dsp56857 Freescale Semiconductor, Inc, dsp56857 Datasheet - Page 25

• Manufacturer Part Number: dsp56857
• Description: Dsp56857 Digital Signal Controller
• Manufacturer: Freescale Semiconductor, Inc

4.3 Supply Voltage Sequencing and Separation Cautions
Figure 4-2
V
supply (1.8V) from the voltage generated by the 3.3V V
rising faster than V
V
Typically this situation is avoided by using external discrete diodes in series between supplies, as shown
in
approximately 2.1, causing V
operation, the difference between supplies will typically be 0.8V and conduction through the diode chain
reduces to essentially leakage current. During supply sequencing, the following general relationship
should be adhered to:
V
In practice, V
Freescale Semiconductor
DD
DD
DDIO
Note: 1. V
Figure
should not be allowed to rise early (1). This is usually avoided by running the regulator for the V
should not rise so late that a large voltage difference is allowed between the two supplies (2).
2. V
> V
3.3V
1.8V
DDIO
DD
4-3. The series diodes forward bias when the difference between V
DD
shows two situations to avoid in sequencing the V
Supply
0
rising before V
, V
DDA
> (V
Figure 4-2 Supply Voltage Sequencing and Separation Cautions
DDA
rising much faster than V
is typically connected directly to V
Figure 4-3 Example Circuit to Control Supply Sequencing
DDIO
DDIO
Regulator
DDIO
3.3V
.
- 2.1V)
1
, V
DDA
DD
to rise as V
DD
56857 Technical Data, Rev. 6
DDIO
Regulator
1.8V
2
ramps up. When the V
DDIO
DDIO
with some filtering.
supply, see
DD
and V
Supply Voltage Sequencing and Separation Cautions
Supplies Stable
DDIO,
Figure
DD
V
V
DDA
4-3. This keeps V
DDIO,
regulator begins proper
DDIO
V
supplies.
V
DD
DDA
and V
V
DDIO,
V
Time
DD
DD
V
DDA
DD
reaches
from
DD
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