My Inquiry
My Account
Vishay Siliconix SI9121DY-5-T1-E3
- Part No.:
- SI9121DY-5-T1-E3
- Manufacturer:
- Vishay Siliconix
- Category:
- Special Purpose Regulators
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SI9121DY-5-T1-E3.pdf
- Description:
- IC REG CONV ISDN 1OUT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,061
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SI9121DY-5-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 integrates a 70-V, 1.5-Ω N-channel MOSFET switch, fixed +5-V output (±4% over load/temperature), current-mode PWM control at 95 kHz, and an internal VCC regulator. It operates from −10 V to −60 V input and delivers up to 400 mA at +5 V.
For engineers reviewing the SI9121DY-5-T1-E3 datasheet, SI9121DY-5-T1-E3 pinout, SI9121DY-5-T1-E3 application, or SI9121DY-5-T1-E3 equivalent, this device serves as a single-chip solution for −48-V bus to +5-V conversion in telecom terminal equipment-requiring no external shunt regulator, no external start-up circuit, and minimal magnetics due to its non-isolated topology.
Technical Context
The SI9121DY-5-T1-E3 implements current-mode PWM control with cycle-by-cycle peak current limiting triggered at 0.67 V on the CS pin. Its floating feedback error amplifier directly regulates output voltage referenced to GND while operating from a negative input rail (VNEG), eliminating need for optocouplers or secondary-side references.
It features integrated soft-start (≈10 ms), under-voltage lockout (7.6 V turn-on threshold with 0.6 V hysteresis), hiccup-mode short-circuit protection, and thermal shutdown at 170 °C. The internal 95-kHz oscillator requires no external timing components, and the VCC regulator supplies bias from VNEG, supporting both internally regulated and externally supplied VCC configurations.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | +5.00 V ±4% (4.80–5.20 V) at 10–250 mA load, referenced to GND |
| Input Voltage Range | −10 V to −60 V referenced to GND; supports standard −48-V telecom bus |
| Switching Frequency | 95 kHz nominal (80–110 kHz); enables compact magnetics and stable PWM operation at low duty cycles |
| MOSFET rDS(on) | 1.5 Ω typical (2.5 Ω max); supports ≥2 W output power with low conduction loss |
| Current Sense Threshold | 0.67 V (typical) on CS pin; sets precise peak inductor current limit for overcurrent protection |
| UVLO Turn-On Threshold | VCC − VNEG = 7.6 V (typical); prevents erratic startup during negative rail ramp-up |
| Operating Temperature | −40 °C to +85 °C junction; qualified for industrial telecom environments |
| Package | SOIC-8 narrow-body (MS-012); 5.0 × 4.0 mm footprint, 100 °C/W θJA |
Pinout & Package
SI9121DY-5-T1-E3 is housed in an 8-pin SOIC narrow-body package (JEDEC MS-012), surface-mount compatible, with 1.27 mm lead pitch. Pin 1 is marked by a beveled corner or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - CS | Current sense input | Detects inductor current via RSENSE; triggers PWM shutdown when voltage exceeds 0.67 V |
| 2 - VNEG | Negative supply rail | Primary input reference (−10 V to −60 V); all internal voltages referenced to this node |
| 3 - BYPASS | Bandgap reference decoupling | Provides stable +1.5 V reference for oscillator/soft-start; requires 0.1 µF ceramic 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 output divider (internal for fixed +5 V); feeds PWM comparator for regulation |
| 6 - GND | System ground reference | 0 V reference for +5 V output; must be low-impedance connection to PCB ground plane |
| 7 - VCC | Internal bias supply | Internally regulated ~8.5 V (7.5–9.5 V); bypass with 0.1 µF to VNEG; disableable with external 9.5–12 V supply |
| 8 - LX | Switch node | Drains integrated N-MOSFET; connects to inductor; handles pulsed current up to 3 A peak |
Key Features
| Feature | Design Value |
|---|---|
| Floating feedback amplifier | Enables direct +5 V regulation referenced to GND without optocoupler or shunt regulator |
| Integrated 70-V, 1.5-Ω N-MOSFET | Eliminates external high-voltage switch and start-up resistor; reduces BOM count and board space |
| High-voltage start-up circuit | Allows direct boot from −48 V bus; no auxiliary winding or external bias supply required |
| Hiccup-mode short-circuit protection | Automatically recovers after fault removal; prevents thermal runaway during sustained overload |
| Thermal shutdown with hysteresis | Shuts down at 170 °C; re-enables at 145 °C; protects against sustained overtemperature conditions |
| Fixed +5-V output with internal resistors | R1/R2 factory-set for 5 V; removes need for external feedback divider and associated layout sensitivity |
Applications
| ISDN Terminal Power Supply | Digital Phone Base Station |
|---|---|
|
Use Scenario: Converting −48 V central office battery feed to regulated +5 V for logic and interface circuitry in ISDN terminal adapters. IC Role / Device Role / Timing Role: Primary non-isolated buck-boost controller; provides system power with integrated switching, regulation, and protection. Use Value: Reduces component count by 6+ parts (shunt regulator, start-up resistor, external MOSFET, feedback divider) versus discrete solutions. |
Use Scenario: Generating local +5 V rail in multi-line digital phone base stations where space and reliability are critical. IC Role / Device Role / Timing Role: Fixed-output DC-DC converter; handles wide input variation (−10 V to −60 V) across battery backup and line-powered modes. Use Value: Maintains 77% efficiency at 400 mA/−48 V input, minimizing heat rise in sealed enclosures. |
| Telecom Network Interface Unit | Legacy PBX Line Card |
|
