AN4536 Application Note Rev. 2.0 1/2014
Freescale Semiconductor
29
Hardware Considerations
3.1
Programming the MMPF0100 on an Application Board
When programming the MMPF0100 in an application board, voltages must be applied at the VIN, VDDIO and
VDDOTP pins. Considerations must be made to allow voltages to be applied on these rails in a fully populated
system board.
3.2
Isolating SCL/SDA
During OTP programming of the MMPF0100, commands are sent to the MMPF0100 via the SCL/SDA pins using
an I
2
C communications bridge, typically a programming dongle such as the KITPFPGMEVME. In a typical
application, the SCL and SDA pins of the MMPF0100 are connected to communication ports of an I
2
C master,
typically the processor. Depending on how the ports in the processor are designed, it may or may not be valid to
communicate with the MMPF0100 using an external dongle while the SCL/SDA pins are still connected to the
processor especially when the processor is unpowered due to a yet-to-be-programmed MMPF0100.
It is recommended to isolate the SCL/SDA lines going to the processor while communicating with the MMPF0100
using an external dongle as shown in the example in
Figure 2
. In the normally closed position of the analog switch
(NLAS3158 or similar), SCL and SDA of the MMPF0100 are connected to the processor. When the signal
Programmer_Select_O/P is high, SCL and SDA of the MMPF0100 are connected to the external programming
interface. The Programmer_Select_O/P signal can be generated by the programming interface as well.
Figure 2. Isolating SCL and SDA Using an Analog Switch
Note: Using the analog switch may not be the most cost effective option to isolate the I
2
C bus. Similar functionality
can be achieved by using solder shorts or 0 Ohm resistors. However, minor rework of the board would be required
once OTP programming is completed.
Processor_SCL
Processor_SDA
Program
m
e
r_SCL
Program
m
e
r_SDA
Program
m
e
r_Selec
t_O
/P
MMPF0100/Z
SCL
54
SDA
53
VDDIO
55
NLAS3158
1
2
3
5
4
12
11
9
6
8
7
10
R98
4.7K
R97
4.7K
