PMC-Sierra, Inc. ISSUE OCTOBER 2002 RELEASED 8555 Baxte

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PMC-Sierra, Inc. ISSUE OCTOBER 2002 RELEASED 8555 Baxte

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RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
PMC-Sierra, Inc.
ISSUE OCTOBER 2002
RELEASED
8555 Baxter Place Burnaby, Canada .415.6000
USING EXTERNAL PULL-DOWN RESISTORS WITH TOLERANT 3.3V INPUTS
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Issue
Issue Date December 2001 November 2002
Originator Jeff Brown Bill Richardson
Details Change Document created.
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
Customer Notification
REVISION HISTORY
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
TOLERANT INPUT BEHAVIOR.
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
REFERENCES.
DESIGN GUIDELINE READING "ZERO" TRI-STATE
INTRODUCTION.
CONTENTS
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Device PM4388 (TOCTL) PM6388 (EOCTL) PM5351 (S/UNI Tetra) PM5349 (S/UNI Quad) PM5313 (Spectra-622) PM7346 (QJET) PM7347 (JET) PM7349 (4xD3F) PM7339 (CDB) PM4351 (Comet) PM5356 (S/UNI-622 Max) PM5357 (S/UNI-622POS) PM7351 (S/UNI-VORTEX) PM7350 (S/UNI-DUPLEX)
Tolerant I/Os
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
PM7324 (S/UNI Atlas)
Bi-directional data bus. D[15:0]
Bi-directional data bus. D[7:0]
TABLE
Relevant Device I/Os
These input pins/pads exhibit temporary active pull-up behavior small portion signal transition. only situation where this could have impact circuit design when external pull-down resistor used tri-stated line. This application note describes behavior these input pins/pads provides simple design guidelines considering attaching external pull-down these inputs.
This document relates specific PMC-Sierra devices having 3.3V core voltage tolerant input pins. tolerance allows these 3.3V devices connect legacy devices without requiring external voltage converters. list relevant devices pins provided below. This document applies only connecting these inputs tri-state considering using external pull-down resistors force more lines this zero when tri-stated.
INTRODUCTION
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Figure Current voltage transitions from
These devices have 3.3v core, contain pads designed tolerate inputs connection legacy systems. With these tolerant pads, input voltage transitions between 2.3v 2.8v 2.0ma (Vdd 3.65v, Vbias 3.65v, temperature 85C) current sourced onto pad. time during which this additional current present determined rise fall time transition. other levels there current present. Figures illustrate effects additional current, actual measurements.
Voltage
Vih=2.0v Vil=0.8v
time
Current
Device Driver
Tolerant Current
time
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
case where voltage level driven from (see Figure current from tolerant will added current that driven external device driver. added current will increase slope voltage level. Therefore, this will have significant effect other than slightly improving rise time response.
TOLERANT INPUT BEHAVIOR
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Figure Current voltage transitions from
Voltage
Vih=2.0v
Vil=0.8v
Tolerant Current
Current
TABLE
Table below lists specific condition where extra current affect. other conditions effects negligible. States
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
Note that supply available board, VBIAS tied This will reduce maximum current during transition less than 350uA.
During transition (see Figure internal sources current onto during transition from 2.8v 2.3v levels. source 2.0mA current during this brief period. ensure rapid fall times, output drivers designed sink large currents. output driver external device will typically sink least 20ma 40ma current during "Vdd" "zero" volt transition hence will affected this characteristic.
Device Driver
time
time
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Situation tolerant input driven external device's output
Condition transition
Effect
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
Pads tri-stated with last voltage value
Pads Tristated, with external pull-down resistor
Pads tri-stated with last voltage value
Pads tri-stated with last voltage value
