MAX11902 Datasheet, PDF (19/29 Pages) Maxim Integrated Products – Fully Differential SAR ADC

MAX11902
18-Bit, 1Msps, Low-Power,
Fully Differential SAR ADC
Digital Interface
The MAX11902 has a SPI interface with CNVST control-
ling the sampling, and SCLK, DOUT, DIN forming the
standard SPI signals. The SAR conversion begins with
the rising edge of CNVST. The minimum CNVST high
time is 20ns and CNVST should be brought low before
DOUT goes low, which signals the completion of a SAR
conversion. The DOUT goes low for 15ns, followed by
the output of the MSB on the DOUT pin. The 18-bit con-
version result can then be read via the SPI interface by
sending 18 SCLK pulses. DOUT going low also signals
the start of the track phase. The ADC stays in track phase
until the next rising edge of CNVST.
The MAX11902 has three different modes to read the data:
●● Reading during track phase (Figure 5)
●● Reading during SAR conversion phase (Figure 6)
●● Split reading (Figure 7)
When reading during track phase mode, the data is read
only while the ADC is in track mode. Figure 5 shows the
SPI signal for this reading mode.
In the reading during SAR conversion phase mode,
the data is read only in the SAR conversion phase.
Figure 6 illustrates all SPI signals for this mode. Note that
the data being read only during the SAR conversion phase
corresponds to the previous conversion frame.
CNVST
SAR Conversion
Sample 1
1/Sample Rate
Track
Read Data
SAR Conversion
Sample 2
1/Sample Rate
Track
Read Data
SCLK
DOUT
Figure 5. Read During Track Phase
Sample 1
MSB MSB-1
LSB+1 LSB
Reading sample1 during track
Sample 2
MSB MSB-1
LSB+1 LSB
Reading sample 2 during track
CNVST
SAMPLE 1
1/SAMPLE RATE
SAR CONVERSION
READ DATA
TRACK
SCLK
SAMPLE 0
DOUT
MSB
MSB-1
LSB+1 LSB
MSB
READING SAMPLE 0 DURING SAR
CONVERSION
Figure 6. Read During SAR Conversion Phase
SAMPLE 2
1/SAMPLE RATE
SAR CONVERSION
READ DATA
SAMPLE 1
MSB-1
LSB+1 LSB
READING SAMPLE 1 DURING SAR
CONVERSION
TRACK
MSB
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