85311AMLFT - INTEGRATED DEVICE TECHNOLOGY

General Description

The 85311 is a low skew, high performance 1-to-2 Differential-to-

2.5V/3.3V ECL/LVPECL Fanout Buffer and a member of the high

performance clock solutions from IDT. The CLK, nCLK pair can

accept most standard differential input levels. The 85311 is

characterized to operate from either a 2.5V or a 3.3V power supply.

Guaranteed output and part-to-part skew characteristics make the

85311 ideal for those clock distribution applications demanding well

defined performance and repeatability.

Features

•Two differential 2.5V/3.3V LVPECL / ECL outputs

•One CLK, nCLK input pair

•CLK, nCLK pair can accept the following differential input levels:

LVDS, LVPECL, LVHSTL, SSTL, HCSL

•Maximum output frequency: 1GHz

•Translates any single ended input signal to 3.3V LVPECL levels

with resistor bias on nCLK input

•Output skew: 15ps (maximum)

•Part-to-part skew: 100ps (maximum)

•Propagation delay: 1.4ns (maximum)

•Additive phase jitter, RMS: 0.14ps (typical), 3.3V

•LVPECL mode operating voltage supply range: 

VCC = 2.375V to 3.465V, VEE = 0V

•ECL mode operating voltage supply range:

VCC = 0V, VEE = -2.375V to -3.465V

•0°C to 70°C ambient operating temperature

•Available in lead-free (RoHS 6) package

nQ0

nQ1

CLK

nCLK Pullup

Pulldown

VCC

CLK

nCLK

VEE

nQ1

nQ0

85311

8-Lead SOIC

3.90mm x 4.903mm x 1.37mm package body

M Package

Top View

Pin Assignment

Block Diagram

Low Skew, 1-to-2, Differential-to-2.5V, 3.3V

LVPECL/ ECL Fanout Buffer 85311

Datasheet

85311 Data sheet

Pin Descriptions and Pin Characteristic Tables

Table 1. Pin Descriptions

NOTE: Pullup and Pulldown refer to internal input resistors. See Table 2, Pin Characteristics, for typical values.

Table 2. Pin Characteristics

Number Name Type Description

1, 2 Q0, nQ0 Output Differential output pair. LVPECL interface levels.

3, 4 Q1, nQ1 Output Differential output pair. LVPECL interface levels.

EE Power Negative supply pin.

6 nCLK Input Pullup Inverting differential clock input.

7 CLK Input Pulldown Non-inverting differential clock input.

CC Power Positive supply pin.

Symbol Parameter Test Conditions Minimum Typical Maximum Units

CIN Input Capacitance 4pF

RPULLUP Input Pullup Resistor 51 k

RPULLDOWN Input Pulldown Resistor 51 k

85311 Data sheet

Absolute Maximum Ratings

NOTE: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. 

These ratings are stress specifications only. Functional operation of product at these conditions or any conditions beyond 

those listed in the DC Characteristics or AC Characteristics is not implied. Exposure to absolute maximum rating conditions for 

extended periods may affect product reliability.

DC Electrical Characteristics

Table 3A. Power Supply DC Characteristics, VCC = 3.3V±5% or 2.5V±5%, VEE = 0V, TA = 0°C to 70°C

Table 3B. Differential DC Characteristics, VCC = 3.3V±5% or 2.5V±5%, VEE = 0V, TA = 0°C to 70°C

NOTE 1: VIL should not be less than -0.3V.

NOTE 2: Common mode voltage is defined as VIH.

Table 3C. LVPECL DC Characteristics, VCC = 3.3V±5% or 2.5V±5%, VEE = 0V, TA = 0°C to 70°C

NOTE1: Outputs terminated with 50 to VCC – 2V.

