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Analog Devices Inc. LT1938IDD#PBF
- Part No.:
- LT1938IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT1938IDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 2.2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:149
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Product details
Overview
LT1938IDD#PBF from Analog Devices (formerly Linear Technology) is a monolithic current-mode step-down switching regulator with adjustable frequency (300 kHz to 2.8 MHz), 25 V max input, 2.2 A continuous output current, and integrated 0.18 Ω NPN switch and boost Schottky diode. It delivers regulated 1.265 V to 20 V output in automotive battery regulation and portable power applications.
For engineers reviewing the LT1938IDD#PBF datasheet, LT1938IDD#PBF pinout, LT1938IDD#PBF application, or LT1938IDD#PBF equivalent, this page provides verified technical context, validated pin functions, confirmed thermal package data, and real-world selection guidance for high-efficiency DC/DC conversion in space-constrained industrial and embedded systems.
Technical Context
The LT1938IDD#PBF implements constant-frequency current-mode control using an internal transconductance error amplifier (330 µ℧), slope-compensated PWM, and oscillator frequency set by an external RT resistor. Its bipolar NPN switch is driven via BOOST pin voltage-generated by an integrated Schottky diode and external capacitor-to ensure saturation at high duty cycles.
Operation includes frequency foldback during startup/overload, active VC-clamp current limiting (3.1–4.0 A), soft-start via RUN/SS pin ramp, and open-collector power-good flag (PG) asserting at 90% of programmed VOUT. Thermal performance relies on the exposed-pad DFN package (θJC = 10°C/W) soldered to PCB ground.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6 V to 25 V - supports wide-range industrial and automotive supplies without external pre-regulation |
| Max Output Current | 2.2 A continuous - sufficient for FPGA core rails, DSPs, and multi-rail PMIC subsystems |
| Switching Frequency | 300 kHz to 2.8 MHz - enables compact 3 mm × 3 mm solution size with ceramic capacitors and sub-5 µH inductors |
| Feedback Reference | 1.265 V ±10 mV - sets output accuracy and enables precise 3.3 V, 5 V, or custom rail generation |
| Shutdown Quiescent Current | <1 µA - meets ultra-low-power requirements for battery-backed or always-on monitoring circuits |
| Power Good Threshold | VOUT ≥ 90% of regulation - provides reliable system enable signaling with 10 mV hysteresis |
| On-Resistance (SW) | 0.18 Ω typical - minimizes conduction loss at full load, supporting >85% efficiency at 12 V → 3.3 V/2 A |
Pinout & Package
LT1938IDD#PBF uses a thermally enhanced 10-lead (3 mm × 3 mm) plastic DFN package with exposed pad (Pin 11), rated for –40°C to 125°C junction temperature and θJA = 45°C/W. The exposed pad must be soldered to PCB ground for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (Pin 1) | Boost Diode Anode | Connects to internal Schottky anode; requires external capacitor to generate BOOST voltage above VIN |
| BOOST (Pin 2) | Bootstrap Drive | Supplies elevated gate drive to internal NPN switch; must exceed SW voltage by ≥1.6 V for full saturation |
| SW (Pin 3) | Switch Node | High-side switch output; connects to inductor, catch diode cathode, and BOOST capacitor |
| VIN (Pin 4) | Main Input Supply | Powers internal regulator and switch; requires local 4.7 µF ceramic bypass near pin |
| RUN/SS (Pin 5) | Enable & Soft-Start Control | Logic-level shutdown input (≤0.2 V = off); RC network here controls output voltage ramp rate |
| PG (Pin 6) | Power Good Flag | Open-collector output; pulled low until FB reaches 90% of 1.265 V reference |
| BIAS (Pin 7) | Efficiency Boost Input | Accepts external ≥3 V supply (e.g., VOUT) to reduce quiescent loss when VIN ≫ VOUT |
| FB (Pin 8) | Feedback Sense | Regulated to 1.265 V; connects to resistor divider tap for output voltage programming |
| VC (Pin 9) | Error Amplifier Output | Controls peak switch current; RC compensation network here stabilizes current-mode loop |
| RT (Pin 10) | Frequency Set | Resistor-to-ground sets oscillator frequency (e.g., 8.66 kΩ = 2.8 MHz) |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Boost Schottky Diode | Eliminates external bootstrap diode, reducing BOM count and layout area in high-VIN applications |
| Thermally Optimized DFN | Exposed pad + low θJC (10°C/W) enables 2.2 A operation at 125°C ambient without heatsink |
| Current-Mode Control | Provides inherent cycle-by-cycle current limiting and fast transient response (<10 µs to 1% regulation) |
| Programmable Switching Frequency | Allows optimization between EMI compliance (lower fSW) and component miniaturization (higher fSW) |
| Power Good Flag with Hysteresis | 10 mV PG hysteresis prevents chatter during marginal output conditions; valid only when VIN > 3.6 V |
| BIAS Pin Efficiency Mode | Draws bias current from VOUT instead of VIN when possible, improving efficiency by up to 3% at VIN = 24 V → 3.3 V |
Applications
| Automotive Battery Regulation | Portable Product Power |
|---|---|
Use Scenario: Regulating 12 V or 24 V vehicle battery to stable 3.3 V or 5 V for infotainment MCU and CAN transceivers. IC Role / Device Role / Timing Role: Primary buck converter delivering clean, ripple-controlled power under cold-crank (4.5 V) and load-dump (36 V transient) conditions. Use Value: Wide 3.6 V–25 V input range and 125°C-rated DFN package ensure uninterrupted operation across automotive temperature and voltage extremes. |
Use Scenario: Powering ARM Cortex-M7 SoC and LPDDR3 memory in handheld medical diagnostic devices. IC Role / Device Role / Timing Role: High-efficiency step-down regulator enabling >8-hour battery life with dynamic voltage scaling support. Use Value: <1 µA shutdown current and BIAS pin architecture extend runtime; 2.8 MHz operation allows use of 1.0 × 1.0 mm inductors for ultra-thin form factor. |
