My Inquiry
My Account
Vishay Siliconix SI9121DY-3-T1-E3
- Part No.:
- SI9121DY-3-T1-E3
- Manufacturer:
- Vishay Siliconix
- Category:
- Special Purpose Regulators
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SI9121DY-3-T1-E3.pdf
- Description:
- IC REG CONV ISDN 1OUT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,702
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SI9121DY-3-T1-E3 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 SI9121DY-3-T1-E3 datasheet, SI9121DY-3-T1-E3 pinout, SI9121DY-3-T1-E3 application, or SI9121DY-3-T1-E3 equivalent, this device serves as a single-chip solution for −48 V bus to +3.3 V conversion in telecom terminal equipment-requiring no external shunt regulator, no external start-up circuit, and minimal passive component count.
Technical Context
The SI9121DY-3-T1-E3 implements current-mode PWM control with cycle-by-cycle peak current limiting triggered at 0.67 V on the CS pin. Its integrated floating feedback amplifier directly regulates output voltage referenced to GND while operating from a negative input rail (VNEG), eliminating need for optocouplers or secondary-side sensing.
It includes an internal VCC regulator powered from VNEG, UVLO with 7.6 V turn-on threshold and 0.6 V hysteresis, soft-start via COMP pin charging/discharging, and thermal shutdown at 170 °C with 25 °C hysteresis. The 95 kHz oscillator requires no external timing components.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | +3.3 V ±3.3% (3.17–3.43 V) at 10–250 mA load; enables direct powering of 3.3 V logic in ISDN terminals |
| Input Voltage Range | −10 V to −60 V referenced to GND; supports standard −48 V telecom bus with margin for transients |
| Switching Frequency | 95 kHz nominal (80–110 kHz); balances efficiency, magnetics size, and EMI in compact designs |
| MOSFET rDS(on) | 1.5 Ω typical (2.5 Ω max); enables ≥2 W output power with low conduction loss at full load |
| Current Limit Threshold | 0.67 V on CS pin; sets peak inductor current limit for robust overload and short-circuit handling |
| Efficiency | 73% at 400 mA, VNEG = −48 V; achieves high conversion efficiency without isolation or complex control |
| Operating Temperature | −40 °C to +85 °C junction; qualified for industrial-grade reliability in telecom environments |
Pinout & Package
SI9121DY-3-T1-E3 is housed in an SOIC-8 narrow-body package (JEDEC MS-012), 4.8–5.0 mm × 3.8–4.0 mm footprint, 1.35–1.75 mm height, with gull-wing leads and 1.27 mm pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - CS | Current sense input | Detects inductor current for PWM current-mode control and overcurrent protection; threshold = 0.67 V |
| 2 - VNEG | Negative supply rail | Primary input reference (−10 V to −60 V); all internal circuits referenced to this node |
| 3 - BYPASS | Bandgap reference decoupling | Provides stable +1.5 V reference for oscillator/soft-start; requires 0.1 µF ceramic capacitor to VNEG |
| 4 - COMP | Error amplifier compensation node | External RC network sets loop stability; also used for hiccup-mode discharge during short-circuit recovery |
| 5 - VOUT | Output voltage feedback | Connects to regulated +3.3 V output; internal resistive divider sets feedback ratio for fixed-output operation |
| 6 - GND | System ground reference | Low-impedance 0 V reference for output voltage and logic-level interfaces; separate from VNEG |
| 7 - VCC | Internal bias supply | Internally regulated ~8.5 V supply for gate drive and control logic; bypass with 0.1 µF to VNEG |
| 8 - LX | Switch node | Drain connection of integrated N-MOSFET; connects to inductor and freewheeling diode in buck-boost topology |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 70-V, 1.5-Ω N-MOSFET | Eliminates need for external high-voltage switch; reduces BOM count and layout complexity in −48 V systems |
| Floating feedback amplifier | Enables direct regulation of +3.3 V output referenced to GND while controlling from −48 V rail-no optocoupler required |
| High-voltage start-up circuit | Allows direct bootstrapping from VNEG; removes need for external start-up resistor or auxiliary winding |
| Hiccup-mode short-circuit protection | Automatically cycles on/off during sustained overload, limiting average power dissipation and preventing thermal damage |
