si8235 Silicon Laboratories, si8235 Datasheet - Page 15

• Manufacturer Part Number: si8235
• Description: 0.5 And 4.0 A Isodrivers
• Manufacturer: Silicon Laboratories

Si823x
Equation 1 and Equation 2 are graphed in Figure 7 where the points along the load line represent the package
dissipation-limited value of CL for the corresponding switching frequency.
10,000
0.5 A
4 A
1,000
100
10
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
Frequency (kHz)
Figure 7. Max Load vs. Switching Frequency
5.5. Layout Considerations
It is most important to minimize ringing in the drive path and noise on the Si823x VDD lines. Care must be taken to
minimize parasitic inductance in these paths by locating the Si823x 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.
5.6. Device Operation
Device behavior during start-up, normal operation and shutdown is shown in Figure 8, 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.
5.6.1. Device Startup
Outputs VOA and VOB are held low during power-up until VDD is above the UVLO threshold for time period
tSTARTUP. Following this, the outputs follow the states of inputs VIA and VIB.
5.6.2. Under Voltage Lockout (UVLO)
UVLO is provided to prevent erroneous operation during device startup and shutdown or when VDD is below its
specified operating circuits range. The input (control) side, Driver A and Driver B, each have their own under
voltage lockout monitors.
The Si823x input side enters UVLO when VDDI < V
, and exits UVLO when VDDI > VDD
. The driver
IUVH–
IUV+
outputs, VOA and VOB, remain low when the input side of the Si823x is in UVLO and their respective VDD supply
(VDDA, VDDB) is within tolerance. Each driver output can enter or exit UVLO independently. For example, VOA
unconditionally enters UVLO when VDDA falls below VDD
and exits UVLO when VDDA rises above
AUV–
VDD
.
AUV+
Preliminary Rev. 0.11
15