SLRS066D January 2014 – March 2016 TPL7407L
Thin traces can be used on the input due to the low current logic that is typically used to drive TPL7407L. Care must be taken to separate the input channels as much as possible, as to eliminate cross-talk. Thick traces are recommended for the output, in order to drive whatever high currents that may be needed. Wire thickness can be determined by the trace material's current density and desired drive current.
Since all of the channels currents return to a common ground, it is best to size that trace width to be very wide. Some applications require up to 2 A.
Since the COM pin will only draw up to 25 µA thick traces are not necessary.
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, Figure 4, Figure 5, Figure 6, Figure 7, or Figure 8.
For a more accurate determination of number of coils possible, use the below equation to calculate TPL7407L on-chip power dissipation PD:
In order to guarantee reliability of TPL7407L and the system, the on-chip power dissipation must be lower than or equal to the maximum allowable power dissipation (PD(MAX)) dictated by below equation Equation 3.
It is recommended to limit TPL7407L IC’s die junction temperature to less than 125°C. The IC junction temperature is directly proportional to the on-chip power dissipation.
θJA value depends on the PC board layout. An external heat sink and/or a cooling mechanism, like a cold air fan, can help reduce θJA and thus improve device thermal capabilities. Refer to TI’s design support web page at www.ti.com/thermal for a general guidance on improving device thermal performance.