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Analog Devices Inc. LT3999IDD#TRPBF
- Part No.:
- LT3999IDD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3999IDD#TRPBF.pdf
- Description:
- IC REG PUSH-PULL ADJ 1A 10DFN
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
LT3999IDD#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic, high-voltage push-pull DC/DC transformer driver IC designed for isolated power generation in compact, low-noise applications. It integrates dual 1A current-limited switches, programmable 50kHz–1MHz switching frequency, duty cycle control via RDC pin, precision UVLO/OVLO thresholds (1.25V ±0.1V), and <1µA shutdown current. It enables 12V-to-12V, 10W isolated supplies in medical instrumentation and distributed power systems.
For engineers reviewing the LT3999IDD#TRPBF datasheet, LT3999IDD#TRPBF pinout, LT3999IDD#TRPBF application, or LT3999IDD#TRPBF equivalent, key selection criteria include its dual-switch push-pull topology, programmable soft-start via ILIM/SS, cross-conduction prevention, exposed-pad DFN thermal performance, and compatibility with center-tapped transformers for safety-isolated outputs.
Technical Context
The LT3999IDD#TRPBF implements a synchronous, out-of-phase push-pull driver architecture with non-overlap timing (70ns) to prevent shoot-through. Its oscillator supports internal RT-programmed operation up to 1MHz or external synchronization-critical for EMI-sensitive data acquisition and RS485 interfaces.
Duty cycle is actively controlled by the OVLO/DC and RDC pins to compensate for input voltage variation, enabling pseudo-regulation before post-LDO stages. The ILIM/SS pin simultaneously sets cycle-by-cycle current limit (0.4–1.7A range) and soft-start time via RC or C-only configuration, reducing inrush during startup.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Limit | 1.0A typical (internal default); programmable down to 0.5A via ILIM/SS resistor - sets maximum per-cycle energy transfer and fault current threshold |
| Switching Frequency Range | 50kHz to 1MHz (RT-programmable); determines transformer size vs. efficiency trade-off - higher fSW reduces magnetics volume but increases switching loss |
| Input Voltage Range | 2.7V to 36V (operating); UVLO rising threshold 1.25V ±0.1V - enables reliable start-up across wide industrial input rails |
| Duty Cycle Control | 20% to 48% (RDC + OVLO/DC dependent); adjusts output voltage vs. VIN drift - supports line regulation without secondary feedback |
| Shutdown Current | <1µA at VUVLO = 0.3V - ensures ultra-low standby power in battery-backed or always-on isolated supplies |
| Package Thermal Resistance | θJA = 43°C/W, θJC = 5.5°C/W (DD package); exposed pad must be soldered to PCB ground plane - enables 10W operation with minimal heatsinking |
| Operating Temperature | –40°C to +125°C junction - qualified for industrial and medical environments requiring extended thermal reliability |
Pinout & Package
LT3999IDD#TRPBF is housed in a 10-lead (3mm × 3mm) plastic DFN package with exposed thermal pad (Pin 11 = GND). The exposed pad must be soldered to the PCB ground plane for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SWA (Pin 1) | Power switch A collector | High-current open-collector node driving one side of center-tapped transformer primary - requires short, wide PCB traces |
| RBIAS (Pin 2) | Bias current reference | Sets internal bias for SWA/SWB drivers via 49.9kΩ-to-GND resistor - stabilizes switching characteristics over temperature |
| VIN (Pin 3) | Main supply input | Supplies internal regulator and gate drivers; requires ≥4.7µF low-ESR ceramic capacitor - handles pulsed 1A switch currents |
| UVLO (Pin 4) | Undervoltage lockout input | Enables/disables operation at 1.25V threshold with 125mV hysteresis - prevents erratic startup below minimum rail |
| OVLO/DC (Pin 5) | Overvoltage lockout / duty cycle control | Configurable as OVLO disable threshold or duty cycle reference - tied to resistor divider on VIN for line regulation |
| RDC (Pin 6) | Duty cycle programming | Resistor-to-GND sets duty cycle (20–48%) when used with OVLO/DC - floating disables duty control, defaults to ~50% |
| RT (Pin 7) | Oscillator frequency set | Resistor-to-GND programs switching frequency (50kHz–1MHz) - defines transformer size and EMI profile |