| Thermal shutdown with hysteresis | Shuts down at 170 °C junction temperature and re-enables at 145 °C, enabling safe self-recovery in thermally constrained enclosures |
Applications
| ISDN Terminal Power Supply | Digital Phone Base Station |
|---|---|
|
Use Scenario: Converting −48 V telecom central office power to +3.3 V for microcontroller, codec, and interface ICs in desktop ISDN phones. IC Role / Device Role / Timing Role: Primary non-isolated DC-DC converter providing regulated output; replaces discrete MOSFET + controller solutions. Use Value: Reduces component count by integrating MOSFET, error amp, oscillator, and protection-cutting PCB area >40% vs. discrete design. |
Use Scenario: Generating local +3.3 V rail in multi-line ISDN base stations where space and thermal management are critical. IC Role / Device Role / Timing Role: Fixed-output buck-boost regulator operating from shared −48 V backplane; supports parallel outputs via multiple SI9121DY-3 units. Use Value: Delivers 73% efficiency at full 400 mA load without heatsink, enabling fanless operation in sealed enclosures. |
| Telecom Network Interface Unit | Legacy PBX Line Card |
|
Use Scenario: Powering line interface circuits (LICs) and data link controllers in ISDN NT1 devices requiring −48 V input compatibility. IC Role / Device Role / Timing Role: High-reliability DC-DC stage meeting Telcordia GR-63-CORE shock/vibration and thermal cycling requirements. Use Value: Qualified for −40 °C to +85 °C operation with built-in UVLO, thermal shutdown, and hiccup protection-reducing system-level fault testing burden. |
Use Scenario: Retrofitting aging PBX line cards with modern 3.3 V logic while retaining legacy −48 V infrastructure. IC Role / Device Role / Timing Role: Drop-in replacement for obsolete discrete converters; same SOIC-8 footprint and pinout as predecessor designs. Use Value: Enables RoHS-compliant upgrade (E3 suffix) without board redesign-leverages existing magnetics and layout. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck-boost converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX5026ASA+ | Fixed +3.3 V output, −36 V to −72 V input range, 100 kHz switching, integrated 60 V MOSFET (rDS(on) = 2.5 Ω) | Wider input range but lower efficiency (68% @ 400 mA, −48 V); requires external compensation | Preferred when input voltage may exceed −60 V or when higher UVLO threshold is needed |
| TPS54160DGQ | Adjustable output (0.8–28 V), −5.5 V to −60 V input, 100 kHz, integrated 150 V MOSFET (rDS(on) = 0.4 Ω) | Requires external feedback resistors and compensation; no integrated floating error amp-needs optocoupler for isolated feedback | Chosen when output voltage flexibility or higher input transient tolerance is required |
Compared with SI9121DY-3-T1-E3, MAX5026ASA+ offers broader input range but sacrifices efficiency and integration; TPS54160DGQ provides voltage adjustability and higher MOSFET rating but adds design complexity and loses the key floating-feedback advantage for −48 V to +3.3 V conversion.
Availability
SI9121DY-3-T1-E3 is available at Aetrix Electronics and suitable for ISDN terminal power supplies, telecom network interface units, and legacy PBX line card upgrades requiring stable component supply and long-term lifecycle support.
Supply support for SI9121DY-3-T1-E3 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 high-reliability industrial and telecom applications.
The Si9121 product line was developed specifically to simplify −48 V to +3.3 V/+5 V conversion in ISDN and digital telephony equipment-replacing multi-component solutions with a single IC featuring integrated high-voltage switching and floating regulation.
FAQ
What is the maximum output current capability of the SI9121DY-3-T1-E3?
The SI9121DY-3-T1-E3 delivers up to 400 mA continuous output current at +3.3 V when operating from a −48 V input, as verified in the Typical Application Circuit with recommended 68 µH inductor and 220 µF output capacitor. Derating applies at higher ambient temperatures or non-optimal input voltages.
Does the SI9121DY-3-T1-E3 require an external shunt regulator for feedback?
