Selecting the Gate Resistor (Rg)
Step 1: Calculate Rg minimum from the IOL peak specification. The IGBT and Rg in Figure 22 can be analyzed as a simple
RC circuit with a voltage supplied by ACPL-P341/W341.
Rg ≥ VCC – VEE – VOL
IOLPEAK
= 15 V + 5 V – 2.5 V
3A
= 5.8 6
The VOL value of 2.5 V in the previous equation is the VOL at the peak current of 3.0 A.
Step 1: Check the ACPL-P341/W341 power dissipation and increase Rg if necessary. The ACPL-P341/W341 total power
dissipation (PT) is equal to the sum of the emitter power (PE) and the output power (PO).
PT = PE + PO
PE = IF • VF • Duty Cycle
PO = PO(BIAS) + PO(SWITCHING)
= ICC • (VCC-VEE) + ESW(Rg;Cg) • f
Using IF(worst case) = 16 mA, Rg = 5 , Max Duty Cycle = 80%, Cg = 25 nF, f = 25 kHz and TA max = 85° C:
PE = 16 mA • 1.95 V • 0.8 = 25 mW
PO = 3 mA • 20 V + 4.5 J • 25 kHz
= 60 mW + 112.5 mW
= 172.5 mW < 700 mW (PO(MAX) @ 85° C)
The value of 3 mA for ICC in the previous equation is the maximum ICC over the entire operating temperature range.
Since PO is less than PO(MAX), Rg = 6 is alright for the power dissipation.
3.0E-05
2.5E-05
2.0E-05
VCC = 30 V
VCC = 20 V
VCC = 15 V
1.5E-05
1.0E-05
5.0E-06
0.0E+00
0
2
4
6
8
10
Rg - Gate Resistance - 7
Figure 25. Energy Dissipated in the ACPL-P341/W341 for each IGBT switching
cycle.
16