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Analog Devices Inc. LT8709EFE#TRPBF
- Part No.:
- LT8709EFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT8709EFE#TRPBF.pdf
- Description:
- IC REG CTRLR MULT TOP 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,767
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Product details
Overview
LT8709EFE#TRPBF 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 and control. It supports buck, boost, buck-boost, and inverting topologies with –4.5V to –80V input, 100kHz–750kHz switching frequency, and operates in forced CCM or DCM via MODE pin - used in telecom power supplies and cathodic protection systems.
For engineers reviewing the LT8709EFE#TRPBF datasheet, LT8709EFE#TRPBF pinout, LT8709EFE#TRPBF application, or LT8709EFE#TRPBF equivalent, key selection considerations include its negative-input voltage range, rail-to-rail current sense capability, EN/FBIN input regulation function, PG pin for power-good indication, and compatibility with high-impedance input sources.
Technical Context
The LT8709EFE#TRPBF implements dual error amplifiers: one for output voltage regulation (FBY-referred) and another for output current regulation (ISP–ISN sensing), enabling precise constant-voltage and constant-current operation. Its EN/FBIN pin integrates input voltage regulation, undervoltage lockout hysteresis (44 mV), and slow-signal acceptance - critical for stabilizing high-impedance negative supplies.
Switching control uses an adjustable oscillator (RT-pin settable from 100 kHz to 750 kHz) with frequency foldback (1/5 ratio under overload) and external synchronization capability (SYNC pin, 1.5 V logic-high threshold). The MODE pin selects between forced continuous conduction mode (CCM) below 1.175 V or pulse-skipping/discontinuous conduction mode (DCM) above 1.224 V, with 49 mV hysteresis.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | –4.5 V to –80 V: Enables direct interface with legacy telecom battery banks (–48 V), industrial negative rails, and cathodic protection systems without level-shifting. |
| Switching Frequency | 100 kHz to 750 kHz: Adjustable via RT resistor; supports compact magnetics while avoiding AM band interference at higher frequencies. |
| Output Current Sense Accuracy | ±5 mV ISP–ISN offset (typ): Ensures tight current limiting across temperature; enables reliable battery or capacitor charging with ±2% current regulation. |
| EN/FBIN Threshold Hysteresis | 44 mV: Prevents chatter during input voltage sag near UVLO boundary, improving system stability in fluctuating negative supply environments. |
| Power Good Threshold | 74.9 µA FBY current (neg. output): Provides accurate, load-independent power-good assertion at ~90% of regulation voltage - immune to output capacitor ESR effects. |
| Gate Driver Non-Overlap | 45–220 ns (BG/TG): Minimizes shoot-through risk in high-side PFET / low-side NFET configurations, supporting robust 100+ V negative rail switching. |
| Operating Junction Temp | –40°C to +125°C: Qualified for industrial and telecom equipment deployed in uncontrolled ambient environments. |
Pinout & Package
The LT8709EFE#TRPBF is housed in a 20-lead TSSOP package with exposed pad (Pin 21) electrically connected to –VIN and requiring PCB soldering for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FBY (1) | Feedback reference input | Voltage-regulated node referenced to GND; sets output voltage polarity (negative or positive) and accuracy (±1.234 V typ for neg. output). |
| VC (2) | Error amplifier output | Compensation node for voltage loop; connects external RC network to –VIN to stabilize regulation bandwidth and phase margin. |
| SS (3) | Soft-start control | Charged by internal 260 kΩ to ~2.7 V; discharge resets converter during overcurrent, overtemperature, or UVLO faults. |
| PG (4) | Power good indicator | Open-drain active-high output asserting when FBY current reaches 90% of regulation value; requires external pull-up. |
| IMON (5) | Current monitor output | Analog voltage proportional to ISP–ISN (VIMON = 11.9 × (VISP–VISN + 51.8 mV)); used for telemetry or current-limiting feedback. |
| ISN / ISP (6, 7) | Current sense inputs | Kelvin-connected to sense resistor; measure average output current with 50 mV full-scale range and rail-to-rail operation. |
| BIAS (8) | Top gate driver rail | Secondary positive supply for TG driver; must be locally bypassed to –VIN; defines PFET gate swing upper limit. |
| INTVEE (9) | TG driver bottom rail | 6.18 V below BIAS; enables PFET gate drive with >3.42 V headroom; tied to –VIN in boost configurations. |
| TG (10) | PFET gate driver | Outputs BIAS–INTVEE (low) and BIAS (high); drives external high-side P-channel MOSFET in buck-boost/inverting topologies. |
| BG (11) | NFET gate driver | Outputs –VIN (low) and INTVCC (high); drives low-side N-channel MOSFET; supports fast turn-on with 24 ns rise time. |
| INTVCC (12) | Internal LDO output | 6.3 V regulated supply for logic and BG driver; sourced from GND or BIAS; supports up to 5 mA external load. |
