Analog Devices Inc. LTC1682IMS8#PBF

Summary of LTC1682IMS8#PBF Products

The LTC1682IMS8#PBF from Analog Devices Inc. is a highly integrated charge pump switching regulator designed to deliver low noise, regulated voltage supplies—an essential requirement for noise-sensitive applications such as high-frequency voltage-controlled oscillators (VCOs) in wireless communications. This device consists of a doubler charge pump circuit paired with a low dropout (LDO) linear regulator, allowing it to efficiently boost an input voltage in the range of 1.8V to 4.4V and deliver an adjustable or fixed low noise output voltage. Packaged in an 8-lead MSOP, the LTC1682IMS8#PBF supports up to 50mA output current and is engineered for compact, low-profile system designs.

Highlights and Advantages of LTC1682IMS8#PBF

The LTC1682IMS8#PBF incorporates several features geared towards simplified system design and optimal performance:

Extremely low output noise, specified at 60μV RMS within a 100kHz bandwidth, ensures minimal interference with sensitive analog and RF sections.

Flexible output voltage options: adjustable (2.5V to 5.5V) or fixed at 3.3V or 5V, accommodating a wide range of circuit requirements.

Wide input voltage operation (1.8V–4.4V) for compatibility with modern low-voltage battery-powered systems.

No inductor required, simplifying PCB layout and minimizing electromagnetic interference (EMI).

High switching frequency (550kHz) permits the use of small ceramic capacitors, minimizing overall solution size.

Low quiescent operating current (150μA) and deep shutdown mode (<5μA), crucial for energy-sensitive applications.

Comprehensive integrated protection: thermal shutdown, output current limiting, as well as indefinite short-circuit tolerance.

Industry-standard compact package options (8-pin MSOP and SO).

Operation Principles and Functional Details of LTC1682IMS8#PBF

At its core, the LTC1682IMS8#PBF uses a switched-capacitor charge pump topology to double its input voltage. An internal two-phase non-overlapping clock orchestrates the switching network, driving the charge pump and thereby increasing the supply voltage with minimal external components—only a single flying capacitor is required.

Once a sufficiently high internal CPO (charge pump output) voltage is achieved, an integrated LDO linear regulator filters the ripple generated by the switched-capacitor doubler, providing a clean, stable output voltage. The regulator is either fixed (3.3V, 5V variants) or programmable—via an external resistor divider—between 2.5V and 5.5V, referenced to an internal precision 1.235V bandgap.

The device intelligently manages operation by monitoring output load and charge pump status:

During low load, a Burst Mode operation enhances efficiency, momentarily shutting down the charge pump oscillator until the CPO voltage drops by a set threshold.

When disabled via the SHDN pin (logic low), supply current is minimized, and the regulated output is safely discharged to ground through an internal 100Ω switch.

Thermal and output current monitoring circuits provide robust protection against excessive junction temperature and prolonged output short circuits, guaranteeing reliability in challenging environments.

Electrical Characteristics of LTC1682IMS8#PBF

The LTC1682IMS8#PBF’s key electrical characteristics include:

Input voltage range: 1.8V to 4.4V

Output voltage: Adjustable from 2.5V to 5.5V, or fixed at 3.3V/5V, depending on the variant

Output current: Up to 50mA, with the programmable capability to support lower loads at higher output voltages

Output noise: 60μV RMS over a 100kHz bandwidth

Quiescent supply current: 150μA (active), <5μA (shutdown)

Maximum output current protection: 90mA

Thermal shutdown activation: 150°C junction temperature

Package: 8-pin MSOP (3.0mm width), also available in SO packages

Additionally, the LTC1682IMS8#PBF is RoHS compliant, unaffected by REACH, and rated for an industrial temperature range of -40°C to 85°C.

Pin Mapping and Schematic Diagram of LTC1682IMS8#PBF

The 8-lead configuration consists of the following notable pins:

VOUT (low noise regulated output): Requires a ≥2μF low ESR bypass capacitor for optimal performance.

