LTM2889 datasheet(24/30 Pages) LINER

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LTM2889

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• For large ground planes a small capacitance (≤ 330pF)

from GND to GND2, either discrete or embedded within

the substrate, provides a low impedance current return

path for the module parasitic capacitance, minimizing

anyhighfrequencydifferentialvoltagesandsubstantially

reducing radiated emissions. Discrete capacitance will

not be as effective due to parasitic ESL. In addition, volt-

age rating, leakage, and clearance must be considered

for component selection. Embedding the capacitance

within the PCB substrate provides a near ideal capacitor

and eliminates component selection issues; however,

the PCB must be 4 layers. Care must be exercised in

applying either technique to insure the voltage rating

of the barrier is not compromised. The PCB layout in

Figures 17-21 show the low EMI demo board for the

LTM2889. The demo board uses a combination of EMI

mitigation techniques, including both embedded PCB

bridge capacitance and discrete GND to GND2 capaci-

tors (C3 + C4). Two safety rated type Y2 capacitors are

used in series, manufactured by Murata, part number

GA342QR7GF471KW01L. The embedded capacitor

effectively suppresses emissions above 400MHz,

whereas the discrete capacitors are more effective be-

low 400MHz. EMI performance is shown in Figure 22,

measuredusingaGigahertzTransverseElectromagnetic

(GTEM) cell and method detailed in IEC 61000-4-20,

“Testing and Measurement Techniques – Emission

and Immunity Testing in Transverse Electromagnetic

Waveguides.”

RF, MAGNETIC FIELD IMMUNITY

TheisolatorμModuletechnologyusedwithintheLTM2889

hasbeenindependentlyevaluated,andsuccessfullypassed

the RF and magnetic field immunity testing requirements

per European Standard EN 55024, in accordance with the

following test standards:

APPLICATIONS INFORMATION

EN61000-4-3Radiated,Radio-Frequency,Electromagnetic

Field Immunity

EN 61000-4-8 Power Frequency Magnetic Field Immunity

EN 61000-4-9 Pulse Magnetic Field Immunity

Tests were performed using an unshielded test card de-

signed per the data sheet PCB layout recommendations.

Specific limits per test are detailed in Table 3.

Table 3.

TEST

FREQUENCY

FIELD STRENGTH

EN61000-4-3 Annex D

80MHz to 16Hz

10V/m

1.4MHz to 2Hz

3V/m

2MHz to 2.7Hz

1V/m

EN61000-4-8 Level 4

50MHz to 60Hz

30A/m

EN61000-4-8 Level 5

60Hz

100A/m*

EN61000-4-9 Level 5

Pulse

100A/m

*Non IEC method

Operation Above 105°C (LTM2889H)

Operation of the H temperature grade LTM2889H above

105°C is limited by the internal power dissipation of the

module,anddependsonthePVCCvoltagerangeoption,the

externalICC2loadcurrent,andwhethertheCANtransceiver

is on or off. Refer to the Typical Performance Character-

istics chart labeled Derating for 125°C Maximum Internal

Operating Temperature on page 13. The CAN transceiver

of the LTM2889H may operate up to 125°C if VCC2 is

supplied by an external power supply and the PVCC pins

are grounded. Refer to PVCC Power Supply on page 16.

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