SY88982L - Electronic component Microchip - Free user manual and instructions

USER MANUAL SY88982L Microchip

3.3V, 2.7Gbps High-Current, Low-Power Laser Driver for FP/DFB Lasers

General Description

The SY88982L is a single 3.3V supply, low power consumption, small form factor driver for telecom/datacom applications using FP/DFB lasers at data rates up to 2.7Gbps. The driver can deliver modulation current up to 90mA, and the high compliance voltage if offers, makes the part suitable for high-current operation (with the laser AC- or DC-coupled to it). This device is intended to be used with Micrel's MIC3003 Optical Transceiver Management IC, which allows for both modulation and bias current control and monitoring, automatic power control, and temperature compensation.

All support documentation can be found on Micrel's web site at: www.micrel.com.

Features

• 2.4V minimum laser compliance voltage for high-current DC-coupled applications
  • 48mA power supply current typical
  • Operation up to 2.7Gbps
  • Modulation current up to 90mA
• Designed for use with the MIC3003
• Laser may be DC- or AC-coupled
• Small form factor 16-pin (3mm x 3mm) QFN package

Applications

• Multi-rate LAN, MAN applications up to 2.7Gbps: FC, GbE, SONET OC3/12/24/48 and SDH STM1/4/8/16
• SFF, SFP modules

Markets

- Telecom, Datacom

Typical Application

SY88912L +3.3V -3.3V +3.3V DATA GND IN JIN GND EN M_SET REF GND +3.3V To VBIAS L To FB/VMPD MIC3001 +3.3V +3.3V Serial interface to computer microcontroller DATA TXDISABLE VDDO NC GND0 RSIN VIN CLK DATA TXDISABLE TPFALLT XPN VDDA VDDA VLD+ VLD+ VLD- +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V

Laser DC-Coupled to the Driver

+3.3V MCD- +3.3V MCD- MDD+ MDD- TL +3.3V LD PD To VBIAS To FBVMPD To VILD+

Laser AC-Coupled to the Driver

Functional Block Diagram

VCC DIN+ 50Ω DIN- Input Buffer 50Ω VREF /EN Pre-Driver MOD+ MOD- GND

Ordering Information ^(1)

Part Number	Package Type	Operating Range	Package Marking	Lead Finish
SY88982LMG	QFN-16	Industrial	982L with Pb-Free bar-line indicator	NiPdAu Pb-Free
SY88982LMGTR(2)	QFN-16	Industrial	982L with Pb-Free bar-line indicator	NiPdAu Pb-Free

Notes:
1. Contact factory for die availability. Dice are guaranteed at T_A = +25^ , DC Electricals only.
2. Tape and Reel.

Pin Configuration

/EN IM_SET VREF GND 16 15 14 13 GND 1 12 MOD+ DIN- 2 11 MOD+ DIN- 3 10 MOD- GND 4 9 MOD- 5 6 7 8 VCC VCC GND GND

16-Pin QFN

Pin Description

Pin Number	Pin Name	Pin Function
1, 4, 7, 8, 13	GND	Ground. Ground and exposed pad must be connected to the plane of the most negative potential.
2 DIN+		Non-Inverting Input Data. Internally terminated with 50Ω to a reference voltage.
3 DIN-		Inverting Input Data. Internally terminated with 50Ω to a reference voltage.
5, 6	VCC	Supply Voltage. Bypass with a 0.1μF//0.01μF low ESR capacitor as close to VCC pin as possible.
9, 10	MOD-	Inverted Modulation Current Output. Provides modulation current when input data is negative.
11, 12	MOD+	Non-Inverted Modulation Current Output. Provides modulation current when input data is positive.
14	VREF	Reference Voltage. Install a 0.1μF capacitor between VREF and VCC.
15	IM_SET	Modulation current setting and control. The voltage applied to this pin will set the modulation current. To be connected to the MIC3003 pin 24 (VMOD+). Input impedance 25kΩ.
16	/EN	A high level signal applied to this pin will disable the output stage of the driver. Internally pulled down with 25kΩ resistor.

