TH8062 Datasheet, PDF (24/38 Pages) Melexis Microelectronic Systems – Voltage Regulator with LIN Transceiver

TH8062
Voltage Regulator with LIN Transceiver
4. Application Hints
4.1 Safe Operating Area
The maximum power dissipation depends on the thermal resistance of the package and the PCB, the
temperature difference between Junction and Ambient as well as the airflow.
The power dissipation can be calculated with:
P_D = (V_SUP – V_CC) * I_VCC + P_{D_TX}
The power dissipation of the transmitter P_{D_TX} depends on the transceiver configuration and its parameters
as well as on the bus voltage V_BUS=V_BAT-V_D, the resulting termination resistance R_L, the capacitive bus load
C_L and the bit rate. Figure 16 shows the dependence of power dissipation of the transmitter as function of
V_SUP. The conditions for calculation of the power dissipation is R_L=500Ω, C_L=10nF, bit rate=20kbit and duty
cycle on TxD of 50%
50
45
40
35
30
25
20
15
10
5
0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
V_SUP [V]
Figure 16 - Power dissipation LIN transceiver @ 20kbit
The permitted package power dissipation can be calculated:
P_Dmax
=
T _j − T_A
R_{THJ − A}
If we consider that P_{D_TX_max}= f (V_SUP) the max output current I_VCC on V_{CC can} be calculated:
I _VCCmax
=
T _j − T_A
R_{THJ − A}
− P_{D _ TX _ max} @ VSUP
VSUP − VCC
T_J -T_A is the temperature difference between junction and ambient and R_th is the thermal resistance of the
package. The thermal energy is transferred via the package and the pins to the ambient. This transfer can be
improved with additional ground areas on the PCB as well as ground areas under the IC.
TH8062 – Datasheet
3901008062
Page 24 of 38
March 2006
Rev 002