Datasheet

ADM2490E
Rev. A | Page 12 of 16
CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
In the ADM2490E, electrical isolation is implemented on the
logic side of the interface. Therefore, the part has two main
sections: a digital isolation section and a transceiver section
(see Figure 21). The driver input signal, which is applied to the
TxD pin and referenced to logic ground (GND
1
), is coupled
across an isolation barrier to appear at the transceiver section
referenced to isolated ground (GND
2
). Similarly, the receiver
input, which is referenced to isolated ground in the transceiver
section, is coupled across the isolation barrier to appear at the
RxD pin referenced to logic ground.
iCoupler Technology
The digital signals transmit across the isolation barrier using
iCoupler technology. This technique uses chip scale transformer
windings to couple the digital signals magnetically from one
side of the barrier to the other. Digital inputs are encoded into
waveforms that are capable of exciting the primary transformer
winding. At the secondary winding, the induced waveforms are
decoded into the binary value that was originally transmitted.
Positive and negative logic transitions at the input cause narrow
pulses (~1 ns) to be sent to the decoder via the transformer. The
decoder is bistable and is, therefore, either set or reset by the
pulses, indicating input logic transitions. In the absence of logic
transitions at the input for more than ~1 μs, a periodic set of
refresh pulses indicative of the correct input state are sent to
ensure dc correctness at the output. If the decoder receives no
internal pulses for more than about 5 μs, the input side is
assumed to be unpowered or nonfunctional, in which case the
output is forced to a default state (see Table 12).
TRUTH TABLES
The truth tables in this section use the abbreviations shown in
Table 10.
Table 10. Truth Table Abbreviations
Abbreviation Description
H High level
I Indeterminate
L Low level
X Irrelevant
Table 11. Transmitting
Supply Status Input Outputs
V
DD1
V
DD2
TxD Y Z
On On H H L
On On L L H
Table 12. Receiving
Supply Status Inputs Output
V
DD1
V
DD2
A − B (V) RxD
On On >0.2 H
On On <−0.2 L
On On −0.2 < A − B < +0.2 I
On On Inputs open H
On Off X H
Off On X H
Off Off X L
ISOLATION
BARRIER
V
DD2
V
DD1
Y
Z
A
B
GND
2
GND
1
TxD
RxD
ENCODE
DECODE
DECODE
ENCODE
D
R
TRANSCEIVER
DIGITAL ISOLATION
05889-009
Figure 21. ADM2490E Digital Isolation and Transceiver Sections