HCS12 datasheet(98/126 Pages) NXP

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Device User Guide — 9S12KT256DGV1/D V01.09

Freescale Semiconductor

Table A-12 3.3V ATD Operating Characteristics

A.5.2 Factors influencing accuracy

Three factors - source resistance, source capacitance and current injection - have an influence on the

accuracy of the ATD.

A.5.2.1 Source Resistance:

Due to the input pin leakage current as specified in Table A-6 and Table A-7in conjunction with the

source resistance there will be a voltage drop from the signal source to the ATD input. The maximum

source resistance RS specifies results in an error of less than 1/2 LSB (2.5mV) at the maximum leakage

current. If device or operating conditions are less than worst case or leakage-induced error is acceptable,

larger values of source resistance are allowed.

A.5.2.2 Source capacitance

When sampling an additional internal capacitor is switched to the input. This can cause a voltage drop due

to charge sharing with the external and the pin capacitance. For a maximum sampling error of the input

voltage

≤ 1LSB, then the external filter capacitor, C

f ≥ 1024 * (CINS- CINN).

A.5.2.3 Current injection

There are two cases to consider.

Conditions are shown in Table A-4 unless otherwise noted; Supply Voltage 3.3V-10% <= VDDA <= 3.3V+10%

Num C

Rating

Symbol

Min

Typ

Max

Unit

Reference Potential

Low

High

VRL

VRH

VSSA

VDDA/2

VDDA

C Differential Reference Voltage

VRH-VRL

3.0

3.3

3.6

D ATD Clock Frequency

fATDCLK

0.5

2.0

MHz

ATD 10-Bit Conversion Period

Clock Cycles1

Conv, Time at 2.0MHz ATD Clock fATDCLK

Conv, Time at 4.0MHz2 ATD Clock fATDCLK

NOTES:

1. The minimum time assumes a final sample period of 2 ATD clocks cycles while the maximum time assumes a final sample

period of 16 ATD clocks.

2. Reduced accuracy see Table A-14 and Table A-15.

NCONV10

TCONV10

3.5

Cycles

µs

ATD 8-Bit Conversion Period

Clock Cycles(1)

Conv, Time at 2.0MHz ATD Clock fATDCLK

NCONV8

TCONV8

Cycles

µs

D Recovery Time (VDDA=3.3 Volts)

tREC

µs

Reference Supply current (two ATD modules)

IREF

0.500

Reference Supply current (one ATD module)

IREF

0.250

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