Tri-stated line will stay `1'. Since voltage remains above 2.8V internal active pull-up will have impact. Tri-stated line will stay `0'. Since voltage remains below 2.3V internal active pull-up will have impact. Tri-stated line will pulled down from `0'. internal active pull-up works against external pull-down between 2.8V 2.3V. weak pulldown resistor able pull tri-stated line `0'.
Pads Tristated, with external pull-up resistor
Pads tri-stated with last voltage value
Tri-stated line will pulled `1'. internal active pull-up works with external pull-up while voltage moves between 2.3V 2.8V.
Small amount extra current onto line input during transition 2.8V 2.3V region works against output driver, these drivers able sink much higher levels current.
transition
Small amount extra current onto line input during transition 2.8V 2.3V region works with output driver.
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Buffer
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
pull-down resistor strong enough overcome maximum current that PMC-Sierra device generate worst case conditions) used, recommended VBIAS input tied 3.3v. This resistor would have ohms less, draw undesirable level current. VBIAS input were tied external resistor would 5000 ohms, which tolerable.
PMC-Sierra (e.g. QJET PM7346-BI)
D[7:0]
Figure Buffer added between PMC-Sierra device Micro-controller device
Because characteristics described above, more robust design buffer between PMC-Sierra device external device reading tri-stated bus. This particularly true device reading this example processor) weak internal pull-down (e.g. ohm). Such weak pull-down able pull tri-stated zero operating conditions.
D[7:0]
signals that require specific value during reset idle cycles (when tri-state), external pull-down resistor often used pull zero. example, processor needs read zeros data during reset cycle itself certain state then external pulldown used. Alternatively, processor have this internal pull-down incorporated into data pads.
Micro-controller
DESIGN GUIDELINE READING "ZERO" TRI-STATE
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
PM7346 S/UNI-QJET Long Form Datasheet, PMC-960835, Issue
PM7347 S/UNI J2/E3/T3 (S/UNI-JET) Datasheet, PMC-1990267, Issue
PM4388 TOCTL Datasheet, PMC-1960840, Issue PM6388 EOCTL Datasheet, PMC-1971019, Issue
PM5351 S/UNI-TETRA Long Form Datasheet, PMC-1971240, Issue
PM5313 SPECTRA-622 Telecom Standard Product Datasheet, PMC-1981162, Issue
PM7350 S/UNI-DUPLEX Dual Serial Link Multiplexer Datasheet, PMC-1980581, Issue
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
PM7324 S/UNI-ATLAS Datasheet, PMC-1971154, Issue
PM7351 Octal Serial Link Multiplexer (S/UNI-VORTEX Datasheet, PMC-1980582, Issue
PM5357 S/UNI-622-POS Long Form Datasheet, PMC-1980911, Issue
PM5356 S/UNI-622-MAX Long Form Datasheet, PMC-1980589, Issue
PM4351 Combined E1/T1 Transceiver Standard Product Datasheet, PMC-1970624, Issue
PM5349 S/UNI-QUAD Long Form Datasheet, PMC-1971239, Issue
PM7349 S/UNI-4xD3F Data Sheet, PMC-2000314, Issue
PM7339 S/UNI-CDB Long Form Datasheet, PMC-2000367, Issue
REFERENCES
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
NOTES
PROPRIETARY CONFIDENTIAL PMC-SIERRA, INC., INTERNAL CUSTOMERS
RELEASED APPLICATION NOTE PMC-2012282 ISSUE USING PULL-DOWN RESISTORS
Tel: Fax:
(604) 415-6000
event will PMC-Sierra, Inc. liable direct, indirect, special, incidental consequential damages, including, limited lost profits, lost business lost data resulting from reliance upon information, whether PMC-Sierra, Inc. been advised possibility such damage. 2002 PMC-Sierra, Inc. PMC-2012282 (R2) Issue date: October, 2002
PMC-Sierra, Inc.
None information contained this document constitutes express implied warranty PMC-Sierra, Inc. sufficiency, fitness suitability particular purpose such information fitness, suitability particular purpose, merchantability, performance, compatibility with other parts systems, products PMC-Sierra, Inc., portion thereof, referred this document. PMC-Sierra, Inc. expressly disclaims representations warranties kind regarding contents information, including, limited express implied warranties accuracy, completeness, merchantability, fitness particular use, non-infringement.
8555 Baxter Place Burnaby, Canada .415.6000
Document Information: document@pmc-sierra.com Corporate Information: info@pmc-sierra.com Application Information: apps@pmc-sierra.com Site: http://www.pmc-sierra.com
(604) 415-6200
PMC-Sierra, Inc. 8555 Baxter Place Burnaby, Canada
CONTACTING PMC-SIERRA, INC.

PMC-Sierra, Inc. ISSUE OCTOBER 2002 RELEASED 8555 Baxte

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