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Analog Devices Inc. LT1959IS8#PBF
- Part No.:
- LT1959IS8#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1959IS8#PBF.pdf
- Description:
- IC REG BUCK SEPIC ADJ 4.5A 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:397
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Product details
Overview
LT1959IS8#PBF from Analog Devices (formerly Linear Technology) is a monolithic 500kHz current-mode buck switching regulator with integrated 4.5A NPN power switch, 1.21V feedback reference, and BOOST pin for switch saturation. It operates from 4V minimum input and delivers adjustable output down to 1.21V, optimized for portable computers and battery-powered systems requiring high efficiency at light-to-full load.
For engineers reviewing the LT1959IS8#PBF datasheet, LT1959IS8#PBF pinout, LT1959IS8#PBF application, or LT1959IS8#PBF equivalent, key selection considerations include its 0.07Ω typical switch on-resistance, cycle-by-cycle current limiting, shutdown current of 15µA, synchronization capability up to 1MHz, and SO-8 package thermal performance with fused GND.
Technical Context
The LT1959IS8#PBF implements constant-frequency current-mode control using an internal 500kHz oscillator and dual-loop architecture: an error amplifier sets the peak switch current threshold via the VC pin, while a current-sense amplifier monitors switch current on a cycle-by-cycle basis. Slope compensation prevents subharmonic oscillation across duty cycles up to 93%.
Its bipolar NPN switch uses BOOST pin voltage (≥VIN + 2.3V) to achieve saturation, reducing conduction loss to that of a 0.07Ω FET. The FB pin provides triple functionality: output voltage regulation at 1.21V, frequency foldback below 0.5V, and current limit foldback below 0.8V-enabling robust short-circuit protection without external circuitry.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Rating | 4.5A at ≤50% duty cycle; decreases nonlinearly to 3.7A at 80% DC-limits max continuous output current based on VIN/VOUT ratio and inductor value |
| Feedback Reference Voltage | 1.21V ±20mV over full temperature range-sets output voltage via external resistor divider with <0.1% error when R2 ≤ 2.5kΩ |
| Switch On Resistance | 0.07Ω typical at 4.5A-enables >89% efficiency at 5V→3.3V/4A with proper BOOST capacitor and layout |
| Shutdown Supply Current | 15µA typical-reduces system standby power in battery applications; full micropower shutdown triggered at SHDN < 0.37V |
| Synchronization Range | 580kHz to 1MHz-allows noise-sensitive systems to avoid EMI bands; logic-compatible SYNC pin requires no level-shifting |
| Minimum Input Voltage | 4.0V guaranteed-supports operation from single-cell Li-ion (fully charged) or two-cell NiMH under load |
| Operating Junction Temp | –40°C to 125°C-qualified for industrial temperature range; θJA = 80°C/W in SO-8 without thermal pad enhancement |
Pinout & Package
The LT1959IS8#PBF is housed in an 8-lead plastic SO (SO-8) package with fused GND pin connected internally to the exposed tab for improved thermal dissipation. Pin 5 (SYNC) is exclusive to the SO-8 variant and absent in the 7-lead DD package.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN | Input supply and collector of internal NPN switch | Carries high dI/dt switching current; requires low-inductance path to input capacitor and catch diode to minimize VCE spikes |
| BOOST | Boost drive voltage for NPN switch saturation | Must be ≥VIN + 2.3V; supplies ~140mA peak during switch-on to maintain 0.07Ω RON under full load |
| GND | Power and signal reference ground | Fused GND pin tied to internal tab; must connect to large copper area for thermal management and low-noise feedback reference |
| VSW | Emitter of internal NPN switch | Swings from 0V to VIN; drives inductor; clamped to –0.8V max by external catch diode during off-time |
| SYNC | External oscillator synchronization input | Logic-compatible (10–90% duty); enables EMI reduction by aligning switching edges to system clock; grounded when unused |
| SHDN | Shutdown and undervoltage lockout control | Two thresholds: 2.38V disables switching (UVLO), 0.37V forces micropower mode; bias current <100nA |
