AN1836 Motorola / Freescale Semiconductor, AN1836 Datasheet - Page 22

• Manufacturer Part Number: AN1836
• Description: FLASH Programming for Motorola MC68HC912 Microcontrollers
• Manufacturer: Motorola / Freescale Semiconductor

Application Note
Example V
Protection
Circuitry
22
FP
Figure 10
can maintain the appropriate voltage levels on the V
outlines the design for this circuit, what each component is intended to
do, and some design considerations when designing V
The general idea of this circuit implementation is to supply V
dc-dc 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-k pullup resistor
(R1) does, the output V
that the programming and erasing routines assert a 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
power-down, ensuring that they rise and fall together. Capacitors C5 and
C6 are the normal decoupling capacitors on the V
used to reduce electromagnetic interference (EMI) in the circuit. If C3 is
too large, V
shows an example of a circuit which, if properly implemented,
FP
will not be allowed to fall with V
Figure 10. V
Out
is shorted to the V
FP
FP
is tied to V
Supply Circuit
DD
DD
DD
, potentially causing data
supply. This requires
on power-up and
DD
FP
supply lines. C3 is
FP
pin. This section
pin protection.
FP
MOTOROLA
from a
AN1836