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Semtech Corporation ACS1790IMLT
- Part No.:
- ACS1790IMLT
- Manufacturer:
- Semtech Corporation
- Package:
- 24-VFQFN Exposed Pad
- Datasheet:
-
ACS1790IMLT.pdf
- Description:
- IC FREQ SYNTH 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,377
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Product details
Overview
ACS1790IMLT from Semtech is a programmable PLL frequency synthesizer with integrated VCO, designed for precision clock generation in Synchronous Ethernet and telecom systems. It delivers dual-output clocks (LVPECL OUT1P/OUT1N at 10–200 MHz; LVCMOS OUT2 at 2 kHz–125 MHz), features ultra-fine 1 ppb frequency resolution, <0.29 ps RMS jitter (4–80 MHz) for 10G Ethernet, and operates from 3.0–3.6 V.
For engineers reviewing the ACS1790IMLT datasheet, pinout, applications, or equivalent options, this page provides verified technical context, I²C-programmable operation details, differential LVPECL output stage design considerations, and validated alternatives for Synchronous Ethernet timing subsystems.
Technical Context
The ACS1790IMLT implements a fully self-contained VCO-based PLL with fractional-N feedback division, supporting VCO tuning from 2.3–2.7 GHz and enabling sub-ppb output frequency accuracy. Its architecture includes independent O-, B-, P-, and T-dividers to route and scale the VCO output to three distinct clock domains: high-speed LVPECL (OUT1), low-speed LVCMOS (OUT2), and feedback LVCMOS (FBCLK).
Operation relies on an external reference clock (10/12.8/20/25 MHz), with internal R-divider bypass or ÷2 configuration determining the PFD frequency (10 or 12.5/12.8 MHz). Lock detection (LD) is provided as open-drain output, and calibration enables ±500 ppm fine-tuning without relock after initial VCO centering at 2.5 GHz.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCO Frequency Range | 2.3–2.7 GHz - defines fundamental synthesis range; enables wide output coverage via integer/fractional division |
| OUT1 Output Type | LVPECL differential (OUT1P/OUT1N) - requires AC-coupled 50 Ω termination per IEEE Std 1149.1; supports 10–200 MHz |
| OUT2 Output Type | LVCMOS single-ended - configurable 1.8/2.5/3.3 V supply (VDDD2); supports 2 kHz–125 MHz with slew-rate control |
| RMS Jitter (10G Ethernet) | 0.29 ps (4–80 MHz band) - meets IEEE 802.3-2008 Clause 53/54 mask for 10GBase-R physical layer timing |
| I²C Interface | Standard-mode (100 kHz) with 4 selectable slave addresses (A0/A1 pins) - allows multi-device bus sharing without address conflict |
| Reference Spurs | < –67 dBc - ensures clean spectral purity critical for SONET/SDH OC-48 and STM-16 compliance |
| Operating Temperature | –40°C to +85°C - qualified for industrial-grade telecom infrastructure deployment |
Pinout & Package
The ACS1790IMLT is housed in a 4 × 4 mm QFN-24 package with exposed thermal pad (connected to GND). Pin 25 is the center ground contact; all power/ground pins are segregated by domain (VDDA/VSSA analog, VDDF/VSSF RF, VDDD/VSSD digital logic, VDDD2/VSSD2 OUT2 buffer).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RESETB | Active-low asynchronous reset | Forces device into known state; resets register contents and disables outputs until deasserted |
| CLK | Reference clock input | Accepts 10/12.8/20/25 MHz CMOS-level signal; drives internal R-divider and PFD |
| OUT1P / OUT1N | Differential LVPECL clock output | High-speed primary output; requires 50 Ω termination to VCC–2 V; supports 10–200 MHz |
| OUT2 | Single-ended LVCMOS clock output | Configurable voltage rail (VDDD2); supports low-frequency system clocks and synchronization signals |
| FBCLK | Feedback clock output | LVCMOS 3.3 V output for connection to ToPSync® or external PFD; divided from VCO via T-divider |
| LD | Lock detect indicator | Open-drain output pulled low during calibration/unlocked state; released high when VCO achieves phase lock |
| OEB | Output enable control | Active-low hardware disable for both OUT1 and OUT2; complements software-controlled output gating |
| SCL / SDA | I²C serial interface | Standard bidirectional bus; requires external pull-ups; supports register read/write and status polling |
Key Features
| Feature | Design Value |
