MIC5312-DKBML 查看數據表（PDF） - Micrel
零件编号
产品描述 (功能)
生产厂家
MIC5312-DKBML Datasheet PDF : 11 Pages
| |||
Micrel, Inc.
MIC5312
The actual power dissipation of the regulator circuit can
be determined using the equation:
PDTOTAL = PD LDO1 + PD LDO2
PD LDO1 = (VIN-VOUT1) x IOUT1
PD LDO2 = (VIN-VOUT2) x IOUT2
Substituting PD(max) for PD and solving for the operating
conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit.
For example, when operating the MIC5312 at 60°C with
a minimum footprint layout, the maximum load currents
can be calculated as follows:
PD (max) = (TJ (max) - TA) /θJA
PD (max) = (125°C - 60°C) / 63°C /W
PD (max) = 1.03W
The junction-to-ambient thermal resistance for the
minimum footprint is 63°C/W, from Table 1. The
maximum power dissipation must not be exceeded for
proper operation. Using a lithium-ion battery as the
supply voltage of 4.2V, 1.8VOUT/150mA for channel 1
and 2.8VOUT/100mA for channel 2, power dissipation
can be calculated as follows:
PD LDO1 = (VIN-VOUT1) x IOUT1
PD LDO1 = (4.2V-1.8V) x 150mA
PD LDO1 = 360mW
PD LDO2 = (VIN-VOUT2) x IOUT2
PD LDO1 = (4.2V-2.8V) x 100mA
PD LDO1 = 140mW
PDTOTAL = PD LDO1 + PD LDO2
PDTOTAL = 360mW + 140mW
PDTOTAL = 500mW
The calculation shows that we are well below the
maximum allowable power dissipation of 1.03W for a
60° ambient temperature.
After the maximum power dissipation has been
calculated, it is always a good idea to calculate the
maximum ambient temperature for a 125° junction
temperature. Calculating maximum ambient temperature
as follows:
TA(max) = TJ(max) – (PD x θJA)
TA(max) = 125°C – (500mW x 63°C/W)
TA(max) = 93.5°C
For a full discussion of heat sinking and thermal effects
on voltage regulators, refer to the “Regulator Thermals”
section of Micrel’s Designing with Low-Dropout Voltage
Regulators handbook.
This information can be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
February 2005
10
M9999-021105
(408) 955-1690
Share Link: 