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Analog Devices Inc. LT1108CS8-5#TRPBF
- Part No.:
- LT1108CS8-5#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1108CS8-5#TRPBF.pdf
- Description:
- IC REG BUCK BOOST 5V 1.5A 8SO
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
LT1108CS8-5#TRPBF from Analog Devices (formerly Linear Technology) is a micropower step-up/step-down DC/DC converter in fixed 5V output configuration, housed in an 8-lead SOIC package. It operates from 2V to 30V input, delivers up to 300mA at 5V in step-down mode, consumes only 135µA quiescent current in boost mode, and integrates a 1A internal NPN power switch with programmable current limit. It is used in battery-powered palmtop computers and 9V-to-5V peripheral supplies.
For engineers reviewing the LT1108CS8-5#TRPBF datasheet, LT1108CS8-5#TRPBF pinout, LT1108CS8-5#TRPBF application, or LT1108CS8-5#TRPBF equivalent, key selection criteria include its 70% duty cycle, on-chip low-battery comparator, adjustable current limit via ILIM pin, and compatibility with standard 100µH–300µH inductors for compact 5V bias generation.
Technical Context
The LT1108CS8-5#TRPBF implements a gated-oscillator architecture with internal 1.245V reference and comparator-based feedback control. Its oscillator runs at 14–25kHz with 36µs typical ON-time, enabling discontinuous and continuous conduction modes depending on input/output conditions.
It supports three topologies: step-up (boost), step-down (buck), and inverting - with SW1 as collector and SW2 as emitter of the integrated NPN switch. The fixed 5V version uses internal resistor divider on FB/SENSE (Pin 8), eliminating external feedback components.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 5V ±5% (4.75V–5.25V), internally trimmed; no external resistors required. |
| Input Voltage Range | 2V–12.6V in step-up mode; up to 30V in step-down mode - enables wide-input industrial and battery-supply designs. |
| Quiescent Current | 135µA typical in boost mode (no load); enables >1-year runtime on two AA cells in low-duty-cycle systems. |
| Switch Current Limit | Programmable from ~400mA (220Ω ILIM-to-VIN) to 1.5A max; prevents inductor saturation and switch overstress. |
| Oscillator Frequency | 14–25kHz typical; low frequency reduces EMI and allows use of low-cost, high-saturation-current ferrite inductors. |
| Internal Power Switch | NPN transistor rated for 1.5A peak, 1A continuous; eliminates need for external switch in ≤300mA 5V applications. |
| Operating Temperature | 0°C to +70°C ambient; suitable for commercial-grade embedded instrumentation and portable electronics. |
Pinout & Package
LT1108CS8-5#TRPBF is supplied in an 8-lead plastic SOIC (S8) package, 3.9mm × 4.9mm body, 1.27mm pitch, RoHS-compliant and tape-and-reel packaged (#TRPBF).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ILIM (Pin 1) | Current limit programming input | Connect to VIN via resistor to set switch current threshold; open or tied to VIN for full 1.5A capability. |
| VIN (Pin 2) | Main power input | Accepts 2V–30V; powers internal circuitry and switch driver; must be bypassed with ≥10µF ceramic capacitor. |
| SW1 (Pin 3) | Collector of internal NPN switch | In boost: connects to inductor/diode node; in buck: connects directly to VIN; withstands up to 50V. |
| SW2 (Pin 4) | Emitter of internal NPN switch | In boost: grounded; in buck: drives inductor; voltage must not fall below –0.5V (Schottky clamping required). |
| GND (Pin 5) | Analog and power ground reference | Common return for feedback, gain block, and switch; requires low-impedance connection to PCB ground plane. |
| A0 (Pin 6) | Open-collector auxiliary gain block output | Sinks 100µA max; used for low-battery detection, post-regulation, or UVLO - requires external pull-up. |
| SET (Pin 7) | Gain block non-inverting input | Accepts voltage divider from VIN to configure comparator trip point; bias current <100nA minimizes error. |
| FB/SENSE (Pin 8) | Feedback input / fixed-output sense node | Internally connected to 5V divider; must be tied directly to regulated 5V output in LT1108CS8-5#TRPBF. |
Key Features
| Feature | Design Value |
|---|---|
| Pin-compatible upgrade to LT1173 | 70% duty cycle increases output current capability in same footprint; no layout change needed for migration. |
| Integrated low-battery detector | On-chip comparator with 1.245V reference and 5–10mV hysteresis enables reliable system shutdown at defined VIN. |
| Three-mode topology support | Single IC configures as boost, buck, or inverting converter - reduces BOM count and design validation effort. |
| Programmable switch current limit | Resistor-based ILIM interface allows precise current limiting across input voltage range - prevents thermal runaway. |
| Space-saving SOIC-8 package | Standard 8-pin SOIC footprint enables high-density PCB layouts; compatible with automated SMT assembly. |
Applications
| Palmtop Computer Logic Supply | 9V Battery to 5V Peripheral Converter |
|---|---|
|
Use Scenario: Powering 5V logic rails in handheld computing devices powered by dual AA or 9V alkaline batteries. IC Role / Device Role / Timing Role: Primary DC/DC regulator delivering regulated 5V from 2V–3V (AA) or 6.5V–9V (PP3) inputs. Use Value: 135µA quiescent current extends battery life; 300mA output supports LCD controllers and microcontrollers without external pass devices. |
Use Scenario: Converting 9V battery input to stable 5V for add-on cards, sensors, or USB peripherals in portable test equipment. IC Role / Device Role / Timing Role: Step-down controller with internal switch, configured for high-efficiency 9V→5V conversion at up to 300mA. Use Value: Eliminates need for external MOSFET and gate driver; 1.5A switch rating allows margin for cold-start and transient loads. |
| LCD Bias Generator | Battery Backup Supply |
|