Truth Table

DIN+	DIN-	/EN	MOD_+^(1)	MOD-	Laser Output^(2)
L	H	L	H	L	L
H	L	L	L	H	H
X	X	H	H	H	L

Notes:
1. I_MOD = 0 when MOD_+ = H .
2. Assuming that the laser is tied to MOD+.

Absolute Maximum Ratings ^(1)

Supply Voltage ( V_IN ) -0.5V to +4.0V

CML Input Voltage ( V_IN ) ...... V_CC-1.2V to V_CC+0.5V

TTL Control Input Voltage ( V_IN ) 0V to V_CC

Lead Temperature (soldering, 20sec.) .....+260°C

Storage Temperature ( T_s )....-65°C to +150°C

Operating Ratings ^(2)

Supply Voltage (Vcc)....+3.0V to +3.6V

Ambient Temperature ( T_A )....-40°C to +85°C

Package Thermal Resistance ^(3) QFN

(θ JA) Still-air 60°C/W

(ψ JB) 33°C/W

DC Electrical Characteristics

T_A = -40^ to 85^ and V_CC = +3.0V to +3.6V , unless otherwise noted. Typical values are V_CC = +3.3V , T_A = 25^ , I_MOD = 60mA .

Symbol	Parameter	Condition	Min	Typ	Max	Units
I_CC	Power Supply Current	Modulation current excluded		48	65^(4)	mA
V_MOD\_MIN	Minimum Voltage Required at the Driver Output (headroom) for Proper Operation		0.6			V
R_IN(DATA)	Input Resistance (DIN+, DIN-)		45	50	55	Ω
V_ID	Differential Input Voltage Swing		200		2400	mV_PP
/EN Low					0.8	V
/EN High			2			V
R_IN (IMOD\_SET)	I_M\_SET Input Resistance			25		kΩ
V_IM\_SET	Voltage Range on I_M\_SET Pin	I_MOD range 10mA – 90mA			1.2	V

AC Electrical Characteristics

T_A = -40^ to 85^ and V_CC = +3.0V to +3.6V , unless otherwise noted. Typical values are V_CC = +3.3V , T_A = 25^ , I_MOD = 60mA .

Symbol	Parameter	Condition	Min	Typ	Max	Units
	Data Rate	NRZ	0.155		2.7	Gbps
I_MOD	Modulation Current(5)	AC-coupled	10		90	mA
		DC-coupled	10		70(6)	mA
I_MOD\_OFF	Modulation OFF Current	Current at MOD+ when the device is disabled.			750	μA
t_r	Output Current Rise Time	20% to 80%, I_MOD = 60mA, 15Ω load		55	80	ps
t_f	Output Current Fall Time	20% to 80%, I_MOD = 60mA, 15Ω load		55	80	ps
	Total Jitter	@2.5Gbps data rate			20	p_SPP
	Pulse-Width Distortion	I_MOD range 10mA – 90mA			20	ps

Notes:

1. Permanent device damage may occur if absolute maximum ratings are exceeded. This is a stress rating only and functional operation is not implied at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum ratings conditions for extended periods may affect device reliability.
2. The data sheet limits are not guaranteed if the device is operated beyond the operating ratings.
3. Package Thermal Resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB. _JB uses a 4-layer and _JA in still air unless otherwise stated.
4. I_CC = 48mA for worst-case conditions with I_MOD = 90mA , T_A = +85^ , V_CC = 3.6 .
5. Load = 15Ω.
6. Assuming VCC = 3.0V, Laser bandgap voltage = 1V, laser package inductance = 1nH, laser equivalent series resistor = 5Ω, and damping resistor = 10Ω.

Typical Operating Characteristics

Test Circuit

SY88982L MOD- MOD- MOD+ MOD+ +3.3V 22Ω Z0 = 50Ω +3.3V 22Ω Z0 = 50Ω 50Ω 50Ω

Functional Characteristics

Electrical Eye Diagram
2.5Gbps, PRBS 2 ^23 -1, 15Ω Load, 60mA Modulation

Abstract waveforms on grid background, no text or symbols present

TIME (66ps/div.)