| VC | Error amplifier output / current limit comparator input | Used for loop compensation; also serves as current clamp point; swings 1V–2V under normal load; can override regulation |
| FB | Feedback input for output voltage regulation | Senses 1.21V reference; also enables frequency foldback (<0.5V) and current limit foldback (<0.8V) during overload |
Key Features
| Feature | Design Value |
|---|---|
| Current-mode control with slope compensation | Enables stable operation across 0–93% duty cycle without subharmonic oscillation; supports wide VIN/VOUT ratios including 5V→1.8V |
| Integrated BOOST driver circuitry | Eliminates need for external charge pump; sustains NPN saturation at high current, achieving FET-like 0.07Ω RON with smaller die area |
| Triple-function FB pin | Combines precision 1.21V reference, frequency foldback (2kHz/µA below 0.7V), and current limit foldback-reducing external protection components |
| Cycle-by-cycle current limiting | Detects overcurrent every switching cycle; limits peak switch current to 4.5A typical-prevents thermal runaway during transient faults |
| Thermal shutdown and full-cycle short-circuit protection | Shuts down at TJ ≥ 150°C; latches off until cool-down; prevents damage during sustained overload or output short |
Applications
| Portable Computers | Battery-Powered Systems |
|---|---|
Use Scenario: Point-of-load conversion from main 5V rail to 3.3V or 2.5V for CPU I/O, memory, or peripheral logic. IC Role / Device Role / Timing Role: Primary buck regulator delivering up to 4A with fast transient response to handle burst-mode processor loads. Use Value: 500kHz fixed frequency enables compact 1.8µH inductor; 15µA shutdown current extends battery life during sleep states. | Use Scenario: Power management in handheld test equipment or portable medical devices operating from 2-cell NiMH or Li-ion batteries. IC Role / Device Role / Timing Role: Main DC/DC converter stepping down variable battery voltage (4.0–12.6V) to stable 3.3V or 1.8V system rail. Use Value: 4V minimum input supports operation down to end-of-discharge; current foldback protects against shorted sensor cables or probe faults. |
| Battery Chargers | Distributed Power |
Use Scenario: Constant-current/constant-voltage stage in multi-cell Li-ion charger, regulating charging voltage with high accuracy. IC Role / Device Role / Timing Role: Precision-adjustable output regulator controlling charge voltage via FB divider; SHDN used for charge enable/disable. Use Value: 1.21V reference tolerance (±20mV) ensures ±0.5% output accuracy; BOOST-assisted saturation maintains efficiency across charge cycle. | Use Scenario: Local regulation in telecom line cards or industrial PLC modules where centralized 5V or 12V backplane powers multiple isolated subsystems. IC Role / Device Role / Timing Role: High-current local DC/DC converter providing clean, regulated 3.3V or 2.5V to FPGA, ADC, or interface ICs. Use Value: SO-8 thermal design supports 4A continuous load in confined spaces; SYNC pin allows synchronization to master clock to reduce conducted EMI. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3850EMSE#PBF | Higher 600kHz switching frequency; external MOSFET drive; no integrated switch; requires external gate drivers and sense resistors | Designed for higher-efficiency, higher-power (>10A) applications with programmable frequency and phase sync | Select LTC3850EMSE#PBF only when needing >6A output or synchronous rectification; not drop-in compatible due to external switch architecture |
| TPS544B20RQF | 4.5A integrated buck with 2.2MHz switching; PMBus interface; digital loop compensation; different pinout and thermal pad requirement | Targeted at server VRMs and digitally controlled power systems requiring telemetry and dynamic voltage scaling | Choose TPS544B20RQF for systems requiring PMBus monitoring or >1MHz operation; incompatible pinout and layout require redesign |
Compared with LT1959IS8#PBF, LTC3850EMSE#PBF offers greater flexibility but demands more external components and board space, while TPS544B20RQF provides digital control and higher frequency at the cost of analog simplicity and SO-8 compatibility.
