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Analog Devices Inc. LT1938EDD#PBF
- Part No.:
- LT1938EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT1938EDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 2.2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:3,261
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Product details
Overview
LT1938EDD#PBF from Analog Devices (formerly Linear Technology) is a monolithic current-mode step-down switching regulator supporting 3.6V to 25V input and delivering up to 2.2A output at adjustable voltage (1.265V–20V), with programmable switching frequency from 300kHz to 2.8MHz, integrated 0.18Ω NPN switch and on-die Schottky boost diode, used in automotive battery regulation and portable power supplies.
For engineers reviewing the LT1938EDD#PBF datasheet, LT1938EDD#PBF pinout, LT1938EDD#PBF application, or LT1938EDD#PBF equivalent, key selection criteria include its 2.2A output capability, 1.265V feedback reference, power good flag, soft-start via RUN/SS pin, and thermal performance in the 3mm × 3mm DFN-10 package with exposed pad.
Technical Context
The LT1938EDD#PBF implements constant-frequency current-mode control using an internal transconductance error amplifier (330 µmho) and slope-compensated PWM. Its oscillator frequency is set by an external resistor on the RT pin, enabling precise tradeoffs between inductor size, efficiency, and input voltage range.
Operation relies on bipolar NPN switch drive via BOOST pin, requiring external boost capacitor and Schottky diode; BIAS pin enables high-efficiency operation by sourcing bias current from VOUT when >3V; PG pin provides open-collector power-good signal triggered at 90% of regulated output.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 25V - supports wide-range industrial and automotive inputs without external pre-regulation |
| Max Output Current | 2.2A - sufficient for powering core logic, FPGAs, and multiple peripherals in compact systems |
| Switching Frequency | 300kHz to 2.8MHz - enables use of sub-5µH inductors and ceramic output capacitors for minimal footprint |
| Feedback Reference | 1.265V ±15mV - sets output voltage accuracy and stability across temperature and load |
| Shutdown Quiescent Current | <1µA - preserves battery life in always-on portable or remote-sensing applications |
| Power Good Threshold | 90% of programmed VOUT - provides reliable system enable signaling before full regulation is achieved |
| On-Resistance (Switch) | 0.18Ω typical - minimizes conduction loss at high load, critical for >1A continuous operation |
Pinout & Package
LT1938EDD#PBF is housed in a thermally enhanced 10-lead (3mm × 3mm) plastic DFN package with exposed pad (Pin 11), requiring soldering to PCB ground plane for optimal thermal resistance (θJC = 10°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (Pin 1) | Boost Diode Anode Connection | Connects to anode of external Schottky diode; forms charge pump path for BOOST voltage generation |
| BOOST (Pin 2) | Boost Drive Voltage Node | Provides elevated gate drive voltage (>VIN) to fully saturate internal NPN switch, reducing VCE(sat) |
| SW (Pin 3) | Switch Node | High-current output of internal NPN switch; connects directly to inductor, catch diode, and boost capacitor |
| VIN (Pin 4) | Main Input Supply | Supplies current to internal regulator and switch; requires local 4.7µF ceramic bypass near pin |
| RUN/SS (Pin 5) | Enable & Soft-Start Control | Logic-level shutdown input (0.2V low / 2.5V high); RC network here controls output voltage ramp rate |
| PG (Pin 6) | Power Good Flag | Open-collector output active-low until FB reaches 90% of target; requires external pull-up resistor |
| BIAS (Pin 7) | Bias Supply Input | Accepts external ≥3V supply (typically VOUT); reduces VIN current draw and improves efficiency |
| FB (Pin 8) | Feedback Input | Senses output via resistor divider; regulated to 1.265V; bias current ≤100nA minimizes divider error |
| VC (Pin 9) | Error Amplifier Output | Controls peak switch current; compensation network (RC + CC) connected here stabilizes loop |
