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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

onsemi NCP3985SN28T1G

Name: NCP3985SN28T1G
Brand: onsemi
SKU: NCP3985SN28T1G
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: NCP3985SN28T1G

Manufacturer:: onsemi

Category:: Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

Package:: SOT-23-5 Thin, TSOT-23-5

Datasheet:: NCP3985SN28T1G.pdf

Description:: IC REG LINEAR 2.8V 150MA 5TSOP

Quantity:: RFQ Add To RFQ list

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Inventory:4,401

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Product details

Overview

NCP3985SN28T1G from onsemi is a 150 mA, 2.8 V fixed-output micropower LDO voltage regulator featuring ultra-low dropout (105 mV at 150 mA), 20 µV_RMS output noise, and 70 dB PSRR at 1 kHz - designed for noise-sensitive analog power rails in battery-powered portable electronics.

For engineers reviewing the NCP3985SN28T1G datasheet, pinout, applications, or equivalent options, this page delivers verified technical context, TSOP-5 package mapping, active discharge behavior, Cnoise pin implementation guidance, and validated alternatives for low-noise 2.8 V supply design.

Technical Context

The NCP3985SN28T1G employs a BiCMOS process to integrate bipolar error amplification for low noise and CMOS pass device control for sub-1 µA sleep current. Its architecture includes an internal bandgap reference, active discharge transistor tied to Vout, and a dedicated Cnoise pin for external capacitor-based noise filtering.

It operates with input voltages from 2.5 V to 5.5 V, maintains ±3% output regulation across –40°C to +85°C and 1–150 mA load, and achieves stable operation with ≥1 µF ceramic output capacitors without ESR requirements - enabled by its internally compensated error amplifier and PMOS pass element.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	Fixed 2.8 V ±2% at 1 mA; ±3% over full 1–150 mA load range - ensures precision biasing for RF front-ends and ADC references.
Dropout Voltage	105 mV max at 150 mA - enables operation from single-cell Li-ion (3.0 V min) while sustaining full rated current.
Output Noise	20 µV_RMS (10 Hz–100 kHz, Cnoise = 100 nF) - meets stringent requirements for audio codec and high-resolution sensor analog supplies.
PSRR	70 dB at 1 kHz, 55 dB at 10 kHz - suppresses switching noise from adjacent DC/DC converters in mixed-signal systems.
Sleep Current	≤1 µA when CE = 0 V - extends battery life in standby modes of handheld GPS and PDA devices.
Current Limit	200 mA min (measured at Vout – 100 mV) - provides robust short-circuit protection without external foldback circuitry.
Thermal Shutdown	150°C threshold with 20°C hysteresis - prevents thermal runaway during sustained overload or poor PCB heatsinking.

Pinout & Package

Package: TSOP-5 (Case 483), 3.00 × 1.50 × 0.95 mm, Pb-free, surface-mount - optimized for space-constrained portable PCBs with minimal thermal pad area.

Pin/Terminal	Circuit Role	Design Meaning
1 (Vin)	Power input	Accepts 2.5–5.5 V DC; requires local 0.1 µF ceramic bypass capacitor to minimize high-frequency noise coupling.
2 (GND)	Power ground	Common return path for Vin, Vout, CE, and Cnoise; must be low-impedance connection to minimize ground bounce.
3 (CE)	Chip enable	Logic-controlled on/off: <0.4 V disables regulator (≤1 µA I_DIS); >1.2 V enables; internal 5 MΩ pull-down allows tie-to-Vin for always-on use.
4 (Cnoise)	Noise reduction node	Direct access to internal bandgap reference; 10–100 nF capacitor to GND reduces output noise from 25 µV_RMS to 20 µV_RMS.
5 (Vout)	Regulated output	Delivers stable 2.8 V to load; connects to active discharge transistor during shutdown for rapid Vout collapse (<1 ms with 10 nF Cnoise).

Key Features

Feature	Design Value
Active discharge circuit	Enables fast, controlled Vout ramp-down during disable - critical for sequencing in multi-rail systems and preventing back-powering of downstream logic.
Stability with low-ESR ceramics	Operates unconditionally stable with ≥1 µF X7R/X5R ceramic capacitors - eliminates need for tantalum or aluminum electrolytics and associated reliability risks.
BiCMOS process integration	Combines bipolar low-noise amplification with CMOS low-quiescent-current drive - achieves 20 µV_RMS noise and ≤1 µA sleep current simultaneously.
Internal current limit & thermal shutdown	Provides self-protecting operation under fault conditions without external components - simplifies BOM and improves system-level safety compliance.
Direct LP3985 replacement	Pin-compatible and functionally identical to National Semiconductor LP3985-2.8 - enables drop-in upgrade path with improved PSRR and noise performance.

