HCPL-5300-200 Просмотр технического описания (PDF) - Avago Technologies

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HCPL-5300-200

Intelligent Power Module and Gate Drive Interface Hermetically Sealed Optocouplers

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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 18, 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 6-5 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 optocoupler output voltage and a 3 V IPM

threshold during a 10 kV/s transient with VCM = 1000 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 VF(OFF).

Since the open collector drive circuit, shown in Figure 19,

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

not desirable for applications requiring ultra high CMRH

performance. Figure 20 is the AC equivalent circuit for

Figure 16 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 21 is an

alternative drive circuit which does achieve ultra high

CMR performance by shunting the LED in the off state.

IPM Dead Time and Propagation Delay Specifications

These devices include a Propagation Delay Difference

specification intended to help designers minimize “dead

time”in their power inverter designs. Dead time is the time

period during which both the high and low side power

transistors (Q1 and Q2 in Figure 22) are off. Any overlap in

Q1 and Q2 conduction will result in large currents flowing

through the power devices between the high and low

voltage motor rails.

To minimize dead time the designer must consider the

propagation delay characteristics of the optocoupler

as well as the characteristics of the IPM IGBT gate drive

circuit. Considering only the delay characteristics of the

optocoupler (the characteristics of the IPM IGBT gate drive

circuit can be analyzed in the same way) it is important

to know the minimum and maximum turn-on (tPHL) and

turn-off (tPLH) propagation delay specifications, preferably

over the desired operating temperature range.

The limiting case of zero dead time occurs when the input

to Q1 turns off at the same time that the input to Q2 turns

on. This case determines the minimum delay between

LED1 turn-off and LED2 turn-on, which is related to the

worst case optocoupler propagation delay waveforms,

as shown in Figure 23. A minimum dead time of zero is

achieved in Figure 23 when the signal to turn on LED2

is delayed by (tPLH max - tPHL min) from the LED1 turn off.

This delay is the maximum value for the propagation

delay difference specification which is specified at 500 ns

for the HCPL-530X over an operating temperature range

of -55° C to +125° C.

Delaying the LED signal by the maximum propagation

delay difference ensures that the minimum dead time is

zero, but it does not tell a designer what the maximum

dead time will be. The maximum dead time occurs in

the highly unlikely case where one optocoupler with the

fastest tPLH and another with the slowest tPHL are in the

same inverter leg. The maximum dead time in this case

becomes the sum of the spread in the tPLH and tPHL pro-

pagation delays as shown in Figure 24. The maximum

dead time is also equivalent to the difference between the

maximum and minimum propagation delay difference

specifications. The maximum dead time (due to the opto-

couplers) for the HCPL-530X is 670 ns (= 500 ns - (-170 ns))

over an operating temperature range of -55° C to +125° C.

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