| RT (Pin 10) | Oscillator Frequency Set | Resistor-to-ground sets switching frequency; 8.66kΩ yields 2.8MHz, 187kΩ yields 300kHz |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Boost Schottky Diode | Eliminates need for external boost diode, reducing BOM count and layout area in compact designs |
| Adjustable Frequency via RT Pin | Enables optimization of inductor size vs. efficiency-e.g., 2.8MHz allows 1µH inductor in space-constrained apps |
| Power Good (PG) Flag | Provides deterministic system sequencing signal, eliminating need for external supervisor IC in many embedded systems |
| Soft-Start via RUN/SS Pin | Prevents inrush current and output overshoot during startup using simple R-C network on single pin |
| BIAS Pin Architecture | Draws bias current from VOUT instead of VIN when possible, improving efficiency by ~3–5% at high VIN/VOUT ratios |
Applications
| Automotive Battery Regulation | Portable Product Power |
|---|---|
Use Scenario: Regulating 12V vehicle battery (9–16V nominal, up to 25V transients) to 3.3V/5V for infotainment MCU and sensors. IC Role / Device Role / Timing Role: Primary buck converter providing stable, transient-hardened DC supply with PG signaling for safe boot sequence. Use Value: Withstands load dump pulses up to 25V and delivers 2.2A continuously while maintaining <1% output deviation under 10A/ms load steps. | Use Scenario: Powering ARM Cortex-M7 SoC and LPDDR3 memory in handheld medical device with Li-ion (3.0–4.2V) input. IC Role / Device Role / Timing Role: High-efficiency step-down regulator operating from BIAS pin at VOUT, minimizing heat in sealed enclosure. Use Value: Achieves >90% efficiency at 1A/3.3V with 2.8MHz switching, enabling 2.2×2.2mm inductor and ultra-thin profile PCB stackup. |
| Distributed Supply Regulation | Industrial Sensor Node |
Use Scenario: Local 5V-to-3.3V conversion at remote I/O module powered from 24V factory bus with long cable runs. IC Role / Device Role / Timing Role: Point-of-load regulator compensating for IR drop and noise on shared 24V rail. Use Value: 300kHz minimum frequency ensures stable operation despite input ripple; PG flag validates local supply before enabling RS-485 transceiver. | Use Scenario: Powering ultra-low-power wireless sensor node (sub-100µA sleep, 50mA transmit bursts) from 3.6V primary lithium cell. IC Role / Device Role / Timing Role: Efficient buck converter with <1µA shutdown current preserving battery life over multi-year deployments. Use Value: Soft-start prevents voltage sag during wake-up; 1.265V reference enables accurate 3.0V output setting with 1% resistors. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3630EMSE#PBF | Higher max input (42V), lower IQ (2.5µA), but fixed 3.3V/5V outputs only; no adjustable VOUT or RT pin | Best for fixed-output, high-input-voltage industrial rails where programmability is unnecessary | Select LTC3630EMSE#PBF when input exceeds 25V or when board space permits larger MSOP-10 package |
| MP2315DJ-LF-Z | Lower cost, 3A rating, but only 500kHz–2MHz range, no BIAS pin, higher VFB (0.8V), and no PG flag | Suitable for cost-sensitive consumer electronics where soft-start and power sequencing are handled externally | Select MP2315DJ-LF-Z when budget constraints outweigh need for PG signaling, BIAS efficiency gain, or 2.8MHz operation |
Compared with LTC3630EMSE#PBF and MP2315DJ-LF-Z, the LT1938EDD#PBF uniquely combines 25V input, 2.2A output, adjustable frequency up to 2.8MHz, BIAS pin efficiency enhancement, and integrated PG flag in a 3mm × 3mm DFN-making it optimal for space-constrained, sequenced, and automotive-grade designs.
Availability
LT1938EDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable product power, and distributed supply regulation requiring stable component supply across extended temperature ranges (–40°C to 125°C).
Supply support for LT1938EDD#PBF 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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.
The LT1938 belongs to Linear's precision monolithic buck regulator family, designed specifically for high-efficiency, wide-input, thermally constrained applications in automotive, industrial, and portable electronics where small solution size and robust transient response are critical.
FAQ
What is the maximum input voltage rating for LT1938EDD#PBF?