Item Rating

Supply Voltage, VCC 4.6V

Inputs, VI-0.5V to VCC + 0.5V

Outputs, IO 

Continuous Current

Surge Current



50mA

100mA

Storage Temperature, TSTG -65C to 150C

Package Thermal Impedance, JA 103C/W (0 lfpm)

Symbol Parameter Test Conditions Minimum Typical Maximum Units

VCC Positive Supply Voltage 3.135 3.3 3.465 V

2.375 2.5 2.625 V

IEE Power Supply Current 25 mA

Symbol Parameter Test Conditions Minimum Typical Maximum Units

IIH Input High Current nCLK VCC = VIN = 3.465V or 2.625V 5 µA

CLK VCC = VIN = 3.465V or 2.625V 150 µA

IIL Input Low Current nCLK VCC = 3.465V or 2.625V, VIN = 0V -150 µA

CLK VCC = 3.465V or 2.625V, VIN = 0V -5 µA

VPP

Peak-to-Peak Input Voltage;

NOTE 1 0.15 1.3 V

VCMR

Common Mode Input Voltage; 

NOTE 1, 2 VEE + 0.5 VCC – 0.85 V

Symbol Parameter Test Conditions Minimum Typical Maximum Units

VOH Output High Current; NOTE 1 VCC – 1.4 VCC – 0.9 V

VOL Output Low Current; NOTE 1 VCC – 2.0 VCC – 1.7 V

VSWING Peak-to-Peak Output Voltage Swing 0.65 1.0 V

85311 Data sheet

AC Electrical Characteristics

Table 4A. AC Characteristics, VCC = 3.3V±5%, VEE = 0V, TA = 0°C to 70°C

NOTE: Electrical parameters are guaranteed over the specified ambient operating temperature range, which is established when device is

mounted in a test socket with maintained transverse airflow greater than 500 lfpm. Device will meet specifications after thermal equilibrium has

been reached under these conditions.

All parameters are measured 500MHz unless otherwise noted.

NOTE 1: Measured from the differential input crossing point to the differential output crossing point.

NOTE 2: Defined as skew between outputs at the same supply voltage and with equal load conditions. Measured at the differential cross

points.

NOTE 3: Defined as skew between outputs on different devices operating at the same supply voltages and with equal load conditions. Using

the same type of inputs on each device, the outputs are measured at the differential cross points.

NOTE 4: This parameter is defined in accordance with JEDEC Standard 65.

Table 4B. AC Characteristics, VCC = 2.5V±5%, VEE = 0V, TA = 0°C to 70°C

See Table 5A for NOTES.

Symbol Parameter Test Conditions Minimum Typical Maximum Units

fMAX Maximum Output Frequency 1GHz

tPD Propagation Delay; NOTE 1 ƒ  1GHz 0.9 1.4 ns

tjit

Buffer Additive Phase Jitter,

RMS; refer to Additive Phase

Jitter Section

156.25MHz, Integration Range

(12kHz – 20MHz) 0.14 ps

tsk(o) Output Skew; NOTE 2, 4 15 ps

tsk(pp) Part-to-Part Skew; NOTE 3, 4 100 ps

tR / tFOutput Rise/Fall Time 20% to 80% @ 50MHz 300 700 ps

odc Output Duty Cycle 48 52 %

Symbol Parameter Test Conditions Minimum Typical Maximum Units

fMAX Maximum Output Frequency 1GHz

tPD Propagation Delay; NOTE 1 ƒ  1GHz 0.9 1.4 ns

tjit

Buffer Additive Phase Jitter,

RMS; refer to Additive Phase

Jitter Section

156.25MHz, Integration Range

(12kHz – 20MHz) 0.135 ps

tsk(o) Output Skew; NOTE 2, 4 15 ps

tsk(pp) Part-to-Part Skew; NOTE 3, 4 100 ps

tR / tFOutput Rise/Fall Time 20% to 80% @ 50MHz 300 700 ps

odc Output Duty Cycle 48 52 %

85311 Data sheet

Additive Phase Jitter (3.3V)

The spectral purity in a band at a specific offset from the fundamental

compared to the power of the fundamental is called the dBc Phase

Noise. This value is normally expressed using a Phase noise plot

and is most often the specified plot in many applications. Phase noise

is defined as the ratio of the noise power present in a 1Hz band at a

specified offset from the fundamental frequency to the power value of

the fundamental. This ratio is expressed in decibels (dBm) or a ratio

of the power in the 1Hz band to the power in the fundamental. When

the required offset is specified, the phase noise is called a dBc value,

which simply means dBm at a specified offset from the fundamental.

