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STMicroelectronics L7985A
- Part No.:
- L7985A
- Manufacturer:
- STMicroelectronics
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
L7985A.pdf
- Description:
- IC REG BUCK ADJ 2A 8HSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,114
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Product details
Overview
L7985A from STMicroelectronics is a 2 A step-down switching regulator with integrated P-channel MOSFET, designed for mid-power DC-DC conversion in space-constrained industrial and consumer systems. It operates from 4.5 V to 38 V input, delivers adjustable output down to 0.6 V, features 250 kHz–1 MHz programmable switching frequency, internal soft-start, and supports zero-load operation - used in FPGA power supplies, LCD TV main rails, and XDSL line cards.
For engineers reviewing the L7985A datasheet, L7985A pinout, L7985A application, or L7985A equivalent, key selection criteria include input voltage range (4.5–38 V), output current capability (2 A continuous), thermal resistance (HSOP8: 40 °C/W), synchronization capability via SYNCH pin, and voltage-mode control architecture with feed-forward compensation.
Technical Context
The L7985A implements voltage-mode PWM control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage and frequency feed-forward to maintain constant loop gain across input voltage and switching frequency variations. Its error amplifier features 100 dB DC gain, 4.5 MHz GBWP, and rail-to-rail COMP output swing (0–3.3 V).
Synchronization is achieved through the bidirectional SYNCH pin: when floating, it outputs a 180° phase-shifted clock; when driven externally, it locks the device to an external frequency with zero phase shift. Overcurrent protection uses blanking-time–gated peak-current sensing with pulse-skipping down to 1/8 nominal frequency under sustained overload.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output current | 2 A continuous load current - determined by thermal limits and MOSFET RDS(on) (max 400 mΩ) under real PCB layout conditions. |
| Input voltage range | 4.5 V to 38 V - supports wide-input industrial rails including 12 V, 24 V, and 36 V battery/supply systems. |
| Output voltage range | 0.6 V to VIN - enables direct low-voltage core supply (e.g., 1.2 V FPGA I/O, 1.8 V memory) using external resistor divider on FB pin. |
| Switching frequency | 250 kHz (default) to 1 MHz - adjustable via resistor on FSW pin; higher frequencies reduce inductor size but increase switching losses. |
| Feedback reference | 0.6 V ±1.8% (0.582–0.618 V) - sets regulation accuracy and defines minimum output voltage without external divider. |
| Thermal resistance | HSOP8: 40 °C/W; VFDFPN10: 60 °C/W - measured on demo board; dictates maximum power dissipation before thermal shutdown at 150 °C. |
| Enable threshold | EN high = ≥1.2 V; EN low = ≤0.3 V - TTL/CMOS-compatible logic interface with internal pull-down for safe default-off behavior. |
Pinout & Package
Available in two thermally optimized packages: HSOP8 (exposed pad, 40 °C/W) and VFDFPN10 (3 × 3 mm, 60 °C/W). Both support high-current routing and require proper thermal pad soldering per ST's AN4180 guidelines.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| OUT | Power output node | Connects directly to LC filter output; carries full 2 A switched current - requires low-inductance path to minimize ringing. |
| EN | Enable control input | Active-high logic input; floats to OFF state via internal pull-down - enables system-level power sequencing and standby mode. |
| FB | Feedback sense input | High-impedance node referenced to 0.6 V internal bandgap - sets output voltage via resistor divider; sensitive to noise coupling. |
| COMP | Error amplifier output | Drives external Type II/III compensation network - source/sink capability (19 mA/30 mA) supports stable loop design up to 1 MHz. |
| FSW | Frequency set input | Resistor-to-ground sets oscillator frequency (250 kHz–1 MHz); floating = default 250 kHz - enables EMI optimization via spread-spectrum tuning. |
| SYNCH | Master/slave sync I/O | Bidirectional pin: outputs 180° phase-shifted clock when floating; accepts external clock for multi-phase synchronization - reduces input capacitor RMS current. |
| GND | Power and signal ground | Common return for power stage, control circuitry, and feedback - must be tied to thermal pad and kept separate from noisy analog ground paths. |
| VCC | Unregulated input supply | Primary power input (4.5–38 V); powers internal bias circuitry and gate driver - requires local 10 µF ceramic bypass near pin. |
Key Features
| Feature | Design Value |
|---|---|
| Voltage feed-forward | Adjusts sawtooth slope in real time to maintain constant PWM gain across input voltage changes - improves line transient response without loop redesign. |
| Programmable soft-start | Staircase ramp (64 steps × 9.5 mV) with frequency-dependent duration (e.g., 8.2 ms @ 250 kHz) - prevents inrush current and ensures monotonic VOUT rise. |
| Pulse-skipping overcurrent protection | Reduces effective switching frequency to 1/8 nominal under overload - maintains regulated current limit (2.5 A min) while avoiding thermal runaway during short-circuit. |
| Hysteretic thermal shutdown | Shuts down at 150 °C junction temperature; restarts at ~120 °C - fast, localized detection near P-MOSFET die area ensures reliable long-term reliability. |
| Zero-load operation | Operates stably with no output load - enables always-on auxiliary rails and low-power standby modes without burst-mode instability or audible noise. |
Applications
| PLD/FPGA Core Supply | Car Audio Power Rail |
|---|---|
|
Use Scenario: Providing clean, adjustable 1.2 V or 1.8 V to Xilinx Spartan or Intel MAX 10 FPGA core logic under varying load transients. IC Role / Device Role / Timing Role: Primary buck regulator delivering regulated core voltage; handles >1 A step-load changes within 10 µs via feed-forward-enhanced loop response. Use Value: Eliminates need for external controller + MOSFET discrete solution - reduces BOM count and layout area while maintaining <±2% output regulation. |