Optical Eye Diagram
2.7Gbps, PRBS 2 ^23 -1, Laser AC-Coupled

10% 20.0% Measure Mask

TIME (66ps/div.)
ER = 10dB, 30% Mask Margin

Optical Eye Diagram
2.5Gbps, PRBS 2 ^23 -1, Laser DC-Coupled

20.0 % Measure Mask

TIME (65ps/div.)
ER = 11dB, 30% Mask Margin

Optical Eye Diagram with OC-48 Filter
1.25Gbps, PRBS 2 ^23 -1, Laser DC-Coupled

80.0% 20.0% 1 Measure Mask

TIME (133ps/div.)
ER = 11dB, 55% Mask Margin

Optical Eye Diagram
622Mbps, PRBS 2 ^23 -1, Laser DC-Coupled

0.0% 20.0% Measure Mask

TIME (267ps/div.)
ER = 11.3dB, 60% Mask Margin

Optical Eye Diagram
155Mbps, PRBS 2 ^23 -1, Laser DC-Coupled

0.0% 20.6% Measure Mask

TIME (1075ps/div.)
ER = 11.3dB, 60% Mask Margin

Input and Output Stages

VCC IN 50Ω VREF 50Ω /IN +3.3V GND

Figure 1a. Simplified Input Stage

MOD+ MOD- GND

Figure 1b. Simplified Output Stage

Interfacing the Input to Different Logic Drivers

LVPEC1 GND 50Ω IN 50Ω /IN +3.3V 0.1μF VREF 50Ω GND SY88982L

Figure 2a. DC-Coupling to LVPECL Driver

LVPECL Rpd GND 50Ω IN 50Ω /IN +3.3V 0.1μF VREF Note: Rpd = 140Ω to 220Ω. SY88982L

Figure 2b. AC-Coupling to LVPECL Driver

CML 50Ω IN 50Ω /IN +3.3V 0.1μF SY88982L VREF

Figure 2c. AC-Coupling to CML Driver

LVDS +3.3V 0.1μF IN 50Ω 50Ω /IN SY88962L VREF

Figure 2d. AC-Coupling to LVDS Driver

Application Information

The typical applications diagram on the first page shows how to connect the driver to the laser, single ended. To improve transition time and laser response, the laser can be driven differentially as shown in Figures 3 and 4. Driving the laser differentially will also minimize the crosstalk with the rest of the circuitry on the board, especially the receiver.

DC-Coupling

In addition to the low power consumption and high modulation current, the SY88982L offers a high compliance voltage. As can be seen in the "Typical Operating Characteristics" section ( I_MOD vs. V_MOD curves), the minimum voltage needed at the output of the driver for proper operation is less than 600mV, leaving a large headroom, V_CC-600mV , to the laser with the damping resistor. To show the importance of this high compliance voltage, consider the voltage drops along the path from V_CC to ground through the laser, damping resistor, and driver:

$$ V _ {C C} = \text { Driver Headroom } + V _ {R d} + V _ {\text { laser }} $$

$$ V _ {R d} = R d \times I _ {M O D} $$

$$ V _ {\text { laser }} = V _ {\text { band - gap }} + R _ {\text { laser }} \times I _ {\text { MOD }} + L d i / d t $$

$$ \begin{array}{l} \mathrm {V_ {band - gap} + R_ {laser} \times I_ {MOD} = 1.6V at maximum for} \ \text { a Fabry Perrot or a DFB laser. } \end{array} $$

Ldi/dt is the voltage drop due to the laser parasitic inductance during I_MOD transitions. Assuming L = 1nH, t_f = t_f = 80ps (measured between 20% and 80% of I_MOD ), and I_MOD = 70mA (42mA from 20% to 80%), then Ldi/dt will be equal to 525mV. This number can be minimized by making the laser leads as short as possible and using and RC compensation network between the cathode of the laser and ground or across the laser driver outputs as shown in Figure 3.