|---|---|
| Integrated VCO + PFD + loop filter | Eliminates external loop components and VCO tuning varactors; reduces BOM count and layout sensitivity |
| ±500 ppm post-calibration tuning | Enables dynamic frequency adjustment (e.g., for wander compensation or holdover drift correction) without full recalibration cycle |
| Dual-domain power supplies | Separate VDDA/VSSA (analog), VDDF/VSSF (RF), VDDD/VSSD (logic), and VDDD2/VSSD2 (OUT2 buffer) minimize cross-domain noise coupling |
| Hardware + software output enable | OEB pin and register-controlled gating allow flexible power sequencing and fail-safe clock shutdown |
| Four I²C slave addresses | A0/A1 pin strapping supports up to four ACS1790IMLT devices on one I²C bus-critical for multi-port SyncE line cards |
Applications
| Synchronous Ethernet Line Card | SONET/SDH OC-48 Timing Module |
|---|---|
Use Scenario: Generating synchronized 155.52 MHz and 125 MHz transmit clocks across multiple Ethernet PHYs in a carrier-grade switch. IC Role / Device Role / Timing Role: Primary clock synthesizer providing phase-aligned, low-jitter outputs locked to ToPSync®-derived reference. Use Value: Meets ITU-T G.8262 EEC-2 mask with 0.56 ps RMS jitter (12 kHz–20 MHz), eliminating need for discrete jitter cleaners. | Use Scenario: Replacing legacy discrete PLL designs in OC-48 line interface units requiring ANSI T1.105.03-compliant timing. IC Role / Device Role / Timing Role: Standalone frequency synthesizer generating 155.52 MHz and 622.08 MHz (via OUT1 ÷2) from 12.8 MHz reference. Use Value: Integrated VCO and fractional-N divider achieve <–67 dBc reference spurs-exceeding SONET OC-48 spectral purity requirements. |
| Gigabit Ethernet PHY Clocking | 10GBase-R Reference Generation |
Use Scenario: Providing 125 MHz LVPECL clock to multiple Gigabit Ethernet MAC/PHY chips on a server NIC. IC Role / Device Role / Timing Role: Low-jitter clock source meeting IEEE 802.3-2008 Clause 38/39 jitter limits (0.15 ps RMS, 637 kHz–20 MHz). Use Value: Single-chip solution eliminates external crystal oscillator + PLL IC + buffer chain-reducing board area by >40%. | Use Scenario: Generating precise 156.25 MHz or 155.52 MHz reference for 10GBase-R SerDes in optical transport equipment. IC Role / Device Role / Timing Role: High-resolution synthesizer delivering 1 ppb step size and 0.29 ps RMS jitter (4–80 MHz) for 10GBase-R physical layer. Use Value: Enables direct synthesis without multiplication stages-reducing phase noise accumulation and simplifying layout. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PLL frequency synthesizer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| Si5338A-D-GM | Quad-output, I²C-programmable; wider output range (0.16–350 MHz); no integrated VCO (requires external XO/VCXO) | Requires external crystal; better suited for multi-protocol clock trees with mixed voltage outputs | Select when needing >2 outputs or flexible input reference options beyond 10/12.8/20/25 MHz |
| LTC6946IUH-3#PBF | Integer-N PLL with integrated VCO (1.39–2.95 GHz); lower jitter (0.11 ps RMS for 10G); no FBCLK output or ToPSync® interface support | Optimized for RF/data converter clocking-not designed for SyncE/SONET compliance testing or feedback-loop integration | Select when ultra-low jitter is prioritized over telecom standards compliance and external PLL feedback capability |
Compared with Si5338A-D-GM and LTC6946IUH-3#PBF, the ACS1790IMLT uniquely integrates FBCLK output and ToPSync®-ready architecture for Synchronous Ethernet holdover and re-lock scenarios, while maintaining sub-0.3 ps RMS jitter and ±500 ppm tunability without recalibration-making it purpose-built for carrier-class timing subsystems.
Availability
ACS1790IMLT is available at Aetrix Electronics and suitable for Synchronous Ethernet line cards, SONET/SDH timing modules, Gigabit Ethernet PHY clocking, and 10GBase-R reference generation requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.
Supply support for ACS1790IMLT 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
Semtech Corporation is a U.S.-based semiconductor company specializing in high-performance analog and mixed-signal ICs for communications, enterprise computing, and industrial markets.