| SYNC (Pin 8) | External clock sync input | Accepts >2V square wave; locks oscillator to external source - enables precise harmonic placement for EMC compliance |
| ILIM/SS (Pin 9) | Current limit / soft-start | Resistor sets current limit (0.4–1.7A); capacitor adds soft-start ramp - prevents input inrush and limits fault energy |
| SWB (Pin 10) | Power switch B collector | Complementary high-current node to SWA - drives opposite end of transformer primary; identical layout requirements |
| GND (Pin 11) | Ground / thermal pad | Exposed pad connected internally to GND - mandatory soldering to PCB ground plane for thermal dissipation and noise control |
Key Features
| Feature | Design Value |
|---|---|
| Low-noise push-pull topology | Eliminates transformer saturation risk and minimizes common-mode EMI - critical for RS232/RS485 data isolation and medical sensor front-ends |
| Programmable duty cycle control | Compensates for ±30% VIN variation using RDC + OVLO/DC - reduces post-regulator dropout and thermal stress in LDO-based isolated supplies |
| Cross-conduction prevention | 70ns non-overlap timing between SWA/SWB - guarantees zero shoot-through current even under fast transient conditions |
| Adjustable soft-start | RC or C-only configuration on ILIM/SS pin - controls inrush current ramp rate to avoid input rail collapse during cold start |
| Wide input UVLO/OVLO | Independent 1.25V ±0.1V thresholds with 125mV hysteresis - enables robust operation across 2.7–36V inputs with configurable trip points |
Applications
| Medical Isolated Power | Distributed Industrial Power |
|---|---|
|
Use Scenario: Providing isolated ±12V rails for analog front-end amplifiers and ADCs in portable patient monitors. IC Role / Device Role / Timing Role: Push-pull transformer driver generating galvanically isolated output from a single 12V system rail. Use Value: Low 100mVP-P output noise (with optional LC filter) preserves signal integrity in sub-µV biomedical measurements. |
Use Scenario: Generating isolated 5V/3.3V auxiliary supplies for PLC I/O modules operating from 24V DC field buses. IC Role / Device Role / Timing Role: High-efficiency, thermally robust DC/DC driver enabling compact, fanless enclosure designs. Use Value: Exposed-pad DFN package with θJC = 5.5°C/W sustains 10W output without heatsinks in convection-cooled enclosures. |
| Noise-Sensitive Data Interfaces | Positive-to-Negative Conversion |
|
Use Scenario: Powering isolated RS485 transceivers in factory automation networks where EMI immunity is critical. IC Role / Device Role / Timing Role: Synchronized switching driver (via SYNC pin) enabling precise harmonic placement away from data bands. Use Value: External clock synchronization reduces conducted EMI peaks by >20dB at critical frequencies near 1MHz harmonics. |
Use Scenario: Generating –12V rail from +12V input for op-amp biasing in precision instrumentation amplifiers. IC Role / Device Role / Timing Role: Dual-switch push-pull controller driving center-tapped transformer with full-wave rectification. Use Value: Programmable duty cycle maintains stable negative output despite ±10% input rail variation - simplifies feedback design. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar isolated push-pull driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3439EFE#TRPBF | SO-16 package; slew-rate controlled switches; lower max fSW (500kHz); higher quiescent current (12mA) | Better EMI control via adjustable dV/dt, but larger footprint and higher no-load power - suited for ultra-low-noise lab equipment | Select LT3439EFE#TRPBF only if <100mVP-P noise and independent slew control outweigh size/power penalties. |
| LT1533CS#TRPBF | SO-16; 2.7–23V input; no duty cycle control; fixed 50% duty cycle; no SYNC pin | Lacks line regulation and EMI synchronization - limited to fixed-rail, low-EMI-critical applications like isolated sensors | Choose LT1533CS#TRPBF only for cost-sensitive, fixed-input designs where duty cycle adaptability and sync are unnecessary. |
Compared with LT3439EFE#TRPBF and LT1533CS#TRPBF, LT3999IDD#TRPBF offers superior integration (DFN size, duty control, SYNC), lower shutdown current (<1µA vs. 12mA), and wider input range (2.7–36V), making it optimal for space-constrained, multi-rail industrial and medical isolated supplies.
