Figure 7. ADC Simplified Schematic
By switching each element of the capacitor array between REFGND
or REF, the comparator input varies by binary weighted voltage
steps (VREF/2, VREF/4. . .VREF/65536). The control logic
toggles these switches, starting with the MSB first, in order to
bring the comparator back into a balanced condition. After the
completion of this process, the control logic generates the ADC
output code and brings BUSY output low.
Modes of Operation
The ADC features three modes of operation: warp, normal,
and impulse. Each of these modes is more suitable for specific
The warp mode allows the fastest conversion rate up to
1 MSPS. However, in this mode and this mode only, the full
specified accuracy is guaranteed only when the time between
conversion does not exceed 1 ms. If the time between two con-
secutive conversions is longer than 1 ms, for instance, after
power-up, the first conversion result should be ignored. This
mode makes the ADC ideal for applications where both high
accuracy and fast sample rate are required.
The normal mode is the fastest mode (800 kSPS) without any
limitation about the time between conversions. This mode makes
the ADC ideal for asynchronous applications such as data
acquisition systems, where both high accuracy and fast sample
rate are required.
The impulse mode, the lowest power dissipation mode, allows
power saving between conversions. The maximum throughput
in this mode is 666 kSPS. When operating at 100 SPS, for
example, it typically consumes only 15 mW. This feature makes
the ADC ideal for battery-powered applications.
Using the OB/2C digital input, the ADC offers two output
codings: straight binary and twos complement. The ideal transfer
characteristic for the ADC is shown in Figure 8 and Table III.
–FS + 1LSB
–FS + 0.5LSB
+FS – 1LSB
+FS – 1.5LSB
Figure 8. ADC Ideal Transfer Function
Table III. Output Codes and Ideal Input Voltages
Digital Output Code
Full-Scale Range ± 10 V
Least Significant Bit 305.2 mV
FSR –1 LSB
Midscale +1 LSB 305.2 mV
Midscale –1 LSB
–FSR +1 LSB
± 2.5 V
0 V to 10 V
152.6 mV 76.3 mV
4.999847 V 2.499924 V 9.999847 V
152.6 mV 76.3 mV
–152.6 mV –76.3 mV 4.999847 V
–4.999847 V –2.499924 V 152.6 mV
0 V to 5 V
0 V to 2.5 V
1This is also the code for an overrange analog input.
2This is also the code for an underrange analog input.