Device Architecture
2-112
Revision 4
Sample time is computed based on the period of ADCCLK.
Distribution Phase
The second phase is called the distribution phase. During distribution phase, the ADC computes the
equivalent digital value from the value stored in the input capacitor. In this phase, the output signal
SAMPLE goes back to '0', indicating the sample is completed; but the BUSY signal remains '1', indicating
the ADC is still busy for distribution. The distribution time depends strictly on the number of bits. If the
ADC is configured as a 10-bit ADC, then 10 ADCCLK cycles are needed.
EQ 8 describes the distribution
time.
EQ 21
N: Number of bits
Post-Calibration Phase
The last phase is the post-calibration phase. This is an optional phase. The post-calibration phase takes
two ADCCLK cycles. The output BUSY signal will remain '1' until the post-calibration phase is completed.
If the post-calibration phase is skipped, then the BUSY signal goes to '0' after distribution phase. As soon
as BUSY signal goes to '0', the DATAVALID signal goes to '1', indicating the digital result is available on
the RESULT output signals. DATAVAILD will remain '1' until the next ADCSTART is asserted. Microsemi
recommends enabling post-calibration to compensate for drift and temperature-dependent effects. This
ensures that the ADC remains consistent over time and with temperature. The post-calibration phase is
enabled by bit 3 of the Mode register.
EQ 9 describes the post-calibration time.
EQ 22
The calculation for the conversion time for the ADC is summarized in
EQ 23.tconv = tsync_read + tsample + tdistrib + tpost-cal + tsync_write
EQ 23
tconv: conversion time
tsync_read: maximum time for a signal to synchronize with SYSCLK. For calculation purposes, the
worst case is a period of SYSCLK, tSYSCLK.
tsample: Sample time
tdistrib: Distribution time
tpost-cal: Post-calibration time
tsync_write: Maximum time for a signal to synchronize with SYSCLK. For calculation purposes, the
worst case is a period of SYSCLK, tSYSCLK.
Intra-Conversion
Performing a conversion during power-up calibration is possible but should be avoided, since the
calibration).
Injected Conversion
A conversion can be interrupted by another conversion. Before the current conversion is finished, a
second conversion can be started by issuing a pulse on signal ADCSTART. When a second conversion
is issued before the current conversion is completed, the current conversion would be dropped and the
ADC would start the second conversion on the rising edge of the SYSCLK. This is known as injected
conversion. Since the ADC is synchronous, the minimum time to issue a second conversion is two clock
Table 2-46 STC Bits Function
Name
Bits
Function
STC
[7:0]
Sample time control
tdistrib
NtADCCLK
=
tpost-cal
MODE 3
2tADCCLK
=