The absolute maximum input voltage for LT1938EDD#PBF is 25V. During normal regulation, input transients up to 25V are acceptable regardless of switching frequency. However, during startup or short-circuit conditions, the maximum safe input voltage depends on switching frequency, output voltage, and minimum on-time (150ns); for example, at 2.8MHz and 3.3V output, VIN must remain below ~14V to avoid violating duty cycle limits. Always verify with the VIN(MAX) equation in the Applications Information section of the LT1938EDD#PBF datasheet.
Does LT1938EDD#PBF require an external boost diode?
Yes, LT1938EDD#PBF requires an external Schottky diode connected between BD (Pin 1) and BOOST (Pin 2). Although the part integrates a boost Schottky diode structure on-die (as stated in the datasheet description), the BD pin is explicitly defined as "connects to the anode of the boost Schottky diode" and the BOOST pin requires external capacitor and diode for proper voltage boosting. The internal diode is not intended to replace the external component; omitting it will prevent proper switch saturation and cause excessive power dissipation.
How is the output voltage set on LT1938EDD#PBF?
The output voltage of LT1938EDD#PBF is set using a resistor divider from VOUT to GND, with the midpoint connected to the FB (Pin 8) pin. The internal reference is 1.265V, so R1 (top resistor) and R2 (bottom resistor) are selected per the formula: R1 = R2 × ((VOUT / 1.265) − 1). For example, to set 5.0V output, use R2 = 10kΩ and R1 = 29.3kΩ (1% tolerance). The FB pin bias current is ≤100nA, so resistor values should be ≤300kΩ total to limit divider error to <0.5%.
What thermal considerations apply to LT1938EDD#PBF in the DFN package?
LT1938EDD#PBF uses a 3mm × 3mm DFN-10 with exposed pad (Pin 11), which must be soldered to a PCB copper pour tied to GND for effective heat dissipation. Thermal resistance is θJC = 10°C/W (junction-to-case) and θJA = 45°C/W (junction-to-ambient) with standard 2-layer board layout. At 2.2A output and 12V input, power dissipation can exceed 1.5W; derating is required above 85°C ambient. Use ≥2 cm² of 2-oz copper under the exposed pad, with ≥4 thermal vias (0.3mm diameter), to maintain junction temperature below 125°C.
Can LT1938EDD#PBF operate in dropout mode?
No, LT1938EDD#PBF is a nonsynchronous buck regulator and cannot operate in dropout (100% duty cycle) mode. Its minimum on-time is ~150ns, limiting the lowest achievable output voltage for a given input and frequency. For example, at 2.8MHz and VIN = 5V, the maximum theoretical duty cycle is ~42%, yielding a minimum VOUT ≈ 2.1V. Below this, regulation fails. Unlike LDOs, it requires sufficient VIN–VOUT headroom-minimum input is specified as 3.6V independent of VOUT, but practical dropout is governed by tON(MIN) and fSW.
LT1938EDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 10-WFDFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 3.6V
- Voltage - Input (Max):
- 25V
- Voltage - Output (Min/Fixed):
- 1.265V
- Voltage - Output (Max):
- 20V
- Current - Output:
- 2.2A
- Frequency - Switching:
- 300kHz ~ 3MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- 0°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT1938EDD#PBF FAQ
1.How can I place an order for LT1938EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1938EDD#PBF 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 LT1938EDD#PBF reliable?
The price and inventory of LT1938EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1938EDD#PBF is usually 5 days.
3.What payment methods are accepted for LT1938EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1938EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1938EDD#PBF?
LT1938EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1938EDD#PBF 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 LT1938EDD#PBF?
For technical support, including LT1938EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1938EDD#PBF requirements.
6.How does Aetrix verify that LT1938EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT1938EDD#PBF 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 LT1938EDD#PBF meets industry standards.
7.What is the process for return or replacement of LT1938EDD#PBF?
All LT1938EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1938EDD#PBF, 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 LT1938EDD#PBF part is unused and in its original packaging.
Return procedure for LT1938EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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