TH8056_12 Datasheet, PDF (21/34 Pages) Melexis Microelectronic Systems – Enhanced Single Wire CAN Transceiver

TH8056
Enhanced Single Wire CAN Transceiver
Assumptions:
V_BAT = 26.5V
R_load = 6.49 kΩ
Network with 32 nodes
V_CANH = 5.1V
I_BAT = 6mA
D = 50%
T_a = 125°C
Θ_JA = 70k/W (Thermally enhanced SOIC14 package)
Computations:
R_{load_net} = 6.49kΩ / 32nodes = 203Ω
I_load = 5.1V / 203Ω = 25mA
P_load = 5.1V * 25mA * 0.5 = 64mW
P_{INT_a} = (26.5V – 5.1V) * 25mA * 0.5 = 267mW
P_{INT_P} = 26.5V * 6mA = 159mW
P_tot = 267mW + 159mW = 426mW
T_j = 125°C + 426mW * 70k/W = 155°C
The above calculation shows that under worst case conditions (max. operating voltage, max bus load, max
ambient temperature) the TH8056 with the thermally enhanced SOIC14 package operates below the thermal
limit. A stable functioning is possible up to these limits.
3.9.1.Thermal behaviour of TH8056 with SOIC8 – TH8056 KDC A8
The thermal impedance of an SOIC8 package is about twice in comparison to the thermally enhanced
SOIC14 package. Therefore the maximum power dissipation within this package is only about the half.
The using of the SOIC8 version of TH8056 depends on the network architecture (number of nodes), the
max. ambient temperature and the needed functionality (using of INH pin).
The following diagram shows the relationship between junction temperature, ambient temperature and
number of nodes, which have to be taken into account for using the SOIC8 version.
TH8056 – Datasheet
3901008056
Page 21 of 34
June 2012
Rev 014