LTC4310-1/LTC4310-2
16
431012fa
Using the LTC4310-1 at Frequencies Above 100kHz
Users who implement custom two-wire buses may use the
LTC4310-1 at bus frequencies above 100kHz provided that
all other devices on the bus can tolerate the approximately
1µs bus rise times resulting from the LTC4310-1’s bus rise
rate regulation circuitry.
Transformer Selection Guide
As shown in Figure 1, a transformer passes transmit and
receive signals between the two LTC4310’s. The transmit
signals have 1.25V magnitude and 35ns pulse width. The
receive circuitry has an equivalent input impedance of
16.5kΩ and can receive differential signals ranging from
0.875V to 1.55V. To meet these requirements, choose a
transformer having a magnetizing inductance ranging
from 50µH to 350µH, a 1:1 turns ratio and a maximum
insertion loss of –1.5dB. For optimal common mode noise
rejection, choose a center-tapped transformer and connect
the center tap on the receiving side to local ground using a
0.01µF capacitor. Ringing at the LTC4310’s RXP and RXN
pins can effectively be damped by inserting 50Ω series
resistors between each LTC4310’s TXP and TXN pins and
the corresponding transformer primary windings.
Table 1 shows a recommended list of transformers for use
with the LTC4310. 10/100BaseTX Ethernet transformers
are inexpensive and work very well in this application for
isolation voltages up to 1500V. For applications requiring
4000V isolation, the Würth Electronics Midcom 749014012
transformer is recommended.
RF Radiated Emissions
The LTC4310 evaluation board passes CISPR22 Class B
requirements for radiated emissions. The results of
CISPR22 testing are shown in the evaluation board manual.
To reduce radiated emission levels further, enclose the
LTC4310 application circuit in a shielded enclosure.
Common Mode Transient Immunity
The LTC4310 has high immunity to common mode tran-
sients. This is tested by applying a square voltage pulse
having very fast edges between the isolated grounds. The
LTC4310 passes 20kV/us edges without corruption of the
I
2
C bus logic states.
Table 1. LTC4310 Recommended Transformers
MANUFACTURER PART NUMBER
ISOLATION
VOLTAGE
FORM FACTOR (mm)
TURNS
RATIO
CENTER
TAP
OPERATING
TEMPERATUREx y z
PCA Electronics EPF8119S 1500V
RMS
10.41 12.45 5.84 1:1 Yes 0°C TO 70°C
EPF8119SE 1500V
RMS
10.2 12.7 5.96 1:1 Yes –40°C TO 85°C
Pulse E5017 1500V
RMS
9.4 12.7 5.08 1:1 Yes 0°C TO 70°C
Würth Electronics
Midcom
000-7090-37R-LF1 1500V
RMS
9.4 12.95 5.33 1:1 Yes –40°C TO 85°C
749014012 4000V
RMS
17 24.55 10.85 1:1 Yes 0°C TO 70°C
applicaTions inForMaTion
