MIC7400_15 Datasheet, PDF (33/68 Pages) Micrel Semiconductor – Configurable PMIC, Five-Channel Buck Regulator Plus One-Boost with HyperLight Load® and I2C Control

Micrel, Inc.
Once the total power dissipation is calculated, the IC
junction temperature can be estimated using Equation 7:
MIC7400
T_J(MAX) ≈ T_A + P_{D_TOTAL} × θ_JA
Eq. 7
Where:
T_J(MAX) = The maximum junction temperature
T_A = The ambient temperature
θ_JA = The junction-to-ambient thermal resistance of the
package (30°C/W)
Figure 16 shows the measured junction temperature
versus power dissipation of the MIC7400 evaluation
board. The actual junction temperature of the IC depends
upon many factors. The significant factors influencing the
die temperature rise are copper thickness in the PCB, the
surface area available for convection heat transfer, air
flow and power dissipation from other components,
including inductors, SOCs and processor ICs. It is good
engineering practice to measure all power components
temperature during the final design review using a
thermal couple or IR thermometer, see the “Thermal
Measurements” sub-section for details.
Figure 17. Power Derating Curve
The maximum power dissipation of the package can be
calculated by Equation 8:
P_D(MAX)
≈

T_J(MAX) −
θ _JA
T_A

Eq. 8
Where:
T_J(MAX) = Maximum junction temperature (125°C)
T_A = Ambient temperature
θ_JA = Junction-to-ambient thermal resistance of the
package (30°C/W).
Figure 16. Power Dissipation
Power Derating
The MIC7400 package has a 2W power dissipation limit.
To keep the IC junction temperature below a 125°C
design limit, the output power has to be limited above an
ambient temperature of 65°C. Figure 17 shows the power
dissipation derating curve.
Overtemperature Fault
An overtemperature fault is triggered when the IC
junction temperature reaches 160°C. When this occurs,
both the overtemperature fault flag is set to “1”, the global
power good output is pulled low and all the outputs are
turned off. During the fault condition the I²C interface
remains active and all registers values are maintained.
When the die temperature decreases by 20°C the
overtemperature fault bit can be cleared. To clear the
fault, either recycle power or write a logic “0” to the over
temperature fault register. Once the fault bit is cleared,
the outputs power up to their default values and are
sequenced according to the time slot settings.
March 3, 2015
33
Revision 2.0