
ATD DC Electrical Characteristcs
MC68HC812A4 Data Sheet, Rev. 7
Freescale Semiconductor
225
18.7 ATD DC Electrical Characteristcs
18.8 Analog Converter Operating Characteristics
Characteristic(1)
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TL to TH, ATD clock = 2 MHz, unless otherwise noted
Symbol
Min
Max
Unit
Analog supply voltage
VDDA
4.5
5.5
V
Analog supply current, normal operation
IDDA
—1.0
mA
Reference voltage, low
VRL
VSSA
VDDA/2
V
Reference voltage, high
VRH
VDDA/2VDDA
V
VREF differential reference voltage
(2)
2. Accuracy is guaranteed at VRH VRL = 5.0 Vdc ± 10%.
VRHVRL
4.5
5.5
V
Input voltage(3)
3. To obtain full-scale, full-range results, VSSA ≤ VRL ≤ VINDC ≤ VRH ≤ VDDA.
VINDC
VSSA
VDDA
V
Input current, off channel(4)
4. Maximum leakage occurs at maximum operating temperature. Current decreases by approximately one-half for each
10
°C decrease from maximum temperature.
IOFF
—100
nA
Reference supply current
IREF
—250
A
Input capacitance
Not sampling
Sampling
CINN
CINS
—
10
15
pF
Characteristic(1)
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TL to TH, ATD clock = 2 MHz, unless otherwise noted
Symbol
Min
Typical
Max
Unit
8-bit resolution(2)
2. VRHVRL ≥ 5.12 V; VDDA—VSSA = 5.12 V
2 counts
—
24
—
mV
Differential non-linearity(3)
3. At VREF = 5.12 V, one 8-bit count = 20 mV.
DNL
0.5
—
+0.5
Count
Integral non-linearity(3)
INL
1—
+1
Count
Absolute error(3),(4)
2, 4, 8, and 16 ATD sample clocks
4. 8-bit absolute error of 1 count (20 mV) includes 1/2 count (10 mv) inherent quantization error and 1/2 count (10 mV) circuit
(differential, integral, and offset) error.
AE
2—
+2
Count
Maximum source impedance
RS
—20
See note(5)
5. Maximum source impedance is application-dependent. Error resulting from pin leakage depends on junction leakage into
the pin and on leakage due to charge-sharing with internal capacitance.
Error from junction leakage is a function of external source impedance and input leakage current. Expected error in result
value due to junction leakage is expressed in voltage (VERRJ):
VERRJ = RS × IOFF
where IOFF is a function of operating temperature. Charge-sharing effects with internal capacitors are a function of ATD
clock speed, the number of channels being scanned, and source impedance. For 8-bit conversions, charge pump leakage
is computed as follows:
VERRJ = .25 pF × VDDA × RS × ATDCLK/(8 × number of channels)
k