But the diodes have about 0.8V forward voltage. So for big current, use MOSFET, for example:
STV300NH02L+LTC4352IMS
This can take low to 0.8mohm resistance.
Even this, the power of the chip can rise to 1.28W under 40A current, we should use the thermal pad for heat dissipating.
How to calculate the Rth?(thermal resistant 热阻)
Rth=H/(Tc*A)
热阻(`C/W)=厚度/(导热系数*面积)
导热系数单位：W/m.k
For example:
CHIP STV300H02L, Rthj-case=0.5`C/W, Rthj-amb=50`C/W
Because we use thermal pad between chip and heat sink, so, we will use Rth-case only. And if use no thermal pad, the heat will dissipate to air directly, Rthj-amb will be used.
Rthj-case, junction到case的热阻，用于case外面有其他导热材料，需将导热材料的热阻相加。。。Rthj-amb，junction到ambient的热阻，就是指到片子周围的环境的热阻，相当于直接向空气传热，如果无其他导热材料，用此参数计算芯片温升。
We select thermal pad: T-global H48-6, Tc=3.2W/m.k, 37x27x5mm, and assume that the heat sink is ideal.
Rth-all=Rthj-case+Rth-pad=0.5+5E-3/(3.2*37E-3*27E-3)=2.64`C/W
Note that this result is very ideal because we assume that the heat to heat sink will be totally dissipated immediately.
Also, the thermal compound can be used too and the calculate method is similar.
No comments:
Post a Comment