Datasheet

12
Selecting the Gate Resistor (R
g
) for HCPL-3180
Step 1: Calculate R
g
minimum from the I
OL
peak specication. The IGBT and
R
g
in Figure 25 can be analyzed as a simple RC circuit with a voltage supplied
by the HCPL-3180.
The V
OL
value of 3 V in the previous equation is the V
OL
at the peak current of
2 A. (See Figure 6.)
Step 2: Check the HCPL-3180 power dissipation and increase R
g
if necessary.
The HCPL-3180 total power dissipation (P
T
) is equal to the sum of the emitter
power (P
E
) and the output power (P
O
).
PT = PE + PO
PE = IF * VF * Duty Cycle
PO = PO(BIAS) + PO(SWITCHING)
= ICC * VCC + ESW (R
g
;Q
g
) * f
For the circuit in Figure 25 with IF (worst case) = 16 mA, R
g
= 10 Ω, Max Duty
Cycle = 80%, Q
g
= 100 nC, f = 200 kHz and T
AMAX
= +75°C:
PE = 16 mA * 1.8 V * 0.8 = 23 mW
PO = 4.5 mA * 20 V + 0.85 µ * 200 kHz
= 260 mW ≥ 226 mW (PO(MAX) @ 75°C = 250 mW (5°C * 4.8 mW/°C))
The value of 4.5 mA for I
CC
in the previous equation was obtained by derating
the I
CC
max of 6 mA to I
CC
max at +75°C. Since P
O
for this case is greater than
the P
O(MAX)
, R
g
must be increased to reduce the HCPL-3180 power dissipa-
tion.
PO(SWITCHING MAX) = PO(MAX) – PO(BIAS)
= 226 mW – 90 mW
= 136 mW
ESW(MAX) = PO(SWITCHING MAX)
f
= 136 mW
200 kHz
= 0.68 µW
For Q
g
= 100 nC, a value of E
sw
= 0.68 µW gives a R
g
= 15 W.
=
20 – 3
2
= 8.5 Ω
Figure 26. Energy dissipated in the HCPL-3180 and for
each IGBT.
R
g
≥
V
CC
– V
OL
I
OLPEAK
E
sw
– ENERGY PER SWITCHING CYCLE – µJ
0
0
R
g
— GATE RESISTANCE — Ω
50
0.6
10
2.0
1.4
1.6
1.8
20
0.4
30 40
1.2
Q
g
= 100 nC
1.0
0.8
0.2