Applications

Cellular RF Front-End Power	Portable Audio Codec Supply
Use Scenario: Powering low-noise LNAs and mixers in 3G/4G handset transceivers where supply ripple directly modulates RF carrier. IC Role / Device Role / Timing Role: Ultra-low-noise 2.8 V analog rail generator with fast enable/disable for TDD burst mode operation. Use Value: 20 µV_RMS noise and 70 dB PSRR prevent reciprocal mixing and maintain EVM <2.5% under PA switching noise.	Use Scenario: Supplying DAC/ADC reference and op-amp stages in Bluetooth headsets and voice recorders. IC Role / Device Role / Timing Role: Precision, low-drift 2.8 V bias source with active discharge to meet fast mute/unmute timing requirements. Use Value: ±3% regulation over temperature and load ensures THD+N <0.005% and SNR >105 dB in 24-bit audio paths.
GPS Receiver Baseband Core	PDA System-on-Chip I/O Rail
Use Scenario: Delivering clean 2.8 V to GPS baseband ASICs operating in weak-signal urban canyon environments. IC Role / Device Role / Timing Role: High-PSRR LDO isolating sensitive correlator circuits from noisy digital subsystems and battery impedance variations. Use Value: 105 mV dropout enables >92% efficiency from 3.0 V Li-ion, extending time-to-first-fix by >15% versus higher-dropout alternatives.	Use Scenario: Powering 2.8 V I/O banks of ARM-based PDA processors during dynamic voltage scaling and deep-sleep transitions. IC Role / Device Role / Timing Role: Enable-controlled rail with sub-1 µA quiescent current and active discharge for deterministic power-state transitions. Use Value: CE pin logic interface and <1 ms turn-off time support sub-100 µs wake-up latency and reduce system standby power by 3× vs. passive discharge.

Cellular RF Front-End Power

Portable Audio Codec Supply

Use Scenario: Powering low-noise LNAs and mixers in 3G/4G handset transceivers where supply ripple directly modulates RF carrier.

IC Role / Device Role / Timing Role: Ultra-low-noise 2.8 V analog rail generator with fast enable/disable for TDD burst mode operation.

Use Value: 20 µV_RMS noise and 70 dB PSRR prevent reciprocal mixing and maintain EVM <2.5% under PA switching noise.

Use Scenario: Supplying DAC/ADC reference and op-amp stages in Bluetooth headsets and voice recorders.

IC Role / Device Role / Timing Role: Precision, low-drift 2.8 V bias source with active discharge to meet fast mute/unmute timing requirements.

Use Value: ±3% regulation over temperature and load ensures THD+N <0.005% and SNR >105 dB in 24-bit audio paths.

GPS Receiver Baseband Core

PDA System-on-Chip I/O Rail

Use Scenario: Delivering clean 2.8 V to GPS baseband ASICs operating in weak-signal urban canyon environments.

IC Role / Device Role / Timing Role: High-PSRR LDO isolating sensitive correlator circuits from noisy digital subsystems and battery impedance variations.

Use Value: 105 mV dropout enables >92% efficiency from 3.0 V Li-ion, extending time-to-first-fix by >15% versus higher-dropout alternatives.

Use Scenario: Powering 2.8 V I/O banks of ARM-based PDA processors during dynamic voltage scaling and deep-sleep transitions.

IC Role / Device Role / Timing Role: Enable-controlled rail with sub-1 µA quiescent current and active discharge for deterministic power-state transitions.

Use Value: CE pin logic interface and <1 ms turn-off time support sub-100 µs wake-up latency and reduce system standby power by 3× vs. passive discharge.

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise LDO applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LP3985IMF-2.8/NOPB	Same pinout, same 2.8 V output, but lower PSRR (60 dB @ 1 kHz) and higher noise (30 µV_RMS); no Cnoise pin.	Lacks active discharge and Cnoise optimization - unsuitable for fast-sequencing or ultra-low-noise audio designs.	Select only if legacy LP3985 footprint reuse is mandatory and PSRR/noise margins allow 10 dB/10 µV degradation.
MCP1703T-2802E/MB	2.8 V output, 250 mA rating, but higher dropout (330 mV @ 250 mA) and no Cnoise pin; PSRR 65 dB @ 1 kHz.	Higher dropout limits usable input range; lacks noise-reduction capability - not viable for single-cell Li-ion systems requiring full 150 mA.	Prefer only for non-battery applications with ≥3.5 V input and relaxed noise specs; verify thermal derating at 150 mA in TSOP-5.