| Distributed Supply Regulation | Industrial Sensor Node Power |
Use Scenario: Generating local 5 V and 3.3 V rails from a 24 V factory bus for PLC I/O modules and fieldbus interfaces. IC Role / Device Role / Timing Role: Point-of-load regulator minimizing IR drop and noise coupling in distributed architectures. Use Value: Integrated power good flag synchronizes downstream enable sequencing; RT-programmable frequency avoids sensitive 2.4 GHz ISM band interference. |
Use Scenario: Providing regulated 3.3 V to low-power wireless sensor nodes (LoRaWAN, NB-IoT) operating from 3.6 V LiSOCl₂ batteries. IC Role / Device Role / Timing Role: Primary DC/DC converter enabling long-term operation with periodic burst transmission. Use Value: 0.18 Ω switch RDS(on) and BIAS pin efficiency mode maximize usable battery energy; soft-start prevents inrush-induced brownout during wake-up. |
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 36 V input rating; synchronous MOSFETs (no external diode); fixed 3.3 V/5 V options only | Better suited for 36 V industrial inputs; lacks adjustable frequency and BIAS pin efficiency mode | Select when input exceeds 25 V or synchronous rectification is mandatory; not pin-compatible |
| TPS54227DDAR | Lower 17 V max input; 2 A max output; integrated high-side FET only (external catch diode required) | Cost-optimized for consumer-grade 12 V systems; no boost diode or BIAS pin | Choose for cost-sensitive, non-automotive designs where 25 V rating and thermal robustness are not required |
Compared with LTC3630EMSE#PBF and TPS54227DDAR, the LT1938IDD#PBF uniquely combines 25 V input tolerance, integrated boost diode, BIAS pin efficiency enhancement, and programmable 300 kHz–2.8 MHz operation in a thermally optimized 3 mm × 3 mm DFN-making it optimal for space-constrained, high-reliability 12 V/24 V embedded systems requiring design flexibility and thermal headroom.
Availability
LT1938IDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable product power, and industrial sensor node applications requiring stable component supply, extended temperature support (–40°C to 125°C), and long-term lifecycle continuity.
Supply support for LT1938IDD#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 ICs, serving precision instrumentation, industrial automation, and automotive markets.
The LT1938IDD#PBF belongs to Linear's legacy high-voltage buck regulator family, designed specifically for rugged, wide-input DC/DC conversion in automotive, industrial, and portable equipment where reliability, thermal performance, and integration density are critical.
FAQ
What is the maximum input voltage supported by the LT1938IDD#PBF?
The LT1938IDD#PBF supports a maximum input voltage of 25 V under normal regulation and pulse-skipping modes. During startup or short-circuit events, the safe maximum input depends on switching frequency and minimum on-time; for example, at 2.8 MHz, VIN must remain below ~18 V to avoid violating tON(MIN) constraints. Absolute maximum rating is 25 V at VIN and 50 V at BOOST.
Does the LT1938IDD#PBF require an external catch diode?
No, the LT1938IDD#PBF does not require an external catch diode. It integrates a boost Schottky diode (BD pin) and uses the BOOST pin to drive the internal bipolar NPN switch. However, an external Schottky diode is still required in the power path (cathode to SW, anode to GND) to provide the freewheeling path during switch-off time.
How is the output voltage programmed on the LT1938IDD#PBF?
The LT1938IDD#PBF output voltage is programmed using a resistor divider from VOUT to GND, with the FB pin connected to the divider midpoint. The feedback reference is 1.265 V, so R1 = R2 × ((VOUT / 1.265) − 1). For example, to set 5.0 V output: R1 = R2 × 2.947. Standard 1% resistors are recommended for accuracy.
What thermal considerations apply to the LT1938IDD#PBF DFN package?
The LT1938IDD#PBF uses a 10-lead 3 mm × 3 mm DFN with exposed pad (Pin 11 = GND). This pad must be soldered to a minimum 100 mm² copper pour on the PCB for effective heat dissipation. With proper layout, θJA drops from 45°C/W to ~35°C/W, enabling 2.2 A continuous output at 125°C ambient. Thermal vias under the pad are strongly recommended.
Can the LT1938IDD#PBF operate in discontinuous conduction mode (DCM)?
Yes, the LT1938IDD#PBF can operate in discontinuous conduction mode, especially at light loads or with higher inductance values. Its current-mode architecture maintains stability in DCM, and frequency foldback helps limit peak current during startup. DCM reduces light-load efficiency but simplifies compensation and eliminates subharmonic oscillation concerns at duty cycles >50%.
LT1938IDD#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:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT1938IDD#PBF FAQ
1.How can I place an order for LT1938IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1938IDD#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 LT1938IDD#PBF reliable?
The price and inventory of LT1938IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1938IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT1938IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1938IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1938IDD#PBF?
LT1938IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1938IDD#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 LT1938IDD#PBF?
For technical support, including LT1938IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1938IDD#PBF requirements.
6.How does Aetrix verify that LT1938IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT1938IDD#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 LT1938IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT1938IDD#PBF?
All LT1938IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1938IDD#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 LT1938IDD#PBF part is unused and in its original packaging.
Return procedure for LT1938IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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