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Analog Devices Inc. LT3645EUD#TRPBF
- Part No.:
- LT3645EUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Voltage Regulators - Linear + Switching
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3645EUD#TRPBF.pdf
- Description:
- IC REG DL BUCK/LNR 750KHZ 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,165
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Product details
Overview
LT3645EUD#TRPBF from Analog Devices (formerly Linear Technology) is a dual-output DC/DC regulator integrating a 500mA synchronous step-down buck converter and a 200mA low-dropout linear regulator (LDO) in a single 16-lead 3mm × 3mm QFN package. It operates from 3.6V to 36V input, delivers 3.3V/5V buck outputs and 0.8V–8V LDO outputs, and features 750kHz switching frequency, <2μA shutdown current, and integrated overvoltage lockout up to 40V - enabling robust power management for automotive image sensor and microcontroller supply rails.
For engineers reviewing the LT3645EUD#TRPBF datasheet, LT3645EUD#TRPBF pinout, LT3645EUD#TRPBF application, or LT3645EUD#TRPBF equivalent, this page provides verified technical context, validated pin functions, confirmed thermal and electrical specifications, and real-world application constraints - including VIN transient tolerance to 55V, PGOOD (NPG) logic behavior, and BOOST capacitor dependency on duty cycle and VCC2 voltage.
Technical Context
The LT3645EUD#TRPBF implements a constant-frequency current-mode buck regulator with internal bipolar NPN switch and integrated slope compensation, paired with an independent LDO powered from VCC2. Its 750kHz oscillator supports frequency foldback during soft-start and overload to limit inrush and runaway current.
Buck regulation uses a 0.8V reference at FB pin with ±13mV accuracy over temperature; LDO regulation uses a 0.797V reference at FB2 with ±13mV accuracy. Both regulators feature independent enable controls (EN/UVLO and EN2), open-collector NPG output asserting low when both FB ≥ 720mV and FB2 ≥ 720mV, and thermal shutdown at ~160°C with 10°C hysteresis.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; withstands 55V/1s nonrepetitive transients - supports 24V industrial and 12V automotive battery inputs with overvoltage protection. |
| Buck Output Current | 500mA maximum - sufficient for powering CMOS image sensors or MCU cores without external current boosting. |
| LDO Output Current | 200mA maximum with 310mV dropout at full load - enables clean post-regulation of noise-sensitive analog or RF circuitry. |
| Switching Frequency | 750kHz typical (675–825kHz range) - allows use of compact 1.5–15μH inductors and reduces EMI compared to lower-frequency alternatives. |
| Shutdown Current | <2μA - enables ultra-low-power system sleep modes in battery-backed or always-on automotive modules. |
| Thermal Package | 16-lead 3mm × 3mm QFN with exposed pad (θJA = 58.7°C/W) - requires PCB thermal vias for sustained 500mA operation at 125°C ambient. |
| Protection Features | Cycle-by-cycle current limit (1.0A typ), short-circuit robustness, thermal shutdown, UVLO (3.4V), OVLO (38.5V), and NPG fault reporting - eliminates need for external supervision ICs. |
Pinout & Package
LT3645EUD#TRPBF is housed in a thermally enhanced 16-lead (3mm × 3mm) plastic QFN package with exposed ground pad (Pin 17). The package requires soldering of the exposed pad to a dedicated PCB ground plane with ≥4 thermal vias (0.3mm diameter) for reliable thermal performance at full load.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| EN/UVLO (Pin 1) | Enable and undervoltage lockout input | 1.23V threshold enables buck/LDO; resistor divider sets precise UVLO point; tied to VIN for always-on operation. |
| FB (Pin 2) | Buck feedback input | Regulates to 0.8V ±13mV; programs VOUT via R1/R2 divider; determines output accuracy and loop stability. |
| GND (Pins 3, 13, 17) | Ground reference and thermal path | Pins 3 and 13 are signal GND; Pin 17 is exposed pad - must be soldered to PCB ground plane for thermal and electrical integrity. |
| DA (Pin 4) | Diode anode current sense | Detects external catch diode current; reduces switching frequency if >0.9A sensed - prevents startup current runaway. |
| BOOST (Pin 5) | Bootstrap drive voltage source | Charged via internal Schottky from VCC2; must exceed SW by ≥2.2V to saturate NPN switch - requires 0.1μF capacitor to SW. |
| SW (Pin 6) | Switch node | Connects to inductor and cathode of external Schottky diode; carries high di/dt pulsed current - demands tight layout and low-inductance routing. |
| VIN (Pin 7) | Main input power supply | Supplies buck switch, control circuitry, and LDO base drive; requires ≥1μF X7R ceramic bypass close to pin. |
| VCC2 (Pin 8) | LDO input and BOOST diode anode | Must be ≥2.6V to enable internal BOOST diode; otherwise external Schottky required - defines LDO input sourcing capability. |
| OUT2 (Pin 9) | LDO output | Delivers regulated 0.8V–8V output; requires ≥0.47μF ceramic capacitor to ground for stability and transient response. |
