SI82390AD-IS Datasheet, PDF (10/38 Pages) Silicon Laboratories – 4.0 A ISODrivers with 2.5 V VDDI and Safety Features

Si8239x Data Sheet
System Overview
Substituting values for PDmax Tjmax, TA, and θ_ja into Equation 2 results in a maximum allowable total power dissipation of 1.19 W.
Maximum allowable load is found by substituting this limit and the appropriate data sheet values from Table 4.1 Electrical Characteris-
tics^1,2 on page 15 into Equation 1 and simplifying. The result is Equation 3 (4.0 A driver), which assumes VDDI = 5 V and VDDA =
VDDB = 18 V.
Equation 3 is graphed in the following figure where the points along the load line represent the package dissipation-limited value of C_L
for the corresponding switching frequency.
Figure 2.15. Max Load vs. Switching Frequency
2.5 Layout Considerations
It is most important to minimize ringing in the drive path and noise on the Si8239x VDD lines. Care must be taken to minimize parasitic
inductance in these paths by locating the Si8239x as close to the device it is driving as possible. In addition, the VDD supply and
ground trace paths must be kept short. For this reason, the use of power and ground planes is highly recommended. A split ground
plane system having separate ground and VDD planes for power devices and small signal components provides the best overall noise
performance.
2.6 Undervoltage Lockout Operation
Device behavior during start-up, normal operation and shutdown is shown in Figure 2.16 Si82391/6/8 Device Behavior during Normal
Operation and Shutdown on page 10, where UVLO+ and UVLO- are the positive-going and negative-going thresholds respectively.
Note that outputs VOA and VOB default low when input side power supply (VDDI) is not present.
2.6.1 Device Startup
Outputs VOA and VOB are held low during power-up until VDD is above the UVLO threshold for time period tSTART. Following this,
the outputs follow the states of inputs VIA and VIB.
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