ACPL-W456-560E データシートの表示（PDF） - Broadcom Corporation

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ACPL-W456-560E

High CMR Intelligent Power Module and Gate Drive Interface Optocoupler

Broadcom Corporation 

ACPL-P456 and ACPL-W456

Data Sheet

transients. In this case, the LED current is not reduced during a

+dVCM/dt transient because the current fl owing through the

package capacitance is supplied by the power supply. During a

-dVCM/dt transient, however, the LED current is reduced by the

amount of current flowing through CLEDN. But, better CMR

performance is achieved since the current fl owing in CLEDO1

during a negative transient acts to keep the output low.

Figure 15 LED Drive Circuit with Resistor Connected to LED Anode

(Not Recommended)

+5V

1

2

3

CMOS

SHIELD

6

5

VOUT +

-

VCC = 15V

CL*

4

* 100 pF TOTAL

CAPACITANCE

Figure 16 AC Equivalent Circuit for Figure 15 During Common

Mode Transients

ITOTAL*

300 Ω

1 ICLEDP

IF

2

ICLED01

CLED01

6

5 VOUT

3 CLEDN

SHIELD

4

* THE ARROWS INDICATE THE DIRECTION

OF CURRENT FLOW DURING + dVCM /dt

20 kΩ

100pF

CMR With The LED Off (CMRH)

A high CMR LED drive circuit must keep the LED off (VF ≤

VF(OFF)) during common mode transients. For example, during

a +dVCM/dt transient in Figure 17, the current flowing through

CLEDN is supplied by the parallel combination of the LED and

series resistor. As long as the voltage developed across the

resistor is less than VF(OFF) the LED will 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 12) provides about 10V of margin

between the lowest optocoupler output voltage and a 3V IPM

threshold during a 15 kV/μs transient with VCM = 1500V.

Additional margin can be obtained by adding a diode in

parallel with the resistor, as shown by the dashed line

connection in Figure 17, to clamp the voltage across the LED

below VF(OFF).

Since the open collector drive circuit, shown in Figure 18,

cannot keep the LED off during a +dVCM/dt transient, it is not

desirable for applications requiring ultra high CMRH

performance. Figure 19 is the AC equivalent circuit for

Figure 18 during common mode transients. Essentially all the

current flowing through CLEDN during a +dVCM/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 20 is an alternative drive circuit

which does achieve ultra high CMR performance by shunting

the LED in the off state.

Figure 18 Not Recommended Open Collector LED Drive Circuit

VCM

Figure 17 AC Equivalent Circuit for Figure 12 During Common

Mode Transients

+ VR**-

1 CLEDP

2

CLED01

6

5 VOUT

3 ICLEDN* CLEDN SHIELD

4

* THE ARROWS INDICATE THE DIRECTION OF CURRENT

FLOW FOR + dVCM /dt TRANSIENTS.

** OPTIONAL CLAMPING DIODE FOR IMPROVED CMH

PERFORMANCE. VR < VF (OFF)DURING + dVCM/dt

100 pF

VCM

+5V

1

2

3

Q1

6

5

SHIELD

4

Figure 19 AC Equivalent Circuit for Figure 18 During Common

Mode Transients

1 CLEDP

2

CLED01

6

20

5 VOUT

Q1

3 ICLEDN* CLEDN SHIELD

100 pF

4

* THE ARROWS INDICATE THE DIRECTION OF CURRENT

FLOW FOR + dVCM/dt TRANSIENTS.

VCM

Broadcom

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