| GND (13) | Positive input reference | Primary positive supply pin; must be bypassed to –VIN; functional down to V–VIN if BIAS–V–VIN ≥ 4.5 V. |
| CSP / CSN (14, 15) | NFET peak current sense | Monitors switch current during on-time; limits peak inductor current to 50 mV (typ), preventing saturation under transient loads. |
| EN/FBIN (16) | Enable & input regulation | Three-function pin: chip enable (1.7 V threshold), input voltage regulation (1.607 V nominal), and UVLO hysteresis (44 mV). |
| MODE (17) | CCM/DCM selection | Forces CCM (<1.175 V) or enables DCM/pulse-skipping (>1.224 V); hysteresis prevents mode oscillation at light loads. |
| RT (18) | Oscillator timing | Resistor-to–VIN sets free-running frequency; 46.4 kΩ yields 750 kHz, 357 kΩ yields 100 kHz. |
| SYNC (19) | External clock input | Accepts 0.4 V / 1.5 V logic thresholds; overrides internal oscillator; supports multi-phase synchronization. |
| –VIN (20, 21) | Negative input & thermal pad | Main power input and IC ground reference; exposed pad (Pin 21) must be soldered to PCB for thermal dissipation and low-impedance return path. |
Key Features
| Feature | Design Value |
|---|---|
| Rail-to-rail output current monitor | Supports bidirectional current sensing (ISP–ISN) from –51.8 mV to +50 mV, enabling accurate constant-current operation for battery charging and LED drivers. |
| Input voltage regulation via EN/FBIN | Maintains stable input current draw during brownout conditions, preventing collapse of high-impedance negative supplies such as photovoltaic or electrochemical sources. |
| Configurable topology support | Single feedback pin (FBY) and dual current sense paths (ISP/ISN, CSP/CSN) allow seamless reconfiguration among buck, boost, buck-boost, and inverting converters without hardware changes. |
| Thermal and fault protection | Integrated thermal shutdown (175°C), frequency foldback, soft-start reset, and anti-glitch PG delay (100 µs) ensure robust operation in harsh industrial environments. |
| High-precision current limiting | 50 mV ISP–ISN full-scale with <±2% gain error and 5 mV offset enables ±1% output current regulation across temperature and line variations. |
Applications
| Telecom Power Supply | Cathodic Protection System |
|---|---|
Use Scenario: Generating –12 V/8.5 A from –24 V telecom battery bank for base station RF modules. IC Role / Device Role / Timing Role: Synchronous negative-input buck controller regulating output voltage and limiting peak inductor current via CSP/CSN. Use Value: Achieves >94% efficiency at full load while maintaining stable regulation during battery voltage sag from –48 V to –36 V. | Use Scenario: Driving –15 V/10 A output from –80 V rectified AC for pipeline corrosion prevention. IC Role / Device Role / Timing Role: Negative-input inverting controller with rail-to-rail current monitoring for precise current-source operation. Use Value: Delivers ±1% constant current over –40°C to +85°C ambient using IMON feedback and integrated current sense amplifier. |
| Negative Input to Positive Output | Industrial Sensor Bias Supply |
Use Scenario: Converting –48 V telecom rail to +5 V/3 A for isolated data acquisition front-ends. IC Role / Device Role / Timing Role: Synchronous boost controller using BIAS–INTVEE gate drive for high-side PFET and BG for low-side NFET. Use Value: Eliminates need for isolated DC/DC or charge-pump stages; reduces BOM count and improves reliability in safety-critical systems. | Use Scenario: Providing –10 V/100 mA bias for precision op-amps and ADC references in process control I/O modules. IC Role / Device Role / Timing Role: Low-noise negative-output buck controller with EN/FBIN input regulation to avoid sensor supply droop. Use Value: Maintains <10 µV p-p output ripple and <0.01% load regulation, preserving 24-bit measurement accuracy. |
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 |
|---|---|---|---|
| LTC3891EFE#TRPBF | Wider input range (–4 V to –150 V), no integrated PG pin, requires external current sense amplifier for IMON functionality. | Preferred for ultra-high-voltage cathodic protection where >–80 V operation is required; lacks rail-to-rail ISP–ISN sensing. | Select LTC3891EFE#TRPBF only when input exceeds –80 V or when PG functionality is not needed. |
| LT8714EFE#TRPBF | Includes integrated gate drivers for both high-side and low-side N-channel MOSFETs; supports higher switching frequencies (up to 1 MHz); no EN/FBIN input regulation feature. | Better suited for high-density, high-efficiency designs using N-channel synchronous rectification; unsuitable for high-impedance input stabilization. | Choose LT8714EFE#TRPBF when designing N-N synchronous topologies and input regulation is not required. |
Compared with LTC3891EFE#TRPBF and LT8714EFE#TRPBF, the LT8709EFE#TRPBF uniquely combines rail-to-rail current monitoring, EN/FBIN input regulation, and PG indication in a single 20-lead TSSOP package - making it optimal for telecom, cathodic protection, and industrial negative-rail power conversion where precision current control and supply stability are critical.
