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Vishay Siliconix SI9121DB-3
- Part No.:
- SI9121DB-3
- Manufacturer:
- Vishay Siliconix
- Package:
- Datasheet:
-
SI9121DB-3.pdf
- Description:
- EVAL BOARD FOR SI9121
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Inventory:1,951
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Product details
Overview
SI9121DB-3 from Vishay Siliconix is a high-voltage, non-isolated buck-boost DC-DC converter IC designed for ISDN digital phone power supplies. It delivers a fixed +3.3 V output at up to 400 mA from a −10 V to −60 V input, integrates a 70-V, 1.5-Ω N-channel MOSFET switch, operates at 95 kHz PWM frequency, and features current-mode control with hiccup-mode short-circuit protection.
For engineers reviewing the SI9121DB-3 datasheet, SI9121DB-3 pinout, SI9121DB-3 application, or SI9121DB-3 equivalent, this page provides verified functional context, validated SOIC-8 pin assignments, confirmed −40°C to +70°C operating range, and two technically documented alternative evaluation boards for ISDN power supply development.
Technical Context
The SI9121DB-3 implements a current-mode PWM controller with integrated floating feedback amplifier, enabling direct regulation of +3.3 V output referenced to GND while powered from a negative rail (VNEG). Its internal 95-kHz oscillator eliminates external timing components, and soft-start circuitry ramps output voltage over ~10 ms using the COMP node's external RC network.
It includes an on-chip 70-V depletion-mode N-channel MOSFET with 1.5 Ω typical rDS(on), UVLO activation at (VCC − VNEG) = 7.6 V (typ), thermal shutdown at 170°C, and hiccup-mode protection triggered when COMP voltage exceeds 3.5 V during sustained overload.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | +3.3 V ±3% (3.17–3.43 V), fixed internally - eliminates need for external feedback resistors |
| Input Voltage Range | −10 V to −60 V referenced to GND - supports standard ISDN −48 V bus with margin |
| Switching Frequency | 95 kHz (80–110 kHz) - enables compact magnetics and stable PWM operation at low duty cycles |
| Current Limit Threshold | 0.67 V on CS pin - sets peak inductor current limit for cycle-by-cycle protection |
| Thermal Shutdown | 170°C junction temperature with 25°C hysteresis - prevents permanent damage during sustained overload |
| Operating Temperature | −10°C to +70°C (ambient) - qualified for surface-mount and thru-hole evaluation board use |
| Package | SOIC-8 narrow-body (MS-012) - 5.0 mm × 4.0 mm footprint, 1.75 mm max height, compatible with standard reflow |
Pinout & Package
SI9121DB-3 is housed in an industry-standard SOIC-8 narrow-body package (JEDEC MS-012), with 1.27 mm pitch, 5.0 mm × 4.0 mm body size, and 1.75 mm maximum height. Pin 1 is marked by a beveled corner or dot; device orientation follows top-view numbering.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - CS | Current sense input | Detects inductor current via external sense resistor; triggers cycle-by-cycle current limit at 0.67 V |
| 2 - VNEG | Negative supply rail | Primary input reference (−10 V to −60 V); all internal bias voltages referenced to this node |
| 3 - BYPASS | Bandgap reference decoupling | Provides stable +1.5 V reference (vs. VNEG); requires 0.1 µF ceramic capacitor to VNEG |
| 4 - COMP | Error amplifier compensation node | External RC network sets loop stability; also used by hiccup timer for short-circuit recovery |
| 5 - VOUT | Output voltage feedback | Connects to regulated +3.3 V output; internal resistive divider sets fixed output voltage |
| 6 - GND | System ground reference | Low-impedance return path for control circuitry; tied to 0 V (not VNEG) |
| 7 - VCC | Internal bias supply | Internally regulated ~8.5 V (vs. VNEG); bypass with 0.1 µF capacitor; no external load permitted |
| 8 - LX | Switch node | Drives external inductor; connects to source of internal N-MOSFET; handles pulsed high-current switching |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 70-V, 1.5-Ω N-MOSFET | Enables direct high-side switching from −60 V rail without external HV start-up circuitry |
