XC912BC32CFU8 Motorola Semiconductor Products, XC912BC32CFU8 Datasheet - Page 344

• Manufacturer Part Number: XC912BC32CFU8
• Description: M68HC12B Family Data Sheet
• Manufacturer: Motorola Semiconductor Products

Electrical Specifications
Data Sheet
344
NOTE:
The general idea of this circuit implementation is to supply V
converter. This dc-dc converter, like most, provides a shutdown feature which
allows the converter’s output to be shut off. When the SHDN pin on the converter
is pulled high, as the 10-kΩ pullup resistor (R1) does, the output V
the V
port pin on the MCU to turn on the converter and supply the 12-volt programming
voltage during the programming or erasing cycle. Simple programming and erasing
routines, such as those shown earlier in this application note, will no longer suffice.
By implementing this solution, V
ensuring that they rise and fall together. Capacitors C5 and C6 are the normal
decoupling capacitors on the V
electromagnetic interference (EMI) in the circuit. If C3 is too large, V
allowed to fall with V
(Refer to
V
of current for at least 20 µs (based on programming cycle requirements) and 4 mA
of current for at least 10 ms (based on erase cycle requirements).
A certain degree of experimentation might be required when selecting C4 and C3.
When trying different capacitor values, always monitor the effects on V
during power-down and current supplied to the V
R1 must be no larger than 10 kΩ, to make certain that the SHDN pin on the dc-dc
converter is never allowed to fall below V
microcontroller is driven low. The external pullup ensures this behavior, no matter
what port pin is used on the microcontroller or what the internal structure of that pin
looks like. Without a strong enough pullup resistor on R1, the voltage on the SHDN
pin might drop during a reset event, causing the dc-dc converter to activate and
begin driving the voltage on V
data corruption in the FLASH.
Figure 19-2
ST662A from ST Microelectronics, but it is correct. The change is in the location of
the capacitor C4, which is now placed between V
implemented with the cooperation of ST Microelectronics to aid in tracking a rapidly
falling V
has been verified with the Maxim Integrated Products device (MAX662).
Be certain that V
values are tested. The rate of decay of the V
define how large the C3 capacitance can be made.
Out
to the target device. The supply must be able to source approximately 30 mA
DD
DD
supply. This requires that the programming and erasing routines assert a
Figure
voltage level, such as in
is different from the recommended circuit shown in information about
FP
19-3.) C4 is where the dc-dc converter stores charge to supply
decays with V
Electrical Specifications
DD
, potentially causing data corruption in the FLASH array.
Out
DD
FP
DD
to begin to rise to 12 volts. This would result in
supply lines. C3 is used to reduce
is tied to V
, as shown in
Figure 19-3
DD
unless the output pin of the
DD
DD
supply powering down will help
and
Figure
on power-up and power-down,
FP
DD
pin.
and V
Figure
19-4, as new capacitance
M68HC12B Family — Rev. 8.0
FP
19-4. This circuit also
FP
. This change was
from a dc-dc
Out
FP
is shorted to
FP
will not be
MOTOROLA
decay