10.3 Thermal Considerations

The number of coils driven is dependent on the coil current and on-chip power dissipation. The number of coils driven can be determined by Figure 3 or Figure 4.

For a more accurate determination of number of coils possible, use Equation 3 to calculate TPL7407LA on-chip power dissipation P_D:

Equation 3.

where

• N is the number of channels active together
• V_OLi is the OUT_i pin voltage for the load current I_Li. This is the same as V_CE(SAT)

In order to guarantee reliability of TPL7407LA and the system, the on-chip power dissipation must be lower than or equal to the maximum allowable power dissipation (P_D(MAX)) dictated by below equation Equation 4.

Equation 4.

where

• T_J(MAX) is the target maximum junction temperature
• T_A is the operating ambient temperature
• θ_JA is the package junction to ambient thermal resistance

It is recommended to limit rhe TPL7407LA IC’s die junction temperature to less than 125°C. The IC junction temperature is directly proportional to the on-chip power dissipation.