HCPL-3180-500E Datasheet, PDF (13/16 Pages) AVAGO TECHNOLOGIES LIMITED – 2.5 Amp Output Current, High Speed, Gate Drive Optocoupler

Thermal Model
(Discussion applies to HCPL-3180)
The steady state thermal model for the HCPL-3180 is
shown in Figure 27. The thermal resistance values given
in this model can be used to calculate the temperatures
at each node for a given operating condition. As shown
by the model, all heat generated flows through q_CA which
raises the case temperature TC accordingly. The value of
q_CA depends on the conditions of the board design and
is, therefore, determined by the designer. The value of
q_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- 3180 soldered into the
center of the board and still air. The absolute maximum
power dissipation derating specifications assume a q_CA
value of +83 °C/W. From the thermal mode in Figure 27,
the LED and detector IC junction temperatures can be
expressed as:
[ ] T_JE = P_E * (q_LC//q_LD + q_DC) + q_CA) + P_D * _qLC^q₊^LC_qD^*_C^qD₊^C_qLD+ q_CA + T_A
[ ] T_JD = P_E * _qLC^q₊^LC_qD^*_C^qD₊^C_qLD+ q_CA + P_{D *} (q_LC//q_LD + q_DC) + q_CA) + T_A
θ_LD = 442 °C/W
T_JE
T_JD
θ_LC = 467 °C/W
θ_DC = 126 °C/W
T_C
θ_CA = 83 °C/W*
T_A
Figure 27. Thermal model.
T_JE = LED JUNCTION TEMPERATURE
T_JD = DETECTOR IC JUNCTION TEMPERATURE
T_C = CASE TEMPERATURE MEASURED AT THE
CENTER OF THE PACKAGE BOTTOM
θ_LC = LED-TO-CASE THERMAL RESISTANCE
θ_LD = LED-TO-DETECTOR THERMAL RESISTANCE
θ_DC = DETECTOR-TO-CASE THERMAL RESISTANCE
θ_CA = CASE-TO-AMBIENT THERMAL RESISTANCE
*θ_CA WILL DEPEND ON THE BOARD DESIGN AND
THE PLACEMENT OF THE PART.
T_JE = P_E * (256°C/W + q_CA) + P_D * (57°C/W + q_CA) + T_A
T_JD = P_E * (57°C/W + q_CA) + P_D * (111°C/W + q_CA) + T_A
For example, given P_E = 45 mW,
P_O = 250 mW, T_A = +70 °C and q_CA = +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
T_JD = P_E * 140°C/W + P_D * 194°C/W + T_A
= 45 mW * 140°C/W + 250 mW * 194°C/W + 70°C
= 125°C
T_JE and T_JD should be limited to +125 °C based on the board layout and part
placement (q_CA) specific to the application.
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