Table 1. Design Parameters

10.2.2.1 Drive Current

The coil current is determined by the coil voltage (VSUP), coil resistance & output low voltage (V_OL or V_CE(SAT)).

10.2.2.2 Output Low Voltage

The output low voltage (V_OL) is the same thing as V_CE(SAT) and can be determined by the Electrical Characteristics table, Figure 1, or Figure 2.

10.2.2.3 Power Dissipation & Temperature

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 4 or Figure 5.

For a more accurate determination of number of coils possible, use the below equation to calculate SN75468 on-chip power dissipation P_D:

Equation 2.

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 SN75468 and the system the on-chip power dissipation must be lower that or equal to the maximum allowable power dissipation (PD_(MAX)) dictated by below equation Equation 3.

Equation 3.

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 SN75468 IC’s die junction temperature to less than 125°C. The IC junction temperature is directly proportional to the on-chip power dissipation.