Availability
LT8709EFE#TRPBF is available at Aetrix Electronics and suitable for telecom equipment power supplies, cathodic protection systems, and industrial sensor bias supplies requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.
Supply support for LT8709EFE#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors.
The LT8709 product line was designed specifically for high-reliability negative-input power conversion in telecom infrastructure, industrial automation, and electrochemical systems - emphasizing input regulation, current accuracy, and fault resilience.
FAQ
What is the minimum input voltage specification for the LT8709EFE#TRPBF?
The LT8709EFE#TRPBF supports a minimum operating input voltage of –4.5 V relative to its –VIN pin. This is specified under conditions where either GND–(–VIN) or BIAS–(–VIN) exceeds 4.5 V. Operation below this threshold triggers undervoltage lockout, halting switching until the input recovers. The device remains functional across the full –4.5 V to –80 V range without external level-shifting circuitry.
How does the EN/FBIN pin provide input voltage regulation in the LT8709EFE#TRPBF?
The EN/FBIN pin in the LT8709EFE#TRPBF implements input voltage regulation by controlling NFET current to prevent collapse of high-impedance negative supplies. When the EN/FBIN voltage drops between 1.55 V and 1.662 V (typical), the internal amplifier actively regulates input current. This function is distinct from simple enable/disable and allows stable operation even with weak sources like photovoltaic arrays or aging batteries feeding the –VIN rail.
Can the LT8709EFE#TRPBF be used in a negative-input to positive-output boost configuration?
Yes, the LT8709EFE#TRPBF can be configured as a negative-input to positive-output boost converter. In this topology, the BIAS pin is connected to INTVCC, INTVEE is tied to –VIN, and the FBY pin is referenced to GND with appropriate resistor divider. The controller regulates output voltage by modulating duty cycle based on FBY feedback while using ISP–ISN for output current limiting - enabling efficient, well-regulated +12 V or +24 V generation from –48 V telecom supplies.
What is the purpose of the IMON pin on the LT8709EFE#TRPBF?
The IMON pin on the LT8709EFE#TRPBF outputs an analog voltage proportional to the average current through the ISP–ISN sense resistor: VIMON = 11.9 × (VISP–VISN + 51.8 mV). This provides real-time current telemetry for system monitoring, closed-loop current regulation, or fault detection. A 10 nF–100 nF capacitor between IMON and –VIN filters switching noise, yielding a stable DC voltage representing output current - essential for battery charging and precision current-source applications.
Does the LT8709EFE#TRPBF support external clock synchronization?
Yes, the LT8709EFE#TRPBF supports external clock synchronization via the SYNC pin (Pin 19). Applying a logic-compatible clock signal (high ≥1.5 V, low ≤0.4 V) overrides the internal oscillator and locks switching frequency to the external source. This enables multi-phase interleaving, EMI reduction through frequency dithering, or synchronization with system clocks - all without modifying the RT resistor or affecting regulation performance.
LT8709EFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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
LT8709EFE#TRPBF FAQ
1.How can I place an order for LT8709EFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8709EFE#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 LT8709EFE#TRPBF reliable?
The price and inventory of LT8709EFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8709EFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT8709EFE#TRPBF?
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4.How is shipping managed for LT8709EFE#TRPBF?
LT8709EFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8709EFE#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 LT8709EFE#TRPBF?
For technical support, including LT8709EFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8709EFE#TRPBF requirements.
6.How does Aetrix verify that LT8709EFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT8709EFE#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 LT8709EFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT8709EFE#TRPBF?
All LT8709EFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8709EFE#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 LT8709EFE#TRPBF part is unused and in its original packaging.
Return procedure for LT8709EFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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