AN1830 datasheet(6/15 Pages) STMICROELECTRONICS

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ACHIEVING HIGH ACCURACY AND 13-BIT RESOLUTION WITH ST7LITE2 ADC

2.3 OPERATING MODES

The amplifier functions in different modes depending on the state of the digital control signals

AMPSEL and AMPCAL. These are explained below,

1) Analog input going directly to Amplifier output (Amplifier OFF)

When the amplifier is OFF, the ADC gets connected to the selected analog channel

through sample and hold circuitry. In this the case analog input goes directly to the Am-

plifier output. The maximum and minimum input that can be given is VDD and VSS respec-

tively with a resolution of 10 bits, which is equal to VDD/1024.

The state of control signals for this mode should be:

AMPSEL = 0

AMPCAL = 0

2) Analog input amplified and appearing at Amplifier output (Amplifier ON)

In this case amplifier is ON thus ADC input is,

VOUT(Amplifier) = VOFFSET + 8 x VIN

The maximum voltage that can be applied at the analog input (VIN) is 500mV at VDD = 5V

and 350mV at VDD =3.6V with a resolution of 13 bits. The 13-bit resolution is because the

minimum signal that can be measured when the amplifier is ON, is 0.6103mV at 5V (e.g.

0.6103 x 8 (23)= 4.8828 = 1LSB for 10-bit ADC) and 0.4394mV at 3.6V.

This maximum input voltage limitation is due to the nonlinearity of the amplifier as shown

in Figure 4 in the amplifier transfer curve for 5V.

AN1830 Fiches technique(PDF) 6 Page - STMicroelectronics