No, the SI9121DY-3-T1-E3 does not require an external shunt regulator. Its integrated floating feedback amplifier directly regulates the +3.3 V output referenced to GND while operating from the −48 V VNEG rail-eliminating optocouplers, TL431s, or other secondary-side regulation components.
Can the SI9121DY-3-T1-E3 operate with an externally supplied VCC?
Yes, the SI9121DY-3-T1-E3 supports external VCC supply between VNEG + 9.5 V and VNEG + 12.0 V. When applied, the internal VCC regulator is disabled. This mode is useful when a clean, low-noise auxiliary supply is available-reducing internal power dissipation and improving PSRR.
What protection features are built into the SI9121DY-3-T1-E3?
The SI9121DY-3-T1-E3 includes under-voltage lockout (UVLO), cycle-by-cycle current limiting, hiccup-mode short-circuit protection, thermal shutdown at 170 °C, and soft-start. These features collectively prevent damage during startup, overload, output short, or overheating-enabling robust unattended operation in telecom equipment.
Is the SI9121DY-3-T1-E3 RoHS-compliant and lead-free?
Yes, the SI9121DY-3-T1-E3 carries the "E3" suffix, indicating Vishay's lead (Pb)-free, RoHS-compliant construction per JEDEC J-STD-609. It uses matte tin (Sn) lead finish and meets IPC/JEDEC J-STD-020 moisture sensitivity level 3 (MSL3) for standard reflow assembly.
SI9121DY-3-T1-E3 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Vishay Siliconix
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Applications:
- Converter, ISDN Power Supplies
- Voltage - Input:
- -10V ~ -60V
- Number of Outputs:
- 1
- Voltage - Output:
- 3V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
SI9121DY-3-T1-E3 FAQ
1.How can I place an order for SI9121DY-3-T1-E3 through Aetrix?
Please submit a Request for Quotation (RFQ) for SI9121DY-3-T1-E3 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 SI9121DY-3-T1-E3 reliable?
The price and inventory of SI9121DY-3-T1-E3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SI9121DY-3-T1-E3 is usually 5 days.
3.What payment methods are accepted for SI9121DY-3-T1-E3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SI9121DY-3-T1-E3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SI9121DY-3-T1-E3?
SI9121DY-3-T1-E3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SI9121DY-3-T1-E3 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 SI9121DY-3-T1-E3?
For technical support, including SI9121DY-3-T1-E3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SI9121DY-3-T1-E3 requirements.
6.How does Aetrix verify that SI9121DY-3-T1-E3 is sourced from the original manufacturer or authorized distributors?
All SI9121DY-3-T1-E3 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 SI9121DY-3-T1-E3 meets industry standards.
7.What is the process for return or replacement of SI9121DY-3-T1-E3?
All SI9121DY-3-T1-E3 units undergo pre-shipment inspection (PSI). If there is an issue with SI9121DY-3-T1-E3, 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 SI9121DY-3-T1-E3 part is unused and in its original packaging.
Return procedure for SI9121DY-3-T1-E3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SI9121DY-3-T1-E3 Tags
-
TPS51206DSQR
Texas Instruments
-
TPS51200DRCR
Texas Instruments
-
TPS51200DRCT
Texas Instruments
-
TPS62740DSSR
Texas Instruments
-
TPS51100DGQR
Texas Instruments
-
NCP51200MNTXG
onsemi
-
NCP51400MNTXG
onsemi
-
RT9026GSP
Richtek USA Inc.
-
LP2998MRX/NOPB
Texas Instruments
-
TPS51200QDRCRQ1
Texas Instruments
-
DPA423GN-TL
Power Integrations
-
LM10011SD/NOPB
Texas Instruments
Tech Hub
Comparator circuit design covering voltage thresholds, input limits, open-collector outputs, LM393 wiring, op-amp differences, hysteresis, timing, window detection and practical fault diagnosis.
Schmitt triggers use separate rising and falling thresholds to stabilize slow or noisy signals. This guide covers hysteresis, 74HC14 and 74HCT14 selection, comparator calculations, RC oscillators and p…
Counterfeit components can hide behind convincing markings and passing basic function tests. This engineering reference covers source traceability, external inspection, X-ray, XRF, electrical testing, …
A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.
TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
