LTM2883 datasheet(13/24 Pages) AD

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LTM2884

Rev. D

For more information www.analog.com

The LTM2884 µModule transceiver provides a galvanically

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 pow-

ered. Applications include isolation in hosts, hubs, periph-

erals, or standalone inline bus splitters. Automatically

configured pull-up resistors are included to represent

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 common mode transients between ground potentials.

Error free operation is maintained through common

mode events exceeding 30kV/µs providing excellent

noise isolation.

The LTM2884 contains a fully integrated DC/DC con-

verter including the transformer, so that no external

components are necessary in many configurations. The

upstream side contains a flyback converter that regulates

the downstream output voltage through primary sensing

techniques. The internal power solution is sufficient to

support the transceiver interface and supply up to 500mA

at 5V through VCC2 to an attached device dependent on

the supply voltage 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 the USB 2.0 specification. The communication through

the 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 direc-

tion 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 propa-

gation 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

at connection time. Disconnection of a downstream

device automatically releases the pull-up resistor on the

upstream facing port allowing the upstream 15k pull-

down resistors to pull the bus signals to a disconnect

condition. This function 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

using 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

conditions from D1+ and D1– to GND, VLO, or VBUS and

from 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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