R5F21257SNFP#U0 Renesas Electronics America, R5F21257SNFP#U0 Datasheet - Page 414

• Manufacturer Part Number: R5F21257SNFP#U0
• Description: IC R8C/25 MCU FLASH 52LQFP
• Manufacturer: Renesas Electronics America
• Series: R8C/2x/25r

Specifications of R5F21257SNFP#U0

• Core Processor: R8C
• Core Size: 16/32-Bit
• Speed: 20MHz
• Connectivity: I²C, LIN, SIO, SSU, UART/USART
• Peripherals: POR, Voltage Detect, WDT
• Number Of I /o: 41
• Program Memory Size: 48KB (48K x 8)
• Program Memory Type: FLASH
• Ram Size: 2.5K x 8
• Voltage - Supply (vcc/vdd): 2.2 V ~ 5.5 V
• Data Converters: A/D 12x10b
• Oscillator Type: Internal
• Operating Temperature: -20°C ~ 85°C
• Package / Case: 52-LQFP
• For Use With: R0K521256S000BE - KIT EVAL STARTER FOR R8C/25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -

R8C/24 Group, R8C/25 Group
Rev.3.00
REJ09B0244-0300
18.6
Figure 18.11
To carry out A/D conversion properly, charging the internal capacitor C shown in Figure 18.11 has to be completed
within a specified period of time. T (sampling time) as the specified time. Let output impedance of sensor
equivalent circuit be R0, internal resistance of microcomputer be R, precision (error) of the A/D converter be X,
and the resolution of A/D converter be Y (Y is 1024 in the 10-bit mode, and 256 in the 8-bit mode).
Figure 18.11 shows the Analog Input Pin and External Sensor Equivalent Circuit. When the difference between
VIN and VC becomes 0.1LSB, we find impedance R0 when voltage between pins VC changes from 0 to VIN-
(0.1/1024) VIN in time T. (0.1/1024) means that A/D precision drop due to insufficient capacitor charge is held to
0.1LSB at time of A/D conversion in the 10-bit mode. Actual error however is the value of absolute precision
added to 0.1LSB.
When f(XIN) = 10 MHz, T = 0.25 µs in the A/D conversion mode without sample & hold. Output impedance R0
for sufficiently charging capacitor C within time T is determined as follows.
Thus, the allowable output impedance of the sensor equivalent circuit, making the precision (error) 0.1LSB or less,
is approximately 1.7 kΩ. maximum.
Output Impedance of Sensor under A/D Conversion
Feb 29, 2008
VC is generally
And when t = T,
Hence,
T = 0.25 µs, R = 2.8 kΩ, C = 6.0 pF, X = 0.1, and Y = 1024. Hence,
R0
Analog Input Pin and External Sensor Equivalent Circuit
=
R0
–
-------------------------------------------------- -
6.0
=
×
Page 395 of 485
–
0.25
10
VC
-------------------
C
Sensor equivalent
circuit
VC
•
–
–
e
12
T
=
×
VIN
NOTE:
ln
–
--------------------------
C R0
10
1. The capacity of the terminal is assumed to be 4.5 pF.
•
VIN 1 e
X
--- -
Y
=
--------------------------T
C R0
(
ln
(
6 –
–
VIN
1
----------- -
1024
R
0.1



1
+
+
R
–
–
R
R0
–
)
X
--- - VIN
Y
T
2.8
)
–
=
--------------------------
C R0
=
×10
ln
(
X
--- -
Y
X
--- -
Y
3
1
=
≈
+
VIN 1
1.7
R
MCU
)
×10
t
C (6.0 pF)


R (2.8 kΩ)



3
–
X
--- -
Y


VC
18. A/D Converter