PXAS30 datasheet(16/52 Pages) PHILIPS

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Philips Semiconductors

Preliminary specification

XA-S3

XA 16-bit microcontroller

32 K/1 K OTP/ROM/ROMless, 8-channel 8-bit A/D, low voltage (2.7 V–5.5 V),

I2C, 2 UARTs, 16 MB address range

2000 Dec 01

Table 3. A/D Timing Configuration for 10-bit Mode

ADCFG 3 0

Max. Oscillator

Conversion Time

Sampling Time

ADCFG.3–0

Frequency (MHz)

Osc. Clocks

µsec at max. Osc.

(Osc. Clocks)

0h (0000)

6.66

13.21

1h (0001)

9.2

2h (0010)

8.64

3h (0011)

116

8.7

4h (0100)

120

7.2

5h (0101)

124

6.2

6h (0110)

136

6.8

7h (0111)

128

5.77

8h (1000)

148

6.35

9h (1001)

152

5.71

Ah (1010)

156

5.2

Bh (1011)

170

5.67

Ch (1100)

160

5.0

Dh (1101)

180

5.41

Eh (1110)

204

5.57

Fh (1111)

208

5.2

A/D Inputs

In order to obtain accurate measurements with the A/D Converter,

the source drive must be sufficient to adequately charge the

sampling capacitor during the sampling time. Figure 4 shows the

equivalent resistance and capacitance related to the A/D inputs.

A/D timing configurations indicated in Table 1 allow for full A/D

accuracy (according to the A/D specifications) assuming a source

resistance of less than or equal to 20k

Ω. Larger source resistances

may be accommodated by increasing the sampling time with a

different A/D timing configuration.

VANALOG

INPUT

TO COMPARATOR

ADN

ADN+1

SmN+1

SmN

RmN+1

RmN

Multiplexer

Rm (multiplexer resistance)

= 3 k

Ω maximum

CS (pin capacitance)

= 10 pF maximum

CC (sampling capacitor)

= 2 pF maximum

RS (source resistance)

= Recommended less than 20k

Ω for full specified accuracy. This allows time for the sampling

capacitor (CC) to fully charge while the multiplexer switch is closed. Please note that sampling

causes the analog input to present a varying load to the pin.

SU00948

Figure 4. A/D Input: Equivalent Circuit

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