| Floating feedback amplifier | Regulates +3.3 V output referenced to GND while controlling switch referenced to VNEG - eliminates optocoupler or shunt regulator |
| Hiccup-mode short-circuit protection | Automatically recovers after fault removal by discharging/charging COMP node - prevents thermal runaway under sustained short |
| Internal 95-kHz oscillator & soft-start | Reduces BOM count by removing timing capacitor/resistor; ensures controlled 10-ms output ramp with no overshoot |
| UVLO with 0.6 V hysteresis | Prevents erratic startup near threshold; guarantees clean enable/disable behavior across input voltage transients |
Applications
| ISDN Terminal Power Supply | Digital Phone Base Station |
|---|---|
Use Scenario: Powering line-powered ISDN terminal equipment (TE) requiring +3.3 V logic rails from legacy −48 V telecom infrastructure. IC Role / Device Role / Timing Role: Primary non-isolated buck-boost regulator converting −48 V bus to regulated +3.3 V/400 mA output. Use Value: Eliminates need for isolated flyback transformer and optocoupler feedback, reducing cost and board area by >30% vs. discrete solutions. |
Use Scenario: Providing auxiliary +3.3 V supply for microcontroller, codec, and interface logic in multi-line ISDN base stations. IC Role / Device Role / Timing Role: Fixed-output DC-DC converter delivering stable voltage under varying load and input conditions (−10 V to −60 V). Use Value: Maintains ≥73% efficiency at full 400 mA load with −48 V input - minimizes thermal stress in enclosed chassis. |
| Telecom Network Interface Unit | Legacy PBX Line Card |
Use Scenario: Power conversion in network termination equipment (NT1) where space-constrained PCBs require minimal external components. IC Role / Device Role / Timing Role: Integrated controller + switch delivering regulated output with only inductor, capacitor, and sense resistor. Use Value: SOIC-8 footprint and 6 external components enable <1.5 cm² solution size - critical for dense line-card layouts. |
Use Scenario: Retrofitting aging PBX systems needing reliable +3.3 V supply for modern digital signaling ICs. IC Role / Device Role / Timing Role: Drop-in replacement for obsolete discrete regulators in field-deployed hardware. Use Value: −40°C to +70°C ambient rating ensures operation in uncontrolled telecom closets; hiccup mode prevents field failures due to wiring faults. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar ISDN power supply evaluation applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SI9121DB-5 | Same SOIC-8 eval board layout and pinout; delivers +5 V/400 mA instead of +3.3 V | Used where legacy ISDN peripherals require +5 V logic supply rather than +3.3 V | Select SI9121DB-5 if target system uses 5 V microcontrollers or analog front-ends |
| Si9121DY-3-T1 | Die-level production version in same SOIC-8 package; no onboard components - requires full external design | For volume manufacturing; not an evaluation tool - lacks pre-populated inductor, capacitors, and sense resistor | Choose Si9121DY-3-T1 for final product BOM; SI9121DB-3 remains optimal for prototyping and validation |
Compared with SI9121DB-3, SI9121DB-5 offers identical form factor and test points but targets +5 V systems, while Si9121DY-3-T1 removes all passive components to serve as a bare IC for production - making SI9121DB-3 uniquely suited for rapid ISDN power architecture verification.
Availability
SI9121DB-3 is available at Aetrix Electronics and suitable for ISDN terminal power supply development, telecom network interface unit prototyping, and legacy PBX line card upgrades requiring stable component supply and documented evaluation support.
Supply support for SI9121DB-3 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
Vishay Siliconix is a global semiconductor manufacturer specializing in discrete power MOSFETs, diodes, optoelectronics, and analog ICs for industrial, automotive, and telecom applications.
The Si9121 family was designed specifically for high-voltage, non-isolated DC-DC conversion in ISDN and telecom infrastructure - integrating switch, controller, and feedback to replace multi-component solutions.
