ADC imput resistance - LPC1114

[lpcware]

Content originally posted in LPCWare by sipel_tp on Thu Aug 02 06:26:37 MST 2012
I have to measure a battery voltage using LPC1114 ADC. I would like to use a resistor divider to reduce the imput voltage to the ADC pin. The problem I have is I don't know the imput resistance of the pin so I can't design the resistor divider. Can somebody tell me the imput resistance of the LPC1114 ADC pin? Thank you very much.

[lpcware]

Content originally posted in LPCWare by sipel_tp on Fri Aug 03 04:17:53 MST 2012
Thank you all for your help

[lpcware]

Content originally posted in LPCWare by madid87 on Thu Aug 02 07:42:41 MST 2012

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Quote: sipel_tp
I have to measure a battery voltage using LPC1114 ADC. I would like to use a resistor divider to reduce the imput voltage to the ADC pin. The problem I have is I don't know the imput resistance of the pin so I can't design the resistor divider. Can somebody tell me the imput resistance of the LPC1114 ADC pin? Thank you very much.

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Datasheet page 60.
2.5MR for DC in your case.

If this is to low you can use smaller divider resistors and a FET in series to save power between measurements.

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Thu Aug 02 07:40:25 MST 2012
LPC1114 datasheet:

LPC1110/11/12/13/14/15 32-bit ARM Cortex-M0 microcontroller; up to 64 kB flash and 8 kB SRAM Rev. 7.3 — 6 July 2012

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Quote:

Table 8. ADC static characteristics
Tamb = -40 °C to +85 °C unless otherwise specified; ADC frequency 4.5 MHz, VDD = 2.5 V to 3.6 V.
Symbol Parameter Conditions Min Typ Max Unit
VIA analog input voltage 0 - VDD V
Cia analog input capacitance - - 1 pF
ED differential linearity error [1][2]- - ± 1 LSB
EL(adj) integral non-linearity [3]- - ± 1.5 LSB
EO offset error [4]- - ± 3.5 LSB
EG gain error [5]- - 0.6 %
ET absolute error [6]- - ± 4 LSB
Rvsi voltage source interface
resistance
- - 40 kO
[COLOR=Red]Ri input resistance [7][8]- - 2.5 MO[/COLOR]

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