Datasheet

IN1
MUX
GND
SAMPLING
CAPACITOR
SW1
-
+
CONTROL
LOGIC
CHARGE
REDISTRIBUTION
DAC
SW2
IN2
V
A
2
IN1
MUX
GND
SAMPLING
CAPACITOR
SW1
-
+
CONTROL
LOGIC
CHARGE
REDISTRIBUTION
DAC
SW2
IN2
V
A
2
ADC082S021
www.ti.com SNAS282D –APRIL 2005–REVISED MARCH 2013
APPLICATIONS INFORMATION
ADC082S021 OPERATION
The ADC082S021 is a successive-approximation analog-to-digital converter designed around a charge-
redistribution digital-to-analog converter. Simplified schematics of the ADC082S021 in both track and hold modes
are shown in Figure 46 and Figure 47, respectively. In Figure 46, the ADC082S021 is in track mode: switch SW1
connects the sampling capacitor to one of two analog input channels through the multiplexer, and SW2 balances
the comparator inputs. The ADC082S021 is in this state for the first three SCLK cycles after CS is brought low.
Figure 47 shows the ADC082S021 in hold mode: switch SW1 connects the sampling capacitor to ground,
maintaining the sampled voltage, and switch SW2 unbalances the comparator. The control logic then instructs
the charge-redistribution DAC to add fixed amounts of charge to the sampling capacitor until the comparator is
balanced. When the comparator is balanced, the digital word supplied to the DAC is the digital representation of
the analog input voltage. The ADC082S021 is in this state for the fourth through sixteenth SCLK cycles after CS
is brought low.
The time when CS is low is considered a serial frame. Each of these frames should contain an integer multiple of
16 SCLK cycles, during which time a conversion is performed and the result is clocked out at the DOUT pin while
the multiplexer address for the next conversion is clocked in at the DIN pin.
Figure 46. ADC082S021 in Track Mode
Figure 47. ADC082S021 in Hold Mode
USING THE ADC082S021
An ADC082S021 timing diagram and a serial interface timing diagram for the ADC082S021 are shown in the
Timing Diagrams section. CS is chip select, which initiates conversions and frames the serial data transfers.
SCLK (serial clock) controls both the conversion process and the timing of serial data. DOUT is the serial data
output pin, where the conversion result is sent out as a serial data stream, MSB first. Data to be written to the
ADC082S021's Control Register is placed at DIN, the serial data input pin. New data is written in at DIN with
each conversion.
A serial frame is initiated on the falling edge of CS and ends on the rising edge of CS. Each frame must contain
an integer multiple of 16 rising SCLK edges. The ADC output data (DOUT) is in a high impedance state when
CS is high and is active when CS is low. Thus, CS acts as an output enable. Additionally, the device goes into a
power down state when CS is high and also between continuous conversion cycles.
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