Availability
LT3999IDD#TRPBF is available at Aetrix Electronics and suitable for medical instrumentation, industrial PLCs, and noise-sensitive data interface designs requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LT3999IDD#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 industrial, automotive, communications, and healthcare markets.
The LT3999IDD#TRPBF belongs to Linear's isolated power driver product line, engineered specifically for compact, low-noise, transformer-based isolated DC/DC conversion in safety-critical and EMI-sensitive applications.
FAQ
What is the maximum switching frequency supported by the LT3999IDD#TRPBF?
The LT3999IDD#TRPBF supports an internal switching frequency up to 1MHz, set by the RT resistor (12.1kΩ for 1MHz). When synchronized externally, the maximum sync frequency is also 1MHz, resulting in a 500kHz actual switch frequency per output due to the push-pull topology's two-phase operation.
How does the LT3999IDD#TRPBF achieve line regulation without secondary feedback?
The LT3999IDD#TRPBF achieves pseudo-line regulation by using the OVLO/DC and RDC pins to dynamically adjust duty cycle in response to input voltage changes. With a resistor divider on OVLO/DC referenced to VIN and a grounded RDC resistor, the duty cycle scales inversely with VIN - maintaining stable VOUT across 2.7–36V input range.
Can the LT3999IDD#TRPBF drive a transformer with non-center-tapped primary?
No - the LT3999IDD#TRPBF is specifically designed for center-tapped transformer topologies. Its dual out-of-phase switches (SWA/SWB) drive opposite ends of the primary winding. Using a non-center-tapped transformer would violate the intended current path and disable cross-conduction protection, risking device failure.
What is the purpose of the RBIAS pin on the LT3999IDD#TRPBF?
The RBIAS pin on the LT3999IDD#TRPBF sets the internal bias current for both power switches. A 49.9kΩ resistor to GND establishes optimal drive strength and thermal stability across temperature. Omitting this resistor causes inconsistent switching behavior and potential thermal runaway under load.
Is the exposed thermal pad on the LT3999IDD#TRPBF electrically connected internally?
Yes - the exposed pad (Pin 11) of the LT3999IDD#TRPBF is internally connected to GND. It must be soldered to a PCB ground plane with multiple thermal vias to ensure both electrical integrity and effective heat dissipation (θJC = 5.5°C/W). Leaving it unconnected degrades thermal performance and risks junction overheating at >5W output.
LT3999IDD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 10-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Push-Pull
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2.7V
- Voltage - Input (Max):
- 36V
- Voltage - Output (Min/Fixed):
- -
- Voltage - Output (Max):
- -
- Current - Output:
- 1A
- Frequency - Switching:
- 50kHz ~ 1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT3999IDD#TRPBF FAQ
1.How can I place an order for LT3999IDD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3999IDD#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 LT3999IDD#TRPBF reliable?
The price and inventory of LT3999IDD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3999IDD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3999IDD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3999IDD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3999IDD#TRPBF?
LT3999IDD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3999IDD#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 LT3999IDD#TRPBF?
For technical support, including LT3999IDD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3999IDD#TRPBF requirements.
6.How does Aetrix verify that LT3999IDD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3999IDD#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 LT3999IDD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3999IDD#TRPBF?
All LT3999IDD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3999IDD#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 LT3999IDD#TRPBF part is unused and in its original packaging.
Return procedure for LT3999IDD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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