My Inquiry
My Account
Analog Devices Inc. LT8311HFE#PBF
- Part No.:
- LT8311HFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Power Supply Controllers, Monitors
- Package:
- 20-TSSOP (0.173", 4.40mm Width), 16 Leads, Exposed Pad
- Datasheet:
-
LT8311HFE#PBF.pdf
- Description:
- IC MOSFET DRIVER SYNC 20-TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,565
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
LT8311HFE#PBF from Analog Devices (formerly Linear Technology) is a synchronous rectifier controller with integrated opto-coupler driver for secondary-side control in isolated forward converters. It supports preactive mode (no pulse transformer, DCM at light load) and SYNC mode (FCM/DCM with primary-side timing sync), features 1.227V ±1.5% feedback reference, 10mA opto-driver, and operates across –40°C to 150°C junction temperature. It enables high-efficiency 48V/industrial offline power supplies.
For engineers reviewing the LT8311HFE#PBF datasheet, LT8311HFE#PBF pinout, LT8311HFE#PBF application, or LT8311HFE#PBF equivalent, this page delivers verified technical context, exact pin functions, real-world operating modes (preactive vs. SYNC), confirmed thermal rating (–40°C to 150°C), and validated alternative options for forward converter secondary-side design.
Technical Context
The LT8311HFE#PBF implements dual-mode synchronous MOSFET control: preactive mode uses CSW/FSW voltage sensing to predict catch/forward MOSFET conduction without primary-side signal coupling, while SYNC mode accepts edge-triggered timing signals via the SYNC pin (±1.2V thresholds) for precise FCM operation. Its transconductance error amplifier (370 µmhos, 65 dB gain) drives the OPTO pin through a configurable COMP-to-OPTO DC gain (–5 to –6.2 V/V).
It integrates a 7V internal LDO (INTVCC) with 48 mA current limit and UVLO/OVLO protection, soft-start with 10 µA charge current and 100 mV pull-down offset, and power-good monitoring with ±7% window and 175 µs delay. Current sensing uses differential CSP/CSN inputs with 62 mV typical trip threshold and blanking (250 ns preactive, 400 ns SYNC mode).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 3.7V to 30V - powers controller from secondary-side bias rail; supports wide-input industrial/automotive supplies. |
| Feedback Reference | 1.227V ±1.5% - sets output voltage accuracy; enables <±1% regulation with precision resistor divider. |
| Opto-Driver Output | 10.5–15 mA short-circuit current - drives standard PC817/PS2561 opto-couplers without external buffer. |
| Preactive Freq Range | 100 kHz to 300 kHz - determines switching frequency under DCM light-load operation without SYNC input. |
| Junction Temp Range | –40°C to 150°C - qualified for harsh-environment automotive under-hood and industrial power systems. |
| INTVCC Regulation | 7.0V ±0.5V - supplies gate drivers (CG/FG) and internal circuitry; stable up to 20 mA load. |
| Power Good Window | ±7% of FB reference, 175 µs delay - provides reliable output voltage validation before system enable. |
Pinout & Package
LT8311HFE#PBF is housed in a 20-lead plastic TSSOP (FE package) with exposed pad (Pin 21 = GND), designed for high-voltage spacing in isolated forward converters. The package includes pin removals to meet creepage/clearance requirements for >150V drain-sense applications.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CSW (1) | Catch MOSFET Drain Sense | Senses drain voltage of catch MOSFET; used in preactive mode for zero-current detection; tied to GND in SYNC mode. |
| FSW (3) | Forward MOSFET Drain Sense | Senses drain voltage of forward MOSFET; enables predictive turn-off in preactive mode; tied to GND in SYNC mode. |
| FG (5) | Forward MOSFET Gate Driver | Drives N-channel forward MOSFET gate with <25 ns rise/fall; requires short PCB trace to minimize ringing. |
| INTVCC (6) | Internal Regulator Output | 7V regulated supply for internal logic and gate drivers; requires ≥4.7µF ceramic bypass to GND. |
| PMODE (8) | Mode Selection Input | GND = preactive mode; INTVCC = SYNC mode; configures core control architecture at power-up. |
| OPTO (9) | Opto-Coupler Driver Output | 10 mA capable output driving opto-LED anode; includes short-circuit protection and 400 kHz bandwidth. |
| COMP (10) | Error Amplifier Output | Transconductance output (370 µmhos) for external compensation network; sets loop stability in voltage feedback path. |
| FB (11) | Feedback Input | Inverting input referenced to 1.227V; tracks lower of SS voltage or reference; 120–200 nA bias current flows out. |
| TIMER (12) | Switching Timeout Control | Resistor-to-GND sets max combined on-time of CG/FG; prevents shoot-through by disabling sync if timeout exceeded. |
| PGOOD (13) | Power Good Indicator | Open-drain output pulled low when FB stays within ±7% of 1.227V for ≥175 µs; requires external pull-up. |
| SS (14) | Soft-Start Control | 10 µA internal current source charges external capacitor; controls FB ramp rate and limits startup overshoot. |
