adum1510 Analog Devices, Inc., adum1510 Datasheet - Page 8

• Manufacturer Part Number: adum1510
• Description: 5-channel, Unidirectional Digital Isolator
• Manufacturer: Analog Devices, Inc.

ADuM1510
APPLICATIONS INFORMATION
PCB LAYOUT
The ADuM1510 digital isolator requires no external interface
circuitry for the logic interfaces. Power supply bypassing is
strongly recommended at the input and output supply pins (see
Figure 9). Bypass capacitors are most conveniently connected
between Pin 1 and Pin 2 for V
for V
0.1 μF. The total lead length between both ends of the capacitor
and the input power supply pin must not exceed 10 mm. Bypass-
ing between Pin 1 and Pin 8 and between Pin 9 and Pin 16
should also be considered unless the ground pair on each
package side is connected close to the package.
PROPAGATION DELAY-RELATED PARAMETERS
Propagation delay is a parameter that describes the length of
time it takes for a logic signal to propagate through a component.
The propagation delay to a logic low output can differ from the
propagation delay to a logic high output.
Pulse width distortion is the maximum difference between
these two propagation delay values and is an indication of how
accurately the timing of the input signal is preserved.
Channel-to-channel matching refers to the maximum amount
that the propagation delay differs between channels within a
single ADuM1510 component.
Propagation delay skew refers to the maximum amount that
the propagation delay differs among multiple ADuM1510
components operated under the same conditions.
DC CORRECTNESS AND MAGNETIC FIELD IMMUNITY
Positive and negative logic transitions at the isolator input
cause narrow (~1 ns) pulses to be sent via the transformer to
the decoder. 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 is sent to ensure dc correctness at the output.
INPUT (V
OUTPUT (V
DD2
Ix
. The capacitor value should be between 0.01 μF and
GND
GND
)
V
Ox
DD1
V
V
V
V
V
)
IA
IB
IC
ID
IE
1
1
Figure 10. Propagation Delay Parameters
Figure 9. Recommended PCB Layout
t
PLH
ADuM1510
DD1
and between Pin 15 and Pin 16
t
PHL
50%
50%
V
GND
V
V
V
V
V
GND
DD2
OA
OB
OC
OD
OE
2
2
Rev. A | Page 8 of 12
If the decoder receives no pulses for more than approximately 5 μs,
the input side is assumed to be unpowered or nonfunctional, in
which case, the isolator output is forced to a default low state by
the watchdog timer circuit (see Table 8).
The limitation on the magnetic field immunity of the device is
set by the condition in which induced voltage in the transformer
receiving coil is sufficiently large to either falsely set or reset the
decoder. The analysis below defines such conditions. In the
following analysis, the ADuM1510 is examined in a 3 V
operating condition because it represents the most susceptible
mode of operation of all products in its product family.
The pulses at the transformer output have an amplitude greater
than 1.0 V. The decoder has a sensing threshold of approximately
0.5 V, thus establishing a 0.5 V margin in which induced voltages
can be tolerated. The voltage induced across the receiving coil is
given by
where:
β is the magnetic flux density (gauss).
r
N is the number of turns in the receiving coil.
Given the geometry of the receiving coil in the ADuM1510 and
an imposed requirement that the induced voltage be at most
50% of the 0.5 V margin at the decoder, a maximum allowable
magnetic field can be calculated, as shown in Figure 11.
For example, at a magnetic field frequency of 1 MHz, the maxi-
mum allowable magnetic field of 0.2 kgauss induces a voltage of
0.25 V at the receiving coil. This voltage is approximately 50% of
the sensing threshold and does not cause a faulty output transition.
Similarly, if such an event occurs during a transmitted pulse
(and is of the worst-case polarity), the received pulse is reduced
from >1.0 V to 0.75 V, still well above the 0.5 V sensing threshold
of the decoder.
n
is the radius of the nth turn in the receiving coil (cm).
V = (−dβ/dt) Σπr
0.001
0.01
Figure 11. Maximum Allowable External Magnetic Flux Density
100
0.1
10
1
1k
10k
MAGNETIC FIELD FREQUENCY (Hz)
n
2
; n = 1, 2, … N
100k
1M
10M
100M