ADC Characteristics
MC68HC908GR8B Data Sheet, Rev. 3.0
Freescale Semiconductor
241
19.12 ADC Characteristics
Characteristic(1)
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, VDDAD = 5.0 Vdc ± 10%, VSSAD = 0 Vdc, VREFH = 5.0 Vdc ± 10%, VREFL = 0
Symbol
Min
Max
Unit
Comments
Supply voltage
VDDAD
2.7
(VDD
min)
5.5
(VDD
max)
V
VDDAD should be tied to
the same potential as
VDD via separate
traces.
Input voltages
VADIN
0VDDAD
VVADIN <= VREFH
Resolution
BAD
88
Bits
Absolute accuracy
(VREFL = 0 V, VDDAD = VREFH = 5 V ± 10%)
AAD
± 1
LSB
Includes quantization
ADC internal clock
fADIC
0.5
1.048
MHz
tAIC = 1/fADIC, tested
only at 1 MHz
Conversion range
RAD
VREFL
VREFH
V
VREFH = VDDAD
VREFL = VSSAD
Power-up time
tADPU
16
tAIC cycles
Conversion time
tADC
16
17
tAIC cycles
Sample time(2)
2. Source impedances greater than 10 k
Ω adversely affect internal RC charging time during input sampling.
tADS
5—
tAIC cycles
Zero input reading(3)
3. Zero-input/full-scale reading requires sufficient decoupling measures for accurate conversions.
ZADI
00
01
Hex
VIN = VREFL
Full-scale reading(3)
FADI
FE
FF
Hex
VIN = VREFH
Input capacitance
CADI
—
(20) 8
pF
Not tested
Input leakage(4)
Port B
4. The external system error caused by input leakage current is approximately equal to the product of R source and input
current.
——
± 1
μA