Use Scenario: Powering line interface circuits (LICs) and microcontrollers in network termination equipment compliant with ITU-T I.430. IC Role / Device Role / Timing Role: High-reliability power source with hiccup-mode protection against cable shorts and surge events. Use Value: Survives continuous short-circuit indefinitely when using recommended 68 µH inductor and 220 µF output capacitor. |
Use Scenario: Replacing aging discrete converters on legacy PBX line cards requiring −48 V to +5 V conversion. IC Role / Device Role / Timing Role: Drop-in upgrade path with identical SOIC-8 footprint and simplified external design. Use Value: Eliminates need for external VCC winding or optocoupler-based feedback, easing redesign and qualification. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar non-isolated buck-boost converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX5026ASA+ | Fixed +5 V output; 76-V MOSFET; 1.2 MHz switching; SO-8 package; no integrated VCC regulator | Requires external start-up circuit and VCC bias; higher frequency enables smaller inductors but increases EMI sensitivity | Prefer when board space is constrained and EMI filtering is already implemented; not suitable for direct −48 V bootstrap |
| TPS54160DGQ | Adjustable output (0.8–28 V); 60-V MOSFET; 100 kHz; 1.5-A current limit; WQFN-10 package | Requires external feedback resistors and VCC bootstrap diode; wider VIN range but lower max input voltage than SI9121DY-5-T1-E3 | Prefer when output voltage flexibility or higher current (>400 mA) is needed; incompatible pinout and layout |
Compared with MAX5026ASA+ and TPS54160DGQ, the SI9121DY-5-T1-E3 uniquely integrates a −48 V start-up circuit, floating feedback amplifier, and fixed +5 V output in SOIC-8-enabling true one-chip ISDN power conversion without auxiliary windings or external regulators.
Availability
SI9121DY-5-T1-E3 is available at Aetrix Electronics and suitable for ISDN terminal equipment, telecom network interface units, digital phone base stations, and legacy PBX line card replacements requiring stable component supply and long-term obsolescence management.
Supply support for SI9121DY-5-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, with emphasis on high-reliability, high-voltage, and thermally robust solutions.
The Si9121 product line was designed specifically for telecom power conversion-addressing the −48 V to +5 V/3.3 V challenge in ISDN and digital telephony equipment with integrated high-voltage control and protection.
FAQ
What is the maximum output current capability of the SI9121DY-5-T1-E3?
The SI9121DY-5-T1-E3 delivers up to 400 mA at +5 V with ≥77% efficiency when operating from −48 V input. This rating assumes use of the recommended 68 µH inductor, 220 µF output capacitor, and proper PCB thermal layout per the datasheet. Peak switch current is limited to 3 A, supporting transient loads within this envelope.
Does the SI9121DY-5-T1-E3 require an external shunt regulator for feedback?
No. The SI9121DY-5-T1-E3 integrates a floating feedback error amplifier that directly regulates the +5 V output referenced to GND, eliminating the need for an external shunt regulator like TL431. This is a core differentiator enabling true one-chip ISDN power conversion.
Can the SI9121DY-5-T1-E3 operate with an externally supplied VCC?
Yes. The SI9121DY-5-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 separate bias supply is available and improves light-load efficiency by reducing internal regulator losses.
What protection features are built into the SI9121DY-5-T1-E3?
The SI9121DY-5-T1-E3 includes under-voltage lockout (UVLO), cycle-by-cycle current limiting, hiccup-mode short-circuit protection, thermal shutdown at 170 °C (with 25 °C hysteresis), and soft-start. These features collectively prevent damage during input transients, output faults, and thermal overload without requiring external supervision circuitry.
Is the SI9121DY-5-T1-E3 still in active production?
No. The SI9121DY-5-T1-E3 reached End of Life with last available purchase date of 31-Dec-2014. However, Aetrix Electronics maintains legacy inventory with full traceability and offers lifecycle support-including cross-reference guidance, obsolescence mitigation planning, and verified second-source alternatives-for ongoing production and repair programs.
SI9121DY-5-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:
- 5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
SI9121DY-5-T1-E3 FAQ
1.How can I place an order for SI9121DY-5-T1-E3 through Aetrix?
Please submit a Request for Quotation (RFQ) for SI9121DY-5-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-5-T1-E3 reliable?
The price and inventory of SI9121DY-5-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-5-T1-E3 is usually 5 days.
3.What payment methods are accepted for SI9121DY-5-T1-E3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SI9121DY-5-T1-E3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SI9121DY-5-T1-E3?
SI9121DY-5-T1-E3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SI9121DY-5-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-5-T1-E3?
For technical support, including SI9121DY-5-T1-E3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SI9121DY-5-T1-E3 requirements.
6.How does Aetrix verify that SI9121DY-5-T1-E3 is sourced from the original manufacturer or authorized distributors?
All SI9121DY-5-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-5-T1-E3 meets industry standards.
7.What is the process for return or replacement of SI9121DY-5-T1-E3?
All SI9121DY-5-T1-E3 units undergo pre-shipment inspection (PSI). If there is an issue with SI9121DY-5-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-5-T1-E3 part is unused and in its original packaging.
Return procedure for SI9121DY-5-T1-E3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SI9121DY-5-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 …
