STCC02-ED5 Datasheet, PDF (9/13 Pages) STMicroelectronics – CONTROL CIRCUIT FOR HOME APPLIANCE MCU BASED APPLICATION

STCC02-ED5
APPLICATION RECOMMENDATIONS
■ EVALUATION OF THE STCC02 DISSIPATION IN ITS APPLICATION
In order to define accurately at which maximum input supply voltage the STCC02 can work safely, the dis-
sipated power has to be evaluated. Indeed, the STCC02 device can withstand voltages up to 30V, as
specified in the table 1 "ABSOLUTE RATINGS" section.
However, when the V_IN voltage is high, it will also increase the power dissipation P_DIS and the junction
temperature T_J of the whole circuit.
For the evaluation of the maximum junction temperature, the following equation should be used to calcu-
late dissipated power:
P_DIS
=
(V_IN
–
V_DD)
×
I_DD
+
V_IN
.
I_Q
+
V_ON
×
(I_M@FAN1
+
I_M@MAG2
+
I_M@BUZ3)
+
--^V----^I--^N----–-----^V----^O----^N--
1.2 × R_BUZ
×
τ
Indeed, the power dissipation is mainly due to the regulator and to the currents sunk by the three driver
outputs FAN₁, MAG₂, and BUZ₃.
Furthermore, the input voltage VIN is linked to the relays conduction in most applications. When the relay
coils are driven, the storage supply capacitor is discharged and VINis no longer equal to the peak voltage
of the transformer secondary winding. In this case, VIN should approach the average value of the second-
ary voltage. This value is then approximately 36% lower that in stand-by operation, as explained by the
following equation:
V_IN (relays_on) ≈ ²-_π- × V_IN (relays_off)
When the relays are off, the dissipation losses formula is:
P_DIS
=
(V_IN
–
V_DD)
×
I_DD
×
I_Q
+
--^V----^I--^N----–-----^V----^O----^N--
1.2 × R_BUZ
×
τ
For instance if V_IN = 27V, V_DD = 5V, I_Q = 2.5mA, I_DD = 20mA, R_BUZ = 1.5kΩ, τ = duty cycle = 50%, the
dissipated power in the STCC02 is evaluated at 0.68W.
When the relays are on, the full formula of the dissipation losses is applied. For instance in the
same AC line conditions with the relays on, V_IN drops down to 17.5V. Considering I_{M BUZ3} = 10mA,
I_{M FAN1} = I_{M MAG2} = 100mA and V_ON = 1.5V, the dissipated power in the STCC02 becomes 0.67W.
The maximum junction temperature is given by:
T_{J max} = T_{AMB max} + R_{th (j – |a)} × P_DIS
The maximum allowed input supply voltage is then chosen in order to keep the junction temperature below
its maximum operating value 150°C.
Since the maximumjunction temperature is 150°C, the maximum ambient temperature T_AMB is 80°C in this
application, and the thermal resistance is 100°C/W, the maximum allowed dissipation becomes 0.70 W.
The two dissipation cases described above are compatible with the package dissipation capability.
Otherwise, the ambient temperature T_AMB, the input voltage V_IN or the load current I_DD should limited by
design to meet the circuit thermal requirements.
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