LTM2884 datasheet(13/24 Pages) LINER

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LTM2884

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TheLTM2884µModuletransceiverprovidesagalvanically

isolated robust USB interface, powered by an integrated,

regulated DC/DC converter, complete with decoupling

capacitors. This flexible device can support a variety of

USB configurations, either bus powered or externally

powered. Applications include isolation in hosts, hubs,

peripherals, or standalone inline bus splitters. Automati-

callyconfiguredpull-upresistorsareincludedtorepresent

the condition of the isolated downstream USB bus to the

upstream USB bus. The LTM2884 is ideal for use in USB

connections where grounds between upstream hub/host

and downstream devices can take on different voltages.

Isolation in the LTM2884 blocks high voltage differences

and eliminates ground loops and is extremely tolerant of

commonmodetransientsbetweengroundpotentials.Error

freeoperationismaintainedthroughcommonmodeevents

exceeding 30kV/µs providing excellent noise isolation.

The LTM2884 contains a fully integrated DC/DC converter

including the transformer, so that no external components

are necessary in many configurations. The upstream side

containsaflybackconverterthatregulatesthedownstream

output voltage through primary sensing techniques. The

internal power solution is sufficient to support the trans-

ceiver interface and supply up to 500mA at 5V through

VCC2toanattacheddevicedependentonthesupplyvoltage

and available current on VCC.

The integrated USB transceivers on both sides of the iso-

lation barrier support full and low speed modes defined in

theUSB2.0specification.Thecommunicationthroughthe

isolation barrier for USB is bidirectional and as such the

LTM2884 determines data flow direction based on which

side a start of packet (SOP) begins first. The direction of

data is maintained until an end of packet (EOP) pattern

is observed or a timeout occurs due to a lack of activity.

The USB interface maintains a consistent propagation

delay representative of a hub delay and transfers all data.

Pull-up resistors integrated in the upstream interface

automatically indicate device connections and discon-

nections. A downstream device connection automatically

selects the proper pull-up resistor at the upstream facing

port after sensing the idle state of the downstream device

atconnectiontime.Disconnectionofadownstreamdevice

automaticallyreleasesthepull-upresistorontheupstream

facing port allowing the upstream 15k pull-down resistors

to pull the bus signals to a disconnect condition. This func-

tion makes the LTM2884 ideal for host, hub, bus splitter,

or peripheral device integration.

Isolator µModule Technology

The LTM2884 utilizes isolator µModule technology to

translate signals and power across an isolation barrier.

Signals on either side of the barrier are encoded into

pulses and translated across the isolation boundary us-

ing differential signaling through coreless transformers

formed in the µModule substrate. This system, complete

with data refresh, error checking, safe shutdown on fail,

and extremely high common mode immunity, provides

a robust solution for bidirectional signal isolation. The

µModule technology provides the means to combine the

isolated signaling with a USB transceiver and powerful

isolated DC/DC converter in one small package.

USB Transceiver Pin Protection

The LTM2884 USB transceiver pins D1+, D1–, D2+, and

D2– have protection from ESD and short-circuit faults.

The transceiver pins withstand ±15KV HBM ESD events.

Overcurrent circuitry on the transceiver pins monitor fault

conditionsfromD1+andD1–toGND,VLO,orVBUSandfrom

D2+ and D2– to GND2, VLO2, or VCC2. A current detection

circuit disables the transceiver pin if the pin sinks about

40mA for greater than 600ns. The VLO and VLO2 output

supplies protect the USB transceiver pins from shorts

to GND or GND2 respectively with a 40mA current limit.

operaTion

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