Propagation delay variations
Since IPM-drive photocouplers transfer a PWM signal, they must switch fast enough, generally with propagation delay times (tpHL/tpLH) of less than 800 ns. The TLP104 provides a propagation delay of 550 ns or less, while the TLP2358 has a propagation delay of 250 ns or less. Additionally, the TLP2358 guarantees a tpLH-tpHL difference of at most 70 ns and a propagation delay skew (between different devices), Tpsk, of at most ±130 ns. It helps improve the PWM signal transmission accuracy.
Interfacing with active-Low and active-High IPMs
Commercially available IPMs have either an active-High control input (that turns on an internal IGBT when High) or an active-Low control input (that turns on an internal IGBT when Low). Toshiba offers IPM-drive photocouplers with a noninverting output (that produce a High output when the LED input is on) for active-High IPMs and those with an inverting output (that produce a Low output when the LED input is on) for active-Low IPMs. You can use photocouplers with an appropriate output configuration to adapt system boards for different IPMs without an intervening inverter IC. The elimination of an on-board inverter IC makes it possible to share the same board design across different products.
Guaranteed CMR of 20 kV/µs
Since the IPM control input changes with a steep dv/dt, the photocoupler that drives it typically requires a CMR higher than 10 kV/µs. The CMR of a photocoupler can be improved by adding a shield across its input and output and bypassing displacement current to ground.
To provide a CMR over 10 kV/µs, many of Toshiba's IPM-drive photocouplers have a shield for the photodetector chip. These photocouplers are ideal for interfacing to the IPM control signal. The TLP2355 and TLP2358 in particular provide a CMR as high as 20 kV/µs.