LINEAR Application Note 125
Summary
The LTM2881 is a highly efficient, integrated DC/DC converter and isolated RS485 transceiver designed to provide robust 5V or 3.3V power while maintaining strong electrical isolation barrier capabilities. Functioning without external components, it supports complex signaling even across large ground-to-ground potential differences. This technical guide provides detailed application notes, performance characteristics, and circuit methodologies for electronics engineers building reliable, isolated communication systems such as industrial controls, instrumentation, and safety devices that require dependable power delivery.
Page 1 Text Content
Application Note 125 February 2010
Using the LTM2881 as an Isolated 5V Power Supply
IS IO IE
Brian Jadus
2500VRMS Isolated 5V 1W Power With No External Features:
Components
n 5V (LTM2881-5) or 3.3V (LTM2881-3) Input Supply
The LTM®2881 is an isolated RS485 transceiver that guards Voltage n 5V DC Output Delivers 200m A at 62% Effi ciency with
against large ground-to-ground differentials. An onboard
DC/DC converter provides isolated 5V power to the output. a 5V Input (LTM2881-5) or 120m A at 52% Effi ciency Figure 1 shows the LTM2881 confi gured as a dedicated with a 3.3V Input (LTM2881-3) n Zero Current (Typical) Shutdown Mode When ON Pin
isolated power supply with the RS485 transceiver disabled,
providing a simple powerful general purpose isolated power is Low. n Overcurrent and Overtemperature Protection
supply capable of delivering 1W at 5V. Figure 2 shows a
n No External Components Required. Decoupling
logically-controlled switched output by taking advantage of
the isolated RS485 driver to control a discrete PMOSFET. Capacitors are Integrated. n Small Package: 15mm × 11.25mm × 2.8mm
The controlling signal DI operates relative to the VL sup- ply, which supports voltages from 1.62V to 5.5V. In both
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear confi gurations, observation of a VCC2 fault is accomplished Technology Corporation. All other trademarks are the property of their respective owners.
by observing a high impedance condition on RO or DOUT .
When VCC2 is greater than 2.6V, RO and DOUT are driven IS IO IE
to the appropriate logic level based on the inputs A and B and DIN. When VCC2 is less than 2.4V, RO and DOUT are high impedance.
1.8V TO 5.5V REGULATED 5V
VCC VCC2 REGULATED 5V VL VCC VCC2 SWITCHED 5V
PWR PWR
VL ON
RO RO
IRLML6402
ONOFF ON RE
LTM2881 LTM2881
TE TE DE DE
DI DI
ONOFF DOUT DIN CMOS DOUT DIN CMOS
GND GND2 OUTPUT GND GND2 INPUT
AN125 F01 AN125 F02
Figure 1. LTM2881 Confi gured as a Dedicated Figure 2. Switched 5V Power with Isolated CMOS Logic Connection Isolated 5V Power Supply to VL Voltage Interface
an125f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. AN125-1
Page Summary Contents For LINEAR Application Note 125
Manual Details
| Brand | Linear |
|---|---|
| Pages | 2 |
| File Size | 92.52 KB |
| Published | May 30, 2026 |
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Frequently Asked Questions
What is the maximum isolated power output capability of the LTM2881?
It is capable of delivering 1W at 5V.
Are external capacitors or components required for installation?
No, additional capacitors are integrated and no external decoupling capacitors are needed.
What built-in protections does the power supply offer?
The device includes overcurrent and overtemperature protection.
How is a zero current/low power state achievable?
A typical low current shutdown mode occurs when the RS485 transceiver is disabled.