ACPL-K34T 查看數據表（PDF） - Avago Technologies
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ACPL-K34T Datasheet PDF : 15 Pages
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Initial Power Up and UVLO Operation
Insufficient gate voltage to MOSFET can increase turn on resistance of MOSFET, resulting in large power loss and MOS-
FET damage due to high heat dissipation. ACPL-K34T monitors the output power supply constantly. During initial power
up, the ACPL-K34T requires maximum 50 µs of initial startup time for the internal bias and circuitry to get ready. The gate
driver output (VOUT) is hold at off state during initial startup time. Thereafter, when the output power supply is lower
than under voltage lockout (VUVLO-) threshold, gate driver output will shut off to protect MOSFET from low voltage bias.
When the output power supply is more than the VUVLO+ threshold, VOUT is released from low state and it follows the
input LED drive signal, as shown in Figure 21.
VCC
V UVLO +
V UVLO -
V UVLO+
Vin(LED)
V OUT
Initial startup
time
Figure 21. ACPL-K34T initial power-up and UVLO operation
Dead Time Distortion and Propagation Delay
Dead time is the period of time during which both high side and low side power transistors (shown as Q1 and Q2 in Fig-
ure 16) are off. Any overlap in Q1 and Q2 conduction will result in a shoot-through event and large short circuit current
will flow through the power devices between the high side and low side power rail.
ACPL-K34T includes a Dead Time Distortion (DTD) specification intended to help designers optimize dead time in a
power inverter design. A negative DTD value will decrease the system dead time, and so a negative DTD must be com-
pensated by adding extra dead time to the design. Figure 22a shows that dead time after optocoupler is reduced by
negative DTD. On the other hand, a positive DTD will add to the system original dead time, and so a positive DTD will
cause dead time redundancy to the system. Figure 22b shows that dead time after optocoupler is increased by positive
DTD.
Figure 22a. Negative DTD reduces original DT
Figure 22. Dead Time and Propagation Delay Waveforms
Figure 22b. Positive DTD increased original DT
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