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Texas Instruments LP38851T-ADJ/NOPB
- Part No.:
- LP38851T-ADJ/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- TO-220-7 Formed Leads
- Datasheet:
-
LP38851T-ADJ/NOPB.pdf
- Description:
- IC REG LIN POS ADJ 800MA TO220-7
- Quantity:
- Payment:
- Shipping:
Inventory:331
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Product details
Overview
LP38851T-ADJ/NOPB from Texas Instruments is an adjustable 800 mA low-dropout linear regulator with dual-rail operation (VIN and VBIAS), ±1.5% output voltage accuracy at 25°C, 115 mV typical dropout at full load, and programmable soft-start. It delivers stable core power to DSPs and microcontrollers in space-constrained applications requiring fast transient response and ceramic-capacitor stability.
For engineers reviewing the LP38851T-ADJ/NOPB datasheet, LP38851T-ADJ/NOPB pinout, LP38851T-ADJ/NOPB application, or LP38851T-ADJ/NOPB equivalent, key selection considerations include its dual-supply architecture (VIN/VBIAS), 0.8–1.8 V adjustable output range, SO PowerPad thermal performance, and soft-start capacitor timing dependency on rSS = 14 kΩ (typ).
Technical Context
The LP38851T-ADJ/NOPB uses a CMOS-based N-MOS pass transistor architecture enabling ultra-low quiescent current (7.0 mA from VIN, 3.0 mA from VBIAS at 800 mA load) and wide bandwidth without requiring large external compensation. Its dual-rail design separates power delivery (VIN) from control biasing (VBIAS), allowing operation down to VIN = VOUT + 115 mV while maintaining regulation even when VIN < VBIAS.
Internal circuitry includes precision bandgap reference (VADJ = 500 mV), UVLO with 2.45 V threshold and 150 mV hysteresis, thermal shutdown at 160°C, and over-current protection limiting output to 2.3 A. Soft-start is implemented via internal 14 kΩ resistor charging external CSS, yielding tSS = CSS × 14 kΩ × 5.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Current | 800 mA maximum continuous load - supports high-current digital core rails without derating at TJ ≤ 125°C. |
| Dropout Voltage | 115 mV (typ) at 800 mA - enables regulation from ultra-low VIN, e.g., 0.915 V input for 0.8 V output. |
| VADJ Accuracy | ±1.5% at TJ = 25°C - ensures tight output tolerance with external R1/R2 divider; ±2.0% over 0°C to +125°C. |
| Stability | Stable with ≥10 µF X5R/X7R ceramic COUT - eliminates need for ESR-tuned tantalum or aluminum electrolytics. |
| VBIAS Range | 3.0 V to 5.5 V - supports flexible bias sourcing; requires ≥4.5 V when VOUT > 1.2 V for guaranteed operation. |
| Soft-Start Time | tSS = CSS × 14 kΩ × 5 - allows precise inrush control; 700 µs typical with 10 nF capacitor. |
| PSRR @ 1 kHz | 61 dB (VIN), 53 dB (VBIAS) - suppresses switching noise from upstream SMPS or bias rails. |
Pinout & Package
LP38851T-ADJ/NOPB is housed in an 8-lead SO PowerPad (DDA) package with exposed thermal pad (DAP) connected to GND. The DAP provides low θJ-C = 11°C/W thermal resistance and must be soldered to PCB copper for thermal integrity.
