FB pin and asserting high when output voltage reaches 90% of target (±125mV offset). This enables true per-rail sequencing-e.g., holding DSP reset until both 1.8V core and 3.3V I/O are stable-without external supervisors.
Can LT1940LEFE#TRPBF operate with ceramic output capacitors only?
Yes, LT1940LEFE#TRPBF is fully compatible with ceramic output capacitors due to its current-mode control architecture, which does not rely on capacitor ESR for loop stability. A 10µF X5R/X7R ceramic cap per channel delivers low ripple and fast transient response, eliminating need for bulk electrolytics in most 1.4A applications.
What is the purpose of the exposed pad (Pin 17) on LT1940LEFE#TRPBF?
The exposed pad (Pin 17) on LT1940LEFE#TRPBF serves as the primary thermal and electrical ground connection. It must be soldered to a PCB copper pour to achieve θJA = 45°C/W and prevent thermal shutdown under 1.4A load. Leaving it unconnected degrades thermal performance by >30°C and may cause premature failure.
How does anti-phase switching in LT1940LEFE#TRPBF reduce input ripple?
LT1940LEFE#TRPBF configures its two switching regulators to operate 180° out-of-phase, causing their input current pulses to partially cancel at the VIN node. This reduces RMS input capacitor current by up to 30% compared to in-phase operation, enabling smaller ceramic input caps (e.g., 4.7µF instead of 10µF) and lower conducted EMI.
LT1940LEFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 2
- Voltage - Input (Min):
- 3.6V
- Voltage - Input (Max):
- 7V
- Voltage - Output (Min/Fixed):
- 1.25V
- Voltage - Output (Max):
- 6.16V
- Current - Output:
- 1.4A
- Frequency - Switching:
- 1.1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-TSSOP-EP
LT1940LEFE#TRPBF FAQ
1.How can I place an order for LT1940LEFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1940LEFE#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 LT1940LEFE#TRPBF reliable?
The price and inventory of LT1940LEFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1940LEFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1940LEFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1940LEFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1940LEFE#TRPBF?
LT1940LEFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1940LEFE#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 LT1940LEFE#TRPBF?
For technical support, including LT1940LEFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1940LEFE#TRPBF requirements.
6.How does Aetrix verify that LT1940LEFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1940LEFE#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 LT1940LEFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1940LEFE#TRPBF?
All LT1940LEFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1940LEFE#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 LT1940LEFE#TRPBF part is unused and in its original packaging.
Return procedure for LT1940LEFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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