MC68HC705JP7CDW Freescale Semiconductor, MC68HC705JP7CDW Datasheet - Page 82

• Manufacturer Part Number: MC68HC705JP7CDW
• Description: IC MCU 8BIT 28-SOIC
• Manufacturer: Freescale Semiconductor
• Series: HC05r

Specifications of MC68HC705JP7CDW

• Core Processor: HC05
• Core Size: 8-Bit
• Speed: 2.1MHz
• Connectivity: SIO
• Peripherals: POR, Temp Sensor, WDT
• Number Of I /o: 22
• Program Memory Size: 6KB (6K x 8)
• Program Memory Type: OTP
• Ram Size: 224 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 4x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

Analog Subsystem
these bits and the ISEN bit are cleared when the device is reset, the MC68HC705JJ7/MC68HC705JP7
starts with the charge and discharge function disabled.
The length of time required to reach the maximum voltage to be measured and the speed of the time
counting mechanism will determine the resolution of the reading. The time to ramp the external capacitor
voltage to match the maximum voltage is dependent on:
The charging behavior is described by the general equation:
Where:
Since the MCU can measure time in a variety of ways, the resolution of the conversion will depend on the
length of the time keeping function and its prescaling to the oscillator frequency (f
charge time also equals:
Where:
The previous two equations for the charge time, t
for the full scale count (N
Since a given timing method has a fixed charge current and prescaler, then the variation in the resultant
count for a given unknown voltage is mainly dependent on the operating frequency and the capacitance
value used. The desired external capacitance for a given voltage range, f
resolution is defined as:
82
•
•
•
•
•
t
C
V
I
P= Prescaler value (÷ 2, ÷ 4, ÷ 8, etc.)
N= Number of counts during charge time
f
CHG
CHG
OSC
X
EXT
= Unknown voltage (volts)
Charging current to external capacitor
Value of the external capacitor
Clock rate for timing function
Any prescaling of the clock to the timing function
Desired resolution
= Oscillator clock frequency (Hz)
= Charge time (seconds)
= Charge current (µA)
= Capacitance (µF)
Noise on the system ground or the external ramping capacitor can cause
the comparator to trip prematurely. Therefore, in any given application it is
best to use the fastest possible ramp rate (shortest charge time).
The value of any capacitor connected directly to the PB0/AN0 pin should be
limited to less than 2 microfarads. Larger capacitances will create high
discharge currents which may damage the device or create signal noise.
MC68HC705JJ7 • MC68HC705JP7 Advance Information Data Sheet, Rev. 4.1
FS
) of the measured time versus the full scale unknown voltage (V
N
C
FS
EXT
= C
= N
t
CHG
EXT
t
FS
CHG
= C
x V
x P x I
= P x N / f
EXT
CHG
NOTE
NOTE
FS
x f
CHG
, can be combined to form the following expression
x V
OSC
X
/ (V
OSC
/ I
/ (P x I
CHG
FS
x f
CHG
OSC
)
)
OSC
, conversion method, and
OSC
Freescale Semiconductor
). Therefore, the
FS
):