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Analog Devices Inc. LT1108CS8#TRPBF
- Part No.:
- LT1108CS8#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1108CS8#TRPBF.pdf
- Description:
- IC REG BUCK BOOST ADJ 1.5A 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:3,746
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Product details
Overview
LT1108CS8#TRPBF from Analog Devices (formerly Linear Technology) is a micropower DC/DC converter IC supporting step-up, step-down, and inverting topologies with fixed 5V or 12V output variants or adjustable output via external resistors. It operates from 2V to 30V input, delivers up to 300mA at 5V in buck mode, features 110µA quiescent current, and integrates a 1A internal NPN power switch. It is used in battery-powered palmtop computers and portable instrumentation requiring low-noise, high-efficiency voltage conversion.
For engineers reviewing the LT1108CS8#TRPBF datasheet, LT1108CS8#TRPBF pinout, LT1108CS8#TRPBF application, or LT1108CS8#TRPBF equivalent, key selection criteria include its 70% duty cycle, programmable current limit via ILIM pin, on-chip low-battery comparator, auxiliary gain block for post-regulation or undervoltage lockout, and compatibility with standard 8-lead SOIC layouts.
Technical Context
The LT1108CS8#TRPBF implements a gated-oscillator architecture with a 19kHz nominal switching frequency, 36µs ON-time, and internal 1.245V reference. Its comparator-based control loop enables discontinuous or continuous conduction mode depending on input/output conditions, with hysteresis ensuring stability without external compensation.
It supports three primary configurations: boost (SW2 grounded, SW1 drives inductor), buck (SW1 tied to VIN, SW2 drives inductor), and inverting (SW2 drives load to ground). The ILIM pin allows resistor-programmable switch current limiting, while the SET/A0 pins enable implementation of low-battery detection or linear post-regulation using the integrated PNP-input op amp.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2V–12V (boost), 2V–30V (buck); enables single-cell AA (2.0–3.2V) to 5V conversion and 9V/12V to 5V regulation. |
| Quiescent Current | 110µA (switch OFF); ensures minimal battery drain in standby, critical for long-life portable systems. |
| Switch Current Limit | Programmable up to 1.5A via ILIM-to-VIN resistor; prevents inductor saturation and switch overcurrent during wide VIN ranges. |
| Oscillator Frequency | 14–25kHz (typ. 19kHz); low-frequency operation reduces EMI and enables use of low-cost, high-saturation-current inductors. |
| Output Voltage Accuracy | ±5% (LT1108-5: 4.75–5.25V; LT1108-12: 11.4–12.6V); meets logic supply tolerance requirements without trimming. |
| Internal Power Switch | NPN transistor rated 1A continuous, 1.5A peak; eliminates need for external switch in ≤300mA buck or ≤150mA boost designs. |
| Operating Temperature | 0°C to 70°C; validated for commercial-grade embedded applications including peripherals and add-on cards. |
Pinout & Package
LT1108CS8#TRPBF is housed in an 8-lead plastic SOIC (S8) package, 3.9mm × 4.9mm body, 1.27mm pitch, RoHS-compliant, tape-and-reel packaged.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ILIM (Pin 1) | Current limit programming input | Resistor from ILIM to VIN sets switch current threshold; open or tied to VIN disables limit. |
| VIN (Pin 2) | Main power input | Supplies bias and switch drive; accepts 2V–30V across operating modes. |
| SW1 (Pin 3) | Power switch collector | In boost: connects to inductor/diode; in buck: ties to VIN; max 50V rating. |
| SW2 (Pin 4) | Power switch emitter | In boost: grounded; in buck: drives inductor; must not fall below –0.5V. |
| GND (Pin 5) | Analog and power ground | Common reference for feedback, gain block, and oscillator; requires low-impedance layout. |
| A0 (Pin 6) | Auxiliary gain block output | Open-collector NPN output sinking up to 100µA; used for low-battery flag or error signal. |
| SET (Pin 7) | Gain block non-inverting input | Connects to resistor divider for comparator trip point; bias current <50nA. |
| FB/SENSE (Pin 8) | Feedback input / voltage sense | In adjustable version: connects to resistor divider; in LT1108-5/-12: internal resistor sets 5V/12V. |