The ACS1790IMLT belongs to Semtech's Advanced Communications Product Group and was engineered specifically for Synchronous Ethernet, SONET, and SDH infrastructure-delivering integrated PLL+VCO timing solutions that reduce system complexity and meet stringent telecom jitter and phase noise standards.
FAQ
What is the default output frequency configuration of the ACS1790IMLT at power-up?
At power-up, the ACS1790IMLT defaults to either 25 MHz and 125 MHz or 25 MHz and 156.25 MHz outputs, depending on OSCFSEL0 and OSCFSEL1 pin states. These selections are hardwired via external resistors and determine initial clock frequencies before I²C programming. The ACS1790IMLT does not require firmware load to produce valid clocks-enabling fast system boot and fallback timing.
Does the ACS1790IMLT support both LVPECL and LVCMOS outputs simultaneously?
Yes, the ACS1790IMLT supports concurrent LVPECL (OUT1P/OUT1N) and LVCMOS (OUT2) outputs. OUT1 operates at 10–200 MHz with differential signaling, while OUT2 delivers 2 kHz–125 MHz single-ended clocks. Both outputs are independently enabled/disabled via OEB pin or register control, and OUT2's voltage level is set by VDDD2 supply (1.8/2.5/3.3 V), allowing mixed-voltage system interfacing without level shifters.
How does the ACS1790IMLT achieve ±500 ppm frequency tuning without recalibration?
The ACS1790IMLT performs an initial VCO calibration at power-up or reset, centering the VCO at 2.5 GHz. Once calibrated, the device allows software-adjusted frequency shifts of ±500 ppm (±1.25 MHz) around that center point using fractional-N divider settings-without triggering a new calibration cycle. This enables real-time wander compensation and holdover drift correction in SyncE systems while maintaining lock integrity.
What is the function of the FBCLK output on the ACS1790IMLT, and how is it used?
The FBCLK output on the ACS1790IMLT is a dedicated LVCMOS 3.3 V feedback clock generated from the VCO via the T-divider. It is designed to connect directly to the reference input of a ToPSync® device or external phase-frequency detector in hybrid PLL architectures. This enables the ACS1790IMLT to serve as the controllable oscillator element in higher-level synchronization loops-essential for Synchronous Ethernet boundary clocks and grandmaster timing applications.
Is the ACS1790IMLT pin-compatible with other Semtech timing devices like the ACS1791 or ACS1792?
No, the ACS1790IMLT is not pin-compatible with the ACS1791 or ACS1792. While all belong to the same ACS179x family and share the QFN-24 package, pin assignments differ significantly-for example, ACS1791 relocates FBCLK and adds additional control pins. Board-level replacement requires PCB redesign. Always verify pin mapping against the specific device's datasheet; the ACS1790IMLT's pinout is fixed per Table 1 in its Revision 1.0 datasheet.
ACS1790IMLT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Semtech Corporation
- Series:
- -
- Package/Case:
- 24-VFQFN Exposed Pad
- Packaging:
- Tray
- Product Status:
- Obsolete
- Programmable:
- Not Verified
- Type:
- Frequency Synthesizer (RF)
- PLL:
- Yes with Bypass
- Input:
- Clock
- Output:
- LVCMOS, LVPECL
- Number of Circuits:
- 1
- Ratio - Input:Output:
- 1:2
- Differential - Input:Output:
- No/Yes
- Frequency - Max:
- 2.7GHz
- Divider/Multiplier:
- Yes/No
- Voltage - Supply:
- 1.8V, 2.5V, 3.3V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 24-QFN (4x4)
ACS1790IMLT FAQ
1.How can I place an order for ACS1790IMLT through Aetrix?
Please submit a Request for Quotation (RFQ) for ACS1790IMLT 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 ACS1790IMLT reliable?
The price and inventory of ACS1790IMLT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ACS1790IMLT is usually 5 days.
3.What payment methods are accepted for ACS1790IMLT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ACS1790IMLT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for ACS1790IMLT?
ACS1790IMLT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your ACS1790IMLT 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 ACS1790IMLT?
For technical support, including ACS1790IMLT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ACS1790IMLT requirements.
6.How does Aetrix verify that ACS1790IMLT is sourced from the original manufacturer or authorized distributors?
All ACS1790IMLT 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 ACS1790IMLT meets industry standards.
7.What is the process for return or replacement of ACS1790IMLT?
All ACS1790IMLT units undergo pre-shipment inspection (PSI). If there is an issue with ACS1790IMLT, 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 ACS1790IMLT part is unused and in its original packaging.
Return procedure for ACS1790IMLT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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