By investigating jitter in the frequency domain, we get a better

understanding of its effects on the desired application over the entire

time record of the signal. It is mathematically possible to calculate an

expected bit error rate given a phase noise plot.

As with most timing specifications, phase noise measurements has

issues relating to the limitations of the equipment. Often the noise

floor of the equipment is higher than the noise floor of the device. This

is illustrated above. The device meets the noise floor of what is

shown, but can actually be lower. The phase noise is dependent on

the input source and measurement equipment.

Offset Frequency (Hz)

SSB Phase Noise dBc/Hz

Additive Phase Jitter @ 156.25MHz

12kHz to 20MHz = 0.14ps (typical)

85311 Data sheet

Parameter Measurement Information

3.3V Core/ 3.3V LVPECL Output Load AC Test Circuit

Differential Input Level

Part-to-Part Skew

2.5V Core/ 2.5V LVPECL Output Load AC Test Circuit

Output Skew

Propagation Delay

SCOPE

nQx

VEE

VCC

-1.3V ± 0.165V

VCMR

Cross Points

VPP

VCC

VEE

nCLK

CLK

tsk(pp)

Part 1

Part 2

nQx

nQy

SCOPE

nQx

VEE

VCC

-0.5V ± 0.125V

nQx

nQy

tPD

nCLK

CLK

nQ[0:1]

Q[0:1]

85311 Data sheet

Parameter Measurement Information, continued

Output Duty Cycle/Pulse Width/Period Output Rise/Fall Time

Applications Information

Wiring the Differential Input to Accept Single Ended Levels

Figure 1 shows how the differential input can be wired to accept

single ended levels. The reference voltage V_REF = VCC/2 is

generated by the bias resistors R1, R2 and C1. This bias circuit

should be located as close as possible to the input pin. The ratio of

R1 and R2 might need to be adjusted to position the V_REF in the

center of the input voltage swing. For example, if the input clock

swing is only 2.5V and VCC = 3.3V, V_REF should be 1.25V and

R2/R1 = 0.609.

Figure 1. Single-Ended Signal Driving Differential Input

nQ[0:1]

Q[0:1]

nQ[0:1]

Q[0:1]

V_REF

Single Ended Clock Input

VCC

CLK

nCLK

0.1u R2

85311 Data sheet

Differential Clock Input Interface

The CLK /nCLK accepts LVDS, LVPECL, LVHSTL, SSTL, HCSL

and other differential signals. Both signals must meet the VPP and

VCMR input requirements. Figures 2A to 2F show interface

examples for the CLK/nCLK input driven by the most common

driver types. The input interfaces suggested here are examples

only. Please consult with the vendor of the driver component to

confirm the driver termination requirements. For example, in Figure

2A, the input termination applies for IDT’s open emitter LVHSTL

drivers. If you are using an LVHSTL driver from another vendor,

use their termination recommendation.

Figure 2A. CLK/nCLK Input Driven by an 

IDT Open Emitter LVHSTL Driver

Figure 2C. CLK/nCLK Input Driven by a 

3.3V LVPECL Driver

Figure 2E. CLK/nCLK Input Driven by a 

3.3V HCSL Driver

Figure 2B. CLK/nCLK Input Driven by a 

3.3V LVPECL Driver

Figure 2D. CLK/nCLK Input Driven by a 

3.3V LVDS Driver

Figure 2F. CLK/nCLK Input Driven by a 

2.5V SSTL Driver

50Ω

1.8V

Zo = 50Ω

CLK

nCLK

3.3V

LVHSTL

IDT

LVHSTL Driver

Differential

Input

CSL

Diff

nti

CLK

nCLK

Differential

Input

SSTL

2.5V

Zo = 60Ω

2.5V

3.3V

120Ω

85311 Data sheet

Recommendations for Unused Output Pins

Outputs:

LVPECL Outputs

All unused LVPECL outputs can be left floating. We recommend

that there is no trace attached. Both sides of the differential output

pair should either be left floating or terminated.

Termination for 3.3V LVPECL Outputs

The clock layout topology shown below is a typical termination for

LVPECL outputs. The two different layouts mentioned are

recommended only as guidelines.

