LPC1104UK View Datasheet(PDF) - NXP Semiconductors.

Part Name

Description

Manufacturer

LPC1104UK

32-bit ARM Cortex-M0 microcontroller; 32 kB flash and 8 kB SRAM

NXP Semiconductors. 

NXP Semiconductors

LPC1102/1104

32-bit ARM Cortex-M0 microcontroller

11.5 ADC effective input impedance

A simplified diagram of the ADC input channels can be used to determine the effective

input impedance seen from an external voltage source. See Figure 23.

ADC Block

ADC

COMPARATOR

Rmux

<2 kΩ

Cia

Rsw

<1.3 kΩ

Source

Rs

Rin

Cio

VEXT

VSS

002aah615

Fig 23. ADC input channel

The effective input impedance, Rin, seen by the external voltage source, VEXT, is the

parallel impedance of ((1/fs x Cia) + Rmux + Rsw) and (1/fs x Cio), and can be calculated

using Equation 1 with

fs = sampling frequency

Cia = ADC analog input capacitance

Rmux = analog mux resistance

Rsw = switch resistance

Cio = pin capacitance

Rin

=





--------1---------

fs  Cia

+

Rmu

x

+

Rs



w







f--s------1--C-----i-o-

(1)

Under nominal operating condition VDD = 3.3 V and with the maximum sampling

frequency fs = 400 kHz, the parameters assume the following values:

Cia = 1 pF (max)

Rmux = 2 kΩ (max)

Rsw = 1.3 kΩ (max)

Cio = 7.1 pF (max)

The effective input impedance with these parameters is Rin = 308 kΩ.

LPC1102_1104

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 7 — 26 September 2013

© NXP B.V. 2013. All rights reserved.

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