| Pin | Circuit Role | Design Meaning |
|---|---|---|
| 1 | SS | Soft-start capacitor node - controls VOUT ramp rate; internal 14 kΩ pull-down defines tSS = CSS × 14 kΩ × 5. |
| 2 | EN | Enable input - active-high logic; 1.25 V threshold with 100 mV hysteresis; internal 160 kΩ pull-up to VBIAS. |
| 3 | IN | Main power input - supplies load current; must be ≥ VOUT + 115 mV and ≤ min(VBIAS, 4.5 V). |
| 4 | GND | Analog ground reference - return path for IN, OUT, ADJ, SS, EN; connects to DAP (thermal pad). |
| 5 | OUT | Regulated output - delivers up to 800 mA; requires ≥10 µF ceramic capacitor within 1 cm of pin. |
| 6 | ADJ | Feedback node - connects to R1/R2 divider; VADJ = 500 mV sets VOUT = 0.5 × (1 + R1/R2). |
| 7 | BIAS | Bias supply rail - powers control circuitry and gate driver; must be ≥3.0 V (≥4.5 V if VOUT > 1.2 V). |
| 8 | N/C | No internal connection - electrically isolated; no routing or component attachment required. |
Key Features
| Feature | Design Value |
|---|---|
| Dual-rail architecture (VIN + VBIAS) | Enables ultra-low VIN operation while maintaining gate drive headroom - critical for sub-1 V core supplies. |
| CMOS N-MOS pass transistor | Delivers 7.0 mA typical IGND(IN) at 800 mA load - reduces system standby power vs bipolar LDOs. |
| Programmable soft-start | Eliminates inrush current spikes into large COUT - prevents input rail collapse during power-up sequencing. |
| Stable with 10 µF ceramic output cap | Removes ESR dependency - simplifies layout and improves reliability vs tantalum-based alternatives. |
| Thermal shutdown with hysteresis | 160°C trip point + 10°C hysteresis - protects against sustained overload without nuisance cycling. |
Applications
| ASIC Core Supply | SMPS Post-Regulator |
|---|---|
|
Use Scenario: Powers 0.8–1.2 V CPU/GPU cores in notebooks and graphics cards where input ripple from upstream buck converters must be suppressed. IC Role / Device Role / Timing Role: Final-stage LDO providing clean, low-noise DC to sensitive digital logic; rejects 61 dB of 1 kHz VIN ripple. Use Value: Maintains ±1.5% VOUT accuracy across temperature and load, preventing timing violations in high-speed interfaces. |
Use Scenario: Used after a 3.3 V or 5 V switching regulator to generate precise 1.0–1.5 V FPGA I/O or memory interface rails. IC Role / Device Role / Timing Role: Low-noise post-regulator stabilizing voltage for DDR termination and SerDes analog blocks. Use Value: 115 mV dropout enables tight regulation margin; 150 µVRMS output noise avoids jitter accumulation in clock paths. |
| Server I/O Supply | DSP Core Power |
|
Use Scenario: Supplies 1.2–1.8 V I/O banks in rack-mounted servers where thermal density and long-term reliability are critical. IC Role / Device Role / Timing Role: High-current LDO delivering 800 mA with SO PowerPad thermal dissipation (θJ-A = 168°C/W). Use Value: Stable operation from 3.0–5.5 V VBIAS allows shared bias rail across multiple regulators, reducing BOM count. |
Use Scenario: Powers 0.9–1.1 V DSP cores in industrial motor control and audio processing systems with rapid load transients. IC Role / Device Role / Timing Role: Fast-response regulator handling 100 mA–800 mA step loads with <1 % VOUT deviation. Use Value: Ceramic-stable loop and wide bandwidth minimize output sag during instruction bursts, preserving real-time latency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar adjustable LDO applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TPS7A4700RGWR | Fixed 3.3 V/adjustable, 1 A, 32 µV RMS noise, but requires ≥2.2 V VIN and has no VBIAS rail. | Higher noise performance and tighter load regulation, but cannot operate below VIN = VOUT + 300 mV. | Select TPS7A4700RGWR only when ultra-low noise is prioritized over ultra-low dropout and dual-rail flexibility. |
| TPS74801DRCR | 800 mA, adjustable, single-rail (VIN only), 150 mV dropout, supports 10 µF ceramic, but lacks soft-start. | Lower cost and simpler biasing, but requires external soft-start circuitry for inrush control. | Choose TPS74801DRCR when board space is constrained and soft-start can be implemented externally. |
Compared with LP38851T-ADJ/NOPB, TPS7A4700RGWR offers superior noise performance but sacrifices ultra-low-VIN capability, while TPS74801DRCR simplifies supply design at the cost of integrated soft-start functionality and thermal efficiency in SO PowerPad packaging.
Availability
LP38851T-ADJ/NOPB is available at Aetrix Electronics and suitable for ASIC core supplies, server I/O rails, DSP power domains, and SMPS post-regulation requiring stable component supply, long-lifecycle support, and consistent parametric performance across production batches.
Supply support for LP38851T-ADJ/NOPB 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
Texas Instruments is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of expertise in power management IC design and manufacturing.
The LP38851 series was developed specifically for high-current, low-voltage digital core regulation in computing and communications infrastructure, emphasizing fast transient response, ceramic capacitor compatibility, and thermal robustness in surface-mount packages.
FAQ
What is the minimum input voltage required for LP38851T-ADJ/NOPB to regulate at 0.8 V output?
