HCPL-3120 Datasheet, PDF (12/15 Pages) Agilent(Hewlett-Packard) – 2.0 Amp Output Current IGBT Gate Drive Optocoupler

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
From the thermal mode in Figure shown in Figure 29. The HCPL-
28 the LED and detector IC
3120 improves CMR performance
junction temperatures can be
by using a detector IC with an
expressed as:
optically transparent Faraday
shield, which diverts the capaci-
T_JE = P_E ^• (θ_LC||(θ_LD + θ_DC) + θ_CA)
tively coupled current away from
( ) + P_D^•
–_θ–_L–_C–^θ₊–^L–^C–_θ^*–_D–_C^θ–^D–₊^C––_θ–_L–_D– + θ_CA
the sensitive IC circuitry. How
+ T_{A ever, this shield does not}
eliminate the capacitive coupling
( ) T_JD = P_E –_θ–_L–_C–^θ–₊^L–^C–_θ^•–_D^θ–_CD–₊^C–––_θ–_LD– + θ_CA
between the LED and optocoup-
ler pins 5-8 as shown in
Figure 30. This capacitive
+ P_D^•(θ_DC||(θ_LD + θ_LC) + θ_CA) + T_A
coupling causes perturbations in
the LED current during common
= 93 mW
E_SW(MAX) = –P–^O–⁽–^SW––^IT–^C_f–^H–^I–^N–^G–^M–^A–^X–⁾
= –9–3––m––W– = 4.65 µW
20 kHz
For Qg = 500 nC, from Figure
27, a value of E_SW = 4.65 µW
gives a Rg = 10.3 Ω.
Thermal Model
Inserting the values for θ_LC and
θ_DC shown in Figure 28 gives:
T_JE = P_E^•(256°C/W + θ_CA)
+ P_D^•(57°C/W + θ_CA) + T_A
T_JD = P_E^•(57°C/W + θ_CA)
+ P_D^•(111°C/W + θ_CA) + T_A
For example, given P_E = 45 mW,
P_O = 250 mW, T_A = 70°C and θ_CA
= 83°C/W:
mode transients and becomes the
major source of CMR failures for
a shielded optocoupler. The main
design objective of a high CMR
LED drive circuit becomes
keeping the LED in the proper
state (on or off) during common
mode transients. For example,
the recommended application
circuit (Figure 25), can achieve
15 kV/µs CMR while minimizing
component complexity.
The steady state thermal model
for the HCPL-3120 is shown in
Figure 28. The thermal resistance
values given in this model can be
used to calculate the tempera-
tures at each node for a given
operating condition. As shown by
the model, all heat generated
flows through θ_CA which raises
the case temperature T_C
accordingly. The value of θ_CA
depends on the conditions of the
board design and is, therefore,
determined by the designer. The
value of θ_CA = 83°C/W was
obtained from thermal measure-
ments using a 2.5 x 2.5 inch PC
board, with small traces (no
ground plane), a single HCPL-
3120 soldered into the center of
the board and still air. The
absolute maximum power
dissipation derating specifications
assume a θ_CAvalue of 83°C/W.
T_JE = P_E^•339°C/W + P_D^•140°C/W + T_A
= 45 mW^•339°C/W + 250 mW
•_{140°C/W + 70°C = 120°C}
Techniques to keep the LED in
the proper state are discussed in
the next two sections.
T_JD = P_E^•140°C/W + P_D^•194°C/W + T_A
= 45 mW^•140C/W + 250 mW
•_{194°C/W + 70°C = 125°C}
T_JE and T_JD should be limited to
125C based on the board layout
and part placement (θ_CA) specific
to the application.
LED Drive Circuit
Considerations for Ultra
High CMR Performance.
Without a detector shield, the
dominant cause of optocoupler
CMR failure is capacitive
coupling from the input side of
the optocoupler, through the
package, to the detector IC as
14
Qg = 100 nC
12
Qg = 500 nC
Qg = 1000 nC
10
V_CC = 19 V
8
V_EE = -9 V
6
4
2
0
0
10
20
30 40 50
Rg – GATE RESISTANCE – Ω
Figure 27. Energy Dissipated in the
HCPL-3120 for Each IGBT Switching
Cycle.
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