1
dc1957af
DEMO MANUAL DC1957A
DESCRIPTION
LTM2892-S
SPI/Digital µModule Isolator
Demonstration circuit 1957A is a serial peripheral inter-
face bus (SPI) or digital μModule isolator featuring the
LTM2892-S. The demo circuit operates from external sup-
ply voltages on V
CC1
, V
L1
, V
CC2
, and V
L2
. It communicates
all necessary signaling across the isolation barrier through
LTC’s Isolator™ μModule
®
technology.
L
, LT, LTC, LTM, Linear Technology, the Linear logo and μModule are registered trademarks
and Isolator is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
PERFORMANCE SUMMARY
OPERATING PRINCIPLES
Design files for this circuit board are available at
http://www.linear.com/demo
Specifications are at T
A
= 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
CC1
, V
CC2
Input Supply Range
3.0
5.5
V
V
L1
, V
L2
Logic Supply Range
1.62
5.5
V
f
MAX
Maximum Data Rate
INx
→
OUTx, C
L
= 15pF
20
MHz
SPI Bidirectional Communication
SPI Unidirectional Communication
4
8
MHz
MHz
V
IORM
Maximum Working Insulation Voltage
GND1 to GND2
850
V
DC
600
V
RMS
Common Mode Transient Immunity
50
kV/μs
The LTM2892-S requires two to four external power sup-
plies for operation, one for power and one for the signal
interface, on each side of the isolation barrier. The logic
supplies may be tied to the input supplies. Isolation is
maintained by the separation of GND1 and GND2 where
significant operating voltages and transients can exist
without affecting the operation of the LTM2892-S. The ON1
and/or ON2 pins enable or shut down the LTM2892-S, both
must be driven to their respective logic supply voltage for
proper operation. All SPI or Digital signals are referenced
to the logic supply pins V
L1
or V
L2
.
SPI signaling is typically configured by defining the digital
pins as follows:
Logic
Side:
IN1 = SCK(IN), IN2 = SDI(IN), IN3 =
CS
(IN)
=
SDOE
, and OUTD = SDO(OUT).
Isolated
Side:
OUT1 = SCK(OUT), OUT2 = SDI(OUT),
OUT3 =
CS
(OUT), and IND = SDO(IN).
Reference Figure 1 for schematic representation.
No special precautions are required for low RF emissions.
EMI performance is shown in Figure 2, measured using
a gigahertz transverse electromagnetic (GTEM) cell and
method detailed in IEC 61000-4-20, Testing and Measure-
ment Techniques – Emission and Immunity Testing in
Transverse Electromagnetic Waveguides.
