JAJSFJ1 May 2018 DLPA4000
PRODUCTION DATA.
Integrated circuits in low-profile and fine-pitch surface-mount packages typically require special attention to power dissipation. Many different system-dependent issues affect the power dissipation limits of individual component. These issues include
These three basic approaches enhance thermal performance.
The DLPA4000 device has efficient power converters. But because the power delivered to the LEDs can be quite large (more than 50 W in some case) the power dissipation in the DLPA4000 device can be high. Use proper temperature calculation to minimize power dissipation in the application.
It is important to maintain the junction temperature below the maximum recommended value of 120°C during operation. Calculate PDISS, to determine the junction temperature of the DLPA4000. PDISS is a summation of all power dissipation. Use Equation 16 to calculate TJ.
where
The total power dissipation varies depending on the application specifications. The main variances in the DLPA4000 circuitry are:
Use Equation 17 to calculate the dissipation for the buck converter.
where
shows efficiency for buck converters PWR1, PWR2, PWR5, PWR6, and PWR7.
Buck converters require high power efficiency because they typically handle the highest power levels. Linear regulators,(for example, LDOs) handle lower power levels. Because the efficiency of an LDO can be relative low, the related power dissipation can be significant.
Use Equation 18 to calculate the power dissipation of an LDO, PDISS(ldo).
where
Because the voltage decrease over the LDO (VIN – VOUT) can be relative large, a relatively small load current can yield significant power dissipation in the DLPA4000 device. In this case, consider using one of the general purpose bucks to have a more power-efficient solition (in other words, a less dissipation solution).
It is important to consider the power dissipation of the LDO that supplies the boost power converter (the LDO DMD). The boost converter supplies high voltages for the DMD. This voltages are VBIAS, VOFS, VRST.The maximum simultaneous load current ILOAD(max) for these lines is 10 mA . So, the maximum related power level is moderate. Use Equation 19 An efficiency rate of 80% for the boost converter, ηBOOST, implies a maximum boost converter dissipation, PDISS (DMD_boost,MAX).
The level of power dissipation of the illumination buck converter this is likely negligible. The term that might count to the total power dissipation is Pdiss_LDO_DMD. The input current of the DMD boost converter is supplied by this LDO. In case of an high supply voltage, a non negligible dissipation term is obtained. The worst case load current for the LDO is given by:
where
Dissipation of power in the LDO can be up to 1.5 W for an input supply voltage of 19.5 V. Power dissipation of 1.5 W is a worst case scenario. In most cases the load current of the LDO DMD is significantly less. Make sure to confirm the LDO current level for the specific application.
The DLPA4000 draws a quiescent current. The power supply voltage does not affect this quiescent current. For the buck converters the quiescent current is comprised in the efficiency numbers. For the LDOs a quiescent current on the order of 0.5 mA can be used. For the rest of the DLPA4000 circuitry, not included in the buck converters or LDOs, a quiescent current on the order of 3 mA applies. Use Equation 21 to estimate dissipation, Pdiss_DLPA4000 in the DLPA4000 device.
Use to calculate the maximum ambient temperature,
Use to calculate the junction temperature of the DLPA4000 device after you know the dissipated power and the ambient temperature.
Use Thermal Information to calculate the junction temperature for heat sink configuration and airflow.
Use one of these three design features if the combination of ambient temperature and DLPA4000 power dissipation does not yield an acceptable junction temperature ( <120°C).