The LP38851T-ADJ/NOPB requires VIN ≥ VOUT + VDO, where VDO is 115 mV (typical) at 800 mA. Thus, minimum VIN is 0.915 V. However, VIN must also be ≤ min(VBIAS, 4.5 V); for 0.8 V output, VBIAS ≥ 3.0 V is sufficient. The LP38851T-ADJ/NOPB achieves this ultra-low dropout using its N-MOS pass element and separate VBIAS rail.
Can LP38851T-ADJ/NOPB operate with only one supply rail?
No - LP38851T-ADJ/NOPB requires two independent supplies: VIN (high-current power path) and VBIAS (low-current control/bias rail). VBIAS powers the reference, error amplifier, and gate driver. Omitting VBIAS prevents regulation regardless of VIN level. For single-rail alternatives, consider TPS74801DRCR, but note LP38851T-ADJ/NOPB's unique dual-rail advantage.
What is the purpose of the N/C pin on LP38851T-ADJ/NOPB?
Pin 8 of LP38851T-ADJ/NOPB is designated N/C (No Connection) - it has no internal bond wire or circuit connection. It must remain unconnected on the PCB; routing traces or placing components on this pin may cause mechanical stress or unintended coupling. The SO PowerPad package relies on the exposed DAP (pin 4 GND) for thermal conduction, not pin 8.
How does the soft-start function work on LP38851T-ADJ/NOPB?
The LP38851T-ADJ/NOPB implements soft-start by controlling the internal reference voltage (VREF) via the SS pin. An internal 14 kΩ resistor charges an external capacitor (CSS), causing VREF - and thus VOUT - to rise exponentially. Total soft-start time is tSS = CSS × 14 kΩ × 5. With CSS = 10 nF, tSS ≈ 700 µs. The LP38851T-ADJ/NOPB disables soft-start if VBIAS falls below UVLO or EN drops low.
Is LP38851T-ADJ/NOPB compatible with 10 µF X5R ceramic capacitors on both input and output?
Yes - LP38851T-ADJ/NOPB is explicitly characterized and stabilized with ≥10 µF X5R or X7R ceramic capacitors on CIN and COUT. These dielectrics provide stable capacitance over temperature and low ESR, eliminating phase-margin risks. Z5U or Y5F ceramics are unsuitable due to excessive capacitance drift. The LP38851T-ADJ/NOPB's CMOS architecture inherently tolerates low-ESR outputs unlike older bipolar LDOs.
LP38851T-ADJ/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- TO-220-7 Formed Leads
- Packaging:
- Tube
- Product Status:
- Active
- Output Configuration:
- Positive
- Output Type:
- Adjustable
- Number of Regulators:
- 1
- Voltage - Input (Max):
- 5.5V
- Voltage - Output (Min/Fixed):
- 0.8V
- Voltage - Output (Max):
- 1.8V
- Voltage Dropout (Max):
- 0.2V @ 800mA
- Current - Output:
- 800mA
- Current - Quiescent (Iq):
- 300 µA
- Current - Supply (Max):
- 9 mA
- PSRR:
- 72dB ~ 61dB (120Hz ~ 1kHz)
- Control Features:
- Enable, Soft Start
- Protection Features:
- Over Current, Over Temperature, Short Circuit, Under Voltage Lockout (UVLO)
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- TO-220-7
LP38851T-ADJ/NOPB FAQ
1.How can I place an order for LP38851T-ADJ/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LP38851T-ADJ/NOPB 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 LP38851T-ADJ/NOPB reliable?
The price and inventory of LP38851T-ADJ/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LP38851T-ADJ/NOPB is usually 5 days.
3.What payment methods are accepted for LP38851T-ADJ/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LP38851T-ADJ/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LP38851T-ADJ/NOPB?
LP38851T-ADJ/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LP38851T-ADJ/NOPB 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 LP38851T-ADJ/NOPB?
For technical support, including LP38851T-ADJ/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LP38851T-ADJ/NOPB requirements.
6.How does Aetrix verify that LP38851T-ADJ/NOPB is sourced from the original manufacturer or authorized distributors?
All LP38851T-ADJ/NOPB 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 LP38851T-ADJ/NOPB meets industry standards.
7.What is the process for return or replacement of LP38851T-ADJ/NOPB?
All LP38851T-ADJ/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LP38851T-ADJ/NOPB, 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 LP38851T-ADJ/NOPB part is unused and in its original packaging.
Return procedure for LP38851T-ADJ/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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