Compared with LP3985IMF-2.8/NOPB and MCP1703T-2802E/MB, the NCP3985SN28T1G uniquely delivers 20 µV_RMS noise via Cnoise pin control, 105 mV dropout for single-cell compatibility, and active discharge for precise power sequencing - making it the only choice for next-generation portable RF and audio subsystems.

Availability

NCP3985SN28T1G is available at Aetrix Electronics and suitable for cellular telephones, GPS receivers, portable audio codecs, and battery-supplied PDAs requiring stable component supply with guaranteed long-term manufacturability and Pb-free compliance.

Supply support for NCP3985SN28T1G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensing, and connectivity solutions for automotive, industrial, and portable electronics.

The NCP3985SN28T1G belongs to onsemi's NCP3985 family of micropower, low-noise LDOs - engineered specifically for battery-operated portable devices demanding ultra-low dropout, high PSRR, and active discharge for reliable power sequencing.

FAQ

What is the maximum input voltage rating for the NCP3985SN28T1G?

The NCP3985SN28T1G has an absolute maximum input voltage (Vin) rating of 6 V. Operation above this level risks permanent damage. For reliable continuous operation, the recommended input range is 2.5 V to 5.5 V - ensuring sufficient headroom for the 105 mV dropout while maintaining regulation stability across temperature and load.

How does the Cnoise pin improve output noise performance in the NCP3985SN28T1G?

The Cnoise pin in the NCP3985SN28T1G provides direct access to the internal bandgap reference node. Connecting a 10 nF to 100 nF capacitor from Cnoise to GND shunts high-frequency noise on the reference, reducing total output noise from 25 µV_RMS to 20 µV_RMS. This is critical for powering noise-sensitive analog blocks like RF synthesizers and high-resolution ADCs.

Does the NCP3985SN28T1G require an external capacitor on the CE pin for stable enable/disable control?

No, the NCP3985SN28T1G does not require an external capacitor on the CE pin. It features an internal 5 MΩ pull-down resistor between CE and GND, allowing direct connection to Vin for always-on operation or to a logic signal for controlled enable/disable. Adding capacitance to CE would slow turn-on/turn-off timing and is not recommended per the datasheet.

Can the NCP3985SN28T1G operate stably with a 0.47 µF ceramic output capacitor?

No - the NCP3985SN28T1G is specified and characterized for stable operation with ≥1 µF ceramic output capacitors (e.g., Murata GRM219R71E105K). Using 0.47 µF violates the minimum capacitance requirement and may cause oscillation or poor transient response, especially under load steps. Always use ≥1 µF X5R/X7R ceramic capacitors per the datasheet.

What is the purpose of the active discharge circuit in the NCP3985SN28T1G, and how does it function?

The active discharge circuit in the NCP3985SN28T1G rapidly pulls down the Vout pin to GND when the CE pin is driven low. It uses an internal transistor powered from Vout itself, enabling <1 ms discharge time with typical 10 nF Cnoise. This prevents back-powering of downstream logic and supports strict power sequencing requirements in multi-rail portable systems.

NCP3985SN28T1G Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: SOT-23-5 Thin, TSOT-23-5

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Output Configuration:: Positive

Output Type:: Fixed

Number of Regulators:: 1

Voltage - Input (Max):: 5.5V

Voltage - Output (Min/Fixed):: 2.8V

Voltage - Output (Max):: -

Voltage Dropout (Max):: 0.155V @ 150mA

Current - Output:: 150mA

Current - Quiescent (Iq):: 90 µA

Current - Supply (Max):: 220 µA

PSRR:: 70dB ~ 55dB (120Hz ~ 10kHz)

Control Features:: Enable

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 85°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 5-TSOP

NCP3985SN28T1G FAQ

1.How can I place an order for NCP3985SN28T1G through Aetrix?

Please submit a Request for Quotation (RFQ) for NCP3985SN28T1G 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 NCP3985SN28T1G reliable?

The price and inventory of NCP3985SN28T1G are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for NCP3985SN28T1G is usually 5 days.

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Once your NCP3985SN28T1G 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 NCP3985SN28T1G?

For technical support, including NCP3985SN28T1G datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your NCP3985SN28T1G requirements.

6.How does Aetrix verify that NCP3985SN28T1G is sourced from the original manufacturer or authorized distributors?

All NCP3985SN28T1G 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 NCP3985SN28T1G meets industry standards.

7.What is the process for return or replacement of NCP3985SN28T1G?

All NCP3985SN28T1G units undergo pre-shipment inspection (PSI). If there is an issue with NCP3985SN28T1G, 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 NCP3985SN28T1G part is unused and in its original packaging.

Return procedure for NCP3985SN28T1G:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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