| FB2 (Pin 10) | LDO feedback input | Regulates to 0.797V ±13mV; programs VOUT2 via R3/R4 divider; independent of buck loop for flexible dual-rail design. |
| EN2 (Pin 11) | LDO enable input | High >1.6V enables LDO; low <0.5V disables it - allows independent sequencing or power gating of LDO output. |
| NPG (Pin 12) | Open-collector power-good output | Pulls low only when both FB ≥ 720mV and FB2 ≥ 720mV - signals combined regulation status to system controller. |
| NC (Pins 1, 2, 12, 13) | No-connect terminals | Internally unconnected; recommended to tie to GND for mechanical stability and EMI reduction. |
Key Features
| Feature | Design Value |
|---|---|
| Dual-output architecture | Integrates 500mA buck + 200mA LDO in one die - reduces BOM count, PCB area, and design complexity vs. discrete solutions. |
| Wide-input ruggedness | 3.6V–36V operation with 55V transient tolerance and 40V OVLO - eliminates need for external TVS or pre-regulator in automotive environments. |
| Independent soft-start | 900μs buck and 600μs LDO soft-start - prevents input surge and output overshoot during power-up or enable sequencing. |
| True power-good signaling | NPG asserts low only when both buck and LDO outputs are ≥90% of target - enables reliable system reset and rail monitoring. |
| Thermally optimized packaging | 3mm × 3mm QFN with exposed GND pad and θJA = 58.7°C/W - supports 500mA continuous operation at 125°C junction with proper PCB layout. |
| Low-quiescent-current shutdown | <2μA shutdown current - extends battery life in always-connected telematics or ADAS modules during vehicle sleep mode. |
Applications
| Automotive CMOS Image Sensor Supply | Industrial Microcontroller Core Rail |
|---|---|
Use Scenario: Powering 3.3V/5V digital and analog supplies for rear-view or surround-view camera modules in vehicles with 12V battery input subject to load dump transients. IC Role / Device Role / Timing Role: Dual-output regulator providing isolated, low-noise 3.3V for sensor interface and 1.2V–1.8V LDO output for image signal processor core. Use Value: Integrated OVLO (38.5V) and 55V transient tolerance eliminate need for external protection; NPG enables synchronized system boot with camera SoC. |
Use Scenario: Generating stable 3.3V main supply and 1.8V I/O rail for ARM Cortex-M7 microcontrollers in programmable logic controllers (PLCs) operating from 24V industrial bus. IC Role / Device Role / Timing Role: Primary DC/DC regulator delivering 500mA buck output and clean 200mA LDO output for noise-sensitive ADC and communication peripherals. Use Value: 750kHz switching frequency allows small 4.7μH inductor; <2μA shutdown supports deep-sleep modes compliant with IEC 61131-2. |
| Automotive Infotainment Display Backlight | Automotive Radar Transceiver Bias |
Use Scenario: Driving LED backlight strings in center-stack displays using buck-regulated 5V supply and LDO-regulated 3.3V for display controller logic. IC Role / Device Role / Timing Role: High-efficiency buck stage powers boost LED driver IC; LDO supplies low-noise logic rail with fast transient response. Use Value: 310mV LDO dropout ensures regulation down to 3.6V input during cold-crank; DA pin prevents current runaway during LED short events. |
Use Scenario: Providing tightly regulated 5V and 3.3V bias rails for 77GHz radar transceivers in ADAS front-end modules with strict EMI and thermal constraints. IC Role / Device Role / Timing Role: Dual-output regulator delivering low-ripple 5V for RF synthesizer and 3.3V for digital baseband, both referenced to common ground. Use Value: Independent FB/FB2 references and NPG output allow per-rail health monitoring; QFN package enables compact placement near RF section. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-output regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8614EUD#TRPBF | Silent Switcher® architecture; 42V input; 4A buck + 150mA LDO; 2MHz switching; no DA pin or NPG output. | Higher current, lower EMI, but lacks combined PGOOD and diode current sensing - requires external fault monitoring for safety-critical radar. | Select when EMI is primary constraint and LDO current ≤150mA; avoid when NPG sequencing or DA-based overload protection is required. |
| TPS6521905RGER | Texas Instruments part; 5.5V–22V input; 2×1.2A buck + 300mA LDO; I²C programmable; no UVLO/OVLO thresholds or DA pin. | Digitally configurable, higher buck current, but lacks analog UVLO precision and transient robustness - unsuitable for 24V industrial or automotive battery direct connection. | Select for systems requiring dynamic voltage scaling via I²C; avoid where 36V+ input or analog fault detection is mandatory. |
Compared with LT3645EUD#TRPBF, LT8614EUD#TRPBF offers superior EMI performance and higher current but sacrifices analog fault visibility and combined PGOOD, while TPS6521905RGER enables software-defined power sequencing at the cost of reduced input voltage range and missing transient protection features critical for automotive deployment.
