SI8233 Datasheet, PDF (31/57 Pages) Silicon Laboratories – 0.5 AND 4.0 AMP ISODRIVERS

Si823x
4.2. Dual Driver
Figure 44 shows the Si823x configured as a dual driver. Note that the drain voltages of Q1 and Q2 can be
referenced to a common ground or to different grounds with as much as 1500 V dc between them.
VDDI
C1
1 µF
VDDI
C2
0.1 µF
GNDI
PH1
VIA
PH2
VIB
VOA
Q1
VDDA
VDDA
C3
0.1 µF
GNDA
C4
10 µF
CONTROLLER
Si8232/5/7/8
VDDB
VDDB
I/O
DISABLE
C5
0.1 µF
C6
10 µF
GNDB
Q2
VOB
Figure 44. Si8232/5/7/8 in a Dual Driver Application
Because each output driver resides on its own die, the relative voltage polarities of VOA and VOB can reverse
without damaging the driver. That is, the voltage at VOA can be higher or lower than that of VOB by VDD without
damaging the driver. Therefore, a dual driver in a low-side high side/low side drive application can use either VOA
or VOB as the high side driver. Similarly, a dual driver can operate as a dual low-side or dual high-side driver and is
unaffected by static or dynamic voltage polarity changes.
4.3. Dual Driver with Thermally Enhanced Package (Si8236)
The thermal pad of the Si8236 must be connected to a heat spreader to lower thermal resistance. Generally, the
larger the thermal shield’s area, the lower the thermal resistance. It is recommended that thermal vias also be used
to add mass to the shield. Vias generally have much more mass than the shield alone and consume less space,
thus reducing thermal resistance more effectively. While the heat spreader is not generally a circuit ground, it is a
good reference plane for the Si8236 and is also useful as a shield layer for EMI reduction.
With a 10mm² thermal plane on the outer layers (including 20 thermal vias), the thermal impedance of the Si8236
was measured at 50 °C/W. This is a significant improvement over the Si8235 which does not include a thermal
pad. The Si8235’s thermal resistance was measured at 105 °C /W. In addition, note that the GNDA and GNDB pins
for the Si8236 are connected together through the thermal pad.
Rev. 1.7
31