Data Sheet ADM3053
Rev. C | Page 13 of 20
CIRCUIT DESCRIPTION
CAN TRANSCEIVER OPERATION
A CAN bus has two states called dominant and recessive. A
dominant state is present on the bus when the differential voltage
between CANH and CANL is greater than 0.9 V. A recessive state
is present on the bus when the differential voltage between CANH
and CANL is less than 0.5 V. During a dominant bus state, the
CANH pin is high, and the CANL pin is low. During a recessive
bus state, both the CANH and CANL pins are in the high
impedance state.
Pin 18 (R
S
) allows two different modes of operation to be
selected: high-speed and slope control. For high-speed
operation, the transmitter output transistors are simply
switched on and off as fast as possible. In this mode, no
measures are taken to limit the rise and fall slopes. A shielded
cable is recommended to avoid EMI problems. High-speed
mode is selected by connecting Pin 18 to ground.
Slope control mode allows the use of an unshielded twisted pair
or a parallel pair of wires as bus lines. To reduce EMI, the rise
and fall slopes must be limited. The rise and fall slopes can be
programmed with a resistor connected from Pin 18 to ground.
The slope is proportional to the current output at Pin 18.
SIGNAL ISOLATION
The ADM3053 signal isolation is implemented on the logic side of
the interface. The part achieves signal isolation by having a digital
isolation section and a transceiver section (see Figure 1). Data
applied to the TxD pin referenced to logic ground (GND1) are
coupled across an isolation barrier to appear at the transceiver
section referenced to isolated ground (GND2). Similarly, the single-
ended receiver output signal, referenced to isolated ground in
the transceiver section, is coupled across the isolation barrier to
appear at the RxD pin referenced to logic ground (GND1). The
signal isolation is powered by the V
IO
pin and allows the digital
interface to 3.3 V or 5 V logic.
POWER ISOLATION
The ADM3053 power isolation is implemented using an isoPower
integrated isolated dc-to-dc converter. The dc-to-dc converter
section of the ADM3053 works on principles that are common to
most modern power supplies. It is a secondary side controller
architecture with isolated pulse-width modulation (PWM)
feedback. V
CC
power is supplied to an oscillating circuit that
switches current into a chip-scale air core transformer. Power
transferred to the secondary side is rectified and regulated to 5 V.
The secondary (V
ISO
) side controller regulates the output by
creating a PWM control signal that is sent to the primary (V
CC
)
side by a dedicated iCoupler data channel. The PWM modulates
the oscillator circuit to control the power being sent to the
secondary side. Feedback allows for significantly higher power
and efficiency.
TRUTH TABLES
The truth tables in this section use the abbreviations found in
Table 9.
Table 9. Truth Table Abbreviations
Letter Description
H High level
Z High impedance (off)
I Indeterminate
NC Not connected
Table 10. Transmitting
Supply Status Input Outputs
V
IO
V
CC
TxD Bus State CANH CANL
On On H Recessive Z Z
On On Floating Recessive Z Z
Off On X Recessive Z Z
On Off L Indeterminate I I
Table 11. Receiving
Supply Status Inputs Output
V
IO
V
CC
V
ID
= CANH − CANL Bus State RxD
On On ≥ 0.9 V Dominant L
On On ≤ 0.5 V
Recessive
H
On On 0.5 V < V
ID
< 0.9 V
X
1
I
On On Inputs open
Recessive
H
Off On X
1
X
1
I
On Off X
1
X
1
H
1
X means don’t care.
THERMAL SHUTDOWN
The ADM3053 contains thermal shutdown circuitry that protects
the part from excessive power dissipation during fault conditions.
Shorting the driver outputs to a low impedance source can
result in high driver currents. The thermal sensing circuitry
detects the increase in die temperature under this condition and
disables the driver outputs. This circuitry is designed to disable
the driver outputs when a die temperature of 150°C is reached.
As the device cools, the drivers are reenabled at a temperature of
140°C.
DC CORRECTNESS AND MAGNETIC FIELD IMMUNITY
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.