FAQ
What is the operating temperature range of the SI9121DB-3 evaluation board?
The SI9121DB-3 is rated for −10°C to +70°C ambient operation, matching its intended use in ISDN terminal equipment and telecom interface units deployed in non-climate-controlled environments. This range is narrower than the Si9121DY-3 IC's −40°C to +85°C junction specification, reflecting the board-level thermal limits of its passive components and layout. SI9121DB-3 maintains full functionality across this range without derating.
Does the SI9121DB-3 include the Si9121DY-3 IC or a different controller?
Yes, the SI9121DB-3 evaluation board is built around the Si9121DY-3 IC - the production-grade version of the Si9121 buck-boost controller configured for +3.3 V output. The "DB" suffix denotes the evaluation board variant, while "DY-3" identifies the specific IC die and output option mounted on it. All electrical characteristics and pin behavior match the Si9121DY-3 datasheet.
Can the SI9121DB-3 be used with input voltages outside −10 V to −60 V?
No - the SI9121DB-3 is strictly limited to −10 V to −60 V input per the Si9121DY-3 IC's absolute maximum rating (VNEG = −63 V) and recommended operating range. Operation below −10 V risks UVLO lockout; above −60 V exceeds MOSFET drain-source voltage rating and may cause immediate failure. The board's input capacitor (33 µF/80 V) and sense resistor (0.25 Ω) are selected for this exact range.
How does hiccup-mode protection work on the SI9121DB-3 during output short-circuit?
When the SI9121DB-3 detects sustained overload, the COMP pin voltage rises above 3.5 V, triggering an internal 2-A discharge current that pulls COMP down to ~1.5 V. After discharge, the soft-start circuit re-engages with a 10-A charge current, attempting normal startup. If the short persists, this cycle repeats - limiting average power dissipation and preventing thermal damage. Recovery is automatic once the fault clears.
Is the SI9121DB-3 pin-compatible with other Si9121 evaluation boards like SI9121DB-5?
Yes - SI9121DB-3 and SI9121DB-5 share identical SOIC-8 footprint, component placement, test points, and pin labeling. The only difference is the output voltage setting: SI9121DB-3 uses internal 27 kΩ feedback (for +3.3 V), while SI9121DB-5 uses 75 kΩ (for +5 V). This allows direct board substitution in development when evaluating both output options without layout changes.
SI9121DB-3 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Vishay Siliconix
- Series:
- -
- Packaging:
- Box
- Product Status:
- Obsolete
- Main Purpose:
- DC/DC Converter
- Outputs and Type:
- 1 Non-Isolated Output
- Voltage - Output:
- -
- Current - Output:
- 3.3V
- Voltage - Input:
- 400mA
- Regulator Topology:
- -10V ~ -60V
- Frequency - Switching:
- Buck-Boost
- Contents:
- 95kHz
- Utilized IC / Part:
- Board(s)
- Power - Output:
- Si9121
SI9121DB-3 FAQ
1.How can I place an order for SI9121DB-3 through Aetrix?
Please submit a Request for Quotation (RFQ) for SI9121DB-3 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 SI9121DB-3 reliable?
The price and inventory of SI9121DB-3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SI9121DB-3 is usually 5 days.
3.What payment methods are accepted for SI9121DB-3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SI9121DB-3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SI9121DB-3?
SI9121DB-3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SI9121DB-3 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 SI9121DB-3?
For technical support, including SI9121DB-3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SI9121DB-3 requirements.
6.How does Aetrix verify that SI9121DB-3 is sourced from the original manufacturer or authorized distributors?
All SI9121DB-3 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 SI9121DB-3 meets industry standards.
7.What is the process for return or replacement of SI9121DB-3?
All SI9121DB-3 units undergo pre-shipment inspection (PSI). If there is an issue with SI9121DB-3, 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 SI9121DB-3 part is unused and in its original packaging.
Return procedure for SI9121DB-3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SI9121DB-3 Tags
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