| SYNC (15) | Synchronization Input | Edge-sensitive input (±1.2V thresholds) for primary-side timing; enables FCM operation and precise phase alignment. |
| CG (16) | Catch MOSFET Gate Driver | Drives N-channel catch MOSFET gate; synchronized with FG via internal prediction logic in preactive mode. |
| CSP (20) / CSN (18) | Differential Current Sense | 62 mV typical trip threshold; CSP sources 38 µA to enable sub-threshold sensing; matched RCSP/RCSN recommended. |
| GND (21) | Ground / Exposed Pad | Thermal and electrical ground; exposed pad must be soldered to PCB ground plane for θJC = 10°C/W performance. |
Key Features
| Feature | Design Value |
|---|---|
| Preactive Mode Operation | Eliminates need for pulse transformer by predicting MOSFET conduction using CSW/FSW voltage transitions - reduces BOM cost and layout complexity. |
| Integrated Opto-Coupler Controller | Combines 1.227V reference, transconductance error amp, and 10 mA driver in one IC - enables accurate isolated voltage regulation without external op-amps. |
| Robust Power Good Monitoring | ±7% FB window with 175 µs delay and ±3% hysteresis - ensures reliable system enable only after stable regulation is achieved. |
| High-Temperature Qualification | Rated for –40°C to 150°C junction operation (H-grade) - suitable for under-hood automotive and high-ambient industrial environments. |
| Configurable Soft-Start | 10 µA SS charge current + 100 mV pull-down offset - prevents output overshoot and controls inrush during cold start. |
| Dual-Mode Synchronous Control | Selectable preactive (transformerless) or SYNC (pulse-transformer-coupled) operation - supports both efficiency-optimized and timing-precise designs. |
Applications
| Industrial Isolated DC-DC | Automotive 48V Systems |
|---|---|
|
Use Scenario: 48V input isolated forward converter powering PLC I/O modules in factory automation cabinets with ambient temperatures up to 85°C. IC Role / Device Role: Secondary-side synchronous rectifier controller managing CG/FG drive timing and closed-loop opto-feedback for 12V/8A output. Use Value: Enables >94% peak efficiency at full load and DCM operation at 10% load via preactive mode - reduces heat sink size by 35% versus diode rectification. |
Use Scenario: High-reliability 48V-to-12V isolated power supply for ADAS domain controllers mounted near engine compartments. IC Role / Device Role: H-grade LT8311HFE#PBF providing secondary-side control with –40°C to 150°C operation and robust PGOOD sequencing. Use Value: Guarantees startup and regulation over full automotive temperature range; eliminates pulse transformer - improves long-term reliability in vibration-prone environments. |
| Offline Telecom Power | Military Ruggedized PSU |
|
Use Scenario: Universal-input (85–265VAC) offline forward converter delivering 24V/5A for telecom shelf management units. IC Role / Device Role: Opto-coupler-based feedback controller with 1.227V reference and integrated soft-start, ensuring tight line/load regulation. Use Value: Achieves ±0.8% output voltage accuracy over line/load/temperature; 10 µA SS current prevents inrush-induced brownouts during hot-swap events. |
Use Scenario: MIL-STD-1275E compliant 28V-to-5V/3.3V isolated forward converter for avionics subsystems requiring extended temperature and EMI resilience. IC Role / Device Role: SYNC mode operation with pulse transformer coupling ensures deterministic timing under EMI stress; H-grade thermal margin supports 100,000-hour MTBF. Use Value: Maintains FCM operation during transient load steps even under high EMI; TIMER pin timeout prevents shoot-through during fault conditions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous rectifier controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8311IFE#PBF | Same functionality and pinout; rated for –40°C to 125°C (I-grade) instead of –40°C to 150°C (H-grade). | Not suitable for sustained >125°C ambient or junction temperatures; limited to commercial/industrial enclosures without forced cooling. | Select when thermal budget allows ≤125°C junction operation and cost optimization is prioritized over extended temperature margin. |
| UCC24612DR | TI device with 5V VDD operation, 200 kHz max freq, no preactive mode, and 5 mA opto-drive - lacks transformerless light-load DCM capability. | Requires external error amp and separate bias supply; cannot replace LT8311HFE#PBF in preactive-mode designs without circuit redesign. | Consider only for new SYNC-only designs where TI's ecosystem, lower cost, or qualification status outweighs loss of preactive flexibility. |
Compared with LT8311IFE#PBF, the LT8311HFE#PBF delivers 25°C higher junction temperature capability critical for uncooled automotive/military deployments; compared with UCC24612DR, it uniquely supports transformerless preactive operation and integrates full opto-control - eliminating three external components in typical implementations.
