Diodes Incorporated PI6C557-03BQEX

Overview

PI6C557-03BQEX from Diodes Incorporated is a PCIe 3.0-compliant spread spectrum clock generator with two HCSL differential outputs, 25 MHz crystal input support, selectable output frequencies (25/100/125/200 MHz), and programmable spread (-0.5%, -0.75%, or none). It operates at 3.3 V ±10% across -40°C to +85°C and is used in PC motherboards and embedded PCIe subsystems for EMI reduction.

For engineers reviewing the PI6C557-03BQEX datasheet, PI6C557-03BQEX pinout, PI6C557-03BQEX application, or PI6C557-03BQEX equivalent, key selection criteria include PCIe 3.0 RMS jitter (0.45 ps high-frequency), HCSL current-mode output compliance, external pin-based frequency/spread configuration, and TSSOP/QSOP package compatibility with industrial temperature operation.

Technical Context

The PI6C557-03BQEX implements a proprietary Phase-Locked Loop architecture optimized for PCIe 3.0 timing integrity, accepting only a 25 MHz fundamental-mode crystal or single-ended clock input and generating two independent HCSL differential clock pairs. Its PLL achieves low-jitter synthesis via internal current reference (IREF) and precision resistor biasing (RR = 475 Ω).

Frequency and spread are selected exclusively through four digital control pins (S1/S0 and SS1/SS0), each with internal pull-up resistors-no I²C, SPI, or register programming is supported. Output enable (OE) provides tri-state control of all CLK outputs with 10 µs enable/disable timing.

Key Specifications

Pinout & Package

PI6C557-03BQEX is packaged in a 16-pin QSOP (Q16), 150-mil wide, RoHS-compliant and halogen-free. Pin layout follows standard QSOP footprint with exposed pad not present; thermal resistance θJA = 90°C/W (still air).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PCIe 3.0 clock generator applications.

Compared with IDT8T49N242B and Si53320-B-GM, the PI6C557-03BQEX delivers pin-strapped simplicity, dual configurable outputs, and certified PCIe 3.0 jitter performance in a compact QSOP package - ideal for cost-sensitive, high-volume industrial designs where configuration stability matters more than runtime flexibility.

Availability

PI6C557-03BQEX is available at Aetrix Electronics and suitable for PCIe 3.0 motherboard design, embedded GPU timing, and NVMe storage controller applications requiring stable component supply, long-term industrial temperature support, and RoHS-compliant packaging.

Supply support for PI6C557-03BQEX 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and integrated circuits, specializing in high-performance analog, logic, and timing solutions for computing, industrial, and communications markets.

The PI6C557 product line delivers PCIe-compliant clock generation with spread spectrum capability, designed specifically for EMI reduction in high-speed serial interconnects without compromising jitter performance or design simplicity.

FAQ

What crystal specifications are mandatory for reliable PI6C557-03BQEX operation?

The device requires a 25 MHz fundamental-mode parallel-resonant crystal with load capacitance of 18 pF and frequency tolerance ≤±30 ppm over -40°C to +85°C. Recommended part numbers include FL2500047 (3.2×2.5 mm SMD, ±20 ppm) and FY2500081 (5×3.2 mm SMD, ±30 ppm). Crystal ESR must be <80 Ω, and shunt capacitance should be minimized to ensure stable startup and low jitter.

How is HCSL output termination implemented on the PCB?

HCSL outputs are open-source drivers requiring external series resistors (33 Ω) and ground-return resistors (49.9 Ω) per differential pair, placed adjacent to the PI6C557-03BQEX pins. The IREF pin must connect to a 475 Ω resistor to set 2.32 mA reference current, yielding ~13.9 mA per output leg. Differential routing must follow PCIe Layout Guidelines: L1–L3 non-coupled 50 Ω traces ≤0.5", L4 coupled 100 Ω differential trace 2–16".

Can PI6C557-03BQEX operate with a 25 MHz CMOS clock instead of a crystal?

Yes - the X1/CLK pin accepts either a 25 MHz fundamental crystal (across X1/X2) or a single-ended CMOS clock signal (X2 left unconnected). Input must meet VIH ≥2.0 V and VIL ≤0.8 V, with rise/fall times <5 ns and duty cycle 45–55%. No internal buffering or slew-rate control is provided; external AC coupling and impedance matching are recommended for clock inputs.

What is the functional impact of leaving S1/S0 or SS1/SS0 pins unconnected?

All control pins (S0, S1, SS0, SS1) have internal pull-up resistors, so floating pins default to logic HIGH. With S1=S0=1, output frequency defaults to 200 MHz; with SS1=SS0=1, spread defaults to "No Spread" per Tables 1 and 2. OE also has an internal pull-up, so outputs are enabled by default. No external pull-ups are required unless overriding the default configuration.