To be able to drive the laser DC-coupled with a high current, it is necessary to keep the damping resistor as small as possible. For example, if the drop due to parasitic inductance of the laser is neglected (compensated for) and the maximum drop across the laser (1.6V) considered while keeping a minimum of 600mV headroom for the driver, then the maximum damping resistor that allows a 70mA modulation current into the laser is:

$$ R _ {d m a x} = (V _ {C C} - 0. 6 V - 1. 6 V) / 0. 0 7 A $$

The worst case will be with V_cc = 3.0V , leading to R_dmax = 11.4

On the other hand, the small is the value of R_d , the higher is the overshoot/undershoot on the optical signal from the laser. In the circuit shown in Figure 3, the RC compensation network across the driver outputs (MOD+ and MOD-) allows the user R_d = 10 . The optical eye diagrams at data rates of 155Mbps/622Mbps/1.25Gbps/2.5Gbps, shown in "Functional Characteristics" section, are all obtained with the same circuit using R_d = 10 , R_Comp = 100 , and C_Comp = 3pF . The compensation network may change from one board to another and from one type of laser to another. An additional compensation network (RC) can be added at the laser cathode for further compensation and eye smoothing.

SY88982L MOD- MOD- MOD+ MOD+ Rd CComp RComp Rd LD PD +3.3V L = Murata BLM18HG102SN R C L Bias to APC

Figure 3. Laser DC-Coupled

AC-Coupling

When trying to AC couple the laser to the driver, the headroom of the driver is no longer a problem since it is DC isolated from the laser with the coupling capacitor. At the output, the headroom of the driver is determined by the pull-up network. In Figure 4, the modulation current out of the driver is split between the pull-up network and the laser. If, for example, the total pull-up resistor is twice the sum of the damping resistor and laser equivalent series resistance, only two thirds (2/3) of the modulation current will be used by the laser. So, to keep most of the modulation current going through the laser, the total pull-up resistor must be kept as high as possible. One solution consists in using an inductor alone as pull-up, presenting a high impedance path for the modulation current and zero ohm (0Ω) path for the DC current offering a headroom of the driver equal to Vcc and almost all the modulation current goes into the laser. The inductor alone will cause signal distortion, and, to improve that, a combination of resistors and inductors can be used (as shown on Figure 4). In this case, the headroom of the driver is Vcc-R1 x αlMOD, where αlMOD is the portion of the modulation current that goes through the pull-up network.

When the laser is AC-coupled to the driver, the coupling capacitor creates a low-frequency cutoff in the circuit, and its value must be chosen as large as

possible. If the value of the cap is too high, it will slow down the fast signals edges, and, if its value is too small, it won't be able to hold a constant change between the first bit and the last bit of a long string of identical bits in a low data rate application. This leads to higher pattern-dependent jitter in the transmitter signal. 0.1μF is found to be good for all applications from 155Mbps to 2.7Gbps.

AC-coupling the laser to the driver brings a solution to the driver headroom problem at the expense of extra components, loss of part of the modulation current wasted in the pull-up network, and additional power consumption.

SY88982L L = Murata BLM18HG102SN +3.3V R2 R1 Rd +3.3V L MOD- MOD- MOD+ MOD+ R1 Rd LD PD R C L Bias to APC R2 +3.3V

Figure 4. Laser AC-Coupled

Package Information

Pin 1 Dot By Marking 3.000±0.050 3.000±0.050

TOP VIEW

PIN #1 IDENTIFICATION CHAMFER 0.300 X 45° 1.550±0.050 Exp. DAP 0.400±0.050 1.550±0.050 Exp. DAP 0.500 Bsc 0.230±0.050 0.400±0.050 1.500 Ref.

BOTTOM VIEW

0.850±0.050 0.000-0.050 0.203±0.025

SIDE VIEW

NOTE:

1. ALL DIMENSIONS ARE IN MILLIMETERS.
2. MAX. PACKAGE WARPAGE IS 0.05 nm.
3. MAXIMUM ALLOWABE BURRS IS 0.076 nm IN ALL DIRECTIONS
4. PIN #1 ID ON TOP WILL BE LASER/INK MARKED.

16-Pin (3mm x 3mm) QFN

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