Key Features
| Feature | Design Value |
|---|---|
| Triple topology support | Single IC replaces separate boost/buck/inverting controllers; reduces BOM count and board area. |
| Programmable current limit | Enables robust operation across wide input ranges (e.g., 2V–24V) without inductor saturation or thermal runaway. |
| Integrated low-battery comparator | 1.245V ±5mV reference with 5–10mV hysteresis allows precise, stable battery monitoring without external components. |
| Auxiliary gain block | Configurable as error amplifier for linear post-regulation or undervoltage lockout circuit with <1µs propagation delay. |
| Ultra-low quiescent current | 110µA shutdown current extends battery life in intermittent-use devices like handheld test equipment. |
Applications
| Palmtop Computer Logic Supply | LCD Bias Generator |
|---|---|
Use Scenario: Generating stable 5V logic rail from two AA cells (2.0–3.2V) in space-constrained handheld computing devices. IC Role / Device Role / Timing Role: Primary DC/DC controller implementing boost topology with internal switch and gated oscillator timing. Use Value: Delivers 150mA at 5V with 110µA quiescent current, enabling >100-hour battery life and eliminating need for external MOSFET or diode. | Use Scenario: Producing negative bias voltage (e.g., –5V) for LCD segment drivers from a single 5V system rail. IC Role / Device Role / Timing Role: Inverting converter controller using common-collector switch configuration and internal oscillator. Use Value: Achieves 100mA output with <30mV ripple using only one inductor, one Schottky diode, and two capacitors-reducing component count by 40% vs discrete solutions. |
| 9V-to-5V Peripheral Converter | Battery Backup Supply |
Use Scenario: Regulating 5V for USB peripherals or add-on cards powered from a 9V wall adapter or alkaline battery pack. IC Role / Device Role / Timing Role: Step-down (buck) controller with SW1 tied to VIN and SW2 driving inductor; uses internal 1.245V reference for feedback. Use Value: Delivers 300mA at 5V from 9V input with >82% efficiency and no external pass transistor required. | Use Scenario: Maintaining real-time clock (RTC) or SRAM backup during main power failure in industrial controllers. IC Role / Device Role / Timing Role: Low-quiescent-current buck converter operating from lithium coin cell (3V) to 1.8–3.3V backup rail. Use Value: Draws only 135µA in boost mode at no load, extending CR2032 battery life beyond 5 years in always-on backup mode. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DC/DC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC1173CS8#PBF | Same pinout, but 55% max duty cycle; lower output current capability; no ILIM pin or gain block. | Lacks programmable current limit and auxiliary comparator; unsuitable for wide-input-range or low-battery-detection designs. | Select only if legacy design reuse is required and current limit/gain functions are unused. |
| MAX630CPA+ | 5V fixed output only; 100µA IQ; no adjustable mode or inverting capability; different pinout (8-pin DIP). | Cannot replace LT1108CS8#TRPBF in adjustable or inverting topologies; limited to simple 5V boost applications. | Choose only for cost-sensitive, fixed-output-only 5V boost where SOIC footprint is not required. |
Compared with LTC1173CS8#PBF and MAX630CPA+, the LT1108CS8#TRPBF provides broader topology flexibility, higher duty cycle for increased output current, and integrated system-level functions (ILIM, A0/SET) that reduce external component count and improve reliability in battery-critical applications.
Availability
LT1108CS8#TRPBF is available at Aetrix Electronics and suitable for palmtop computers, LCD bias generation, 9V-to-5V peripheral conversion, and battery backup supplies requiring stable component supply across extended production lifecycles.
Supply support for LT1108CS8#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 full technical and manufacturing continuity for legacy Linear products including the LT1108 family.
The LT1108CS8#TRPBF belongs to Linear's micropower DC/DC converter product line, designed specifically for ultra-low-power, multi-topology voltage conversion in portable and battery-operated instrumentation.
FAQ
What topology configurations does the LT1108CS8#TRPBF support?
