HCPL-J312 Datasheet, PDF (19/24 Pages) AVAGO TECHNOLOGIES LIMITED – 2.5 Amp Output Current IGBT Gate Drive Optocoupler

Selecting the Gate Resistor (Rg) to Minimize IGBT
Switching Losses. (Discussion applies to HCPL-3120,
HCPL-J312 and HCNW3120)
Step 1: Calculate Rg Minimum from the I_OL Peak Specifica­
tion. The IGBT and Rg in Figure 26 can be analyzed as a
simple RC circuit with a voltage supplied by the HCPL-
3120.
_{R g ≥ (— VC—C — I–O}V_{L—PEEEA—-K}V_{ —OL—) }
  _{         === (—(—7 1V .2 5C——C ΩVI— —–2O+@.LV5——P58EEAEVAΩ—— -K-  2——2VV——))    }
The V_OL value of 2 V in the pre­vious equation is a con-
servative value of V_OL at the peak current of 2.5A (see
Figure 6). At lower Rg values the voltage supplied by
the HCPL-3120 is not an ideal voltage step. This results
in lower peak currents (more margin) than predicted by
this analysis. When negative gate drive is not used V_EE in
the previous equation is equal to zero volts.
Step 2: Check the HCPL-3120 Power Dissipation and
Increase Rg if Necessary. The HCPL-3120 total power
dissipa­tion (P_T) is equal to the sum of the emitter power
(P_E) and the output power (P_O):
P_T = P_E + P_O
PE = I_F • V_F · Duty Cycle
P_O = P_O(BIAS) + P_{O (SWITCHING)}
  = I_CC • (V_CC - V_EE)+ E_SW(R_G, Q_G) • f
For the circuit in Figure 26 with I_F (worst case) =
16 mA, Rg = 8 Ω, Max Duty Cycle = 80%, Qg = 500 nC, 
f = 20 kHz and T_A max = 85 °C:
P_E = 16 mA • 1.8 V • 0.8 = 23 mW
P_O = 4.25 mA • 20 V + 5.2 µ J • 20 kHz
  = 85 mW + 104 mW
  = 189 mW > 178 mW (P_O(MAX) @ 85°C
  = 250 mW-15C*4.8 mW/C)
The value of 4.25 mA for I_CC in the previous equation was
obtained by derating the I_CC max of 5 mA (which occurs
at -40°C) to I_CC max at 85C (see Figure 7).
Since P_O for this case is greater than P_O(MAX), Rg must be
increased to reduce the HCPL-3120 power dissipation.
P_{O(SWITCHING MAX)}   
= P_O(MAX) - P_O(BIAS)
  = 178 mW - 85 mW
= 93 mW
  _{E    S W ( M A X)    ==  ­­ ——9P  3O——(mS—  W—WIT— —Cf H=—IN4G—.M65A—Xµ)  W }
  20 ^kHz
For Qg = 500 nC, from Figure 27, a value of E_SW = 4.65 µW
gives a Rg = 10.3 Ω.
+5 V
1
270 Ω
2
CONTROL
INPUT
3
74XXX
OPEN
4
COLLECTOR
HCPL-3120
8
0.1 µF
7
6
5
+ ^{VCC = 15 V}
–
Rg
Q1
+ ^{VEE = -5 V}
–
Q2
+ HVDC
3-PHASE
AC
- HVDC
Figure 26. HCPL-3120 typical application circuit with negative IGBT gate drive.
HCPL-3120 fig 26
19