FMS7401 Datasheet, PDF(16/80 Page) Fairchild Semiconductor

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FMS7401 Datasheet, PDF (16/80 Pages) Fairchild Semiconductor – Digital Power Controller

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FMS7401/7401L

PRODUCT SPECIFICATION

4 ADC Circuit

The Analog-to-Digital Converter (ADC) Circuit extends the features of the FMS7401/7401L by offering a 5-channel 8-bit

ADC. The ADC may be programmed to convert voltages on any of the eight inputs of the analog mux, where ï¬ve are multi-

function input channels (ACH1-ACH5) and three are used for system calibration. The integrated ADC function offers a single

cost-effective solution for applications requiring voltage, current and temperature sensing. The multifunction input channels

may be conï¬gured to perform standard conversions on any of the analog input pins (G4/AIN0, G3/AIN1, G2/AIN2, G3/AIN3

or G7/AIN4). Three of the multifunction input channels may be programmed to perform ADC conversions through the internal

Autozero Ampliï¬er, Uncommitted Ampliï¬er, and Current Source Generator for special control system and battery manage-

ment applications (see Figure 6).

The ADC Circuitâs eight analog inputs are software selectable where their analog input voltage is converted with respect to the

internal ADC reference voltage (VAREF). VAREF may be programmed to use the internal bandgap reference voltage (VREF) or

Vcc as its source. By default, the ADC circuitâs VAREF is conï¬gured to use the internal VREF as its source.1

The ADC performs conversions of 8-bit resolution with accuracy as deï¬ned in the Electrical Characteristics section of the

datasheet. For a standard ADC conversion, the ADC circuit converts the analog input voltage in a total of 13 conversion clock

cycles, and a total of 20 conversion clock cycles when performing an autozero ADC conversion. To yield a better ADC conver-

sion accuracy, the ADC circuit may conï¬gure the ADC clock (FADCLK) to a slower frequency, lengthening the total conversion

time while improving its accuracy. As part of the total conversion time, the ADC circuit completes a sample and hold phase to

measure fast changing analog signals before converting the voltage. An ADC conversion can be initiated by a software com-

mand or automatically (using the gated auto-sampling mode) by the active (on) edge transition of the ADSTROBE PWM

Timer 1 output.2 If enabled, the ADC circuit offers the use of its microcontroller hardware interrupt (ADCI) triggered after

each completed ADC conversion so that the microcontroller core is freed to perform other tasks.

4.1 ADC Circuit Conï¬guration

Software must access the three memory mapped ADC registers to conï¬gure and control the ADC circuit.3 The ADC Control 1

(ADCNTRL1) register is used to select the analog input channel and ADC reference voltage (VAREF) for the conversion. In

addition, it is used to initiate a conversion through software, monitor the ADC pending ï¬ag, and enable the ADC circuitâs

microcontroller hardware interrupt (ADCI). The ADC Control 2 (ADCNTRL2) register is used to enable the internal Autozero

Ampliï¬er, Uncommitted Ampliï¬er, Current Source Generator, and/or ADC Auto-sampling Mode. The ADCNTRL2 register is

also used to divide the ADC FADCLK clock to improve the conversion accuracy. Lastly, the ADC Data (ADATA) register is used

by software to read the ï¬nal converted 8-bit digital value. ADATA is a read only register and is updated automatically at the end

of each ADC conversion.

REV. 1.0.2 6/23/04

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