Maxim’s DS1878 is an SFP+ controller with integrated digital LDD interface that can control and monitor all functions of SFF, SFP and SFP+ modules, including all SFF-8472 functions, and supports VCSEL, DFB and EML-based solutions. Operating voltage is +2.85V to +5.5V, mainly used in SFF, SFP and SFP+ transceiver modules. This article introduces the DS1878 main features, block diagram, high frequency optical transceiver reference design HFRD-49.1 main features, reference design HFRD-49.1 and HFRD-30.1 main PCB block diagram, reference design HFRD-49.1 circuit diagram and bill of materials.

DS1878: SFP+ Controller with Digital LDD Interface

The DS1878 controls and monitors all functions for SFF, SFP, and SFP+ modules including all SFF-8472 functionality.

The combination of the DS1878 with Maxim laser driver/limiting amplifier solutions supports VCSEL, DFB, and EML-based solutions. The device provides APC loop, modulation current control, and eye safety functionality. It continuously monitors for high output current, high bias current , and low and high transmit power to ensure that laser shutdown for eye safety requirements are met without adding external components.

Six ADC channels monitor VCC, temperature, and four external monitor inputs (MON1–MON4) that can be used to meet all monitoring requirements.

MON3 is differential with support for common mode to VCC. Two digital-to-analog (DAC) outputs with temperature-indexed lookup tables (LUTs) are available for additional control functionality.

Main features of DS1878:

♦ Meets All SFF-8472 Control and Monitoring Requirements

♦ Laser Bias Controlled by APC Loop and

Temperature LUT to Compensate for Tracking Error

♦ Laser Modulation Controlled by Temperature LUT

♦ Six Analog Monitor Channels: Temperature, VCC, MON1–MON4

MON1–MON4 Support Internal and External Calibration

Scalable Dynamic Range

Internal Direct-to-Digital Temperature Sensor

Alarm and Warning Flags for All Monitored Channels

♦ Two 9-Bit Delta-Sigma Outputs with 36 Entry Temperature LUTs

♦ Digital I/O Pins: Five Inputs, Four Outputs

♦ Comprehensive Fault-Measurement System with Maskable Laser Shutdown Capability

♦ Flexible, Two-Level Password Scheme Provides Three Levels of Security

♦ 256 Additional Bytes Located at A0h Slave Address

♦ I2C-Compatible Interface

♦ 3-Wire Master to Communicate with a Maxim Laser Driver/Limiting Amplifier

♦ +2.85V to +5.5V Operating Voltage Range

♦ -40℃ to +95℃ Operating Temperature Range

♦ 28-Pin TQFN (5mm x 5mm x 0.75mm) Package

DS1878 application:

SFF, SFP, and SFP+ Transceiver Modules

figure 1. DS1878 block diagram

Reference Design HFRD-49.1

High-Frequency Reference Design (HFRD-49.1) is an optical transceiver presented in the SFP+ form factor for demonstrating the operation of Maxim’s MAX3946 laser driver, the MAX3945 limiting amplifier, and the DS1878 controller.

The MAX3946 is optimized to drive a differential transmitter optical subassembly (TOSA), containing a DFB or FP laser, through a 25Ω flex circuit. The unique design of the output stage enables use of unmatched TOSAs, greatly reducing headroom limitations and lowering power consumption.

The MAX3945 limiting amplifier is optimized to provide standards-compliant sensitivity at data rates of either 1.25Gbps or 10.3125Gbps. All differential inputs and outputs (I/Os) are optimally back terminated for 50Ω transmission line circuit board (PCB) design. The The MAX3945’s dualpath limiting amplifier has programmable filtering to optimize sensitivity for different data rates and to suppress relaxation oscillations that could occur in some optical systems. The MAX3945 incorporates two loss-of-signal (LOS) circuits and a programmable time mask for the LOS output.

Maxim’s DS1878 state machine controller provides the 3-wire interface to both the MAX3945 and the MAX3946. Communication with the SFP+ Module is accomplished through the standard MSA I2C interface offered on the DS1878. The DS1878 provides all the necessary diagnostics and register locations to establish SFF -8472 compliance.

figure 2.Reference Design HFRD-49.1 Outline Drawing

The laser driver portion features:

1 Waveform peaking

2 Pulse-width fine adjustment

3 Control of bias and modulation

4 Input equalization

5 Driver back termination

6 Fully differential drive

7 Up to 80mA modulation

8 Fault-detection capability

The limiting amplifier portion features:

1. Adjustable-output CML level

2. Input-bandwidth select feature

3. Output pre-emphasis enable

4. 5mV input sensitivity

5. LOS polarity/squelch

6. Programmable LOS level

image 3.Reference Design HFRD-49.1 Circuit Diagram

Figure 4.Reference Design HFRD-49.1 and HFRD-30.1 Main PCB Block Diagram
Reference Design HFRD-49.1 Bill of Materials (BOM):


Figure 5.Reference Design HFRD-49.1 PCB Component Layout
For details, see:
http://datasheets.maxim-ic.com/en/ds/DS1878.pdf
and
http://pdfserv.maxim-ic.com/en/an/AN4794.pdf