dsp56858 Freescale Semiconductor, Inc, dsp56858 Datasheet - Page 27

• Manufacturer Part Number: dsp56858
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

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
4.4 AC Electrical Characteristics
Timing waveforms in
all pins except XTAL, which is tested using the input levels in
and V
Freescale Semiconductor
DD
DD
DDIO
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).
Input Signal
IL
Note: The midpoint is V
> V
for an input signal are shown.
4-3. The series diodes forward bias when the difference between V
DD
Supply
DDA
> (V
is typically connected directly to V
Figure 4-3 Example Circuit to Control Supply Sequencing
DDIO
DDIO
Regulator
Section 4.3
3.3V
Figure 4-4 Input Signal Measurement References
.
- 2.1V)
Fall Time
IL
+ (V
Midpoint1
DD
IH
V
– V
are tested with a V
to rise as V
IH
IL
)/2.
56858 Technical Data, Rev. 6
DDIO
Regulator
Low
V
1.8V
IL
ramps up. When the V
IL
DDIO
DDIO
maximum of 0.8V and a V
with some filtering.
supply, see
Section
Rise Time
4.2. In
Figure
High
DD
Figure 4-4
V
4-3. This keeps V
DDIO,
regulator begins proper
DDIO
IH
V
minimum of 2.0V for
AC Electrical Characteristics
V
DD
DDA
90%
and V
50%
10%
the levels of V
DD
DD
reaches
from
DD
27
IH