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ESD Protection
R ~ 100 Ω
ADC10MCTL0.0
–
3
Input
Ax
N
= 1023 ×
ADC
Vin – V
R–
V
– V
R+
R–
ADC10_B Operation
16.2 ADC10_B Operation
The ADC10_B module is configured with user software. The setup and operation of the ADC10_B is
discussed in the following sections.
16.2.1 10-Bit ADC Core
The ADC core converts an analog input to its 10-bit digital representation and stores the result in the
conversion register
. The core uses two programmable and selectable voltage levels (V
R+
and V
R-
) to define the upper and lower limits of the conversion. The digital output (N
ADC
) is full scale
(03FFh) when the input signal is equal to or higher than V
R+
, and zero when the input signal is equal to or
lower than V
R-
. The input channel and the reference voltage levels (V
R+
and V
R-
) are defined in the
conversion-control memory. The conversion formula for the ADC result N
ADC
is:
The ADC10_B core is configured by the control registers
,
and
The core is enabled with the ADC10ON bit. The ADC10_B can be turned off when not in use to save
power. With few exceptions, the ADC10_B control bits can only be modified when ADC10ENC = 0.
ADC10ENC must be set to 1 before any conversion can take place.
16.2.1.1 Conversion Clock Selection
The ADC10CLK is used both as the conversion clock and to generate the sampling period when the pulse
sampling mode is selected. The ADC10_B source clock is selected using the ADC10SSELx bits. Possible
ADC10CLK sources are SMCLK, MCLK, ACLK, and the MODCLK. The input clock can be divided from
1–512 using both the ADC10DIVx bits and the ADC10PDIVx bits.
MODCLK, generated internally in the CS, is in the 5-MHz range but varies with individual devices, supply
voltage, and temperature. See the device-specific data sheet for the MODOSC specification.
The user must ensure that the clock chosen for ADC10CLK remains active until the end of a conversion. If
the clock is removed during a conversion, the operation does not complete and any result is invalid.
16.2.2 ADC10_B Inputs and Multiplexer
The 12 external and 4 internal analog signals are selected as the channel for conversion by the analog
input multiplexer. The input multiplexer is a break-before-make type to reduce input-to-input noise injection
resulting from channel switching (see
). The input multiplexer is also a T-switch to minimize the
coupling between channels. Channels that are not selected are isolated from the A/D and the intermediate
node is connected to analog ground (AV
SS
), so that the stray capacitance is grounded to eliminate
crosstalk.
The ADC10_B uses the charge redistribution method. When the inputs are internally switched, the
switching action may cause transients on the input signal. These transients decay and settle before
causing errant conversion.
Figure 16-2. Analog Multiplexer
436
ADC10_B Module
SLAU272C – May 2011 – Revised November 2013
Copyright © 2011–2013, Texas Instruments Incorporated