FOUT and nFOUT are low impedance follower outputs that

generate ECL/LVPECL compatible outputs. Therefore, terminating

resistors (DC current path to ground) or current sources must be

used for functionality. These outputs are designed to drive 50

transmission lines. Matched impedance techniques should be

used to maximize operating frequency and minimize signal

distortion. Figures 3A and 3B show two different layouts which are

recommended only as guidelines. Other suitable clock layouts may

exist and it would be recommended that the board designers

simulate to guarantee compatibility across all printed circuit and

clock component process variations.

Figure 3A. 3.3V LVPECL Output Termination Figure 3B. 3.3V LVPECL Output Termination

84

3.3V

125

Zo = 50

Zo = 50Input

3.3V

85311 Data sheet

Termination for 2.5V LVPECL Outputs

Figure 4A and Figure 4B show examples of termination for 2.5V

LVPECL driver. These terminations are equivalent to terminating 50

to VCC – 2V. For VCC = 2.5V, the VCC – 2V is very close to ground

level. The R3 in Figure 4B can be eliminated and the termination is

shown in Figure 4C.

Figure 4A. 2.5V LVPECL Driver Termination Example

Figure 4C. 2.5V LVPECL Driver Termination Example

Figure 4B. 2.5V LVPECL Driver Termination Example

2.5V LVPECL Driver

VCC = 2.5V

2.5V

50Ω

250Ω

62.5Ω

–

2.5V LVPECL Driver

VCC = 2.5V

2.5V

50Ω

–

2.5V LVPECL Driver

VCC = 2.5V

2.5V

50Ω

18Ω

–

85311 Data sheet

Power Considerations

This section provides information on power dissipation and junction temperature for the 85311. 

Equations and example calculations are also provided.

1. Power Dissipation.

The total power dissipation for the 85311 is the sum of the core power plus the power dissipated in the load(s). 

The following is the power dissipation for VCC = 3.3V + 5% = 3.465V, which gives worst case results.

NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.

• Power (core)MAX = VCC_MAX * IEE_MAX = 3.465V * 25mA = 86.6mW

• Power (outputs)MAX = 30mW/Loaded Output pair

If all outputs are loaded, the total power is 2 * 30mW = 60mW

Total Power_MAX (3.3V, with all outputs switching) = 86.6mW + 60mW = 146.6mW

2. Junction Temperature.

Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of the device.

The maximum recommended junction temperature for devices is 125°C.

The equation for Tj is as follows: Tj = JA * Pd_total + TA

Tj = Junction Temperature

JA = Junction-to-Ambient Thermal Resistance

Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)

TA = Ambient Temperature

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance JA must be used. Assuming no air flow

and a multi-layer board, the appropriate value is 103°C/W per Table 5 below.

Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:

70°C + 0.147W * 103°C/W = 85.14°C. This is well below the limit of 125°C.

This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow and the type

of board (single layer or multi-layer).

Table 5. Thermal Resistance JA for 8 Lead SOIC, Forced Convection

JA vs. Air Flow

Linear Feet per Minute 0200500

Multi-Layer PCB, JEDEC Standard Test Boards 103°C/W 94°C/W 89°C/W

85311 Data sheet

3. Calculations and Equations.

The purpose of this section is to derive the power dissipated into the load.

LVPECL output driver circuit and termination are shown in Figure 5.

Figure 5. LVPECL Driver Circuit and Termination

To calculate worst case power dissipation into the load, use the following equations which assume a 50 load, and a termination voltage

of VCC – 2V.

