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STMicroelectronics LD2985AM31R
- Part No.:
- LD2985AM31R
- Manufacturer:
- STMicroelectronics
- Package:
- SC-74A, SOT-753
- Datasheet:
-
LD2985AM31R.pdf
- Description:
- IC REG LINEAR 3.1V 150MA SOT23-5
- Quantity:
- Payment:
- Shipping:
Inventory:1,805
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Product details
Overview
LD2985AM31R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 3.1 V output, 280 mV dropout at 150 mA, 30 µVrms output noise, and TTL-compatible inhibit control on Pin 3. It operates from −40 °C to 125 °C and targets battery-powered portable electronics requiring ultra-low quiescent current and clean power delivery.
For engineers reviewing the LD2985AM31R datasheet, LD2985AM31R pinout, LD2985AM31R application, or LD2985AM31R equivalent, this page delivers verified electrical specs, SOT23-5L package mapping, real-world use cases in handheld devices, and validated alternative regulators for low-noise, low-power system design.
Technical Context
The LD2985AM31R uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA) and sub-1 µA shutdown current when INHIBIT is pulled low. Its internal feedback network sets a precise 3.1 V output with ±1.2% tolerance over temperature and load.
No external compensation is required; stability is ensured with ≥2.2 µF ceramic output capacitance (low-ESR) and a 10 nF bypass capacitor on the Bypass pin to achieve 30 µVrms noise. The inhibit function is unbuffered and requires explicit logic-level drive-no internal pull-up exists.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | 3.1 V ±1.2% (guaranteed across −40 °C to 125 °C, 1–150 mA load) |
| Dropout Voltage | 280 mV at 150 mA (enables regulation down to VIN = 3.38 V; critical for Li-ion single-cell systems) |
| Quiescent Current | 80 µA at no load; <1 µA in inhibit-off state (extends battery life in standby mode) |
| Output Noise | 30 µVrms (300 Hz–50 kHz, with 10 nF bypass cap; suitable for RF/analog supply rails) |
| Supply Rejection | 45 dB at 1 kHz (with 10 µF output + 10 nF bypass; suppresses switching noise from upstream DC/DC) |
| Inhibit Threshold | VIL ≤ 0.15 V, VIH ≥ 2 V (TTL-compatible; requires active drive-pin must not float) |
| Thermal Resistance | RthJA = 255 °C/W (SOT23-5L package; derating required above ~80 mW dissipation at ambient) |
Pinout & Package
SOT23-5L surface-mount package (1.6 mm × 2.9 mm × 1.3 mm), RoHS-compliant, ECOPACK2 qualified. Exposed pad not present; thermal path relies on PCB copper area under body.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - IN | Input voltage supply rail | Accepts 2.5–16 V DC; requires ≥1 µF ceramic input capacitor placed within 12.7 mm of pin |
| 2 - GND | Analog ground reference | Common return for IN, OUT, INHIBIT, and Bypass; must connect to low-impedance analog ground plane |
| 3 - INHIBIT | Logic-controlled enable/disable input | TTL-compatible; pulls regulator into <1 µA shutdown when ≤0.15 V; must be driven-not left floating |
| 4 - Bypass | Noise reduction terminal | Connects to 10 nF capacitor to GND; reduces output noise from ~100 µVrms to 30 µVrms |
| 5 - OUT | Regulated 3.1 V output | Delivers up to 150 mA; requires ≥2.2 µF ceramic output capacitor (X7R, low-ESR) within 12.7 mm |
Key Features
| Feature | Design Value |
|---|---|
| Ultra-low dropout | 7 mV at 1 mA load enables operation with minimal headroom-critical for single-cell Li-ion (3.0–3.6 V) systems |
| Sub-µA shutdown | <1 µA quiescent current in inhibit-off state extends battery shelf life in always-on portable devices |
| Bypass-pin noise filtering | Dedicated Bypass pin accepts 10 nF cap to reduce broadband output noise by >50%, supporting sensitive RF/analog ICs |
| Internal protection | Integrated current limiting and thermal shutdown prevent damage during overload or poor PCB thermal design |
| Wide temperature range | Specified from −40 °C to 125 °C junction temperature-supports automotive cabin and industrial edge applications |
Applications
| Smartphone Baseband Power | Portable Medical Sensor Node |
|---|---|
|
Use Scenario: Powers baseband processor core voltage rail in LTE/5G smartphones where input is switched from a 3.6 V buck converter. IC Role / Device Role / Timing Role: Local LDO delivering clean, low-noise 3.1 V to processor I/O or memory interface. Use Value: 30 µVrms noise prevents bit errors in high-speed serial links; 280 mV dropout maintains regulation as battery discharges to 3.38 V. |
Use Scenario: Supplies ADC reference and signal chain in battery-operated wearable ECG monitors. IC Role / Device Role / Timing Role: Precision analog rail generator with shutdown control synchronized to sensor sampling intervals. Use Value: <1 µA inhibit current minimizes average power during 99% sleep duty cycle; ±1.2% output accuracy ensures measurement repeatability. |
| Digital Camera Image Sensor Bias | Industrial IoT Edge Controller Core |
|
Use Scenario: Provides stable 3.1 V bias to CMOS image sensor analog front-end in compact action cameras. IC Role / Device Role / Timing Role: Low-noise analog supply rail decoupled from noisy digital domain via dedicated LDO. Use Value: Bypass pin + 10 nF cap achieves 30 µVrms noise-reducing fixed-pattern noise in raw sensor output. |