SHDN (shutdown control): Logic input to enable/disable the regulator.

FB (adjustable output, LTC1682 only): Used for setting the output voltage using external resistors.

FILT (fixed output variants): Accepts a 1nF filter capacitor to ground for enhanced voltage reference filtering.

VIN (input): Accepts 1.8V–4.4V supply voltage.

C+, C– (flying capacitor connections): Interfaces with the external flying capacitor for charge-pump operation.

CPO (unregulated charge pump output): Bypass with ≥2μF low ESR capacitor for minimum noise.

GND: Common ground connection.

The device’s block diagram (refer to documentation) illustrates the internal charge pump, oscillator, LDO regulator, reference, and protection circuitry.

Use Cases for LTC1682IMS8#PBF

The LTC1682IMS8#PBF’s distinguishing qualities make it ideal for scenarios demanding low noise, regulated voltages derived from single-cell Li-ion batteries or other low-voltage sources, such as:

Powering VCOs in cellular base stations and mobile handsets, where output ripple and phase noise are tightly controlled.

Supplying voltageand noise-sensitive analog modules in portable medical instruments and low-power data acquisition systems.

Providing isolated supplies for RF transceivers and remote transmitters.

Serving as an efficient power source for wireless PCMCIA cards and two-way pagers, especially where board space and EMI are constrained.

Design Guidelines for LTC1682IMS8#PBF Applications

To maximize performance in practical designs, the following engineering considerations are essential:

Capacitor Selection: Prioritize low ESR ceramic capacitors for all bypass and filter positions (typically ≥2μF for most nodes) to minimize switching ripple and noise propagation.

Output Voltage Programming (LTC1682 only): Select feedback resistor values to maintain the LDO out of dropout at max load, ensuring minimum noise is preserved.

Load Sharing: Note that any current drawn from the CPO pin effectively reduces the available regulated output current—a design tradeoff for auxiliary rail needs.

Layout Best Practices: Use short, direct traces and a solid ground plane; minimize inductance and resistance in capacitor return paths. Ensure the FILT pin (for fixed voltage variants) remains well-isolated from noise sources.

Thermal Management: Connect the device’s GND pin to a large PCB copper region and provide airflow if sustained high output currents or elevated ambient temperatures are anticipated.

Shutdown Control: For ultra-low standby power applications, tie SHDN low. For default operation, tie SHDN to VIN.

Fault Tolerance: The regulator securely latches off during severe over-temperature, cycling automatically to prevent damage.

Alternative or Replacement Options for LTC1682IMS8#PBF

While the LTC1682IMS8#PBF offers a distinct combination of low noise, adjustable output, ease of use (no inductor), and robust protection in a compact package, engineers and procurement specialists may also consider potential alternative solutions depending on their system requirements. Devices offering similar charge pump + LDO functionalities, with low output noise and similar current capabilities, include:

LTC3260 (Analog Devices): Features a wider input range and dual-output rails, suitable for positive and negative voltage generation.

MAX1682 (Maxim Integrated): Another low-noise charge pump, albeit without integrated LDO or adjustable output variants.

TPS60100 (Texas Instruments): Charge pump with low dropout linear regulation, suitable for higher output current applications.

It is important to compare noise performance, output current handling, and package dimensions when evaluating possible replacements to ensure compliance with application-critical specifications.

Conclusion

The LTC1682IMS8#PBF stands out as a versatile, high-performance power solution for engineers tasked with supporting noise-sensitive subsystems in compact, battery-operated devices. By integrating a doubler charge pump with a precision low noise LDO, it delivers clean, easily programmable outputs from low-voltage power sources—without the size, EMI, and complexity inherent in inductor-based switching solutions. Careful consideration of application requirements, layout, and component selection will ensure reliable, low-noise operation across a broad range of demanding electronic designs.