Linear DC1957A Demo Manual

DESCRIPTION

DEMO MANUAL DC1957A

LTM2892-S

SPI/Digital µModule Isolator

Demonstration circuit 1957A is a serial peripheral inter­face bus (SPI) or digital µModule isolator featuring the
LTM2892-S. The demo circuit operates from external sup­ply voltages on V

CC1

, VL1, V

, and VL2. It communicates

CC2

Design files for this circuit board are available at
http://www.linear.com/demo

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.

all necessary signaling across the isolation barrier through

®

LTC’s Isolator™ µModule

PERFORMANCE SUMMARY

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

V

f

MAX

V

CC1

, V

L1

IORM

, V

CC2

L2

Input Supply Range 3.0 5.5 V

Logic Supply Range 1.62 5.5 V

Maximum Data Rate

Maximum Working Insulation Voltage GND1 to GND2 850 V

Common Mode Transient Immunity 50 kV/µs

technology.

Specifications are at TA = 25°C

INx → OUTx, C

SPI Bidirectional Communication
SPI Unidirectional Communication

= 15pF

L

20 MHz

4
8

600 V

MHz
MHz

RMS

DC

OPERATING PRINCIPLES

The LTM2892-S requires two to four external power sup­plies 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

or VL2.

L1

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 Measure­ment Techniques – Emission and Immunity Testing in
Transverse Electromagnetic Waveguides.

dc1957af

1

DEMO MANUAL DC1957A

OPERATING PRINCIPLES

LTM2892-S

V

CC1

V

L1

ON1

EOUTD

INC
INB
INA

OUTF
OUTE
OUTD

Figure 1. SPI Pin Definition

60

DETECTOR = PEAK HOLD
RBW = 120kHz
VBW = 300kHz

50

SWEEP TIME = 680ms, ≥ 10 SWEEPS
NUMBER OF POINTS = 501

5V

CS(IN)

SDI(IN)

SCK(IN)

SDO(OUT)

ISOLATION BARRIER

V

CC2
V

L2

ON2

EOUTA

OUTC
OUTB
OUTA

INF
INE

IND

GND2GND1

dc1957a F01

5V

CS(OUT)
SDI(OUT)
SCK(OUT)

SDO(IN)

NOTE: INE AND INF ARE
OPTIONAL CONNECTIONS

40

30

20

dBµV/m

10

TA = 25°C

0

–10

–20

CISPR 22 CLASS B LIMIT

1000400 800200 600100

dn1957a F02

–30

DUT

0

500 900300 700

FREQUENCY (MHz)

2

Figure 2. DC1957A Radiated Emissions

dc1957af