The LT1108CS8#TRPBF supports step-up (boost), step-down (buck), and inverting configurations using external passive components. Its dual-switch pins (SW1 and SW2) allow reconfiguration between topologies without changing the IC. In boost mode, SW2 is grounded and SW1 drives the inductor; in buck mode, SW1 connects to VIN and SW2 drives the inductor. The LT1108CS8#TRPBF datasheet provides schematic examples for all three modes, including component value guidance.
How is output voltage set on the LT1108CS8#TRPBF?
The LT1108CS8#TRPBF offers both fixed and adjustable output versions. The base part number LT1108 is adjustable: output voltage is set by a resistor divider from VOUT to GND, connected to the FB/SENSE pin (Pin 8), using VOUT = 1.245V × (1 + R1/R2). Fixed-output variants LT1108CS8-5 and LT1108CS8-12 integrate internal resistors for 5V or 12V outputs; Pin 8 connects directly to the output. The LT1108CS8#TRPBF itself is the adjustable version and requires external resistors.
What is the purpose of the ILIM pin on the LT1108CS8#TRPBF?
The ILIM pin (Pin 1) on the LT1108CS8#TRPBF enables resistor-programmable current limiting for the internal power switch. Connecting a resistor between ILIM and VIN sets the peak switch current threshold-e.g., a 220Ω resistor limits current to ~400mA. This prevents inductor saturation and switch overstress when input voltage varies widely. If unused, ILIM must be tied directly to VIN. The LT1108CS8#TRPBF's current-limit circuitry adds <2µs delay and improves reliability in dynamic input environments.
Can the LT1108CS8#TRPBF be used for low-battery detection?
Yes, the LT1108CS8#TRPBF includes an on-chip comparator referenced to its 1.245V internal bandgap. By connecting a resistor divider from VIN to GND with the midpoint at the SET pin (Pin 7), the A0 output (Pin 6) sinks current when VIN drops below the programmed threshold. A typical design uses 33kΩ from SET to GND and a variable resistor from VIN to SET to set trip points from ~2.5V to 12V. The LT1108CS8#TRPBF's built-in hysteresis (5–10mV) prevents chatter, and A0's 100µA sink capability interfaces directly with microcontroller interrupt inputs.
What are the thermal limitations of the LT1108CS8#TRPBF in continuous operation?
The LT1108CS8#TRPBF has a maximum junction temperature of 90°C and a thermal resistance θJA of 130°C/W in the SOIC-8 package. At 500mW maximum power dissipation, ambient temperature must remain below 25°C for safe continuous operation without heatsinking. Derating is required above 25°C: for example, at 50°C ambient, maximum allowable power drops to ~385mW. Layout best practices include using ≥2 cm² of 2-oz copper connected to Pin 5 (GND) as a thermal pad and minimizing trace length on SW1/SW2 to reduce switching losses. The LT1108CS8#TRPBF's 110µA quiescent current helps minimize self-heating in light-load conditions.
LT1108CS8#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Function:
- Step-Up, Step-Down
- Output Configuration:
- Positive or Negative
- Topology:
- Buck, Boost
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2V
- Voltage - Input (Max):
- 30V
- Voltage - Output (Min/Fixed):
- 1.245V
- Voltage - Output (Max):
- 50V (Switch)
- Current - Output:
- 1.5A (Switch)
- Frequency - Switching:
- 19kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1108CS8#TRPBF FAQ
1.How can I place an order for LT1108CS8#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1108CS8#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 LT1108CS8#TRPBF reliable?
The price and inventory of LT1108CS8#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1108CS8#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1108CS8#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1108CS8#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1108CS8#TRPBF?
LT1108CS8#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1108CS8#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 LT1108CS8#TRPBF?
For technical support, including LT1108CS8#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1108CS8#TRPBF requirements.
6.How does Aetrix verify that LT1108CS8#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1108CS8#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 LT1108CS8#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1108CS8#TRPBF?
All LT1108CS8#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1108CS8#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 LT1108CS8#TRPBF part is unused and in its original packaging.
Return procedure for LT1108CS8#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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