DSPIC30F2011AT-30ESLASHS datasheet(140/238 Pages) MICROCHIP

140 / 238 page

dsPIC30F6011A/6012A/6013A/6014A

DS70143C-page 138

Preliminary

FIGURE 19-3:

CONVERTING 1 CHANNEL AT 200 KSPS, AUTO-SAMPLE START, 1 TAD

SAMPLING TIME

19.8

ADC Acquisition Requirements

The analog input model of the 12-bit ADC is shown in

Figure 19-4. The total sampling time for the ADC is a

function of the internal amplifier settling time and the

holding capacitor charge time.

For the ADC to meet its specified accuracy, the charge

holding capacitor (CHOLD) must be allowed to fully

charge to the voltage level on the analog input pin. The

source impedance (RS), the interconnect impedance

(RIC) and the internal sampling switch (RSS) imped-

ance combine to directly affect the time required to

charge the capacitor CHOLD. The combined impedance

of the analog sources must therefore be small enough

to fully charge the holding capacitor within the chosen

sample time. To minimize the effects of pin leakage

currents on the accuracy of the ADC, the maximum

recommended source impedance, RS, is 2.5 k

Ω. After

the analog input channel is selected (changed), this

sampling function must be completed prior to starting

the conversion. The internal holding capacitor will be in

a discharged state prior to each sample operation.

FIGURE 19-4:

12-BIT ADC ANALOG INPUT MODEL

TCONV

= 14 TAD

TSAMP

= 1 TAD

TSAMP

= 1 TAD

ADCLK

SAMP

DONE

ADCBUF0

ADCBUF1

Instruction Execution BSET ADCON1, ASAM

TCONV

= 14 TAD

CPIN

ANx

VT = 0.6V

I leakage

RIC

≤ 250Ω

Sampling

Switch

RSS

CHOLD

= DAC capacitance

VSS

VDD

= 18 pF

± 500 nA

Legend: CPIN

I leakage

RIC

RSS

CHOLD

= input capacitance

= threshold voltage

= leakage current at the pin due to

= interconnect resistance

= sampling switch resistance

= sample/hold capacitance (from DAC)

various junctions

Note: CPIN value depends on device package and is not tested. Effect of CPIN negligible if Rs

≤ 2.5 kΩ.

RSS

≤ 3 kΩ

DSPIC30F2011AT-30E/S Datasheet(PDF) 140 Page - Microchip Technology

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