ACPL-38JT-000E Datasheet, PDF (30/33 Pages) AVAGO TECHNOLOGIES LIMITED – Automotive Gate Drive Optocoupler with R2Coupler™ Isolation, 2.5 Amp Output Current, Integrated Desaturation (VCE) Detection and Fault Status Feedback

Power Considerations
Operating Within the Maximum Allowable Power Ratings (Adjusting
Value of R_G):
When choosing the value of R_G, it is important to confirm
that the power dissipation of the ACPL-38JT is within the
maximum allowable power rating.
The steps for doing this are:
1. Calculate the minimum desired R_G;
2. Calculate total power dissipation in the part referring
to Figure 76. (Average switching energy supplied to
ACPL-38JT per cycle vs. R_G plot);
3. Compare the input and output power dissipation
calculated in step #2 to the maximum recommended
dissipation for the ACPL-38JT. (If the maximum rec-
ommended level has been exceeded, it may be nec-
essary to raise the value of R_G to lower the switching
power and repeat step #2.)
Asanexample, the total input and output power dissipation
can be calculated given the following conditions:
 I_{ON, MAX} ~ 2.0 A
 V_CC2 = 18 V
 V_EE = -5 V
 f_CARRIER = 10 kHz
Step 1: Calculate R_G minimum from I_OL peak specification:
To find the peak charging l_OL assume that the gate is
initially charged the steady-state value of V_EE. Therefore
apply the following relationship:
R_G =
=
=
[V_OH@650 A – (V_OL+V_EE)]
I_{OL, PEAK}
[V_CC2 – 1 – (V_OL + V_EE )]
I_{OL, PEAK}
18 V – 1 V – (1.5 V + (-5 V))
2.0 A
= 10.25 
≈ 10.5  (for a 1% resistor)
(Note from Figure 75 that the real value of I_OL may vary
from the value calculated from the simple model shown.)
Step 2: Calculate total power dissipation in the ACPL-38JT:
The ACPL-38JT total power dissipation (P_T) is equal to the
sum of the input-side power (P_I) and output-side power
(P_O):
P_T = P_I + P_O
P_I = I_CC1 * V_CC1
P_O = P_O(BIAS) + P_O(SWTICH)
= I_CC2 * (V_CC2–V_EE ) + E_SWITCH * f_SWITCH
where,
P_{O (BIAS)} = steady-state power dissipation in the ACPL-38JT
due to biasing the device.
P_{O (SWITCH)} = transient power dissipation in the ACPL-38JT
due to charging and discharging power device gate.
E_SWITCH = Average Energy dissipated in ACPL-38JT due to
switching of the power device over one switching cycle
(J/cycle).
f_SWITCH = average carrier signal frequency.
MAX. I_ON, I_OFF vs. GATE RESISTANCE (V_CC2 / V_EE2 = 25 V / 5 V)
4
3
2
1
I_OFF (MAX.)
0
-1
ION (MAX.)
-2
-3
0 20 40 60 80 100 120 140 160 180 200
Rg (Ω)
Figure 75. Typical peak I_ON and I_OFF currents vs. Rg (for ACPL-38JT output
driving an IGBT rated at 600 V/100 A).
For R_G = 10.5, the value read from Figure 76 is E_SWITCH =
6.05 J. Assume a worst-case average I_CC1 = 16.5 mA
(which is given by the average of I_CC1H and I_CC1L). Similarly
the average I_CC2 = 5.5 mA.
P_I = 16.5 mA * 5.5 V = 90.8 mW
P_O = P_O(BIAS) + P_O(SWITCH)
= 5.5 mA * (18 V – (–5 V)) + 6.051 J * 10 kHz
= 126.5 mW + 60.51 mW
= 187.01 mW
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