Use Scenario: Powers microcontroller core in fanless industrial gateways operating in extended temperature environments. IC Role / Device Role / Timing Role: Primary 3.1 V system rail with thermal shutdown protection for unattended operation. Use Value: −40 °C to 125 °C rating ensures reliability in cabinet-mounted deployments; internal current limit prevents latch-up during transient faults. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar low-noise, low-IQ LDO applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS7A0531PDBVR | 300 mA output, 17 µA IQ (active), 25 µVrms noise, no Bypass pin | Lacks dedicated noise-reduction pin; requires higher-performance output cap for same noise floor | Choose if higher output current or lower active IQ is prioritized over pin-count flexibility |
| MCP1703T-3102E/MB | 250 mA output, 4 µA IQ (active), 40 µVrms noise, SOT23-5 package | Higher noise and no inhibit function; requires external enable circuitry for shutdown | Choose if lowest active IQ is critical and shutdown control can be implemented externally |
Compared with TPS7A0531PDBVR and MCP1703T-3102E/MB, the LD2985AM31R uniquely combines 30 µVrms noise (via Bypass pin), <1 µA shutdown, and TTL inhibit in SOT23-5-making it optimal for space-constrained, battery-sensitive designs needing guaranteed noise performance without layout compromises.
Availability
LD2985AM31R is available at Aetrix Electronics and suitable for smartphone power management, portable medical sensors, digital camera imaging subsystems, and industrial edge controllers requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LD2985AM31R 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.
The LD2985 series belongs to ST's precision low-dropout regulator product line, engineered specifically for ultra-low-noise, ultra-low-quiescent-current applications in portable and battery-critical systems.
FAQ
Can the INHIBIT pin be left unconnected?
No. The INHIBIT pin has no internal pull-up or pull-down. Leaving it floating risks undefined regulator state and potential oscillation or partial turn-on. If unused, tie it directly to IN (not VCC of another rail) to ensure reliable ON operation per datasheet Section 6.5.
What is the minimum output capacitance required for stability with LD2985AM31R?
For 3.1 V output, ST specifies ≥2.2 µF ceramic (X7R, low-ESR) as the minimum stable output capacitance. Using less than this value risks instability; adding a series resistor to the capacitor may restore stability but degrades transient response and noise performance.
Does LD2985AM31R support reverse current protection?
Yes-the internal PNP pass transistor lacks a body diode, so no reverse current flows from OUT to IN when VOUT > VIN. However, a small reverse leakage (~160 µA) flows to GND through internal feedback resistors; this is not destructive but must be accounted for in ultra-low-power monitoring circuits.
Is the 30 µVrms noise specification achievable without the Bypass capacitor?
No. The 30 µVrms noise figure is measured with a 10 nF capacitor connected between the Bypass pin and GND. Without it, typical output noise rises to ~100 µVrms due to internal reference amplifier noise; the Bypass pin provides direct access to filter that node.
LD2985AM31R Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- SC-74A, SOT-753
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Output Configuration:
- Positive
- Output Type:
- Fixed
- Number of Regulators:
- 1
- Voltage - Input (Max):
- 16V
- Voltage - Output (Min/Fixed):
- 3.1V
- Voltage - Output (Max):
- -
- Voltage Dropout (Max):
- 0.575V @ 150mA
- Current - Output:
- 150mA
- Current - Quiescent (Iq):
- 150 µA
- Current - Supply (Max):
- 4 mA
- PSRR:
- 45dB (1kHz)
- Control Features:
- Enable
- Protection Features:
- Over Current, Over Temperature
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SOT-23-5
LD2985AM31R FAQ
1.How can I place an order for LD2985AM31R through Aetrix?
Please submit a Request for Quotation (RFQ) for LD2985AM31R 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 LD2985AM31R reliable?
The price and inventory of LD2985AM31R are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LD2985AM31R is usually 5 days.
3.What payment methods are accepted for LD2985AM31R?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LD2985AM31R transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LD2985AM31R?
LD2985AM31R orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LD2985AM31R 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 LD2985AM31R?
For technical support, including LD2985AM31R datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LD2985AM31R requirements.
6.How does Aetrix verify that LD2985AM31R is sourced from the original manufacturer or authorized distributors?
All LD2985AM31R 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 LD2985AM31R meets industry standards.
7.What is the process for return or replacement of LD2985AM31R?
All LD2985AM31R units undergo pre-shipment inspection (PSI). If there is an issue with LD2985AM31R, 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 LD2985AM31R part is unused and in its original packaging.
Return procedure for LD2985AM31R:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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