• For logic high, VOUT = VOH_MAX = VCC_MAX – 0.9V

(VCC_MAX – VOH_MAX) = 0.9V

• For logic low, VOUT = VOL_MAX = VCC_MAX – 1.7V

(VCC_MAX – VOL_MAX) = 1.7V

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(VOH_MAX – (VCC_MAX – 2V))/RL] * (VCC_MAX – VOH_MAX) = [(2V – (VCC_MAX – VOH_MAX))/RL] * (VCC_MAX – VOH_MAX) =

[(2V – 0.9V)/50] * 0.9V = 19.8mW

Pd_L = [(VOL_MAX – (VCC_MAX – 2V))/RL] * (VCC_MAX – VOL_MAX) = [(2V – (VCC_MAX – VOL_MAX))/RL] * (VCC_MAX – VOL_MAX) =

[(2V – 1.7V)/50] * 1.7V = 10.2mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW

OUT

85311 Data sheet

Reliability Information

Table 6. JA vs. Air Flow Table for a 8 Lead SOIC

Transistor Count

The transistor count for 85311 is: 225

Package Outline and Package Dimensions

Package Outline - M Suffix for 8 Lead SOIC Table 7. Package Dimensions

Reference Document: JEDEC Publication 95, MS-012

JA by Velocity

Linear Feet per Minute 0200500

Multi-Layer PCB, JEDEC Standard Test Boards 103°C/W 94°C/W 89°C/W

150 il (N B d ) SOIC

All Dimensions in Millimeters

Symbol Minimum Maximum

A1.35 1.75

A1 0.10 0.25

B0.33 0.51

C0.19 0.25

D4.80 5.00

E3.80 4.00

e1.27 Basic

H5.80 6.20

h0.25 0.50

L0.40 1.27

0° 8°

85311 Data sheet

Ordering Information

Table 8. Ordering Information

Part/Order Number Marking Package Shipping Packaging Temperature

85311AMLF 85311ALF “Lead-Free” 8 Lead SOIC Tube 0C to 70C

85311AMLFT 85311ALF “Lead-Free” 8 Lead SOIC Tape & Reel 0C to 70C

85311 Data sheet

Revision History Sheet

Rev Table Page Description of Change Date

A 8 Added Termination for LVPECL Outputs section. 5/30/02

3.3V Output Load Test Circuit Diagram - corrected VEE equation to read

-1.3V ± 0.165V from ± 0.135V.

Updated Output Rise/Fall Time Diagram.

9/23/02

Add Lead-Free bullet in Features section.

Pin Characteristics table - changed CIN 4pF max. to 4pF typical.

Absolute Maximum Ratings, updated Outputs rating.

Combined 3.3V & 2.5V Power tables and Differential DC Characteristics tables.

Updated Parameter Measurement Information.

Updated Single Ended Signal Driving Differential Input diagram.

Added Termination for 2.5V LVPECL Output section.

Added Differential Clock Input Interface section.

Ordering Information table - added Lead Free part number.

6/17/04

BT8

Added Recommendations for Unused Input and Output Pins.

Ordering Information Table - corrected Lead-Free marking and added

Lead-Free Note.

7/28/05

T3 3

9 - 10

LVPECL DC Characteristics Table -corrected VOH max. from VCC - 1.0V to VCCO -

0.9V; and VSWING max. from 0.9V to 1.0V.

Power Considerations - corrected power dissipation to reflect VOH max in Table 3C.

4/11/07

T4A - T4B 4

Added 2.5V AC Characteristics Table. Added Additive Phase Jitter spec to both AC

Tables.

Added Additive Phase Jitter plot.

Updated Differential Input Clock Interface section.

10/22/08

DT8 14 Ordering Information - removed leaded devices.

Updated data sheet format. 7/8/15

Power Considerations - updated Junction Temperature section and corrected Table

5, Thermal Resistance Table.

Corrected table.

Ordering Information Table - deleted table note.

Deleted HiperClockS reference throughout the datasheet.

Updated datasheet header/footer.

2/16/16

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this document, including descriptions of product features and performance, is subject to change without notice. Performance specifications and the operating parameters of the described products are determined

in the indepe ndent stat e and are n ot gua rant eed to per form th e same w ay when insta lled i n cu stomer p rodu cts. The info rmati on con tain ed he re in is provi ded with out rep resen tati on or wa rranty o f a ny kin d, w hethe r

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document is presented only as a guide and does not convey any license under intellectual property rights of IDT or any third parties.

IDT’s products are not intended for use in applications involving extreme enviro nmental co nd itions o r in lif e suppo rt systems or similar devices whe re th e fa ilure or malfu ncti o n o f an IDT pr od uct can be reasonab ly

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other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial applications. Any other applications, such as

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