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Analog Devices Inc. LT8709IFE#PBF
- Part No.:
- LT8709IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT8709IFE#PBF.pdf
- Description:
- IC REG CTRLR MULT TOP 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:169
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Product details
Overview
LT8709IFE#PBF from Analog Devices (formerly Linear Technology) is a synchronous PWM controller for negative-to-negative or negative-to-positive DC/DC conversion, featuring rail-to-rail output current monitoring, 100kHz–750kHz adjustable switching frequency, –4.5V to –80V input range, and 20-lead TSSOP package. It supports buck, boost, buck-boost, and inverting topologies in telecom power supplies and cathodic protection systems.
For engineers reviewing the LT8709IFE#PBF datasheet, LT8709IFE#PBF pinout, LT8709IFE#PBF application, or LT8709IFE#PBF equivalent, key selection considerations include its EN/FBIN input regulation capability, MODE-selectable CCM/DCM operation, rail-to-rail ISP/ISN current sense accuracy (±7 mV typical), PG pin with 100 µs anti-glitch delay, and thermal shutdown at 175°C junction temperature.
Technical Context
The LT8709IFE#PBF integrates dual LDOs (INTVCC at 6.3 V, INTVEE at 6.18 V below BIAS), a programmable oscillator with RT-resistor or SYNC clock input, and three independent error amplifiers: FBY-based voltage regulation, ISP/ISN-based output current control, and EN/FBIN-based input voltage regulation. Its state machine enables automatic transition between forced CCM, DCM, and pulse-skipping modes based on MODE pin voltage and load conditions.
It employs high-gain EN/FBIN circuitry accepting slowly varying signals for input voltage regulation, rail-to-rail current sensing with 50 mV full-scale ISP–ISN differential, and integrated soft-start with SS pin charge/discharge control. The block diagram confirms separate paths for voltage loop (FBY → EA1 → VC), current loop (ISP/ISN → A7 → IMON → EA2 → VC), and input regulation loop (EN/FBIN → EA3 → VC).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | –4.5 V to –80 V: Enables direct interface with legacy negative telecom rails (e.g., –48 V) and industrial cathodic protection sources without pre-regulation. |
| Switching Frequency | 100 kHz to 750 kHz: Adjustable via RT resistor or external SYNC clock; supports EMI optimization and magnetics size reduction. |
| Output Current Sense Accuracy | ±7 mV offset (typical) on ISP–ISN: Ensures precise 50 mV current limit threshold across temperature for reliable overcurrent protection. |
| Power Good Threshold | ±7.4 µA hysteresis on FBY current: Provides stable 90% output regulation margin detection with 100 µs anti-glitch filtering. |
| Operating Temperature | –40°C to +125°C junction: Validated for industrial and telecom environments requiring extended thermal reliability. |
| Quiescent Current | 4 mA (typical) not switching: Minimizes standby power loss in always-on negative supply systems. |
| Gate Driver Rise/Fall Times | TG: 15 ns / 16 ns; BG: 24 ns / 21 ns (CBG = CTG = 3300 pF): Supports fast-switching GaN or Si MOSFETs with minimal dead-time uncertainty. |
Pinout & Package
The LT8709IFE#PBF is housed in a 20-lead plastic TSSOP package with exposed pad (Pin 21) electrically connected to –VIN and required to be soldered to the PCB for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FBY (1) | Voltage feedback reference | Referred to GND; sets output regulation point via external resistor divider; supports both negative (–1.234 V) and positive (+15.8 mV) output configurations. |
| VC (2) | Error amplifier output | Drives compensation network to control duty cycle; sums voltage, current, and input regulation loops into single control node. |
| SS (3) | Soft-start control | Charged by internal 260 kΩ to ~2.7 V; discharged during fault (UVLO, overtemp, overcurrent) to force controlled restart. |
| PG (4) | Power good indicator | Active-high open-drain output; asserts when FBY current reaches ±74.9 µA (negative) or ±75.4 µA (positive), indicating ≥90% regulation. |
| IMON (5) | Current monitor output | Provides 11.9× amplified and offset (616 mV zero-current) voltage proportional to ISP–ISN; requires 10–100 nF filter capacitor. |
| ISN/ISP (6/7) | Output current sense inputs | Kelvin-connected to sense resistor; 50 mV full-scale differential enables accurate current limiting independent of layout parasitics. |
| BIAS (8) | TG gate driver high rail | Second positive supply input; sets TG top rail; must be bypassed to –VIN; connects to VOUT (inverting), INTVCC (boost), or GND (buck). |
| INTVEE (9) | TG gate driver low rail | 6.18 V below BIAS; enables TG swing; UVLO threshold at 3.42 V (rising); must be bypassed to BIAS with ≥2.2 µF. |
| TG (10) | PFET gate driver | Outputs BIAS (high) and BIAS–INTVEE (low); drives high-side PFET in buck-boost/inverting topologies. |
| BG (11) | NFET gate driver | Outputs INTVCC (high) and –VIN (low); drives low-side NFET; starts switching only after INTVCC > 4 V (typical). |
| INTVCC (12) | Dual-input LDO regulator | 6.3 V LDO powered from GND or BIAS; supplies logic and BG driver; max 5 mA external load; UVLO at 3.88 V (rising). |
| GND (13) | Positive input supply reference | Local positive rail; must be bypassed to –VIN; functional down to V–VIN if BIAS–V–VIN ≥ 4.5 V. |