Use Scenario: Generating stable 5 V or 12 V rail for digital signal processors and DACs in automotive head units operating from 9–16 V battery input. IC Role / Device Role / Timing Role: Mid-power DC-DC converter with wide VIN tolerance and thermal robustness - sustains operation during cold-crank (6.5 V) and load-dump (38 V) events. Use Value: Internal 38 V max rating and 40 °C/W HSOP8 thermal resistance enable direct connection to unregulated vehicle battery without pre-regulator stage. |
| XDSL Line Card Power | LCD TV Main 12 V Rail |
|
Use Scenario: Powering ADSL2+ PHY and microcontroller subsystems in telecom line cards requiring 3.3 V at 1.5 A with low EMI. IC Role / Device Role / Timing Role: Synchronized buck converter - multiple L7985A devices phase-shifted via SYNCH pins to reduce input capacitor ripple current by >40%. Use Value: Phase synchronization capability cuts RMS input current stress, allowing smaller 105 °C X7R ceramics instead of bulk aluminum electrolytics. |
Use Scenario: Delivering 12 V/2 A to LED backlight drivers and TCON logic in 32–55 inch LCD TVs powered from 24 V open-frame SMPS. IC Role / Device Role / Timing Role: Secondary buck stage converting 24 V intermediate bus to precise 12 V output - leverages adjustable VREF and low dropout (100% duty cycle) for efficiency at light loads. Use Value: 100% duty-cycle operation enables seamless transition to dropout during brownout, preserving display functionality down to 12.5 V input. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM5164QWRXMRQ1 | 40 V input, 0.6 A output, current-mode control, integrated N-MOSFET - lower current, higher VIN, different control architecture. | Automotive-qualified (AEC-Q100), suited for infotainment MCU supplies; lacks SYNCH and zero-load operation. | Select for automotive environments requiring qualification; avoid where >1.5 A or synchronization is required. |
| MP2451DT-LF-Z | 36 V input, 0.6 A output, 2 MHz fixed frequency, current-mode - smaller package, lower current, no soft-start adjustment or feed-forward. | Cost-sensitive consumer applications (DVD players, monitors); limited thermal margin and no multi-phase sync capability. | Choose for compact, low-cost designs below 0.6 A; not suitable for FPGA or XDSL where current and thermal performance are critical. |
Compared with LM5164QWRXMRQ1 and MP2451DT-LF-Z, the L7985A uniquely combines 2 A output, 38 V input, voltage-mode feed-forward, and multi-device synchronization - making it optimal for industrial and telecom applications demanding higher current, thermal resilience, and coordinated power delivery.
Availability
L7985A is available at Aetrix Electronics and suitable for FPGA power supplies, car audio systems, XDSL line cards, and LCD TV main rails requiring stable component supply across extended temperature and voltage ranges.
Supply support for L7985A 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.
The L7985A belongs to ST's high-voltage buck regulator product line, engineered for robust, integrated DC-DC conversion in systems with wide input ranges and demanding thermal constraints - targeting space- and reliability-critical applications.
FAQ
What is the minimum output voltage achievable with the L7985A?
The L7985A has an internal 0.6 V feedback reference voltage with ±1.8% tolerance (0.582–0.618 V). With the FB pin connected directly to VOUT, the regulator delivers exactly this reference voltage. No lower output is possible without external circuitry, as the error amplifier is not designed for sub-0.6 V regulation.
Can the L7985A operate in dropout mode?
Yes - the L7985A supports 100% duty cycle operation, enabling dropout mode when VIN approaches VOUT. In this condition, the internal P-MOSFET remains fully enhanced, minimizing conduction loss and sustaining regulation down to VIN = VOUT + VDS(on) × ILOAD, typically within 100 mV at light loads.
How does the SYNCH pin function when connecting two L7985A devices?
When SYNCH pins of two L7985A devices are wired together, the unit with the higher free-running frequency becomes the master and drives the other as slave with 180° phase shift. This interleaving halves input capacitor RMS current - verified in ST application note AN4180 using HSOP8 evaluation boards.
Is external compensation mandatory for stable operation?
Yes - the COMP pin requires an external Type II or Type III compensation network depending on output capacitor ESR. ST provides design equations and Bode plot guidance in Section 6.4 of the datasheet (DocID022446 Rev 8); omitting compensation causes oscillation or poor transient response, especially above 500 kHz switching frequency.
L7985A Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width) 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):
- 4.5V
- Voltage - Input (Max):
- 38V
- Voltage - Output (Min/Fixed):
- 0.6V
- Voltage - Output (Max):
- 38V
- Current - Output:
- 2A
- Frequency - Switching:
- 250kHz ~ 1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-HSOP
L7985A FAQ
1.How can I place an order for L7985A through Aetrix?
Please submit a Request for Quotation (RFQ) for L7985A 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 L7985A reliable?
The price and inventory of L7985A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L7985A is usually 5 days.
3.What payment methods are accepted for L7985A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L7985A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for L7985A?
L7985A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your L7985A 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 L7985A?
For technical support, including L7985A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L7985A requirements.
6.How does Aetrix verify that L7985A is sourced from the original manufacturer or authorized distributors?
All L7985A 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 L7985A meets industry standards.
7.What is the process for return or replacement of L7985A?
All L7985A units undergo pre-shipment inspection (PSI). If there is an issue with L7985A, 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 L7985A part is unused and in its original packaging.
Return procedure for L7985A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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