Use Scenario: Generating clean 5V bias for monochrome or segment LCD modules in medical handhelds and industrial HMIs. IC Role / Device Role / Timing Role: Fixed-output boost converter operating from 3V coin cell or 2xAA supply, driving capacitive LCD loads. Use Value: Low ripple (<40mV hysteresis-induced sawtooth) ensures stable contrast; 220Ω ILIM resistor limits inrush into large hold-up caps. |
Use Scenario: Providing fail-safe 5V standby power during main supply interruption in security panels and data loggers. IC Role / Device Role / Timing Role: Always-on buck converter accepting wide 6.5V–20V input range, powering real-time clock and SRAM. Use Value: 30V absolute max input rating tolerates automotive load-dump transients; GND-referenced FB simplifies backup path isolation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar micropower DC/DC converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT1108CN8-5 | DIP-8 package (N8), higher θJA = 130°C/W vs. SOIC's 150°C/W; identical electrical specs and pinout. | Suitable for prototyping, through-hole assembly, or legacy board upgrades where SOIC rework is impractical. | Select when manual soldering, breadboarding, or thermal mass requirements favor DIP over SOIC. |
| LT1307CS8-5 | Higher 1.3MHz switching frequency, lower IQ (85µA), but reduced max switch current (600mA vs. 1.5A) and no ILIM pin. | Better for ultra-compact designs needing small inductors/caps, but unsuitable for high-current or wide-VIN step-down. | Choose for space-constrained 3V–5V systems where efficiency >300mA isn't required and EMI filtering is critical. |
Compared with LT1108CN8-5, the LT1108CS8-5#TRPBF offers superior thermal performance in surface-mount production; versus LT1307CS8-5, it trades higher quiescent current for robust 1.5A switching and flexible current limiting - making it preferred for industrial battery-backed supplies.
Availability
LT1108CS8-5#TRPBF is available at Aetrix Electronics and suitable for palmtop computers, 9V-to-5V peripheral converters, and LCD bias generators requiring stable component supply across long-lifecycle industrial programs.
Supply support for LT1108CS8-5#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 power products.
The LT1108CS8-5#TRPBF belongs to Linear's micropower DC/DC converter family, designed specifically for battery-operated instrumentation and portable electronics demanding ultra-low IQ and multi-topology flexibility.
FAQ
What is the maximum output current capability of the LT1108CS8-5#TRPBF in step-down mode?
The LT1108CS8-5#TRPBF delivers up to 300mA at 5V from a 9V input in step-down configuration, as confirmed in the Typical Performance Characteristics section. At lower input voltages (e.g., 6.5V), output current drops to ~200mA due to reduced headroom; the internal 1.5A switch and thermal limits constrain sustained operation.
Can the LT1108CS8-5#TRPBF be used in step-up mode, and what is the minimum input voltage?
Yes, the LT1108CS8-5#TRPBF supports step-up operation down to 2V input, enabling 5V output from two AA cells. Its 70% duty cycle and 36µs ON-time allow stable regulation even at 2V–3V inputs, though output current is limited to ~150mA under those conditions per the datasheet's Palmtop Computer Logic Supply example.
How does the ILIM pin function on the LT1108CS8-5#TRPBF, and what resistor value sets 400mA current limit?
The ILIM pin on the LT1108CS8-5#TRPBF programs switch current limit by sensing voltage across an external resistor between ILIM and VIN. A 220Ω resistor sets ~400mA limit, as explicitly stated in the Electrical Characteristics table and confirmed in the "Using the ILIM Pin" application note section.
Is the LT1108CS8-5#TRPBF pin-compatible with the LT1173, and what advantage does it offer?
Yes, the LT1108CS8-5#TRPBF is pin-for-pin compatible with the LT1173. Its key advantage is a 70% duty cycle (vs. LT1173's lower duty cycle), which increases achievable output current in many step-up and step-down configurations without changing PCB layout or external components.
Does the LT1108CS8-5#TRPBF require external feedback resistors for 5V output?
No - the LT1108CS8-5#TRPBF is the fixed 5V version and contains internal resistor dividers connected to the FB/SENSE (Pin 8) terminal. The datasheet states "No external resistors are needed," and Pin 8 must be connected directly to the 5V output node, unlike the adjustable LT1108 variant.
LT1108CS8-5#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:
- Fixed
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2V
- Voltage - Input (Max):
- 30V
- Voltage - Output (Min/Fixed):
- 5V
- Voltage - Output (Max):
- -
- 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
LT1108CS8-5#TRPBF FAQ
1.How can I place an order for LT1108CS8-5#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1108CS8-5#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 LT1108CS8-5#TRPBF reliable?
The price and inventory of LT1108CS8-5#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1108CS8-5#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1108CS8-5#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1108CS8-5#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1108CS8-5#TRPBF?
LT1108CS8-5#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1108CS8-5#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 LT1108CS8-5#TRPBF?
For technical support, including LT1108CS8-5#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1108CS8-5#TRPBF requirements.
6.How does Aetrix verify that LT1108CS8-5#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1108CS8-5#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 LT1108CS8-5#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1108CS8-5#TRPBF?
All LT1108CS8-5#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1108CS8-5#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 LT1108CS8-5#TRPBF part is unused and in its original packaging.
Return procedure for LT1108CS8-5#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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