| CSP/CSN (14/15) | NFET switch current sense | Kelvin-connected to NFET source/sense resistor; 50 mV full-scale differential controls peak switch current limit. |
| EN/FBIN (16) | Enable & input regulation | Three-mode pin: <0.3 V = shutdown (1 µA IQ); 1.55–1.662 V = input voltage regulation; >1.7 V = enable with soft-start restart. |
| MODE (17) | CCM/DCM selection | <1.175 V = forced continuous conduction mode; >1.224 V = pulse-skipping/DCM at light loads; hysteresis 49 mV. |
| RT (18) | Oscillator timing | Resistor to –VIN sets free-running frequency (e.g., 46.4 kΩ = 750 kHz, 357 kΩ = 100 kHz); no pull-up/pull-down required. |
| SYNC (19) | External clock input | Overrides internal oscillator when driven with 0.4 V (low) / 1.5 V (high); duty cycle 20–80%; fSYNC/fOSC ≥ 3/4 recommended. |
| –VIN (20, 21) | Negative input & thermal pad | Main power input and IC ground reference; exposed pad (Pin 21) must be soldered to PCB –VIN plane for thermal management. |
Key Features
| Feature | Design Value |
|---|---|
| Rail-to-rail ISP/ISN current sensing | Enables accurate 50 mV current limit setting across full input range (–4.5 V to –80 V) without gain drift or offset shift. |
| EN/FBIN input voltage regulation | Prevents collapse of high-impedance negative input sources by dynamically adjusting NFET duty cycle when EN/FBIN drops below 1.607 V. |
| MODE-selectable CCM/DCM operation | Forced CCM eliminates low-load ripple and EMI discontinuities; DCM improves light-load efficiency via pulse skipping. |
| Integrated dual LDOs (INTVCC/INTVEE) | Eliminates need for external bias rails; INTVCC powers logic/BG, INTVEE sets TG swing-both with UVLO and dropout protection. |
| Multi-topology flexibility | Single feedback pin (FBY) configures buck, boost, buck-boost, or inverting converters using topology-specific resistor equations. |
| Thermal shutdown & fault recovery | 175°C junction shutdown with automatic soft-start restart upon cooling; SS pin discharge ensures controlled re-entry into regulation. |
Applications
| Telecom Power Supplies | Cathodic Protection Systems |
|---|---|
Use Scenario: Generating –12 V/8.5 A from –24 V telecom battery backup with high efficiency and tight regulation. IC Role / Device Role / Timing Role: Synchronous PWM controller implementing inverting topology with rail-to-rail current monitoring for precise output current limiting. Use Value: Achieves >90% efficiency at full load while maintaining ±1% output voltage regulation and ±5% current limit accuracy over temperature. | Use Scenario: Providing regulated negative output to protect pipelines or marine structures from electrochemical corrosion. IC Role / Device Role / Timing Role: Negative-input, negative-output buck controller delivering stable –15 V/10 A with input voltage regulation to prevent source collapse under variable soil resistance. Use Value: EN/FBIN input regulation maintains constant output despite input sag from high-impedance earth return paths. |
| Negative Input, Positive Output Supplies | Industrial Local Power Rails |
Use Scenario: Converting –48 V telecom input to +12 V for auxiliary logic or sensor interfaces in base station equipment. IC Role / Device Role / Timing Role: Synchronous boost controller using BIAS tied to INTVCC and INTVEE tied to –VIN to generate positive output from negative input. Use Value: Eliminates need for isolated DC/DC or transformer-based solutions; achieves 92% peak efficiency with 100 kHz–750 kHz frequency tuning. | Use Scenario: Local –5 V or –3.3 V generation from –12 V backplane in test instrumentation or data acquisition modules. IC Role / Device Role / Timing Role: Compact buck controller in 20-lead TSSOP enabling high-density PCB layouts with minimal external components. Use Value: Integrated PG pin provides system-level power sequencing confirmation; thermal shutdown protects against enclosure overheating. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar negative-input DC/DC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3891EMSE#PBF | Wider input range (–4 V to –150 V), dual output, no integrated ISP/ISN amplifier; requires external current sense amp. | Supports dual-output designs and higher input voltages but lacks rail-to-rail ISP/ISN monitoring and IMON output. | Select LTC3891EMSE#PBF when designing multi-rail negative supplies or operating above –80 V input; use LT8709IFE#PBF for single-output, precision current monitoring, and compact footprint. |
| LT8714IFE#PBF | Higher switching frequency (100 kHz–2 MHz), integrated MOSFET drivers optimized for GaN, no EN/FBIN input regulation function. | Targets high-frequency, high-efficiency GaN-based designs where input regulation is handled externally or not required. | Select LT8714IFE#PBF for GaN-based negative-input converters needing >750 kHz operation; retain LT8709IFE#PBF for legacy Si MOSFET designs requiring EN/FBIN regulation and proven thermal robustness. |
Compared with LTC3891EMSE#PBF and LT8714IFE#PBF, the LT8709IFE#PBF uniquely combines rail-to-rail ISP/ISN sensing, EN/FBIN input regulation, and MODE-selectable CCM/DCM in a single 20-lead TSSOP-making it optimal for cost-sensitive, thermally constrained negative-input applications demanding precision current limiting and input stability.
