Skyworks Solutions Inc. SI5351C-A-GT

Overview

SI5351C-A-GT from Silicon Labs is an I²C-programmable, 8-output CMOS clock generator with external reference synchronization (CLKIN), PLL/VCXO-based synthesis architecture, 8 kHz–160 MHz output frequency range, 0 ppm synthesis error, and independent 1.8/2.5/3.3 V output supply rails. It replaces crystals, XO, VCXO, and PLLs in video timing, networking, and embedded systems requiring multiple synchronous clocks.

For engineers reviewing the SI5351C-A-GT datasheet, SI5351C-A-GT pinout, SI5351C-A-GT application, or SI5351C-A-GT equivalent, this page delivers verified electrical specs, package mapping to 24-QSOP and 20-QFN, confirmed CLKIN-synchronized operation, real-world jitter values (35–100 ps pk-pk period jitter), and validated alternatives for multi-clock domain designs.

Technical Context

The SI5351C-A-GT uses dual PLL architecture (PLLA and PLLB) with CLKIN as primary reference input (10–100 MHz), enabling fully synchronous clock generation across all eight outputs. Its MultiSynth fractional dividers provide exact-frequency synthesis without integer constraints, supporting non-integer-related frequencies per output.

It implements a dedicated input stage routing CLKIN to both PLLs, while omitting internal VCXO circuitry (distinguishing it from Si5351B). Output stage includes R-divider for sub-MHz clocks down to 8 kHz, programmable rise/fall time control, and glitchless frequency switching via I²C register updates.

Key Specifications

Pinout & Package

SI5351C-A-GT is available in two RoHS-compliant packages: 24-pin QSOP (body size 8.65 × 3.90 mm) and 20-pin QFN (4 × 4 mm, 0.5 mm pitch), both supporting full 8-output functionality and identical pin mapping per Silicon Labs datasheet Rev. 0.95 Sections 11 and 15.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I²C-programmable clock generator applications.

Compared with SI5351C-A-GT, Si5351A-A-GT offers lower BOM cost but no synchronization; Si5351B-A-GT provides analog tuning flexibility but lacks CLKIN-driven deterministic phase alignment - making SI5351C-A-GT the sole choice for externally referenced, multi-domain coherent timing.

Availability

SI5351C-A-GT is available at Aetrix Electronics and suitable for HDMI timing, residential gateway clocking, audio/video equipment, networking switch fabric, and SerDes reference applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for SI5351C-A-GT 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

Silicon Labs is a fabless semiconductor company specializing in timing, wireless, and MCU solutions, with deep expertise in precision clock generation and RF integration.

The Si5351 family was designed to replace discrete timing components in cost-sensitive, space-constrained consumer and communications equipment - delivering programmable flexibility without sacrificing jitter performance or power efficiency.

FAQ

What is the maximum input frequency supported by the CLKIN pin on the SI5351C-A-GT?

The SI5351C-A-GT CLKIN pin accepts an external reference clock from 10 MHz to 100 MHz, as specified in Table 4 of the preliminary datasheet Rev. 0.95. This range enables direct interfacing with common system oscillators, Ethernet PHY references, and recovered clock signals without prescaling. The SI5351C-A-GT uses this input to lock both PLLA and PLLB for fully synchronous multi-output generation.

Does the SI5351C-A-GT support spread spectrum clocking, and on which outputs?

Yes, the SI5351C-A-GT supports spread spectrum clocking exclusively on outputs sourced from PLLA, with configurable down-spread (–0.1% to –2.5%) or center-spread (±0.1% to ±1.5%) modulation at 31.5 kHz. Outputs derived from PLLB or CLKIN-synchronized paths do not support spread spectrum. This feature is controlled per-output via I²C register writes and helps reduce EMI peaks in noise-sensitive applications like HDMI and USB.

Can the SI5351C-A-GT generate sub-1 MHz clock frequencies, and how is this achieved?

Yes, the SI5351C-A-GT can generate clock frequencies as low as 8 kHz using the programmable R-divider at the output stage. Each output bank (CLK0–CLK1, CLK2–CLK3, etc.) has an independent R-divider (2ⁿ, n = 1–7) that divides the MultiSynth output frequency. This allows precise low-frequency generation - such as audio sample rates (44.1 kHz, 48 kHz) or watchdog timers - without requiring external dividers or additional ICs.

What are the valid supply voltage options for the output drivers of the SI5351C-A-GT?

The SI5351C-A-GT supports three independent output supply voltages per bank: 1.8 V (1.71–1.89 V), 2.5 V (2.25–2.75 V), and 3.3 V (3.0–3.6 V). These are applied to VDDOA through VDDOD pins, enabling direct interfacing with mixed-voltage SoCs, FPGAs, and PHYs. Core VDD operates separately at 2.25–3.6 V, and both rails must be powered simultaneously per power sequencing requirements.

Is the SI5351C-A-GT pin-compatible with other variants in the Si5351 family?

No, the SI5351C-A-GT is not pin-compatible with Si5351A-A-GT or Si5351B-A-GT in the same package - although mechanical footprint is identical, the functional pin assignments differ. Specifically, SI5351C-A-GT uses INTR and CLKIN, whereas Si5351A omits INTR and uses SSEN, and Si5351B replaces CLKIN with VC. PCB layout must match the specific variant's pinout per datasheet Sections 9–11.