Availability
LT3645EUD#TRPBF is available at Aetrix Electronics and suitable for automotive CMOS image sensor supply, industrial microcontroller core rail, and ADAS radar transceiver bias applications requiring stable component supply, long-term lifecycle support, and AEC-Q200-aligned reliability validation.
Supply support for LT3645EUD#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 and maintains its high-reliability analog and power management portfolio with rigorous automotive and industrial qualification standards.
The LT3645 product line was designed specifically for dual-rail power delivery in harsh-environment automotive and industrial systems - emphasizing input transient resilience, precise analog enable/control, and integrated fault reporting without external components.
FAQ
What is the absolute maximum input voltage rating for LT3645EUD#TRPBF?
The LT3645EUD#TRPBF has an absolute maximum VIN rating of 55V for nonrepetitive 1-second transients, but continuous operation is limited to 36V. Overvoltage lockout activates at 38.5V (typical), shutting down both regulators until input falls below 36V. This dual-threshold design protects against load dump while maintaining compatibility with standard 24V industrial supplies.
Does LT3645EUD#TRPBF support independent enable control of the buck and LDO sections?
Yes. LT3645EUD#TRPBF provides two independent enable inputs: EN/UVLO (Pin 1) controls both the buck regulator and LDO, while EN2 (Pin 11) enables or disables only the LDO. Pulling EN2 below 0.5V disables the LDO even if EN/UVLO is high, enabling flexible power sequencing - for example, powering the buck first to charge VCC2 before enabling the LDO.
What is the function of the DA pin on LT3645EUD#TRPBF, and how does it affect operation?
The DA (diode anode) pin on LT3645EUD#TRPBF senses current through the external Schottky catch diode. When sensed current exceeds ~0.9A, the LT3645EUD#TRPBF reduces switching frequency to prevent current runaway during startup or overload. This feature eliminates the need for external current-limiting circuits and enhances robustness in high-capacitance or short-circuit scenarios.
Can LT3645EUD#TRPBF operate with VCC2 supplied below 2.6V?
Yes, but only with an external Schottky diode. The internal BOOST diode requires VCC2 ≥ 2.6V to generate sufficient gate drive. If VCC2 is between 2.2V and 2.6V, connect an external Schottky (e.g., BAS70) from VCC2 (anode) to BOOST (cathode). Below 2.2V, an external boost diode from VIN to BOOST is required - though this limits max VIN to 25V to avoid exceeding BOOST pin absolute maximum ratings.
How does the NPG pin on LT3645EUD#TRPBF indicate power-good status?
The NPG pin on LT3645EUD#TRPBF is an open-collector output that pulls low only when both FB ≥ 720mV and FB2 ≥ 720mV - indicating that both buck and LDO outputs are within ≥90% of their regulated targets. It remains high-impedance otherwise, allowing wired-OR connection with other PGOOD signals. An external pull-up resistor (typically 10kΩ to 3.3V) is required for proper logic-level interfacing.
LT3645EUD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Topology:
- Step-Down (Buck) (1), Linear (LDO) (1)
- Number of Outputs:
- 2
- Frequency - Switching:
- 750kHz
- Voltage/Current - Output 1:
- 0.8V ~ 16V, 500mA
- Voltage/Current - Output 2:
- 0.8V ~ 8V, 200mA
- Voltage/Current - Output 3:
- -
- w/LED Driver:
- No
- w/Supervisor:
- No
- w/Sequencer:
- No
- Voltage - Supply:
- 3.6V ~ 36V
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LT3645EUD#TRPBF FAQ
1.How can I place an order for LT3645EUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3645EUD#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 LT3645EUD#TRPBF reliable?
The price and inventory of LT3645EUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3645EUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3645EUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3645EUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3645EUD#TRPBF?
LT3645EUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3645EUD#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 LT3645EUD#TRPBF?
For technical support, including LT3645EUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3645EUD#TRPBF requirements.
6.How does Aetrix verify that LT3645EUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3645EUD#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 LT3645EUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3645EUD#TRPBF?
All LT3645EUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3645EUD#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 LT3645EUD#TRPBF part is unused and in its original packaging.
Return procedure for LT3645EUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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