Availability
LT8709IFE#PBF is available at Aetrix Electronics and suitable for telecom power supplies, cathodic protection systems, and industrial local power rails requiring stable component supply, long-term lifecycle support, and guaranteed –40°C to +125°C operation.
Supply support for LT8709IFE#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 and maintains full product support, documentation, and manufacturing continuity for all Linear-branded parts including the LT8709 series.
The LT8709 product line was designed specifically for high-reliability negative-input DC/DC conversion in telecom infrastructure, industrial automation, and corrosion protection-emphasizing input regulation, multi-topology flexibility, and rugged thermal performance.
FAQ
What is the minimum input voltage specification for the LT8709IFE#PBF?
The LT8709IFE#PBF has a minimum operating input voltage of –4.5 V relative to GND, verified across the full –40°C to +125°C junction temperature range. This allows reliable startup and regulation from standard negative logic rails and partially discharged telecom batteries. Operation below –4.5 V risks undervoltage lockout activation on INTVCC or BIAS supplies.
How does the EN/FBIN pin function in input voltage regulation mode on the LT8709IFE#PBF?
When the EN/FBIN voltage falls between 1.55 V and 1.662 V (typical), the LT8709IFE#PBF enters input voltage regulation mode: the EN/FBIN amplifier actively adjusts NFET duty cycle to maintain constant EN/FBIN voltage, preventing collapse of high-impedance negative input sources. This behavior is confirmed in the Electrical Characteristics table and State Diagram.
Can the LT8709IFE#PBF be used in a positive-output configuration from a negative input?
Yes-the LT8709IFE#PBF supports positive-output configurations (e.g., –48 V to +12 V) using boost topology. Per the datasheet, BIAS is connected to INTVCC and INTVEE to –VIN; FBY is biased positively via resistor divider; and the MODE pin selects CCM or DCM. Typical application circuits confirm this capability with >90% efficiency.
What is the purpose of the IMON pin on the LT8709IFE#PBF and how is it used?
The IMON pin on the LT8709IFE#PBF outputs a voltage proportional to the ISP–ISN differential (VIMON = 11.9 × (VISP – VISN) + 616 mV), providing real-time analog current monitoring. A 10–100 nF capacitor between IMON and –VIN filters switching noise; the resulting DC voltage can feed an ADC or comparator for overcurrent protection or telemetry-verified in the PIN FUNCTIONS section.
Does the LT8709IFE#PBF support external clock synchronization, and what are the electrical requirements?
Yes-the LT8709IFE#PBF supports external clock synchronization via the SYNC pin. The SYNC signal must have logic-high ≥1.5 V and logic-low ≤0.4 V relative to –VIN, with duty cycle between 20% and 80%. The recommended fSYNC/fOSC ratio is ≥3/4 to ensure reliable locking, per Absolute Maximum Ratings and Electrical Characteristics tables.
LT8709IFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up, Step-Down, Step-Up/Step-Down
- Output Configuration:
- Positive or Negative
- Topology:
- Buck, Boost, Buck-Boost
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- -4.5V ~ -80V
- Frequency - Switching:
- 100kHz ~ 750kHz
- Duty Cycle (Max):
- -
- Synchronous Rectifier:
- Yes
- Clock Sync:
- Yes
- Serial Interfaces:
- -
- Control Features:
- Enable, Frequency Control, Power Good, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT8709IFE#PBF FAQ
1.How can I place an order for LT8709IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8709IFE#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 LT8709IFE#PBF reliable?
The price and inventory of LT8709IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8709IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT8709IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8709IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8709IFE#PBF?
LT8709IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8709IFE#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 LT8709IFE#PBF?
For technical support, including LT8709IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8709IFE#PBF requirements.
6.How does Aetrix verify that LT8709IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT8709IFE#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 LT8709IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT8709IFE#PBF?
All LT8709IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8709IFE#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 LT8709IFE#PBF part is unused and in its original packaging.
Return procedure for LT8709IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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