NXP Semiconductors
QN902x
User Manual of QN902x
UM10996
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© NXP Semiconductors N.V. 2018. All rights reserved.
User Manual
Rev 1.3
— 05 November 2018
38 of 128
b) Scan mode
The scan mode sweeps from one channel to the other and is enabled by setting
SCAN_EN to 1. The start channel is controlled by SCAN_CH_START[3:0], and the end
channel by SCAN_CH_END[3:0].
The scan function is available in both single and continuous mode, but please pay
attention that in Scan mode, configuration for all scanned channels should be same
One limitation is that the channel index is not put into the ADC result register. When
reading the ADC result, it can be difficult for the users to know which channel they
are currently reading. If this information is needed users may use software to scan
with the ADC working in the non-scan mode.
4.2.6
ADC Output
The ADC result is stored in the output FIFO and can be read out through the register
ADC_DATA. The result is represented in 2s-complement with 16-bit width. Once the
result is available, a data ready interrupt signal DAT_RDY_IF is generated. If the result
in FIFO is not read out in time and overflow occurs, a FIFO overflow interrupt signal is
generated.
As already stated, the ADC is a differential ADC. The positive maximum value of 2047
is reached when (Vin+ - Vin-) is equal to VREF, and the minimum value of -2048 is
reached when (Vin+ - Vin-) is equal to
–
VREF, when it works in 10-bit mode.
a) Decimation mode
In order to increase the effective resolution of the ADC, a decimation filter based on
over-sampling and averaging principle is used. The decimation rate and number of
additional bits can be set using DECI_DIV[1:0] and are summarized in the table below.
DECI_EN
DECI_DIV[1:0]
Decimation Rate
Additional Effective Bits
1
00b
64
2
1
01b
256
3
1
10b
1024
4
Note:
While Scan mode is enabled, decimation should be disabled as buffer is run out by input
channels.
b)
Window compare
The ADC supports a window compare function. When the ADC result is higher than
WCMP_TH_HI or lower than WCMP_TH_LO, an interrupt will be generated, for the
system to monitor the signal.
4.2.7
ADC Power Control
To limit current consumption, the ADC power supply can be controlled independently
by setting PD_SAR_ADC (@0x4000_0094[11]) to 0.
For low sampling rate applications, users need to power down the ADC intentionally
after one conversion is complete, and power up the ADC again before a new
conversion.