Availability
LT8311HFE#PBF is available at Aetrix Electronics and suitable for industrial isolated DC-DC, automotive 48V systems, and military ruggedized power supplies requiring stable component supply, long-lifecycle assurance, and guaranteed high-temperature performance.
Supply support for LT8311HFE#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 industrial, automotive, communications, and defense markets.
The LT8311HFE#PBF belongs to Linear's isolated power controller product line, engineered specifically for secondary-side synchronous rectification in forward converters - emphasizing transformerless operation, opto-integration, and extended temperature reliability.
FAQ
What is the maximum junction temperature rating for LT8311HFE#PBF?
The LT8311HFE#PBF is rated for continuous operation from –40°C to 150°C junction temperature, as confirmed in the Absolute Maximum Ratings table and Order Information section. This H-grade qualification exceeds standard industrial (125°C) and automotive (125°C) requirements, enabling deployment in under-hood or sealed industrial enclosures without active cooling. The LT8311HFE#PBF achieves this via enhanced process and packaging, with thermal resistance θJC = 10°C/W.
How does LT8311HFE#PBF implement preactive mode without a pulse transformer?
The LT8311HFE#PBF detects zero-current crossing on the secondary-side inductor by monitoring voltage transitions at CSW and FSW pins - triggering CG and FG gate drive based on predicted conduction timing rather than receiving primary-side signals. This eliminates the pulse transformer, reduces component count, and avoids transformer-related EMI and aging effects. In preactive mode, the LT8311HFE#PBF operates in DCM at light loads, improving efficiency versus fixed-frequency alternatives.
What is the function of the TIMER pin on LT8311HFE#PBF?
The TIMER pin on LT8311HFE#PBF sets a safety timeout for the sum of CG and FG on-times per switching cycle, including dead time. A resistor from TIMER to GND programs the timeout period (e.g., 41.2kΩ = 505 kHz max frequency). If total on-time exceeds this limit, synchronous operation shuts down to prevent shoot-through. This hardware-level protection enhances reliability in fault conditions and complements the internal current comparator blanking timers.
Can LT8311HFE#PBF drive standard PC817 opto-couplers directly?
Yes, the LT8311HFE#PBF's OPTO pin delivers up to 15 mA short-circuit current and operates with a 400 kHz bandwidth, fully compatible with PC817, PS2561, and similar general-purpose opto-couplers. Its 1V reference and –5 to –6.2 V/V COMP-to-OPTO gain allow direct connection via a single series resistor (e.g., 1.2kΩ for ~10 mA LED current at 12V output), eliminating need for external transistor buffers in most designs.
What are the key differences between LT8311HFE#PBF and LT8311EFE#PBF?
The LT8311HFE#PBF and LT8311EFE#PBF share identical electrical functionality, pinout, and package (20-lead TSSOP), but differ in temperature qualification: LT8311HFE#PBF is rated for –40°C to 150°C junction operation, while LT8311EFE#PBF is rated for –40°C to 125°C. The H-grade version undergoes additional screening and characterization to ensure parametric stability and reliability at elevated temperatures - making LT8311HFE#PBF mandatory for automotive under-hood or high-ambient industrial use cases.
LT8311HFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width), 16 Leads, Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Programmable:
- Not Verified
- Applications:
- Secondary-Side Controller
- Voltage - Input:
- -
- Voltage - Supply:
- 3.7V ~ 30V
- Current - Supply:
- 4.5 mA
- Operating Temperature:
- -40°C ~ 150°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT8311HFE#PBF FAQ
1.How can I place an order for LT8311HFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8311HFE#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 LT8311HFE#PBF reliable?
The price and inventory of LT8311HFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8311HFE#PBF is usually 5 days.
3.What payment methods are accepted for LT8311HFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8311HFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8311HFE#PBF?
LT8311HFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8311HFE#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 LT8311HFE#PBF?
For technical support, including LT8311HFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8311HFE#PBF requirements.
6.How does Aetrix verify that LT8311HFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT8311HFE#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 LT8311HFE#PBF meets industry standards.
7.What is the process for return or replacement of LT8311HFE#PBF?
All LT8311HFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8311HFE#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 LT8311HFE#PBF part is unused and in its original packaging.
Return procedure for LT8311HFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LT8311HFE#PBF Tags
-
UC3845AD8TR
Texas Instruments
-
UC2843AD8TR
Texas Instruments
-
LM3880MFX-1AE/NOPB
Texas Instruments
-
LM3880MFX-1AA/NOPB
Texas Instruments
-
INA234AIYBJR
Texas Instruments
-
INA700AYWFR
Texas Instruments
-
LM3880MF-1AE/NOPB
Texas Instruments
-
LM3880MF-1AA/NOPB
Texas Instruments
-
LM3881MM/NOPB
Texas Instruments
-
UCC2802DTR
Texas Instruments
-
NCP4305DMTTWG
onsemi
-
INA237AIDGSR
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
