HCPL-M456-560E Avago Technologies US Inc., HCPL-M456-560E Datasheet - Page 7

• Manufacturer Part Number: HCPL-M456-560E
• Description: OPTOCOUPLER IPM 1MBD IEC SO-5
• Manufacturer: Avago Technologies US Inc.

Specifications of HCPL-M456-560E

• Voltage - Isolation: 3750Vrms
• Number Of Channels: 1, Unidirectional
• Current - Output / Channel: 15mA
• Propagation Delay High - Low @ If: 200ns @ 10mA
• Current - Dc Forward (if): 25mA
• Input Type: DC
• Output Type: Open Collector
• Mounting Type: Surface Mount
• Package / Case: 5-SOP
• No. Of Channels: 1
• Optocoupler Output Type: Gate Drive
• Input Current: 20mA
• Output Voltage: 30V
• Opto Case Style: SOIC
• No. Of Pins: 5
• Ctr Max: 90%
• Isolation Voltage: 3.75kV
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LED Drive Circuit Considerations For Ultra High CMR Per-
formance
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 HCPL-M456
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 ca-
pacitive coupling between the LED and the optocoupler
output pin and output ground as shown in Figure 15. This
capacitive coupling causes perturbations in the LED cur-
rent during common mode transients and becomes 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 example, the rec-
ommended 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 optocou-
pler is direct coupling to the optocoupler output pins
through C
effect and 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 minimize the effec t of the direc t cou-
pling are discussed in the next two sections.
CMR With The LED On (CMRL)
A high CMR LED drive circuit must keep the LED on
during common mode transients. This is achieved by
overdriving the LED current beyond the input threshold
so that it is not pulled below the threshold during a
transient. The recommended minimum LED current of
10 mA provides adequate margin over the maximum
I
The placement of the LED current setting resistor effects
the ability of the drive circuit to keep the LED on during
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
7
TH
of 4.0 mA (see Figure ) to achieve 15 kV/µs CMR.
LEDO1
in Figure 15. Many factors influence the
L
).
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
the current through C
the output high (toward a CMR failure) at the same time
the LED current is being reduced. For this reason, the
recommended 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 reduced during a +dV
current flowing through the package capacitance is sup-
plied by the power supply. During a -dV
however, the LED current is reduced by the amount of
current flowing through C
mance is achieved since the current flowing in C
during a 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
during a +dV
ing through C
of the LED and series resistor. As long as the voltage de-
veloped across the resistor is less than V
remain off and no common mode failure will occur. Even
if the LED momentarily turns on, the 100 pF capacitor
from pins 5-4 will keep the output from dipping below
the threshold. The recommended LED drive circuit (Figure
13) provides about 10 V of margin between the lowest op-
tocoupler output voltage and a 3 V IPM threshold during
a 15kV/µs transient with V
can be obtained by adding a diode in parallel with the
resistor, as shown by the dashed line connection in Fig-
ure 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 CMR
performance. Figure 0 is the AC equivalent circuit for
Figure 19 during common mode transients. Essentially
all the current flowing through C
transient must be supplied by the LED. CMR
occur at dv/dt rates where the current through the LED
and C
alternative drive circuit which does achieve ultra high
CMR performance by shunting the LED in the off state.
LEDP
F
≤ V
and C
F(OFF)
LEDN
) during common mode transients. For example,
exceeds the input threshold . Figure 1 is an
LEDO1
CM
LEDN
/dt transient in Figure 18, the current flow-
. The situation is made worse because
is supplied by the parallel combination
LEDO1
CM
CM
F
) is reduced from its DC value
has the effect of trying to pull
LEDN
/dt in Figure 17, the current
CM
= 1500 V . Additional margin
/dt transient because the
. But, better CMR perfor-
LEDN
CM
during a +dV
F(OFF)
/dt transient, it is
CM
/dt transient,
H
the LED will
failures can
CM
F(OFF)
LEDO1
/dt
H
.