Availability
LT1959IS8#PBF is available at Aetrix Electronics and suitable for portable computers, battery-powered systems, and distributed power applications requiring stable component supply, industrial temperature qualification, and long-term production continuity.
Supply support for LT1959IS8#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 its legacy power management portfolio with full technical support and long-term manufacturing commitment.
The LT1959 belongs to Linear's monolithic current-mode buck regulator family, designed specifically for high-efficiency, low-voltage point-of-load conversion in space-constrained portable and industrial systems.
FAQ
What is the minimum input voltage required for stable operation of the LT1959IS8#PBF?
The LT1959IS8#PBF guarantees stable operation down to 4.0V input across the full industrial temperature range (–40°C to 125°C). This minimum is defined by internal bias regulation-not direct measurement-and actual functional minimum depends on output voltage and load current. For example, at 3.3V output, stable regulation begins near 4.3V per typical performance curves, while at 1.8V output it holds regulation closer to 4.0V with appropriate inductor sizing.
How does the BOOST pin function in the LT1959IS8#PBF, and what external components are required?
The BOOST pin in the LT1959IS8#PBF supplies elevated drive voltage to saturate the internal NPN power switch, achieving a low 0.07Ω on-resistance. It requires an external boost capacitor (typically 10nF–100nF ceramic) connected between BOOST and SW pins, plus a small-signal diode (e.g., 1N914) from VIN to BOOST. During switch-on, the diode charges the capacitor to VIN + Vf; during switch-off, the capacitor discharges into the base drive, sustaining saturation and minimizing VCE loss.
Can the LT1959IS8#PBF synchronize to an external clock, and what are the valid frequency and logic levels?
Yes, the LT1959IS8#PBF supports external synchronization via its dedicated SYNC pin (Pin 5 in SO-8 package). It accepts logic-level signals from 580kHz to 1MHz with 10–90% duty cycle and is directly compatible with CMOS/TTL outputs-no level shifting needed. When unused, SYNC must be grounded. Synchronization improves EMI performance by eliminating beat frequencies and enabling coordinated switching in multi-regulator systems.
What protection features are built into the LT1959IS8#PBF, and how do they activate?
The LT1959IS8#PBF integrates cycle-by-cycle current limiting, thermal shutdown at 150°C, full-cycle short-circuit protection, and dual-threshold shutdown (UVLO at 2.38V, micropower at 0.37V). Additionally, the FB pin enables automatic frequency foldback below 0.5V and current limit foldback below 0.8V during output shorts-reducing power dissipation in both IC and external components without external circuitry.
Is the LT1959IS8#PBF pin-compatible with the LT1506, and what are the key functional differences?
The LT1959IS8#PBF is functionally identical to the LT1506 but optimized for lower output voltages: it regulates down to 1.21V versus 2.42V for the LT1506, enabling direct 5V→1.8V or 5V→1.2V conversion. Both share the same SO-8 and DD packages and pinout, making them drop-in replacements in existing designs-provided the lower feedback voltage and updated inductor/capacitor values are validated for the target output.
LT1959IS8#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck, SEPIC
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4.3V
- Voltage - Input (Max):
- 15V
- Voltage - Output (Min/Fixed):
- 1.21V
- Voltage - Output (Max):
- 12.9V
- Current - Output:
- 4.5A (Switch)
- Frequency - Switching:
- 500kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1959IS8#PBF FAQ
1.How can I place an order for LT1959IS8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1959IS8#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 LT1959IS8#PBF reliable?
The price and inventory of LT1959IS8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1959IS8#PBF is usually 5 days.
3.What payment methods are accepted for LT1959IS8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1959IS8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1959IS8#PBF?
LT1959IS8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1959IS8#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 LT1959IS8#PBF?
For technical support, including LT1959IS8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1959IS8#PBF requirements.
6.How does Aetrix verify that LT1959IS8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1959IS8#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 LT1959IS8#PBF meets industry standards.
7.What is the process for return or replacement of LT1959IS8#PBF?
All LT1959IS8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1959IS8#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 LT1959IS8#PBF part is unused and in its original packaging.
Return procedure for LT1959IS8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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