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LTM2887

2887fb

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APPLICATIONS INFORMATION

Overview

The LTM2887 digital µModule isolator provides a

galvanically-isolated robust logic interface, powered by

an integrated, regulated DC/DC converter, complete with

decoupling capacitors. The LTM2887 is ideal for use in

networks where grounds can take on different voltages.

Isolation in the LTM2887 blocks high voltage differences,

eliminates ground loops and is extremely tolerant of com-

mon mode transients between ground planes. Error-free

operation is maintained through common mode events

greater than 30kV/μs providing excellent noise isolation.

Isolator µModule Technology

The LTM2887 utilizes isolator µModule technology to

translate signals and power across an isolation barrier.

Signalsoneithersideofthebarrierareencodedintopulses

and translated across the isolation boundary using core-

less transformers formed in the µModule substrate. This

system, complete with data refresh, error checking, safe

shutdown on fail, and extremely high common mode im-

munity, provides a robust solution for bidirectional signal

isolation. The µModule technology provides the means to

combinetheisolatedsignalingwithmultipleregulatorsand

a powerful isolated DC/DC converter in one small package.

DC/DC Converter

The LTM2887 contains a fully integrated DC/DC converter,

including the transformer, so that no external components

are necessary. The logic side contains a full-bridge driver,

running at 1.6MHz, and is AC-coupled to a single trans-

former primary. A series DC blocking capacitor prevents

transformer saturation due to driver duty cycle imbalance.

The transformer scales the primary voltage, and is recti-

fied by a full-wave voltage doubler. This topology allows

for a single diode drop, as in a center tapped full-wave

bridge, and eliminates transformer saturation caused by

secondary imbalances.

Three low dropout regulators (LDOs) are connected to

the output of the voltage doubler. One LDO powers the

internal circuitry and is not available externally. The other

two LDOs provide regulated 5V nominally for the VCC2and

VL2 outputs. VL2 corresponds to the voltage levels on the

isolated logic pins.

The internal power solution is sufficient to provide a

minimum of 100mA of current from VCC2 and VL2. VCC

is bypassed with 2.2µF, VCC2 and VL2 are each bypassed

with 4.7µF.

VL Logic Supply

A separate logic supply pin VL allows the LTM2887 to in-

terface with any logic signal from 1.62V to 5.5V as shown

in Figure 4. Simply connect the desired logic supply to VL.

There is no interdependency between VCC and VL; they

may simultaneously operate at any voltage within their

specified operating ranges and sequence in any order. VL

is bypassed internally by a 1µF capacitor.

Hot-Plugging Safely

Caution must be exercised in applications where power is

plugged into the LTM2887’s power supplies, VCC or VL,

due to the integrated ceramic decoupling capacitors. The

parasitic cable inductance along with the high Q char-

acteristics of ceramic capacitors can cause substantial

ringing which could exceed the maximum voltage ratings

and damage the LTM2887. Refer to Linear Technology Ap-

plication Note 88, entitled Ceramic Input Capacitors Can

Cause Overvoltage Transients for a detailed discussion

and mitigation of this phenomenon.

2887 F04

DI1

LTM2887-I

ANY VOLTAGE FROM

1.62V TO 5.5V

3V TO 3.6V LTM2887-3

4.5V TO 5.5V LTM2887-5

EXTERNAL

DEVICE

VCC

GND

GND2

SDA

SDA2

SCL

SCL2

VL2

AVL2

IVL2

AVCC2

IVCC2

VCC2

DO2

DO1

Figure 4. VCC and VL Are Independent

LTM2887 Datasheet(PDF) 16 Page - Linear Technology

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