ACPL-M46T-500E Avago Technologies US Inc., ACPL-M46T-500E Datasheet - Page 7

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ACPL-M46T-500E

Manufacturer Part Number
ACPL-M46T-500E
Description
Amplifier-Output Optocoupler,1-CHANNEL,3.75kV ISOLATION,SO
Manufacturer
Avago Technologies US Inc.
Series
R²Coupler™r
Datasheet

Specifications of ACPL-M46T-500E

Voltage - Isolation
3750Vrms
Number Of Channels
1, Unidirectional
Current - Output / Channel
50µA
Data Rate
1MBd
Propagation Delay High - Low @ If
200ns @ 10mA
Current - Dc Forward (if)
20mA
Input Type
DC
Output Type
Open Collector
Mounting Type
Surface Mount
Package / Case
SO-5 (MO-155)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

Available stocks

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Manufacturer
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Price
Part Number:
ACPL-M46T-500E
Manufacturer:
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Quantity:
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Part Number:
ACPL-M46T-500E
Quantity:
4 500
LED Drive Circuit Considerations For Ultra High CMR
Performance
Without a detector shield, the dominant cause of op-
tocoupler CMR failure is capacitive coupling from the
input side of the optocoupler, through the package, to
the detector IC as shown in Figure 14. The ACPL-M46T
improves CMR performance by using a detector IC with
an optically transparent Faraday shield, which diverts
the capacitively coupled current away from the sensitive
IC circuitry. However, this shield does not eliminate the
capacitive coupling between the LED and the optocou-
pler output pin and output ground as shown in Figure
15. This capacitive coupling causes perturbations in the
LED current during common mode transients and be-
comes the major source of CMR failures for a shielded
optocoupler. The main design objective of a high CMR
LED drive circuit becomes keeping the LED in the proper
state (on or off ) during common mode transients. For ex-
ample, the recommended application circuit (Figure 13),
can achieve 15 kV/μs CMR while minimizing component
complexity. Note that a CMOS gate is recommended in
Figure 13 to keep the LED off when the gate is in the high
state.
Another cause of CMR failure for a shielded optocoupler
is direct coupling to the optocoupler output pins through
C
magnitude of the direct coupling including: the position
of the LED current setting resistor and the value of the
capacitor at the optocoupler output (C
Techniques to keep the LED in the proper state and mini-
mize the effect of the direct coupling are discussed in the
next two sections.
CMR with the LED on (CMRL)
A high CMR LED drive circuit must keep the LED on dur-
ing common mode transients. This is achieved by over-
driving the LED current beyond the input threshold so
that it is not pulled below the threshold during a tran-
sient. The recommended minimum LED current of 10 mA
provides adequate margin over the maximum I
mA (see Figure 2) to achieve 15 kV/μs CMR.
The placement of the LED current setting resistor effects
the ability of the drive circuit to keep the LED on dur-
ing transients and interacts with the direct coupling to
the optocoupler output. For example, the LED resistor in
Figure 16 is connected to the anode. Figure 17 shows the
AC equivalent circuit for Figure 16 during common mode
transients. During a +dV
available at the LED anode (Itotal) is limited by the series
resistor. The LED current (I
by an amount equal to the current that flows through
C
7
LEDO1
LEDP
and C
in Figure 15. Many factors influence the effect and
LEDO1
. The situation is made worse because the
CM
F
) is reduced from its DC value
/dt in Figure 17, the current
L
).
TH
of 4.0
current through C
output high (toward a CMR failure) at the same time the
LED current is being reduced. For this reason, the recom-
mended LED drive circuit (Figure 13) places the current
setting resistor in series with the LED cathode. Figure 18
is the AC equivalent circuit for Figure 13 during common
mode transients. In this case, the LED current is not re-
duced during a +dV
flowing through the package capacitance is supplied by
the power supply. During a dV
the LED current is reduced by the amount of current
flowing through CLEDN. But, better CMR performance
is achieved since the current flowing in C
negative transient acts to keep the output low.
CMR with the LED Off (CMRH)
A high CMR LED drive circuit must keep the LED off (V
≤ V
during a +dV
flowing through C
nation of the LED and series resistor. As long as the volt-
age developed across the resistor is less than V
LED will remain off and no common mode failure will oc-
cur. Even if the LED momentarily turns on, the 100 pF ca-
pacitor from pins 5-4 will keep the output from dipping
below the threshold. The recommended LED drive cir-
cuit (Figure 13) provides about 10 V of margin between
the lowest optocoupler output voltage and a 3 V IPM
threshold during a 15kV/μs transient with V
Additional margin can be obtained by adding a diode
in parallel with the resistor, as shown by the dashed line
connection in Figure 18, to clamp the voltage across the
LED below V
Since the open collector drive circuit, shown in Figure 19,
cannot keep the LED off during a +dV
not desirable for applications requiring ultra high CMRH
performance. Figure 20 is the AC equivalent circuit for
Figure 19 during common mode transients. Essentially
all the current flowing through CLEDN during a +dV
dt transient must be supplied by the LED. CMRH failures
can occur at dv/dt rates where the current through the
LED and CLEDN exceeds the input threshold. Figure 21 is
an alternative drive circuit which does achieve ultra high
CMR performance by shunting the LED in the off state.
F(OFF)
) during common mode transients. For example,
F(OFF)
CM
/dt transient in Figure 18, the current
.
LEDO1
LEDN
CM
/dt transient because the current
is supplied by the parallel combi-
has the effect of trying to pull the
CM
/dt transient, however,
CM
/dt transient, it is
LEDO1
CM
= 1500 V.
during a
F(OFF)
the
CM
F
/

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