Part A
AD9557BCPZ
Analog Equipment GmbH.
- Lifecycle
- Active
- Stock
- 7455 PCS
- Package
- VFQFN-40
- Series
- Horloge Timing - applications spécifiques
Replacement verdict
Compatible functional replacement candidate
The AD9557BCPZ and AD9551BCPZ are both multi-service clock translators from the same Analog Devices clock generation family, sharing a common functional role and LFCSP package format, but they differ in output configuration, channel count, and integration level. The AD9557BCPZ offers dual differential outputs with an integrated system clock multiplier, while the AD9551BCPZ provides a single differential output with fewer integrated features. Designers should validate output topology, channel requirements, and control interface compatibility before substituting one for the other in a given clock tree.
Output Type
Validation required
Channel Count
Validation required
Package Type
High match
Control Interface
Validation required
Parts at a glance
Part B
AD9551BCPZ
Analog Equipment GmbH.
- Lifecycle
- Active
- Stock
- 4504 PCS
- Package
- VFQFN-40
- Series
- Horloge Timing - générateur d'horloge, PLL, synthétiseur de fréquence
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD9557BCPZ | AD9551BCPZ | Why it matters |
|---|---|---|---|
| Number of Outputs | 2 | 2 | Both devices provide two differential outputs, so output count alone does not differentiate them for substitutability. |
| Output Frequency Range (Max) | 900 MHz | 900 MHz | Maximum output frequency determines the highest clock rate the device can generate for the target system. |
| Input Frequency Range | 2 kHz to 900 MHz | 2 kHz to 200 MHz | A wider input range allows the AD9557 to accept higher-frequency reference clocks, affecting reference compatibility. |
| Jitter (RMS) | 0.4 ps | 0.5 ps | Lower RMS jitter improves signal integrity and is critical for high-speed serial and data converter clocking applications. |
| Supply Voltage | 1.8 V | 3.3 V | Different supply voltages mean the devices are not pin-compatible in power domains and require different board-level regulation. |
| Package | 40-Lead LFCSP | 40-Lead LFCSP | Identical package and footprint support drop-in replacement at the PCB layout level. |
| Operating Temperature Range | -40°C to +85°C | -40°C to +85°C | Matching industrial temperature ranges ensure equivalent environmental robustness for both parts. |
| Control Interface | SPI/I2C | SPI/I2C | Compatible serial control interfaces simplify firmware reuse when evaluating substitution. |
| Number of PLLs | 2 | 1 | The AD9557's dual PLL architecture enables more flexible frequency translation and holdover than the single-PLL AD9551. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD9557BCPZ | AD9551BCPZ |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Part Status | Active | Obsolete |
| Type | - | Clock Generator |
| PLL | Yes | Yes |
| Input | CMOS, LVDS, LVPECL | Crystal |
| Output | CMOS, HSTL, LVDS | CMOS, LVDS, LVPECL |
| Ratio - Input: Output | 2:2 | 2:2 |
| Differential - Input: Output | Yes/Yes | Yes/Yes |
| Frequency - Max | 1.25GHz | 900MHz |
| Divider / Multiplier | - | No/No |
| Voltage - Supply | 1.71V ~ 3.465V | 3.3V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Main Purpose | Ethernet, SONET/SDH | - |
| Number of Circuits | 1 | - |
Frequently asked questions
What are the primary differences between the AD9557BCPZ and AD9551BCPZ?
The AD9557BCPZ is a dual-loop clock translator with two independent PLLs and integrated VCOs, supporting input frequencies up to 900 MHz and output frequencies up to 900 MHz. The AD9551BCPZ is a single-loop clock translator with one PLL and integrated VCO, supporting input frequencies up to 200 MHz and output frequencies up to 900 MHz. The AD9557 offers more flexible multi-input/multi-output clock management, while the AD9551 targets simpler single-reference frequency translation.
Are the AD9557BCPZ and AD9551BCPZ pin-compatible?
No. Both devices are offered in a 40-lead LFCSP (CP-40-1) package, but their pin functions and internal architectures differ. The AD9557BCPZ provides two PLLs with separate reference inputs and output dividers, whereas the AD9551BCPZ provides a single PLL. Pin assignments are not interchangeable, and the PCB layout must follow the respective datasheet pin configurations.
Can the AD9551BCPZ be used as a drop-in replacement for the AD9557BCPZ?
No. Although both are clock translators in the same 40-lead LFCSP package, the AD9551BCPZ has a single PLL and fewer input/output channels than the AD9557BCPZ. A direct substitution would require redesign of the clock tree, reference inputs, and loop filter components, and must be validated against the AD9551BCPZ datasheet for the target frequency plan.
What are the output frequency ranges of the AD9557BCPZ and AD9551BCPZ?
Both devices integrate VCOs that support output frequencies up to 900 MHz. The AD9557BCPZ provides multiple output drivers with programmable dividers for each output, while the AD9551BCPZ provides output dividers for its single PLL path. Exact output frequency plans depend on the selected reference input and divider settings documented in the respective datasheets.
How do the reference input capabilities compare between the AD9557BCPZ and AD9551BCPZ?
The AD9557BCPZ supports multiple reference inputs with automatic and manual switchover, enabling redundant reference clock architectures. The AD9551BCPZ supports a single reference input path. Designs requiring reference redundancy or multi-source clock selection should use the AD9557BCPZ, while single-reference applications can use the AD9551BCPZ.
Do both devices support the same control interface for configuration?
Both the AD9557BCPZ and AD9551BCPZ are configured through a serial control interface (SPI/I2C-compatible) as specified in their respective datasheets. However, the register maps and configuration parameters differ because the AD9557BCPZ contains two PLLs and additional input/output blocks. Configuration scripts and register settings are not transferable between the two devices.
Which device is better suited for redundant reference clock systems?
The AD9557BCPZ is better suited for redundant reference clock systems because it provides multiple reference inputs with automatic switchover between them. The AD9551BCPZ has a single reference input and does not provide built-in reference redundancy. System requirements for holdover, switchover, and multi-reference management should be verified against the AD9557BCPZ datasheet.
Are the AD9557BCPZ and AD9551BCPZ specified for the same operating temperature range?
Both devices are specified for the industrial temperature range of −40°C to +85°C, as stated in their respective datasheets. Designers should still confirm the exact grade and ordering code against the manufacturer's datasheet for the specific application, since performance parameters may vary over temperature.